Cool Stars 20.5 - virtually cool
March 2-4 2021, virtual meeting
The "Cambridge Workshops of Cool Stars, Stellar Systems and the Sun" are held biennially and have evolved to be the premier conference series for cool star research.
With the ongoing pandemic, the organizers of Cool Stars 21 consider it unlikely we will be able to meet in person in the summer of 2021. This would put a four year gap between our meetings for the first time. Therefore we have decided to hold a virtual conference to keep everyone in our field up to date. But don't worry, we still plan to meet in Toulouse in mid-2022.
Jump to table of all oral contributions, talks, haikus, or posters.
Abstracts for posters are added after the poster is uploaded to Zenodo (detailed instructions - give us a few days after the upload to add the poster here).
Use the table below to view and search abstracts or jump directly to a listing of all talks, haikus, or posters.
| Type | Author | Title | Authorlist | Affiliations | Abstract | |
|---|---|---|---|---|---|---|
| Type | Author | Title | Authorlist | Affiliations | Abstract |
science theme: Stellar systems, clusters, and associations and Young stars
schedule: Tue, 12:00 (invited talk)
Eleonora Zari
Max Planck Institute for Astronomy
TBD
science theme: Young stars
schedule: Tue, 12:30 (contributed talk)
Marusa Zerjal
Australian National University
While precise parallaxes and proper motions for nearby stars are made available by Gaia, spectroscopic youth indicators for a large fraction of low-mass young stars are still missing. I will present our observations of 318 new young late K and early M dwarfs within ~200pc that have a detectable lithium line and are not found in the known catalogs of young stars. We also provide measurements of H$\alpha$ and calcium H&K emission and report on additional 126 stars which have no detectable lithium but signs of stellar activity indicating youth. We measure radial velocities for 756 overluminous young star candidates and plan to use Chronostar, a novel technique for kinematic age determination, to infer the origin of this sample.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 12:45 (contributed talk)
Angela Bragaglia (1); Giada Casali (2,3); Valentina D'Orazi (4); Antonio Frasca (5)
(1) INAF-OAS Bologna; (2) University of Florence; (3) INAF-OA Arcetri; (4) INAF-OA Padova; (5) INAF-OA Catania
Open Clusters are ideal laboratories to test models of stellar and galactic formation and evolution. While Gaia provides very high precision photometry and astrometry for Galactic OCs, ground based follow-up with higher resolution and larger spectral coverage than Gaia-RVS is needed. Large surveys, such as APOGEE, Gaia-ESO and the soon-to-start WEAVE, can provide that, but also smaller and more focused project are important. I will present our Large Program SPA (Stellar Population Astrophysics) on the Italian National Telescope 'Galileo', which combines the two very high resolution instruments HARPS-N in optical and GIANO in IR. We concentrate on the brighter stars of OCs in the solar vicinity, within about 2 kpc, providing a detailed and accurate chemical characterisation (elements of all nucleosynthetic chains, probing different formation sites) also in term of rarely studied species, such as fluorine.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 13:15 (contributed talk)
Isabelle Joncour; Moraux; Gonzalez; Thomasson; Robitaille; Motte
UGA
Spatial distribution of young stellar objects (YSOs) in star forming regions may be used as key tracers of (1) their birth sites and (2) their dynamical evolution with time. We have developed a framework based on dbscan clustering algorithm to identify significant stellar substructures at small scales (the NESTs, for Nested Elementary Stellar sTructures). We first apply this analysis to Taurus and identify 20 NESTs mainly distributed along the gaseous filaments (Joncour+2018) before further assessing the reliability of our method in various type of star forming region (Gonzalez, Joncour+ 2020) and to apply the method to various star forming complex (Gonzalez in prep). The morphological, geometrical and physical properties of the NESTs in Taurus suggest that these stellar structures may be seen as pristine signatures of star formation process from their natal cloud. Furthermore, within the NESTs population, we identify based on their Number of YSOs inside the NESTs versus size of the NESTs relation, two sub-categories that may highlight two modes of fragmentation: a hierarchical mode at small scale compatible with the fragmentation cascade that we found in the ultra wide pairs population of high order multiplicity that we identified (Joncour+2017) and a partition mode at a larger scale. To investigate further this hypothesis in connection with the fragmentation of the cloud in clumps and cores, we start a multiscale study of the gas using Herschel data and develop a graph theoretic approach to identify and characterise their fragmentation signatures (Thomasson+ in prep).
science theme: Stellar systems, clusters, and associations
schedule: Tue, 13:30 (contributed talk)
Javier Arancibia-Silva (1,2); Amelia Bayo (1,2); Jerome Bouvier (3); Phillip A.B. Galli (4); David Barrado (5); Sebastián Zúñiga (1,2)
(1) Instituto de Física y Astronomía, Universidad de Valparaíso, Chile.; (2) Núcleo Milenio Formación Planetaria - NPF, Universidad de Valparaíso, Chile.; (3) IPAG, Univ. Grenoble Alpes, France.; (4) Laboratoire d'Astrophysique de Bordeaux, Univ. Bordeaux, France.; (5) Depto. Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, Spain.
Lithium is a sensitive probe of transport processes occurring in stellar interiors and a trend has been shown in the literature between its abundance and the rotation of stars. We aim to investigate this trend in low-mass members of stellar associations at different ages and in different environments to constrain the possible origin of the relation. To study the environmental effect, we started by analyzing the newly discovered 125 Myr-old Psc-Eri stellar stream (Meingast I). We obtained our own new equivalent width measurements of the 607.8 nm LiI line for 40 members of this stream and the rotational periods were obtained from the literature. We show that a tight correlation exists between the lithium content and rotation rate among the late-G to early-K-type stars where fast rotators are systematically Li richer than their slow rotators siblings (for similar effective temperatures). This trend mimics the previously reported one for the similar age Pleiades cluster. Therefore, the lithium-rotation connection seems to be universal for low-mass stars at ages close to the zero-age main sequence, and does not depend on environmental conditions. To trace the age dependence of the Li-rotation relationship, and connect with the youngest population (NGC2264, ~5Myr) where this relationship has been claimed, we are in the process of studying the Li-rot trend in the TW Hydrae moving group (at an age of ~8 Myr). We collected and analyzed TESS lightcurves from which we obtained rotational periods, assessed possible contamination given the large pixel scale, and complemented this information with Lithium equivalent width values from the literature. We will present our preliminary results for this association and how it ties together the 5-100Myr time scale.
science theme: Young stars
schedule: Tue, 14:00 (contributed talk)
C.F. Manara; PENELLOPE team
ESO
The evolution of young stars and disks is driven by the interplay of several processes, notably accretion and ejection of material. Critical to correctly describe the conditions of planet formation, these processes are best probed spectroscopically, using the fluxes and profiles of emission lines, and the UV to IR continuum emission shape. We are carrying out a large programme with the Very Large Telescope (VLT), PENELLOPE, aiming at observing the targets of the HST/ULLYSES public survey of 82 low-mass ($M_\star \lesssim 2 M_\odot$) young (age$<$10 Myr) stars at UV wavelengths. These UV spectra will be a unique possibility to have for the first time a comprehensive view of the accretion/ejection processes ONLY IF they will be combined with contemporaneous high-resolution and flux-calibrated optical to near-IR spectra. Our programme is starting to provide an unprecedented dataset with contemporaneous ESPRESSO/UVES spectra to spectrally resolve the kinematics of lines, and X-Shooter flux-calibrated spectra to derive extinction, stellar properties, and the fundamental parameters that HST cannot provide. Here I will present the strategy of the program, and the first results based on the observations of targets in the Orion OB1 and sigma-Orionis regions, which were successfully taken in November-December 2020. This data is showing us how variably the accretion process can be, and how relevant it is to have information covering from the UV to the near-IR wavelengths to deepen our understanding of the properties of young stars, and of accretion and ejection at early ages.
science theme: Young stars
schedule: Tue, 14:15 (contributed talk)
Karine Perraut for the GRAVITY Collaboration
Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
Recent advances in star and planet formation studies have been achieved thanks to observations at high-angular resolution in the last few years. In particular, near-infrared (NIR) interferometry probes the inner disk on sub-au scales, allowing to study star-disk interactions, and allows to constrain accretion/ejection phenomena when coupled with spectral resolution. In this contribution, I will show how the GRAVITY instrument installed at the combined focus of the VLTI interferometric array brings unprecedented details on the complex innermost regions of planet-forming disks. I will report on the NIR continuum emission study of 27 Herbig stars, the first critical tests of magnetospheric accretion scenario in young suns, the resolution of CO bandhead emission at sub-au scales. In addition, GRAVITY has provided outstanding, high-quality atmospheric spectra of young hot Jupiter exoplanets, ten times better than previous coronographic integral field spectroscopy. Finally, prospects with the future GRAVITY+ instrument will also be discussed.
science theme: Young stars
schedule: Tue, 14:30 (contributed talk)
Rosaria Bonito (1); Salvatore Orlando (1); Costanza Argiroffi (2, 1); Loredana Prisinzano (1); Guilhem Revet (3); Konstantin Burdonov (3); Julien Fuchs (3)
(1) INAF - Observatory of Palermo; (2) Dip. di Fisica e Chimica E. Segre', Univ. of Palermo; (3) LULI, CNRS, CEA, Sorbonne Universit ́e, ́Ecole Polytechnique, Paris, France
We present the investigation of accretion/ejection properties of young stellar objects (YSOs), combining multi-band observations, numerical simulations, and laboratory experiments: from the Gaia-ESO Survey (GES) spectroscopic optical data of the NGC 2264 cluster (Bonito et al. 2020), to the laser experiments of stellar jets and accretion shocks young stars (e.g. Burdonov et al. 2020, 2021; Revet et al. 2021), to numerical simulations in the UV and X-ray band of accretion shocks, also in the context of next generation telescopes as Athena X-ray Observatory (Bonito et al. in preparation). The analysis of the Hα emission line profile in the GES context, provides us with information on the accretion/ejection activity of young stars, even when the nebular contribution is strong. We have developed a tool, the OHaNA method, to handle the strong nebular contribution and spectra with spurious profiles of the Hα and forbidden emission lines (e.g. [SII] and [NII] doublets). In this case, the mass accretion rate can be related to the full width at zero intensity (FWZI) of the emission line, whose measurement is more robust with respect to any value derived from the peak (e.g. Hα10%) possibly altered by the nebular contribution. The laser experiments of jets and accretion shocks in YSOs will be discussed, focusing on the effect of the local absorption on the detectability of their emission and on the role of the magnetic field on the collimation of jets. For the high energy emission, we will present the new simulations comparing the UV and X-ray shock emission from the models and the observations, taking into account also the local absorption effect and investigating the detectability of the Doppler shift in the line profiles. Future perspectives with next generation instruments, as the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) and the implication on the study of young stellar objects and their variability will be also discussed.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 14:45 (contributed talk)
P. S. Teixeira (1); A. Scholz (1); J. Alves (2)
(1) Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, St. Andrews, UK; (2) University of Vienna,Department of Astrophysics, Türkenschanzstrasse 17, A-1180 Vienna, Austria
Data from the Gaia mission allows us to examine the three-dimensional structure of nearby star forming regions. Combined with mid-infrared photometry from the WISE mission, these datasets are a powerful tool for exploring disk-bearing low mass stars in wider areas, beyond the immediate vicinity of a molecular cloud. We present a wide-area survey covering 494 deg$^2$ of the Lupus complex, a nearby prototypical low-mass star forming region. Our survey includes all known molecular clouds in this region as well as parts of the Upper Scorpius and Upper Centaurus Lupus groups of the Sco-Cen complex. We find 98 new disk-bearing sources, with ages ranging from 1 to 15 Myr, and masses ranging from 0.05 to 0.5M$_\odot$. While the youngest members are concentrated in the clouds and at distances of 160 pc, there is a distributed population of slightly older stars that overlap in proper motion, spatial distribution, distance, and age with the Lupus and Upper Centaurus Lupus groups. Our new sample comprises some of the nearest disks to Earth at these ages, and thus provides an important target for follow-up studies of disks and accretion in very low mass stars, for example with ALMA and ESO-VLT X-Shooter.
science theme: Young stars
schedule: Tue, 15:15 (contributed talk)
Julia Roquette; Sean Matt
University of Exeter
The vast majority of stars are formed in clustered environments. However, to date, most rotational evolution models still consider stars that form and evolve in isolation. In this talk, we will show results of a rotational evolution model that considers how the environment of open clusters can influence the rotational evolution of low mass stars. In particular, we looked at how the presence of massive stars influences the local far-ultraviolet radiation fields in clusters, altering the dissipation timescales of circumstellar disks due to external photoevaporation. Environmentally dependent disk-dissipation timescales directly impact the duration of the star-disk-interaction phase (sometimes called disk-locking phase), in which the star is expected to exchange angular momentum with its disk. By considering the rotational evolution of stars in clusters with varied massive star content, we show how the influence of neighbour massive stars in the disk-locking phase's duration can drastically change the rotational evolution of low mass stars. While modelling the rotational evolution of the low mass population of entire clusters, we show that the environmental influence introduces statistically relevant differences in the period distributions of clusters with varied massive content, which are already visible at ages as early as 3 Myrs and remain until early-MS ages.
science theme: Young stars
schedule: Tue, 15:30 (contributed talk)
Laura Ketzer; Katja Poppenhaeger; Matthias Mallonn
Leibniz-Institute for Astrophysics Potsdam (AIP)
Kepler observations revealed two striking features in the distribution of exoplanet radii: a dearth of short period sub-Neptune-sized planets, and a relatively clean gap around 2 Earth radii. Atmospheric escape of planetary H/He envelopes driven by the high-energy X-ray and UV irradiation from the host star can explain the presence of the desert at short periods as well as the radius valley. The very young (~ 25 Myr) V1298 Tau system with its four Neptune- to Jupiter-sized planets is an excellent system to test planet formation and evolution models.
To investigate the fate of the four planets, we obtained X-ray measurements of V1298 Tau with Chandra. We then calculated the future photoevaporative mass loss rates using PLATYPOS, an open-source tool to model the (energy-limited) atmospheric escape of planetary systems over several Gigayears. We allowed for the host star to spin down at three different ages, which translates into a low, intermediate, and high activity stellar evolutionary track. Our findings show that in certain planetary mass and orbital distance regimes, the stellar high-energy evolution determines if a planet is stripped completely or can retain some fraction of its initial gaseous envelope.
science theme: Results from new instruments
schedule: Tue, 15:45 (contributed talk)
B. Stelzer
Universitaet Tuebingen & INAF/OAPa
In July 2019 eROSITA (the extended ROentgen Survey with an Imaging Telescope Array) which was developed under the leadership of MPE/Garching, was launched as the primary instrument onboard the russian spacecraft Spectrum-Roentgen-Gamma (SRG). After a CalPV phase and having reached its L2 halo orbit eROSITA has started the first of eight planned All-Sky Surveys in the 0.2-10 keV X-ray band in December 2019. Meanwhile two of the surveys have been completed, detecting nearly a million X-ray sources of which about 20 % are expected to be stars. With a sensitivity about 25x higher than that of the only previous All-Sky soft X-ray survey carried out by ROSAT in 1991, and combined with data from advanced missions observing at other wavelengths such as TESS and Gaia, eROSITA is expected to have a major impact on stellar astrophysics during at least the next decade.
I present first results and prospects for eROSITA's contributions to our understanding of stellar activity summarizing a few projects that exploit data both from the CalPV phase and the first survey, eRASS1. The studies comprise a diverse group of objects, including solar-type stars, M dwarfs, ultracool dwarfs and young moving groups of stars.
science theme:
schedule: Wed, 12:00 (invited talk)
Kasper
TBD
science theme: The Sun and the Heliosphere
schedule: Wed, 12:30 (contributed talk)
B. Perri (1), ; A. S. Brun (2), ; A. Strugarek (2), ; V. Réville (3)
(1) (1) CmPA, KU Leuven; (2) (2) AIM, CEA; (3) (3) IRAP
We focus on the connection between the internal dynamo magnetic field and the stellar wind. If the star has a cyclic dynamo, the modulations of the magnetic field can affect the wind, which in turn can back-react on the boundary conditions of the star, creating a feedback loop. We have developed a 2.5-dimensional numerical set-up to model this essential coupling. We have implemented an alpha-Omega mean-field dynamo in the PLUTO code, and then coupled it to a spherical polytropic wind model via an interface composed of four grid layers with dedicated boundary conditions. We present here a dynamo model close to a young Sun with cyclic magnetic activity. First we show how this model allows to track the influence of the dynamo activity on the corona by displaying the correlation between the activity cycle, the coronal structure and the time evolution of integrated quantities. Then we add the feedback of the wind on the dynamo and discuss the changes observed in the dynamo symmetry and the wind variations. We explain these changes in terms of dynamo modes: in this parameter regime, the feedback loop leads to a coupling between the dynamo families via a preferred growth of the quadrupolar mode. We also study our interface in terms of magnetic helicity, and show that it leads to a small injection in the dynamo. This model confirms the importance of coupling physically internal and external stellar layers, as it has a direct impact on both the dynamo and the wind.
science theme: The Sun and the Heliosphere
schedule: Wed, 12:45 (contributed talk)
Cole A Tamburri (1); Maria D Kazachenko (1,2,3); Adam F Kowalski (1,2,3)
(1) Dept. of Astrophysical and Planetary Sciences, CU Boulder; (2) National Solar Observatory; (3) Laboratory for Atmospheric and Space Physics
The Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment (SDO/EVE) provides “Sun-as-a-star” data corresponding to the variability of the Sun’s irradiance in the XUV and EUV wavelengths (0.1 to 106 nm). Using EVE light curves in the 304 Angstrom line, we study 2049 solar flares from 30 April 2010 to 26 May 2014 . We present an algorithm for fitting the flare light curves in the 304 Angstrom line, emitted by He II at around 50000 K from the chromosphere and transition region and therefore representative of the dominant source of radiation in a solar flare. The algorithm is used to identify particularly high signal-to-noise flare light curves within the database, with representatives from C, M, and X X-ray flare classes. The parameters of the model associated with each flare can be used to identify features such as secondary peaks in the decay phase. In addition, we devise a morphological classification scheme based on flare “impulsivity” and apply the scheme to a sub-sample of the flares. While a similar method has been used in the past to classify stellar flares, it has yet to be extensively applied to solar flare light curves. A comparison is made to the X-ray classification for solar flares. Using the modeling algorithm and new classification scheme in the chromospheric 304 Angstrom line, it may be possible to identify and study features not revealed by traditional methods, particularly when Sun-as-a-star light curves are studied together with full-disk images.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:15 (contributed talk)
Seth Redfield (1); Hunter Vannier (1, 2); Jeffrey L. Linsky (3)
(1) Wesleyan University; (2) Purdue University; (3) JILA, University of Colorado and NIST
The Local Interstellar Medium (LISM) is a rich and complex suite of clouds in the immediate vicinity of the Sun. The Sun is located at the edge of the Local Interstellar Cloud (LIC), the interstellar structure that is thought to directly surround the solar system. We present a global three-dimensional model of the LISM, based on ultraviolet absorption line spectroscopy of hundreds of nearby stars, including a dense survey of stars along the historical solar trajectory of our most recent past (e.g., within the last 5 Myr). Stellar winds and a surrounding interstellar medium are ubiquitous. Our heliosphere represents the gold standard with which to evaluate the astrospheres around other stars. While stellar wind strengths change slowly, at least during the main sequence, the density of interstellar clouds ranges by more than six orders of magnitude. The implication is that the solar heliosphere and stellar astrospheres are permanent features of stellar and planetary systems and are constantly changing. The stellar magnetic field and particle interactions, bounded by the astrosphere, can lead to a filtering of low and high-energy (i.e., cosmic rays) particles. The particles that make it through the filter can be deposited in the atmospheres and on the surfaces of planets in the system, impacting the energy balance and photochemistry. While our survey observed the historical solar trajectory, our three-dimensional LISM model can provide insight into the astrospheric response of nearby planet-hosting stars. This model will also be of use in evaluating the influence the LISM has on observations of stellar properties and the characterization of the atmospheres of exoplanets. In the coming decades, as we explore the various stellar and planetary properties that drive habitability, it may be important to include the interaction that stars have with their surrounding interstellar medium environments.
Heliosphere breathes over time as it travels in the midst of stars
science theme: The Sun and the Heliosphere
schedule: Wed, 13:30 (contributed talk)
C. Breu; H. Peter; R. Cameron; S.K. Solanki; L.P. Chitta; D. Przybylski
Max-Planck-Institute for Solar System Research
The corona of the Sun, and probably also of other stars, is built up by loops defined through the magnetic field. High-resolution observations show individual strands with diameters down to a few 100 km, and so far it remains open what defines these strands, in particular their width, and where the energy to heat them is generated.
The aim of our study is to understand how the magnetic field couples the different layers of the solar atmosphere, how energy generated by magnetoconvection is transported into the upper atmosphere and dissipated, and how this process determines the scales of observed bright strands in the loop.
To this end, we conduct 3D resistive MHD simulations with the MURaM code. We study an isolated coronal loop that is rooted in a shallow convection zone layer. To properly resolve the internal structure of the loop, the coronal loop is modelled as a straightened magnetic flux tube.
We find that the energy injected into the loop is generated by internal coherent motions within strong magnetic elements. The resulting Poynting flux is channelled into the loop in vortex tubes forming a magnetic connection between the photosphere and corona, where it is dissipated and heats the upper atmosphere.
The coronal emission as it would be observed in solar extreme UV or X-ray observations shows transient bright strands. The widths of these strands are consistent with observations. From our model we find that the width of the strands is governed by the size of the individual photospheric magnetic field concentrations where the field line through these strands are rooted. Essentially, each coronal strand is rooted in a single magnetic patch in the photosphere, and the energy to heat the strand is generated by internal motions within this magnetic concentration.
With this model we can build a coherent picture of how energy and matter are transported into the upper solar atmosphere and how these processes structure the interior of coronal loops.
science theme: The Sun and the Heliosphere
schedule: Wed, 14:00 (invited talk)
Aleida K. Higginson
NASA Goddard Space Flight Center
TBD
science theme: Very low mass stars
schedule: Wed, 14:30 (contributed talk)
B. Riaz (1); J. Bally (2)
(1) (1) Universita ̈ts-Sternwarte Mu ̈nchen, Ludwig Maximilians Universita ̈t, Scheinerstraβe 1, D-81679 Mu ̈nchen, Germany; (2) (2) Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80389, USA
Mass accretion and ejection are the fundamental processes during the early stages of star formation. We have conducted the first extensive study of the accretion and outflow properties in Class 0/I proto-brown dwarfs (proto-BDs) using VLT SINFONI spectroscopy and spectro-imaging observations. The near-infrared spectra for the proto-BDs show prominent emission in the Paschen β, Brackett γ, Brackett 10–19, and several [FeII] and H$_{2}$ lines. The detection of H$_{2}$ lines from vibrational energy levels of ν = 1 to ν = 6 indicates the presence of both a cold (E(v,J) < 6000 K) and a hot gas component (E(v,J) > 20,000 K). The Class 0 proto-BDs show strong emission in the H$_{2}$ lines but the [Fe II] lines are undetected, while the Class I objects show emission in both [Fe II] and H$_{2}$ lines, suggesting an evolutionary trend in the jets from a molecular to an ionic composition. Extended emission with knots is seen in the [Fe II] and H$_{2}$ spectro-images for 3 proto- BDs, while the rest show compact morphologies with a peak on-source. The peak velocities of the [Fe II] lines (≥100 km s$^{-1}$) are higher than the H$_{2}$ lines (∼10-50 km s$^{-1}$), indicating that these lines trace different flow components. The accretion and outflow activity rates for the proto-BDs are in the range of (2$\times$10$^{-6}$ - 5$\times$10$^{-9}$) M$_{\odot}$ yr$^{-1}$. The outflow rate derived using the [Fe II] lines is at least an order of magnitude higher than H$_{2}$ lines, indicating that [Fe II] traces a large fraction of the total outflow mass. A comparison with Class 0/I protostars indicates that there is no notable decline in the accretion and outflow activity or jet efficiencies over a wide range in bolometric luminosities from ~30 L$_{\odot}$ down to ~0.03 L$_{\odot}$.
science theme: Very low mass stars
schedule: Wed, 14:45 (contributed talk)
Mark W. Phillips (1); Pascal Tremblin (2); Isabelle Baraffe (1,3); Gilles Chabrier (1,3)
(1) Astrophysics Group, University of Exeter, UK; (2) Maison de la Simulation, CEA Saclay, France; (3) Ecole Normale Supérieure de Lyon, France
The study of brown dwarfs and giant exoplanets is rapidly evolving as ever-improving instrumentation becomes sensitive to cooler objects. Accurate and reliable atmosphere and evolutionary models are important for placing mass and age constraints on these newly discovered objects, and understanding the rich chemistry and physics taking place in their atmospheres. We have recently published a new set of atmosphere and evolutionary models named ATMO 2020, which contains numerous improvements to the input physics for modelling substellar objects, superseding the widely used AMES-Cond models. The atmosphere models are generated with our state-of-the-art 1D radiative-convective equilibrium code ATMO, which includes the latest opacities for important molecular absorbers, the latest line shapes for the collisionally broadened alkali lines, and the ability to calculate non-equilibrium chemical abundances self-consistently with the atmospheric temperature structure. These model improvements allow us to more reliably follow the evolution of $0.5-75\,\mathrm{M_{Jup}}$ objects down to the coolest effective temperatures ($T_\mathrm{eff}=200\,$K). I will present comparisons of this new model set to those previously published, illustrating how the evolutionary tracks and the substellar boundary have changed due to improved opacities and the usage of a new equation of state. I will also compare our model grid to observational datasets, highlighting the impact of vertical mixing, metallicity and carbon-to-oxygen ratio on emission spectra of cool T/Y type brown dwarfs and giant exoplanets.
science theme: Very low mass stars
schedule: Wed, 15:15 (contributed talk)
Benjamin P. Brown (1); Jeffrey S. Oishi (2); Geoffrey M. Vasil (3); Daniel Lecoanet (4); Keaton J. Burns (5,6)
(1) Department Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO, USA; (2) Department of Physics and Astronomy, Bates College, Lewiston, ME, USA; (3) School of Mathematics and Statistics, University of Sydney, Sydney, NSW, Australia; (4) Department of Engineering Science and Applied Mathematics, Northwestern University, Evanston, IL, USA; (5) Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA, USA; (6) Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA
Fully convective M-dwarf stars are smaller and less luminous than our Sun. They have vigorous stellar magnetic dynamos in their interiors and are very magnetically active. The ball-like interior geometry of fully-covective M-dwarfs is unique among all the stars on the main-sequence, and studying dynamics in the ball requires new computational techniques. Here we study, for the first time, dynamo action in simulations of stratified, rotating fully convective M-dwarf stars in a full spherical ball domain. We do this using the novel spherical Dedalus pseudospectral framework to capture the coordinate singularity at the center ($r=0$), as well as the north and south pole, in an accurate fashion. We find that surprising single-hemisphere dynamo states are achieved, with most of the global-scale fields located in a single (northern or southern) hemisphere. These dynamos undergo cyclic reversals and exist over a broad range of the parameter space studied so far.
science theme: Very low mass stars
schedule: Wed, 15:30 (contributed talk)
Jennifer G. Winters (1); David Charbonneau (1); Todd J. Henry (2); Jonathan M. Irwin (1); Wei-Chun Jao (3); Adric R. Riedel (4); Kenneth Slatten (2)
(1) Center for Astrophysics | Harvard & Smithsonian; (2) RECONS Institute; (3) Georgia State University; (4) Space Telescope Science Institute
M dwarfs with masses 0.1 < M/Msol < 0.3 are under increasing scrutiny because these fully convective stars pose interesting astrophysical questions regarding their magnetic activity and angular momentum history. They also afford the most accessible near-future opportunity to study the atmospheres of terrestrial planets. Because they are intrinsically low in luminosity, the identification of the nearest examples of these M dwarfs is essential for progress. We present the volume-complete, all-sky list of 512 M dwarfs with masses 0.1 < M/Msol < 0.3 and with trigonometric distances placing them within 15 pc (parallax > 66.67 mas) from which we have created a sample of 413 M dwarfs for spectroscopic study. We present the mass function for these 512 M dwarfs, which increases with decreasing stellar mass in linear mass space, but is flat in logarithmic mass space. We also illustrate that the sample does not show evidence of Malmquist or Eddington biases, indicating that our sample is volume-complete.
This work is made possible by grant from the NSF, NASA, and the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation.
science theme: Very low mass stars
schedule: Wed, 15:45 (contributed talk)
Hiroyuki Tako ISHIKAWA (1,2); Wako Aoki (1,2); Takayuki Kotani (1,2,3); Teruyuki Hirano (2,3); Masayuki Kuzuhara (2,3); Masashi Omiya (2,3)
(1) (1) The Graduate University for Advanced Studies, SOKENDAI; (2) (2) National Astronomical Observatory of Japan; (3) (3) Astrobiology Center
M dwarfs are the most numerous constituents of the Galaxy and have been recently the prominent targets of planet search projects. However, the faintness of M dwarfs and the complexity of their spectra have limited the measurements of their elemental abundances. We here demonstrate the abundance determination of individual elements (Na, Mg, Ca, Ti, Cr, Mn, Fe, and Sr) of 13 nearby M dwarfs (2900 < $T_{\mathrm{eff}}$ < 3500 K) among the targets of the IRD-SSP (InfraRed Doppler planet search project in the framework of the Subaru Strategic Program). The determination was based on the line-by-line equivalent width analysis of high-resolution ($\sim$80,000) near-infrared (Y, J, and H) spectra, which was verified using the CARMENES spectra in Ishikawa et al. (2020, PASJ). The resulting [Fe/H] ranges from approximately –0.6 to +0.4, indicating that such diversity could have an impact on planet formation. We combined our abundance analysis with the astrometric measurements of the Gaia mission to conclude that all but two objects belong to the thin disk of the Galaxy. This fraction of thin disk stars is consistent with that in the FGK stars of the solar neighborhood.
science theme: Post main sequence cool stars
schedule: Thu, 12:00 (invited talk)
Miguel Montargès
LESIA, Observatoire de Paris - PSL
From November 2019 to April 2020, the prototypical red supergiant Betelgeuse experienced an unexpected and historic dimming. This event was observed worldwide by astrophysicists, and also by the general public with the naked eye. I will present the results of our observing campaign with ESO's VLT, and review the different scenarios that have been suggested to explain this remarkable event. Finally, I will put the Great Dimming in the more general context of the mass loss of red supergiant stars, a key element in determining their final mass before the supernova explosion.
science theme: Post main sequence cool stars
schedule: Thu, 12:30 (contributed talk)
L. Decin (1); ATOMIUM consortium
KU Leuven, Belgium
The ALMA Large Program ATOMIUM is the first observational campaign of a large sample of oxygen-rich Asymptotic Giant Branch (AGB) stellar winds at high angular resolution and sensitivity. The main goal of the ATOMIUM program is to establish the dominant physical and chemical processes in the winds of oxygen-rich evolved stars over a range of stellar masses, pulsation behaviours, mass-loss rates, and evolutionary phases. A more general aim of the ATOMIUM project is to build a strong foundation to better understand astrochemical processes in a range of research fields including novae, supernovae, exoplanets, protoplanetary nebulae, and interstellar shocks.
In this talk, we present one of the early successes of ATOMIUM which was published in Science in September 2020. Planetary nebulae (PNe) are well-known to reveal a wide range of morphologies. Bipolarity is the main characteristic, but jets and tori are also detected. Several contending theories of the evolution from a (roughly) spherically symmetric Asymptotic Giant Branch (AGB) stellar wind to a very non-spherical PN have emerged. Here, we present the first observational proof that (sub)stellar binary activity – including the effects of planets, brown dwarfs, and low-mass stellar companions - is the dominant shaping mechanism of AGB stellar winds, and their successors the PNe. We show that low mass-loss rate oxygen-rich AGB winds are more readily prone to complex structural deformations owing to their slow wind acceleration, whereas a binary-induced spiral structure is more prevalent in other classes of AGB stellar winds. These results resolve several previously unexplained phenomena — including the absence of detached shells around oxygen-rich AGB stars and disks around carbon-rich PNe — and have critical implications for the formation of type Ia supernovae. Our results also imply that the effects of planets around evolved stars are more easily detected in early-type oxygen-rich AGB stars.
science theme: Post main sequence cool stars
schedule: Thu, 12:45 (contributed talk)
Roberta M. Humphreys
University of Minnesota
VY CMa is one of the most luminous red supergiants. Imaging and spectroscopy of the knots, clumps, and extended arcs in the complex ejecta of VY CMa confirm a record of high mass loss events over the past few hundred years. Recent HST/STIS spectroscopy of numerous small knots close to the star allow us to measure their radial velocities from the strong K I emission and determine their separate motions, spatial orientations, and time since ejecta. Their ages concentrate around 70, 120, 200 and 250 years ago. A K I emission knot only 50 mas from the star ejected as recently as 1985 -- 1995 may coincide with an H2O maser. Comparison with VY CMa's historic light curve from 1800 to the present, reveals several knots with ejection times that correspond with extended periods of variability and deep minima. The similarity of this correspondence in VY CMa with the remarkable recent dimming of Betelgeuse and an outflow of gas is apparent. The evidence for similar outflows from the surface of a more typical red supergiant suggest that discrete ejections are more common and surface or convective activity is a major source of mass loss for red supergiants.
science theme: Post main sequence cool stars
schedule: Thu, 13:15 (contributed talk)
M. Wittkowski (1); A. Chiavassa (2); F. Baron (3)
(1) (1) ESO, Karl-Schwarzschild-Str. 2, 85586 Garching, Germany; (2) (2) Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Lagrange, CS 34229 Nice, France; (3) (3) Department of Physics and Astronomy, Georgia State University, PO Box 5060 Atlanta, GA 30302-5060, USA
It is currently an open question in stellar astrophysics which physical processes initiate the mass loss of red supergiants. Observations of Betelgeuse during its recent great dimming event in 2019/2020 suggested a discrete highly localised mass ejection event, possibly connected to photospheric motion caused by a stochastic occurence of an extreme convection cell and possibly enhanced by pulsation (Dupree et al. 2020, Harper et al. 2020, Montarges et al., submitted), which may also explain the mass-loss history of the red hypergiant VY CMa, and of RSGs in general (Humphreys et al. 2020). There is indication that corundum, metallic iron, or other large transparent grains auch as Ca-Al-rich silicates may be present as close as down to about 2 stellar radii, which may serve as seeds for Mg-Fe-rich silicates at larger radii (Gail 2020). Here, we image the extended molecular layers and inner dust shell of the red supergaint AH Scorpii (AH Sco), which is known to exhibit a strong and narrow classical 9.7 mu silicate feature. We use the newly available infrared beam combiner MATISSE at the Very Large Telescope Interferometer (VLTI) to image AH Sco in the L band with a spectral resolution of 506, focusing on the SiO (2-0) bandhead, as well as in the N band focusing on the silicate dust. Our spatial resolution ranges from 3 mas at 4 mu to 10 mas at 12.5 mu. We also provide an outlook on comparing the levitation of the atmospheres and the dust condensation sequence between RSG and AGB stars, using the same observational setup for the Mira star R Aqr.
science theme: Post main sequence cool stars
schedule: Thu, 13:30 (contributed talk)
Lars Mattsson, Christer Sandin
Nordita, Stockholm University, Sweden
We present simulations of two-fluid flow on winds including frequency-dependent radiative transfer. Our radiation hydrodynamic models also include stellar pulsations, grain growth and ablation, gas-to-dust drift, dust extinction based on both the small particle limit and Mie scattering, and an accurate numerical scheme. We use high spatial resolution (1024 radial gridpoints) and radiative transfer at 319 frequencies, and demonstrate the effects of drift by comparing drift models to non-drift models. Our results show differences of up to a factor of ten in comparison to previous results. Mass-loss rates and wind velocities of drift models are typically, but not always, lower than in non-drift models. Differences are larger when Mie scattering is used instead of the small particle limit. Yields of dust in the least massive winds increase by a factor four when drift is used. We find drift velocities in the range 10-67 km/s, which is drastically higher than in previous works. We argue that drift is a crucial parameter for wind formation as well as models of dust formation included in stellar evolution codes.
science theme: Stellar systems, clusters, and associations
schedule: Thu, 14:00 (invited talk)
Nate Bastian
Donastia International Physics Center
I will review our current understanding of the multiple poppulations phenomenon, including recent observational results and upcoming expectations, along with a critical assessment of current theories.
science theme: Stellar systems, clusters, and associations
schedule: Thu, 14:30 (contributed talk)
Anna Fabiola Marino
INAF - Osservatorio Astrofisico di Arcetri
The presence of more than one stellar population in globular clusters (GCs) is one of the most fascinating recent discoveries in the field of stellar populations. The properties of the different populations of stars are constrained by chemical abundances coupled with the nicknamed "Chromosome Maps" photometric diagram. One of the most intriguing results is that, contrary to what commonly believed, a significant fraction of GCs, besides Omega Centauri, may host stellar populations with different metallicity and heavy element chemical abundances. If all these objects will be confirmed to host stellar populations with different heavy elements abundances, then we have a quite high frequency of Omega Centauri-like GCs. These objects have experienced a more complex star-formation history, and might be associated with former dwarf galaxies. One of the most shocking discovery in this context is perhaps the apparent metallicity inhomogeneity of even the first stellar population, i.e., that one with elemental ratios similar to that of halo field stars. I will present the latest results on how to read the GC Chromosome Maps in terms of chemical abundances. I will focus on the most intriguing features observed on the maps, namely the features that can be interpreted as proxies of metallicity variations.
science theme: Stellar systems, clusters, and associations
schedule: Thu, 14:45 (contributed talk)
Giacomo Cordoni
University of Padova
Since the first pieces of evidence of Multiple Stellar Populations, Galactic Globular Clusters have been the focus of many astrophysical studies. Despite the efforts of the scientific community, the physical processes that lead to the formation of these chemically peculiar stellar populations remain unclear. While the photometric and spectroscopic features of multiple populations are well characterized, their internal kinematics is still poorly understood. Nevertheless, recent theoretical works suggest that the present-day dynamics of the distinct stellar populations could still carry the imprint of their initial configuration. Thus, it would provide a priceless window on the formation of these puzzling astrophysical systems. In my work, I combine Gaia Data Release 2 (DR2) exquisite proper motions, together with wide-field ground- and space-based photometry to investigate the internal dynamics of multiple stellar populations in 9 Galactic Globular clusters, including the most massive one, Omega Centauri. We find clear evidence of dynamical differences in some of these systems, and kinematically distinct stellar populations also show a different spatial distribution on the plane of the Sky. Furthermore, the analysis of stars with different light- and heavy-element abundances add new constraints to the evermore puzzling enigma that are Multiple Stellar populations in Globular Clusters.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:15 (contributed talk)
Travis Metcalfe (1); Ricky Egeland (2); Jennifer van Saders (3)
(1) White Dwarf Research Corporation; (2) High Altitude Observatory, NCAR; (3) Institute for Astronomy, University of Hawaii
Over the past few years, strong evidence has emerged that something unexpected occurs in the evolution of stellar magnetism near the middle of main-sequence lifetimes. For solar-type stars this transition begins near the age of the Sun, when rotation becomes too slow to imprint Coriolis forces on the global convective patterns, reducing the shear induced by differential rotation, and disrupting the large-scale dynamo. From the best data currently available, the Sun appears to have entered this phase several hundred million years ago, just as life was emerging from the oceans onto land. Younger stars bombard their planets with radiation and charged particles that are hostile to the development of complex life, but older stars quiet down substantially and provide a more stable environment. I will summarize the latest evidence for this magnetic transition from recent X-ray and Zeeman Doppler measurements, outline our current understanding of its likely origin, and speculate on the implications for planetary habitability.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:30 (contributed talk)
Ryan Terrien (1); Gudmundur Stefansson (2); Paul Robertson (3); Joe Ninan (4); Suvrath Mahadevan (4); Katy Oda (1); Ally Keen (1); Freja Olsen (1); Adam Ickler (1); Vanessa Parts (4); Shubham Kanodia (4); The HPF Team
(1) Carleton College; (2) Princeton; (3) UC-Irvine; (4) Penn State
Accurate knowledge of the stellar rotation period is a cornerstone for studies of M dwarfs, particularly for analysis of their stellar activity and for diagnosing the measured radial velocity (RV) signals in exoplanet surveys. Although it is possible to measure rotationally-modulated photometric signals in many M dwarfs, such signals are very difficult to measure in many stars, particularly those older, slowly-rotating stars that are best-suited for exoplanet searches. In R~55,000 spectroscopic monitoring of these types of stars with the Habitable Zone Planet Finder (HPF), we have discovered periodic variations in the widths and depths of several absorption lines, consistent with the rotational modulation of Zeeman broadening and intensification of magnetically-sensitive features. We discuss the measurement of these variations and show how they may be used to inform rotation period measurements. We highlight how measurement of the rotation period using this spectroscopic technique can help to disambiguate between stellar activity and exoplanetary signals in RV time series measurements.
science theme: Stellar systems, clusters, and associations
schedule: Thu, 15:45 (contributed talk)
Antonino Milone
University of Padova
Historically, multiple populations in Globular Clusters (GCs) have been mostly investigated in UV filters that are sensitive to the bizarre chemical composition of GC stars. Due to the observational limits of the UV detectors, only stars more massive than 0.6-0.7 solar masses have been studied in the UV. A major limitation to understand multiple populations is that the faintest portion of the main sequence (MS), which comprises the bulk of GC stars, is almost unexplored.
I illustrate the new methods to identify and characterize the stellar populations among very-low mass GC stars with the Hubble Space Telescope and the James Webb Space Telescope. I also present early results from our ongoing survey of multiple populations among M-dwarfs. The synergy of NIR, optical and UV photometry allows to identify and characterize the multiple populations along the entire CMD, from the RGB tip towards the Hydrogen-burning limit. The comparison of the multiple population properties among very low mass and massive stars provides strong constraints on the formation scenarios of multiple stellar populations in GCs.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 13:00 (haiku)
Marina Kounkel (1,2); Kevin Covey (1); Keivan Stassun (2)
(1) Western Washington University; (2) Vanderbilt University
Gaia DR2 provides unprecedented precision in measurements of the distance and kinematics of stars in the solar neighborhood. Through applying hierarchical clustering on 5D data set (3D position + 2D velocity), we identify a number of clusters, associations, and comoving groups within 3 kpc. Through leveraging machine learning techniques, we can estimate the ages of these stars with pseudo-isochrone fitting. Furthermore, supervised learning then allows for identification of isolated pre-main sequence stars that cannot be recovered through clustering. With these efforts combined, we can produce to date the largest catalog of stars with known ages, allowing for investigation of star formation history of the solar neighborhood. Most of the young stars are commonly found to be filamentary or string-like populations, oriented in parallel to the Galactic plane, and some span hundreds of parsec in length. Most likely, these strings are primordial, tracing the morphology of filamentary clouds that produced them, rather than the result of tidal stripping or dynamical processing. The youngest strings (<100 Myr) tend to be orthogonal to the Local Arm. Stars in a string tend to persist as comoving for time scales of ~300 Myr, after which most dissolve into the Galaxy. These data shed a new light on the local galactic structure and a large-scale cloud collapse.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 13:00 (haiku)
Edward Gillen (1,2); Simon Hodgkin (2); Gareth Smith (2); James Jackman (3); Tyler Moulton (4); Joshua Briegal (2); Peter Wheatley (3); Louise Nielsen (5); Didier Queloz (2); the NGTS consortium (6)
(1) Queen Mary University of London; (2) University of Cambridge; (3) University of Warwick; (4) Harvard University; (5) Université de Genève; (6) Cambridge, Warwick, Genève, DLR Berlin, Leicester, Queen's Belfast, Universidad de Chile
Young open clusters are powerful astrophysical laboratories because their members share broad coevality, composition and location. Combining information from different open clusters, which span a range of ages, offers a powerful probe of both stellar and planetary system evolution. The Next Generation Transit Survey (NGTS) is a state-of-the-art wide-field photometric facility comprised of 12 independent robotic telescopes based at ESO’s Paranal Observatory. NGTS is conducting a systematic survey of nearby young open clusters with ages between 1 Myr - 2 Gyr, which are each being monitored at 12-second cadence every clear night over 200-250 day periods. I will introduce the NGTS clusters survey and present recently published and new results from our first clusters, which include Blanco 1 (115 Myr) and the Orion star forming region (1-10 Myr). These results provide new insights into the early evolution of stellar rotation, flare frequency and the star-disk interaction, as well as precise constraints on stellar evolution theory from new, well-characterised eclipsing binary systems. Finally, I will conclude with an outlook towards future prospects for the survey and our understanding of young stellar systems.
science theme: Young stars
schedule: Tue, 13:00 (haiku)
Kora Muzic
CENTRA, University of Lisbon
Young clusters and star forming regions are home to a large number of substellar objects with masses below the hydrogen-burning limit at ~0.075 M$_\odot$. Most of our knowledge about their populations comes from nearby regions (d$<$400 pc), where we find consistent formation rates of 2-5 young brown dwarfs per 10 newborn stars. Brown dwarf theories, on the other hand, predict that high gas or stellar densities, as well as the presence of massive OB stars, may be factors that boost the incidence of newly formed brown dwarfs with respect to stars. The next frontier in substellar studies, therefore, is the exploration of massive star clusters, characterized by significantly different star-forming environments than those found in our immediate vicinity. In this contribution I will compare the results of our deep survey SONYC (Substellar Objects in Nearby Young Clusters), with the brown dwarf content of several massive young clusters, in which we confirm the first bona fide brown dwarfs beyond 1 kpc. I will also discuss the trials and tribulations of membership confirmation in this mass and age regime.
science theme: Stellar and planetary atmospheres
schedule: Tue, 13:00 (haiku)
M.C. Maimone (1); A. Chiavassa (1); J. Leconte (2); M. Brogi (3)
(1) 1. Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Blvd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France; (2) 2. Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France; (3) 3. Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
The study of exoplanets atmospheres is one of the most intriguing challenges in exoplanet field nowadays and the High Resolution Spectroscopy (HRS) has recently emerged as one of the leading methods for detecting atomic and molecular species in their atmospheres. Nevertheless extraordinary results have been achieved (Birkby, 2018), HRS alone is not enough. 1D models of the host star have been coupled to HRS observations, but they do not reproduce the complexity of stellar convection mechanism (Chiavassa & Brogi, 2019). On the contrary, 3D Radiative Hydrodynamical (3D RHD) simulations take it into account intrinsically, allowing us to correctly reproduce asymmetric and blue-shifted spectral lines due to the granulation pattern of the stellar disk, which is a very important source of uncertainties (Chiavassa et al. 2017). However, numerical simulations have been computed independently for star and planet so far, while the acquired spectrum contains both the signals. For instance, some molecular species (e.g, CO) form in the same region of the spectrum, thus planetary and stellar spectral lines are completely mixed and overlapped. A next step forward is needed: computing stellar and planetary models together during the planet transit. With our work, we aim at upgrading the already-in-place 3D radiative transfer code Optim3D (Chiavassa et al. 2009) — largely used for stellar purposes so far — to take into account also the exoplanetary contribution and finally carry out a full characterisation of planets and their host stars. I will present the advantages of the simultaneous use of 3D RHD stellar simulations and exoplanet’s Global Climate Models (GCMs) in generating unprecedented precise synthetic spectra and mimicking the observation at high resolving power during the planet transit. I will also show the impact of this new approach on the detection of CO and H2O molecules in the well-know benchmark HD189733 spectrum, chosen as springboard to test the code.
science theme: Exoplanets around cool stars
schedule: Tue, 13:00 (haiku)
Joe P. Ninan, (1); Gudmundur Stefansson (2),; Suvrath Mahadevan(1), ; Chad Bender (3),; Paul Robertson(4), ; Ryan Terrien (5), ; HPF Team
(1) The Pennsylvania State University, University Park, PA, 16802, USA; (2) Princeton University, 4 Ivy Lane, Princeton, NJ 08540, USA; (3) Steward Observatory, University of Arizona, Tucson, Arizona 85721, USA; (4) University of California-Irvine, Irvine, California 92697, USA; (5) Carleton College, Northfield, Minnesota 55057, USA
Recently, resonant scattering absorption of meta-stable Helium atoms at 10830 Angstroms has been identified as a powerful probe to detect the extended exospheres from exoplanets. This near-infrared line is observable from the ground and unaffected by the interstellar medium, and has numerous advantages over conventional Ly alpha. The high spectral resolution observations of these meta-stable helium atoms from the exospheres enable us to study the irradiation environment as well as the structure of the outflow from the evaporating atmospheres in M-dwarf planets. In this talk we shall present our first detection of He10830 in the exosphere of a warm Neptune orbiting an M-dwarf, GJ 3470, using the Habitable-Zone Planet Finder (HPF). We shall also present our analysis of the outflow structure via line profile analysis, and the EUV irradiation environment on the planet from this detection.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 13:00 (haiku)
Todd J. Henry (1); Leonardo A. Paredes (1,2); Eliot H. Vrijmoet (1,2); Andrew C. Couperus (1,2); Hodari-Sadiki James (1,2); Wei-Chun Jao (2); Aman Kar (1,2); DeAndre X. Lesley (1); Dana I. Casetti-Dinescu (3); Elliott P. Horch (1,3); Jennifer G. Winters (4)
(1) RECONS Institute; (2) Georgia State University; (3) Southern Connecticut State University; (4) Harvard-Smithsonian CfA
The RECONS (REsearch Consortium On Nearby Stars, www.recons.org) team continues to explore the solar neighborhood by evaluating the nearest stars, both individually and as a population. Key points are becoming clear: we now know that 86% of all stars are K and M dwarfs, and we need to reach to 50 pc and 25 pc, respectively, to create samples of 5000 and 3000 primaries each. These two sizable samples allow us to understand the outcome of the star formation process across a factor of ten in mass as never before. Here we focus on one crucial area of research --- stellar companions --- with results of our surveys combining radial velocities, astrometry, high resolution imaging, and trawls of catalogs and the literature. The surveys are carried out primarily at the CTIO/SMARTS 0.9m and 1.5m, the SOAR 4.1m, and both Gemini 8.1m telescopes. We reveal companions at separations from less than 1 AU to more than 1000 AU from the K and M dwarfs, with the key result that these stellar partners are found most often at separations similar to our Solar System. Thus, the star and planet formation processes work on the same spatial scales ... a fact that we must keep in mind as our solar neighborhood becomes enriched with planetary discoveries at distances comparable to where stellar companions are found.
This work has been supported by NSF grants AST-0507711, AST-0908402, AST-1109445, AST-141206, and AST-1715551 and the SMARTS Consortium.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 13:00 (haiku)
Luisa Rebull ; John Stauffer; Lynne Hillenbrand; Ann Marie Cody
(1) Caltech-IPAC/IRSA; (2) Caltech-IPAC/SSC; (3) Caltech; (4) Bay Area Environmental Research Institute
In recent years, we have been using K2's high precision photometry to probe stellar variability and stellar rotation to lower masses and lower amplitudes than has ever been done before. Younger stars are generally more rapidly rotating and have larger star spots than older stars of similar masses. K2's large field of view was able to monitor a significant fraction of many nearby clusters and associations; some of the nearest associations can only be monitored by TESS, which observes ~85% of the sky. We present initial rotation rates from a TESS study of stars in the ~15 Myr old Upper Centarus-Lupus (UCL)/Lower Centaurus-Crux (LCC) association.
science theme: Star-planet interaction
schedule: Tue, 13:00 (haiku)
Nikoleta Ilic; Katja Poppenhaeger
Leibniz Institute for Astrophysics Potsdam
It is an open question to what degree planets influence the (magnetic) evolution of their host star. As a star ages and evolves, its rotational rate decreases and the star spins down. This is due to angular momentum loss in a process called magnetic braking, which is the usual ’spin-down’ scenario for singular stars and stars without planets. In star-planet systems, the possibility of halting the decrease or even increasing the rotational rate of a star due to tidal interaction with its planet(s) exists. This tidal ’spin-up’ can be traced by an enhanced magnetic activity since a faster rotating star is expected to be more magnetically active. The difficulty here is estimating if the observed magnetic activity level of the star is higher due to the tidal interaction with the planet or due to the relatively young age, when the process of magnetic braking is still undergoing. Our solution for this is to invoke a reference star that does not host a planet and that has the same age as the planet-hosting star. Therefore, we analyzed wide binary stellar systems that have a planet-hosting star and use the stellar companion as a proxy for the measured magnetic activity level. We expect that the more active planet host has a hotter corona and is, therefore, a brighter X-ray source when compared to its stellar companion. We have a sample of 37 stellar systems, observed in X-rays with XMM Newton and Chandra, for which we evaluate the component' X-ray luminosity. We expect that the enhanced magnetic activity of the planet host leads to a hotter corona and hence a brighter X-ray source when compared to its stellar companion, if the enhancement is due to tidal interaction. With this approach, we will be able to determine if the tidal 'spin-up' process can leave an observable footprint on planet-hosting stars and which star-planet system configuration is prone to significantly changing the activity level of the star.
science theme: Stars with planets
schedule: Tue, 13:00 (haiku)
Luan Ghezzi (1); Robert Wilson (2); Cintia Martinez (3); Katia Cunha (3,4); Verne Smith (5); Steven Majewski (2)
(1) Observatório do Valongo/UFRJ; (2) University of Virginia; (3) Observatório Nacional; (4) Steward Observatory/University of Arizona; (5) National Optical Astronomy Observatory
Correlations between stellar and planetary properties provide important information about the processes of planet formation and evolution and the resulting architectures of planetary systems. Recent studies have provided evidence that higher stellar metallicities are connected to the presence of planets of certain sizes and orbital periods. In this work, we explored these relations further by focusing on planetary systems instead of individual planets. We derived independent and homogeneous iron abundances for a sample of 1005 planet hosting stars from the California-Kepler Survey (CKS) using a classical LTE spectroscopic analysis. Although we confirmed the well-known result that the metallicities of stars hosting large planets are significantly skewed to higher metallicities relative to systems with only small planets, we also found that the boundary between the large- and small-planet regimes occurs at Rp = 4.4 R_Earth. We observed that the previously reported differences between the host-star metallicity distributions for hot and warm planets also hold for planetary systems, with the former being more metal-rich. However, we show that planet multiplicity also plays an important role and these differences seem to be larger for multiple relative to single planet systems. The most significant difference is seen for systems hosting only Super-Earths and a similar result is not found for systems hosting only Sub-Neptunes, revealing an important distinction within the regime of small planets.
science theme: Stellar systems, clusters, and associations
schedule: Tue, 13:00 (haiku)
Dario J. Fritzewski (1); Sydney A. Barnes (1); David J. James (2, 3); Klaus G. Strassmeier (1)
(1) Leibniz Institute for Astrophysics Potsdam (AIP); (2) Center for Astrophysics | Harvard & Smithsonian; (3) Black Hole Initiative at Harvard University
The universality of stellar evolution is fundamental to our understanding of stars. The evolution of angular momentum can also be used to test this concept because rotation changes significantly with stellar age, and can be probed sensitively using stellar rotation periods. We present new rotation periods measured from photometric time series observations for stars in the 150Myr-old open cluster NGC 2516. Among the members, selected using Gaia data, radial velocities and multi-colour photometry, we find 308 stars with rotation periods ranging from 0.25d to 25d. Combined with rotation periods for M dwarfs from the literature, our sample contains 555 periods for stars between G and mid-M. This large sample enables a detailed comparison with the K2-based rotation period distribution of the Pleiades and also the corresponding X-Ray activity diagrams. Comparison between NGC 2516 and Pleiades shows that the two open clusters can be considered twins because in addition to the classical parameters, their rotation period distributions are almost indistinguishable across the colour and period ranges. Both clusters also host a group of slowly-rotating M dwarfs with P>15d, unseen before in other open clusters, that constitute what we call the "extended slow rotator sequence". Further comparison between NGC 2516 and the other nearly coeval open clusters M35, Blanco 1 and M50 shows that these rotation period distributions are also substantially similar to that for NGC 2516, at least to the extent that the limitations of the individual studies permit. Based on empirical comparison of these five different open clusters, our study suggests that coeval open clusters of similar composition have identical rotation period distributions, the strongest evidence to date against cluster-to-cluster variations. We conclude that the star formation process in different cluster environments is likely universal enough to result in substantially identical rotation period distributions at the ZAMS.
science theme: Cool Stars on the main sequence
schedule: Tue, 13:00 (haiku)
Joshua T. Briegal (1), Edward Gillen (1), Didier Queloz (1), Simon Hodgkin (2) and the NGTS consortium
(1) Astrophysics Group, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK.; (2) Institute of Astronomy, University of Cambridge, Madingley Rise, Cambridge CB3 0HA, UK.
I present the first comprehensive stellar variability study conducted on the entire Next Generation Transit Survey (NGTS) photometric light curve data set. Based at ESO’s Paranal observatory, NGTS observes each star at 12 second cadence every clear night over a ~250 day period. Almost 1 million sources have been processed using a Generalised Autocorrelation Function (G-ACF) to extract periodic variability. We look at how variability is distributed throughout the HR diagram, identifying distinct populations of variable objects from pre-main-sequence through to highly evolved giants. In addition to confirming results from previous gyrochronological studies, we are able to observe and analyse a much broader stellar population and infer new trends. In particular we explore a bi-modal structure observed in period-colour space between mid-K and mid-M spectral types.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
The Orion Nebula Cluster (ONC) is an ideal astrophysical laboratory to study very young (< 0,5 - 2 Myr) stars. Being the nearest site of massive star formation and hosting a young high-mass near ZAMS stellar population, the core of the ONC is ideal for detailed spectroscopic studies of young embedded cluster stars. Since the launch of the Chandra X-ray Observatory 20 years ago, observations of the ONC have been at the center of star formation studies. In 2003 the Chandra Orion Ultradeep Project (COUP) established global X-ray properties of the stellar propulations with the ONC setting a true milestone in the X-ray studies of star forming regions. Further high resolution X-ray studies revealed unprecedented details about young stars at a wide mass range. In the Chandra Cycle 21 a very large project to observe the core of the ONC was carried out to boost the exposure to 2.2 Ms with the Chandra High Energy Grating Spectrometer. This now allows to harvest more than three dozen high resolution X-ray spectra from young massive, intermediate mass, and low mass stars to determine line widths, line ratios, and abundances in the core of the ONC. Here we highlight specific science projects and show first results which includes longterm variability of young cluster stars, high brilliance X-ray line spectra of the brightest Orion Trapezium stars as well as from some young classical T Tauri stars in the vicinity of the Trapezium.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
Baptiste Klein (1); Jean-François Donati (2); Claire Moutou (2); Xavier Delfosse (3); Xavier Bonfils (3); Eder Martioli (4); Pascal Fouqué (2,5); Ryan Cloutier (6); Étienne Artigau (7); René Doyon (7); Guillaume Hébrard (4); Julien Morin (8); Julien Rameau (3); Peter Plavchan (9); Eric Gaidos (10)
(1) Sub-department of Astrophysics, Department of Physics, University of Oxford, Oxford OX1 3RH, UK; (2) Université de Toulouse, CNRS, IRAP, 14 av. Belin, 31400 Toulouse, France; (3) CNRS, IPAG, Université Grenoble Alpes, 38000 Grenoble, France; (4) Institut dAstrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France; (5) CFHT Corporation; 65-1238 Mamalahoa Hwy; Kamuela, Hawaii 96743; USA; (6) Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA, 02138, USA; (7) Institut de Recherche sur les Exoplanètes (IREx), Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, QC, H3C 3J7,Canada; (8) LUPM, Université de Montpellier, CNRS, Place Eugène Bataillon, F-34095 Montpellier, France; (9) Department of Physics and Astronomy, George Mason University, Fairfax, VA, 22030, USA; (10) Department of Earth Sciences, University of Hawai’i at Manoa, Honoluu, HI 96822 USA
Measuring the mean densities of close-in planets orbiting pre-main-sequence (PMS) stars is crucially needed by planet formation and evolution models. However, PMS stars exhibit intense magnetic activity inducing fluctuations in both photometric and RV curves that overshadow planet signatures. As a result, no close-in planet younger than 25 Myr has a well-constrained bulk density.
In this study, we present a spectropolarimetric and velocimetric analysis of 27 near-infrared observations of the nearby active 22 Myr-old red dwarf AU Microscopii collected with SPIRou at the end of the year 2019. We jointly model the planet and stellar activity RV components, resulting in a 3.9$\sigma$-detection of the recently-discovered close-in Neptune-sized planet AU Mic b, with an estimated mass of 17.1$^{+4.7}_{-4.5}$ M$_{\oplus}$, implying a Neptune-like density for the planet. A consistent detection of the planet is independently obtained by simultaneously reconstructing the surface distribution of bright and dark inhomogeneities and estimating the planet parameters using Doppler imaging (DI). Using Zeeman-Doppler Imaging, we invert our time-series of intensity and circularly-polarized line profiles into distributions of brightness and large-scale magnetic field at the surface of the star and explore how these distributions are sheared by latitudinal differential rotation. Finally, we investigate the magnetic activity of AU Mic by computing various indicators and found that the disk-integrated magnetic flux density correlates best with the stellar activity RV signal, in line with recent solar observations.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
Konstantin V. Getman; Eric D. Feigelson
Pennsylvania State University
Solar-type stars exhibit their highest levels of magnetic activity during early convective pre-main sequence (PMS) phase of evolution. The most powerful PMS flares, super-flares (SFs), have total energies $10^{34-38}$erg. Among 24,000 X-ray members of 40 young star-forming regions emerged from our Chandra MYStIX/SFiNCs surveys, we identify and analyze a sample of 1,086 X-ray SFs, the largest sample ever studied. These are considerably more powerful than optical flares detected on older stars. We find that X-ray SFs are produced by young stars of all masses over a range of evolutionary stages from protostars to diskless stars with the occurrence rate positively correlated with stellar mass. A powerlaw slope in the flare energy distributions is consistent with those of optical/X-ray flaring from older stars. SFs contribute >10-20% to the total PMS X-ray energetics. PMS SFs may have implications for X-ray driven photoevaporation of the protoplanetary disk, variable ionization in disk gas, production of spallogenic radionuclides in disk solids, and hydrodynamic escape of young planetary atmospheres. We fit plasma models to the 55 brightest X-ray SFs and compare them with published SFs from young ONC and older stars. The distributions of SF properties are indistinguishable for disk-bearing and diskless stars, evidence that star-disk magnetic fields are not involved. Inferred positive correlations of the flare X-ray emission and plasma temperature with stellar mass suggest that PMS characteristic emission is composed of micro-flares. Such correlations indicate that RTV loop scaling laws are universal. However our models suggest that flares from more massive stars are associated with thicker coronal loops. In the Sun, the rare X-ray streamers may be the closest analogues to the PMS SFs.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
G. Pantolmos (1); C. Zanni (2); J. Bouvier (1)
(1) Univ. Grenoble Alpes, CNRS, IPAG; (2) INAF – Osservatorio Astrofisico di Torino
Classical T Tauri stars (CTTs) magnetically interact with their surrounding disks, a process that controls their rotational evolution. Observations show that CTTs maintain a constant rotation in time, indicative of angular-momentum-loss processes that prevent their stellar spin rates to increase due to both accretion and contraction. Various types of outflows (e.g., magnetized stellar winds, magnetospheric ejections, disk winds) have been proposed to explain this phenomenon. I will present numerical simulations that quantify the magnetic braking (due to stellar winds) in accreting stars. We find that stellar winds originated from CTTs brake the stellar rotation more efficiently than outflows from diskless stars. However, we predict that these winds should eject at >10% of the mass-accretion rate in order to counteract the stellar spin-up due to accretion.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
Laura Flagg (1); Christopher Johns-Krull (1); Kevin France (2); Gregory Herczeg (3); Joan Najita (4); John Carptenter (5); Scott J. Kenyon (6); Elisabeth R. Newton (7)
(1) Rice University; (2) Laboratory for Atmospheric and Space Physics, University of Colorado; (3) Kavli Institute for Astronomy and Astrophysics, Peking University; (4) National Optical Astronomy Observatory; (5) Joint ALMA Observatory; (6) Smithsonian Astrophysical Observatory; (7) Dartmouth College
We have detected molecular hydrogen in the AU Mic system using high-resolution FUV spectra from HST-STIS. We measured the temperature of the gas at ~1000 K. Based on the velocities and dispersion of the H$_2$ lines, we believe that it is unlikely to be from the disk or the planet, making star spots the most likely origin of this gas. However, the temperature of this gas is significantly below the temperature of the photosphere (~3800 K) and the predicted temperature of its star spots. We discuss the possibility of such a cold star spot on a pre-Main Sequence M dwarf.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
William J. Fischer,; Julia Roman-Duval,; Charles R. Proffitt,; Joanna M. Taylor,; TalaWanda R. Monroe,; Travis C. Fischer,; and the ULLYSES implementation team
Space Telescope Science Institute
The Hubble Space Telescope's Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) is a Director’s Discretionary program of approximately 1,000 orbits that is producing an ultraviolet spectroscopic library of young high- and low-mass stars in the local universe. This presentation addresses the low-mass stars; these are T Tauri stars for which ULLYSES is sampling a broad range of stellar masses and accretion rates. In addition to data already in the MAST archive, we are obtaining single-epoch COS and STIS spectra of about 67 survey targets and time monitoring of 4 prototypical targets. The monitoring targets will be observed four times per rotational period over three periods, with this pattern repeated nine to twelve months later. Observations began in Fall 2020. I will discuss our community-driven sample selection, observing plan, and data products, with the intent of encouraging meeting participants to collaborate on data analysis and coordinated observations.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
Ronan Kerr; Aaron Rizzuto; Adam Kraus
University of Texas at Austin
Young associations provide a record of recent star formation from which the origins of stellar populations can be established and mapped. Using Gaia DR2 astrometric and photometric measurements, combined with a model stellar population, we have identified over 30000 candidate young stars within ~300 pc, tracing an expansive network of nearby associations and clusters. We then apply the HDBSCAN density clustering algorithm to this dataset, identifying 27 primary groups, including some previously unknown associations. Several of these groups, including the Sco-Cen, Taurus, Orion, and Perseus associations fragment into identifiable substructure at smaller scales, and include extensions that go beyond the previous canonical boundaries by up to 100pc. Isochronal ages computed for the substructures reveal large-scale patterns in the star formation histories for many of the nearby associations we identify. This includes broad stellar populations in Taurus with ages older than 10 Myr, and star formation bursts in Perseus that pre-date the current star-formation activity by ~15 Myr. In Sco-Cen, we find age gradients spanning about 15 Myr and up to 60 pc in space that converge on an arc of 20-25 Myr old stars, a feature that appears to mark the earliest source of star formation in the association. In this work, we outline the results from our analysis of this nearby population of young stars, and present some features that merit further investigation.
science theme: Young stars
schedule: Tue, 15:00 (haiku)
Justyn Campbell-White; Aurora Sicilia-Aguilar
University of Dundee
Accretion is a fundamentally important process for pre-main-sequence stars, affecting disk stability and evolution, stellar rotation and activity, and planet formation and migration. The main observational challenge is probing the sub-au scales of the innermost disk, which is not yet possible via interferometry. Such young stars, however, possess a wealth of metallic emission lines that can reveal the nature of these accretion-related processes.
Our analysis involves emission line tomography of time-resolved, high-resolution spectra of young stars. This technique uses the time domain to investigate distortions in the stellar emission line profiles and radial velocity signatures. Local temperatures and densities can be determined for the various emission line species. With both temporal and spatial information, we can then infer a tomographic map of the accretion structures, activity spots and the innermost hot atomic gas; down to scales smaller than those achievable with direct imaging. Our analysis allows for new science results to be obtained from archival data, as well as facilitating timely analysis of new data as it is obtained.
In this talk, we will give a demonstration of the STAR-MELT Python package. Directly from the FITS files, the emission lines are automatically extracted and identified, via matching to a compiled reference database of lines. Line profiles are fitted and quantified, allowing for calculations of physical properties across each individual observation. Temporal variations in lines can readily be displayed and quantified. Our STAR-MELT python package would also be useful for different applications of spectral analysis, where emission line identification is required. Standard data formats for spectra are automatically compatible, with user-defined custom formats also available. Any reference database (atomic or molecular) can also be used for line identification.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
T. Milbourne (1,2); The HARPS-N Solar Telescope Collaboration
(1) Department of Physics, Harvard University; (2) Harvard-Smithsonian Center for Astrophysics
State of the art radial velocity (RV) searches for low-mass exoplanets are limited by the effects of stellar magnetic activity. Previously, we have shown that different types of active regions - spots, plage, and network - have different impacts on the apparent stellar RV. Differentiating the relative coverage of these active regions is thus necessary in order to successfully disentangle the RV signatures of stars from potential planetary signals. However, traditional activity indicators, such as the calcium S-index and photometry, only indicate the overall coverage by magnetized regions: more information is necessary to differentiate the different types of active regions. In this work, we outline techniques to estimate magnetic filling factors from spots, plage, and networks features on stellar targets using only spectroscopic and photometric observations. We demonstrate linear and neural network implementations of our techniques using real solar observations taken by the solar telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard SORCE, and compare the results of each technique to filling factors derived from full-disk images from the Solar Dynamics Observatory. We conclude by assessing the possibilities of applying these techniques to non-solar targets.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
Juan Camilo Guevara Gómez; Sven Wedemeyer
Rosseland Centre for Solar Physics, Institute of Theoretical Astrophysics, University of Oslo
Observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA) now allow for more quantitative determination of temperatures in the chromosphere. ALMA observations of Quiet Sun regions in receiver Band 3 (3 mm; 100 GHz) exhibit small-scale features that resemble a mesh-like chromospheric pattern, similar to what was earlier detected with other chromospheric diagnostics. Tracking the features in time results in lifetimes, velocities and sizes, which are analysed within the context given by co-aligned images of the Solar Dynamics Observatory (SDO). Here we present a statistical analysis and compare the results with a 3D MHD simulation with Bifrost of an enhanced network which has been degraded to the ALMA spatial resolution. The match between observations and simulations suggests that the dark features are post-shock regions. The thermodynamics and kinetic properties derived from the ALMA observations will therefore enhance our understanding of the small-scale dynamics and heating of the solar chromosphere and its potential implications for other solar-like stars.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
K. Sowmya (1); A. I. Shapiro (1); V. Witzke (1); N.-E. Nemec (1,2); T. Chatzistergos (1,3); N. A. Krivova (1); S. K. Solanki (1,4)
(1) Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany; (2) ; (3) Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany; (4) ; (5) INAF Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy; (6) ; (7) School of Space Research, Kyung Hee University, YongIn, Gyeonggi 446-701, Korea
The emission in the near ultraviolet Ca II H&K lines, often quantified via the S-index, has been serving as a prime proxy of solar and stellar magnetic activity. Despite the broad usage of the S-index, the link between the coverage of a stellar disk by magnetic features and Ca II H&K emission is not fully understood. In order to fill this gap we developed a physics-based model to calculate the solar S-index. To this end, we made use of the distributions of the solar magnetic features derived from the simulations of magnetic flux emergence and surface transport, together with the Ca II H&K spectra synthesized using a non-local thermodynamic equilibrium (non-LTE) radiative transfer code.
We show that the value of the solar S-index is influenced by the inclination angle between the solar rotation axis and the observer’s line-of-sight, i.e. the solar S-index values obtained by an out-of-ecliptic observer are different from those obtained by an ecliptic-bound observer. This is important for comparing the magnetic activity of the Sun to other stars. We computed time series of the S-index as they would be observed at various inclinations dating back to 1700. We find that depending on the inclination and period of observations, the activity cycle in solar S-index can appear weaker or stronger than in stars with a solar-like level of magnetic activity. We show that there is nothing unusual about the solar chromospheric emission variations in the context of stars with near-solar magnetic activity.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
R. Reda (1,2); T. Alberti (2); F. Berrilli (1); P. Giobbi (1); L. Giovannelli (1); V. Penza (1)
(1) University of Rome "Tor Vergata"; (2) INAF - Istituto di Astrofisica e Planetologia Spaziali
Solar variability related to its magnetic activity can be quantified by using synthetic indices (e.g. sunspots number) or physical ones (e.g. chromospheric proxies). In order to connect the long-term solar activity variations to solar wind properties, we use Ca II K index and solar wind OMNI data in the time interval between 1965 and 2019, which almost entirely covers the last 5 solar cycles. A time lag in the correlation between the parameters is found. This time shift seems to show a temporal evolution over the different solar cycles. The advantage to use a chromospheric proxy opens the possibility to extend the relation found for the Sun to link stellar variability and stellar wind properties in Sun-like stars.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
Hannah Schunker
The University of Newcastle
The emergence of magnetic field from the interior of the Sun generates a poloidal magnetic field from rising toroidal magnetic field. Solar active regions and sunspots are the strongest concentrations of magnetic field on the surface, and how they emerge is a crucial, but poorly understood aspect of the solar dynamo. Only since the advent of the SDO/HMI monitoring campaign has it been possible to capture the emergence process of hundreds of active regions in observations of the magnetic field, Doppler velocity and intensity continuum. By measuring the average motion of the polarities, the average surface velocities and average supergranulation pattern it is clear that convection plays an important role in the emergence process in the Sun. In order to broadly understand the dynamo mechanism, we need to understand the relationship between convection and the surface magnetic field structure on other Sun-like stars.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
M. Cristina Rabello Soares (1); Vanessa G. Teixeira (1); Frédéric Baudin (2); C. Nous (3)
(1) Physics Department, Universidade Federal de Minas Gerais, Brazil ; (2) Institut d'Astrophysique Spatiale, France; (3) Laboratoire Cogitamus, www.cogitamus.fr, France
We look for the effect of flares on the amplitude of acoustic modes mainly during the period of high solar activity in Cycle 24 (June 2012 to August 2016) using the ring-diagram analysis technique with data observed in five-degree regions of SDO/HMI. Statistical analyses helps to separate out other effects, such as the projection of the line of sight as a region moves across the solar disk and the presence of strong magnetic fields, on the mode amplitudes during the flare. The rapid progress of asteroseismology and the study of stellar flares makes the study of these phenomena in the Sun important to inform our study of the influence of the more energetic stellar flares on asteroseismic waves.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
Hugh S. Hudson
(1) UC Berkeley; (2) U of Glasgow
The Carrington flare of 1859 marked a beginning of multimessenger astronomy as punctuated by an astronomical transient event. Some of the messengers from that event could not be interpreted properly at the time, since they involved unknown concepts such as X-rays, stellar magnetism, and the ionosphere. We discuss the history of this event and argue that its gross energy release could have inferred from the data in hand. We also argue that this event, though extreme, did not outshine more recent events such as the "Halloween" events of 2003.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
Arnab Basak (1); Dibyendu Nandy (1,2)
(1) Center of Excellence in Space Sciences India, IISER Kolkata; (2) Department of Physical Sciences, IISER Kolkata
Since the halting of the Martian dynamo, the constant bombardment of solar wind particles on the planet led to the erosion of a significant portion of its atmosphere due to the lack of proper magnetic shielding. Several missions devoted to the exploration of the “red planet”, such as Phobos, Mars Global Surveyor, Mars Atmosphere and Volatile Evolution, InSight, etc., provide vital information about the Martian environment which is important from the aspect of planetary habitability. We present results of three dimensional compressible magnetohydrodynamic simulations of solar wind and Mars interaction, using the Star Planet Interaction Module (CESSI-SPIM) developed at CESSI, IISER Kolkata. We elucidate mechanisms that lead to the formation of an imposed magnetosphere around Mars and provide a theoretical viewpoint on the interaction of stellar winds with non-magnetized planets with/without atmospheres. The results are found to be in agreement with observational data from various missions. The above study is not only relevant for planets and moons in our solar system but also provides important insight for the exploration of habitable planets in extrasolar systems.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
Loren Matilsky; Juri Toomre
JILA & Dept. Astrophysical and Planetary Sciences, University of Colorado Boulder
The dynamical maintenance of the Sun’s tachocline of rotational shear remains one of the outstanding mysteries of solar physics. We present a series of three-dimensional MHD anealastic simulations in rotating spherical shells that for the first time achieve a tachocline self-consistently, in which a dynamo operates within both the convection zone and underlying stable region. With the introduction of a small, random seed magnetic field to a hydrodynamic progenitor, the initially differentially rotating radiative interior is forced into solid-body rotation by a convectively excited dynamo, and afterward is maintained for centuries-long timescales. The overall result is similar in spirit to one of the “main contenders” for tachocline confinement—Gough and McIntyre (1998)—in which a primordial magnetic field stops the inward radiative spreading of the differential rotation. However, these new simulations using the Rayleigh code make no assumptions about the Sun’s fossil interior magnetic field. They thus offer a possibly more realistic magnetic confinement scenario for the tachocline that is here shown to be achieved by a fully nonlinear MHD convective dynamo operating in the solar interior.
science theme: The Sun and the Heliosphere
schedule: Wed, 13:00 (haiku)
E.Dineva (1, 2); J.Pearson (3); M. Verma (1); C.Denker (1); K.G. Strassmeier (1, 2); I. Ilyin (1)
(1) Leibniz Institute for Astrophysics Potsdam (AIP); (2) University of Potsdam, Institute of Physics and Astronomy ; (3) Ohio State University
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution spectrograph for the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. It can be fed with sunlight from the Solar Disk-Integrated (SDI) telescope. Synoptic solar observations with PEPSI/SDI produce daily spectra with high signal-to-noise ratio, providing access to unprecedented, quasi-continuous, long-term, disk-integrated spectra of the Sun with high spectral and temporal resolution. The observed spectra contain a multitude of photospheric and chromospheric spectral lines in the wavelength range of 380-910 nm. Strong chromospheric absorption lines, such as the Ca II H&K lines, are powerful diagnostic tools for solar activity studies, since they trace the variations of the solar magnetic field. Derivation of activity indices, such as the Ca II H&K emission ratio $S$-index provides insight into the chromospheric magnetic field and its variability over the solar activity cycle. The well known relation between solar calcium indices and UV flux variations motivates us to compute an excess brightness indices from Ca II K full-disk images from of the Chromospheric Telescope (ChroTel) at the Observatory del Teide on Tenerife, Spain and UV data of the Solar Dynamics Observatory (SDO). We present a set of indices representing magnetic activity at various heights in the solar atmosphere. In the present work, we carefully compare the indices computed from various datasets and discuss the differences in terms of physical and observational properties.
science theme: Very low mass stars
schedule: Wed, 15:00 (haiku)
Jacqueline Faherty; Jonathan Gagné; Mark Marley; Stanimir Metchev
(1) American Museum of Natural History; (2) Institute for Research on Exoplanets, Université de Montréal; (3) NASA Ames Research Center; (4) University of Western Ontario
Photometric variability monitoring of brown dwarfs is a unique probe of their atmospheres as it is sensitive to condensate clouds as they rotate in and out of view. Variability has now been robustly observed in a range of L, T and Y spectral type brown dwarfs and more recently in planetary-mass companions and free-floating exoplanet analogs. Emerging as an important insight into brown dwarf and exoplanet atmospheric physics is evidence for a correlation between enhanced clouds and youth. We present results from the first large survey for mid-IR photometric variability in 26 young, low-mass brown dwarfs using the Spitzer Space Telescope. These unique, time-resolved variability monitoring data enable us to compare variability trends between younger and older brown dwarfs to definitively test the potential correlation between cloud-induced variability and youth in brown dwarfs.
science theme: Cool Stars on the main sequence
schedule: Wed, 15:00 (haiku)
Thomas M. Boudreaux (1); Elisabeth R. Newton (1); Nicholas Mondrik (2); David Charbonneau (3); Jonathan Irwin (3)
(1) Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755; (2) Department of Physics , Harvard University , 17 Oxford Street Cambridge MA 02138; (3) Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138
In the canonical formulation of stellar magnetic dynamo theory, the tachocline in partially convective stars serves to arrange small scale randomly oriented fields, which are generated by stochastic movement of plasma, into a large scale coherent field. Mid-to-late M-dwarfs show more magnetic activity than classical magnetic dymano theory predicts. This leads to the open question: what mechanism generates and maintains these fields in fully convective stars? Mid-to-late M-dwarfs show tight correlations between rotation rates and magnetic activity, consistent with elements of classical dynamo theory. We use data from Magellan Inamori Kyocera Echelle (MIKE) Spectrograph to measure $R′_{HK}$ values for 50 spectroscopically identified M-dwarfs selected from the MEarth survey. These stars span spectral classes from M5.0 to M3.5 and have rotation periods ranging from hours to months. Here, we present the rotation–activity relationship as traced through these data. We find power law and saturated regimes consistent to within one sigma of previously published results, and find the saturated value to be mass-dependent.
science theme: Very low mass stars
schedule: Wed, 15:00 (haiku)
Melodie Kao (1); Evgenya Shkolnik (1); J. Sebastian Pineda (2); Tyler Richey-Yowell (1); Gregg Hallinan (3)
(1) Arizona State University; (2) CU Boulder; (3) Caltech
Planetary magnetic fields influence atmospheric evaporation from space weather, yield insights into planet interiors, and are essential for producing aurorae. The most direct way of measuring magnetic fields on exoplanets and their brown dwarf cousins is by observing exo-aurorae at radio frequencies. However, a quasi-stable and non-auroral quiescent radio component accompanies all known examples of substellar exo-aurorae and provides an alternative means for assessing the physics occurring in substellar magnetospheres. The presence of incoherent nonthermal radio emission requires both a source of radiating electrons and magnetic fields to accelerate these electrons. Thus, the absence of quiescent radio emission from a single object cannot distinguish between a lack of strong magnetic fields or magnetospheric plasma. In contrast, examining the occurrence rates of quiescent radio emission can potentially reveal how brown dwarf and ultracool dwarf radio activity depends on various fundamental properties such as effective temperature, mass, and age. Here, we present the first such statistical studies of quiescent radio emission from brown dwarfs and ultracool dwarfs and discuss implications for substellar magnetospheric physics.
science theme: Very low mass stars
schedule: Wed, 15:00 (haiku)
Z. H. ZhangD. J. Pinfield; H. R. A. Jones; B. Burningham; M. C. Galvez-Ortiz; M. R. Zapatero Osorio; E. L. Martın; D. Homeier; N. Lodieu; R. Rebolo; F. Allard; A. J. Burgasser; R. L. Smart; Ya. V. Pavlenko; L. C. Smith; B. Lopez Marti; F. Marocco
(1) Nanjing University, China; (2) University of Hertfordshire, UK; (3) University of Hertfordshire, UK; (4) University of Hertfordshire, UK; (5) Centro de Astrobiologia; Spain; (6) Centro de Astrobiologia; Spain; (7) Centro de Astrobiologia; Spain; (8) Universitat Heidelberg, Germany; (9) Instituto de Astrofisica de Canarias, Spain; (10) Instituto de Astrofisica de Canarias, Spain; (11) ENS de Lyon, France; (12) University of California San Diego, USA; (13) Osservatorio Astronomico di Torino, Italy; (14) Main Astronomical Observatory, Ukraine; (15) University of Cambridge; (16) Saint Louis University – Madrid Campus, Spain; (17) Jet Propulsion Laboratory, USA
The destiny of a star is depending on the status of hydrogen fusion that it can reach after its formation. Stars have steady hydrogen fusion and can maintain their luminosity. Degenerate brown dwarfs (D-BD) have no energy supply from hydrogen fusion thus cool continuously. Transitional brown dwarfs (T-BD) have long-lasting low-rate unsteady hydrogen fusion in their cores to replenish the dissipation of their initial thermal energy, thus have slower cooling rate than D-BDs. T-BDs form a substellar transition zone (STZ) between stars and D-BDs. The STZ covers a narrow mass range and very wide ranges of temperature and spectral type over time. The STZ has been shown by evolutionary models (Burrows & Liebert 1993) before the discovery of brown dwarfs in 1995. However, the STZ was ignored by observers. Because first observers was looking for a clear mass boundary (the hydrogen burning minimum mass, e.g. HBMM) between stars and brown dwarfs. Secondly, the precision of brown dwarf mass measurement is larger or similar to the mass range of the STZ. Thirdly, the temperature range of very low-mass stars, T-BD, and D-BD are overlapped because of mass/age degeneracy of brown dwarfs in the field. Therefore, the STZ could only be resolved in extremely rare metal-poor brown dwarfs population, which all have been cooled for ~10 Gyr. In this talk, I will discuss the discovery of T-BDs and STZ from a well characterized sample of metal-poor brown dwarfs. This talk is partially based on works published in a series titled 'Primeval very low-mass stars and brown dwarfs'.
science theme: Very low mass stars
schedule: Wed, 15:00 (haiku)
E. L. Rickman (1,2,3)
(1) European Space Agency; (2) Space Telescope Science Institute; (3) University of Geneva
Evolutionary models of brown dwarfs are plagued by a lack of observational constraints. The complex molecular chemistry of their atmospheres leaves a relatively wide parameter space for models to span. Placing accurate mass and luminosity data to observationally populate the mass-luminosity relationship provides a major contribution to an understanding of brown dwarf evolutionary models. To date, individual dynamical masses are known for only a handful of brown dwarfs. Radial-velocity measurements provide only a lower limit on the measured masses due to the unknown orbital inclination. Therefore, directly imaging these candidates is needed to break that degeneracy and provide constraints on the dynamical mass of the companion, serving as a benchmark substellar object.
I present a systematic approach to hunt for these benchmark objects using the radial-velocity CORALIE survey with over 20 years worth of data containing a volume-limited sample of 1647 low-mass main sequence stars within 50 parsecs. From this survey I have identified targets that I have directly imaged using VLT/SPHERE, which has led to the direct detection and spectral characterisation of several new benchmark brown dwarfs. This includes the coldest companion ever imaged to a main sequence star, and the first T/Y transition object with a measured dynamical mass. These objects are crucial in probing a parameter space in mass, separation, and age where the occurrence rate of these objects is not well understood, and where the mass-luminosity-age relation is unconstrained, providing important clues to the formation and evolution of these ultracool objects.
science theme: Very low mass stars
schedule: Wed, 15:00 (haiku)
Joshua D. Lothringer; Sarah L. Casewell
(1) Johns Hopkins University; (2) University of Leicester
While highly irradiated brown dwarfs are rare, the handful of known systems provide a unique lens into irradiated atmospheres. Ultra-short-period brown dwarfs around white dwarfs can reach atmospheric temperatures hotter than many stars. Such objects are similar to ultra-hot Jupiters, yet are subject to even more intense UV irradiation, allowing us to test irradiated atmosphere models and reveal new insight into substellar atmospheres. We will present 1D PHOENIX atmosphere models and synthetic spectra, as well as retrievals with the PETRA framework, of two highly irradiated brown dwarfs around white dwarfs. Crucially, these models self-consistently include the effects of the intense UV irradiation on the atmosphere. We will show that we can explain the observed presence of a variety of emission lines in these brown dwarfs through the an irradiation-induced temperature inversion, not unlike those recently seen in several ultra-hot Jupiters. We will then put these highly irradiated brown dwarfs in broader context with their lower mass cousins and their non-irradiated siblings.
science theme: Brown dwarfs
schedule: Wed, 15:00 (haiku)
Ehsan Gharib-Nezhad (1); Mark S. Marley (1) ; Natasha E. Batalha (1) ; Channon Visscher (2, 3)
(1) (1) NASA Ames Research Center, Moffett Field, CA 94035, USA; (2) (2) Dordt University, Sioux Center, IA 51250 USA; (3) (3) Space Science Institute, Boulder, CO 80301 USA
Lithium is an important element for the understanding of ultracool dwarfs because it is lost to fusion at masses above 68 M$_{Jup}$. Hence, the presence or absence of atomic Li has served as an indicator of the nearby H-burning boundary at about 75 M$_{Jup}$ between brown-dwarfs and very low-mass stars. Historically, the “Li test’’, a search for the presence and strength of the Li line at 670.8 nm, has been a marker if an object has a substellar mass with stellar-like spectral energy distribution (e.g., a late-type M dwarf). However, the Li test is not a reliable and straightforward probe to determine the mass and gravity of the ultracool object. In addition, for later T and Y type brown dwarfs, Li is no longer found as an atomic gas, but rather a molecular speciessuch as LiH, LiF, LiOH, and LiCl. Only recently have experimental molecular line lists become available for such species. In this study, we generated a full spectral absorption cross-section of each of these Li-bearing molecules from the most recent line-lists for 75-4000 K and 10$^{-6}$-3000 bar. Then, thermochemical equilibrium atmospheric composition was performed to calculate the abundance of these molecules in this same temperature and pressure domain. Finally, we compute thermal emission spectra for a series of radiative-convective equilibrium modeling on cloudy and cloud-free brown dwarf atmospheres (with T$_{eff}$=1000, 1500, 2000, 2400K) to understand where the presence or absence of atmospheric lithium-bearing species is most easily detected as a function of brown dwarf mass and age. After atomic Li, the best spectral signature was found to be LiF at 10.5-13 micron and LiCl at 15-18 micron. We predict that future missions such as James Webb Space telescopes could detect these LiF and LiCl spectral features. The detection of lithium compounds in cool objects would identify those with masses below the Lithium burning minimum mass, providing a new mass indicator for cool brown dwarfs.
science theme: Very low mass stars
schedule: Wed, 15:00 (haiku)
Victor Sanchez-Gimenez (1); Nadège Lagarde (2)
(1) Barcelona Universidad; (2) UTINAM, Besançon Observatory; (3)
Ultra-cool dwarfs (UCDs) serve as link between the lowest mass stars and the brown dwarfs. Gaia DR2 revealed thousands of ultra-cool dwarfs not identified as such before. In this work, we searched for companions to those in the Gaia catalogue from their common proper motions and parallaxes. We found about 1,700 stars in multiple systems out of the original 16,000 sample. Among the companions, there are several tens of young stellar objects and white dwarfs, but also new M7-L2 candidates. Such a sample can be used to better understand the binary properties of UCDs and to better characterize the physics of UCDs thanks to the characterization of higher mass companions.
science theme: Very low mass stars
schedule: Wed, 15:00 (haiku)
Patrick Tamburo (1); Philip Muirhead (1); Allie McCarthy (1); Murdock Hart (2); Julie Skinner; Daniella Bardalez Gagliuffi (3); Jacqueline Faherty (3); Johanna Vos (3); Christopher Theissen (4); Eric Agol (5)
(1) Boston University; (2) Perkins Telescope Observatory; (3) American Museum of Natural History; (4) University of California San Diego; (5) University of Washington
The Perkins INfrared Exosatellite Survey (PINES) is a search for transiting satellites (planets or moons) around a sample of almost 400 spectroscopically confirmed L- and T-type dwarfs. The survey is conducted with the 1.8-m Perkins telescope located in Anderson Mesa, Arizona, and utilizes near-infrared observations to enable the highest photometric precision possible on intrinsically faint L and T dwarfs. This is the most ambitious photometric monitoring campaign of L and T dwarfs to date, and a detailed simulation suggests that a handful of transiting companions will be detected over the course of the three-year survey. The survey will probe an unexplored region of exoplanet parameter space, and will potentially provide excellent targets for future atmospheric characterization. In this talk, I will provide an overview of PINES, focusing on the survey's target sample and observational strategy. I will describe the first year of PINES observations, along with the custom photometric pipeline that we have built to generate lightcurves from raw PINES data. Finally, I will compare the measured photometric uncertainty of these lightcurves to our simulations, and discuss how our actual performance impacts our expected satellite detection yield.
science theme: Young stars
schedule: Wed, 15:00 (haiku)
Jamila Pegues (1); Karin Öberg (1); Sean Andrews (1); Jennifer Bergner (2); Ian Czekala (3); Jane Huang (4); Richard Teague (1); Edwin Bergin (4); L. Ilsedore Cleeves (5); Viviana Guzmán (6); Gregory Herczeg (7); Feng Long (1); Ilaria Pascucci (8); Chunhua Qi (1); David Wilner (1)
(1) Center for Astrophysics | Harvard & Smithsonian; (2) University of Chicago; (3) Pennsylvania State University; (4) University of Michigan; (5) University of Virginia; (6) Instituto de Astrofísica; (7) Kavli Institute for Astronomy and Astrophysics; (8) University of Arizona
M-stars are the most common hosts of planetary systems in the local Galaxy. Observations of protoplanetary disks around these cool stars are remarkable tools for understanding the environment within which their planets form. In this seminar, we present a small sample of protoplanetary disks around M-stars (spectral types M4-M5). Using spectrally and spatially resolved ALMA observations of a range of molecular lines, we measure the dynamical masses of these stars and characterize the chemistry in their disks. We find that dynamical masses for our sample exceed fiducial stellar evolutionary model predictions, and we use this discrepancy to constrain the nature of young, cool M-stars. In terms of chemistry, we find that the distribution of key molecular probes, which offer insight into the organic chemistry and C/N/O ratios, are different both between and across disks around these M-stars. This diversity is similar to what has been previously observed towards solar-type stars. Overall, we find similar patterns of chemistry between our M-star sample and solar-type disks, and we investigate hydrocarbons as one important possible exception. We also discuss future observations, which are crucial to obtain a holistic view of the chemistry of planet formation around the "coolest" stars.
science theme: Post main sequence cool stars
schedule: Thu, 13:00 (haiku)
Benjamin T. Montet
University of New South Wales
Several mechanisms to produce lithium-rich red giants have been proposed, including interactions between the red giant and a binary companions as the star reaches the tip of the red giant branch. One consequence of this model would be tidal spin-up of the red giant to the few km/s level. This level of rotation could in principle be detected in photometry from missions like Kepler and TESS, but signals longer than $\sim 50$ days are typically overwhelmed by instrumental systematics and removed by the processing pipeline. Here, I will describe our data-driven reanalysis of Kepler pixel-level data that more accurately preserves slower signals in the data and our measurements of rotation periods of the lithium-rich giants in the Kepler field compared to lithium-normal giants and the implications for the formation of lithium-rich giants, as well as the potential to apply this method to other cool stars with up to $\sim 100$-day rotation periods.
science theme: The Sun and the Heliosphere
schedule: Thu, 13:00 (haiku)
Adam J. Finley
(1) University of Exeter, UK; (2) CEA Paris-Saclay, France
The rate at which the solar wind extracts angular momentum from the Sun has been predicted by theoretical models for many decades, and yet we lack a conclusive measurement from in-situ spacecraft. Complementary information can be gained by studying other Sun-like stars, as it is known that the rotation rates of Sun-like stars follow a tight relationship with age. This allows us to evaluate their angular momentum-loss rates, without any knowledge of stellar wind physics, and produce an independent prediction of the current solar angular momentum-loss rate to compare with numerical models and in-situ observations of the solar wind. I will discuss recent measurements of the solar wind angular momentum flux from Parker Solar Probe, in context with previous observations and model predictions. I aim to show that by better understanding the current solar angular momentum-loss rate we can further constrain rotation-evolution models of low-mass stars, which will subsequently influence how magnetic activity evolves during the late main sequence. It is thought that in future, a combination of observations from Parker Solar Probe and Solar Orbiter may lead to a better evaluation the solar wind angular momentum-loss rate.
science theme: Post main sequence cool stars
schedule: Thu, 13:00 (haiku)
Shreeya Shetye (1); Sophie Van Eck (1); Alain Jorissen (1); Stephane Goriely (1); Lionel Siess (1)
(1) Institute of Astronomy and Astrophysics, Universite libre de Bruxelles
Asymptotic Giant Branch (AGB) stars are low- to intermediate-mass stars in the late stages of stellar evolution. Due to their huge mass-loss and sheer number, these stars are major contributors of heavy (s-process) elements in the interstellar medium. AGB stars are ideal testbeds for understanding the mixing processes that take place in the stellar interiors. Despite its importance, the AGB is one of the least understood phases of stellar evolution, owing to the complex atmospheres and molecule-rich spectra of AGB stars. In this talk, I will present a novel method to determine the intricate atmospheric parameters of AGB stars. This method combines the recently released Gaia parallaxes and the high-resolution visible spectra with the state-of-the-art AGB models to derive the stellar parameters and abundances. With this method, we have been able to obtain observational constraints on the most crucial mixing process on the AGB namely, the third dredge-up. Furthermore, our investigation led to the discovery of low-mass AGB (initial mass ~ 1 Msun) stars. This is an evidence for third dredge-up occurrence at low-mass and solar metallicity which was not accounted for by most AGB models. Finally, I will discuss how the derived AGB s-process abundances provide crucial constraints to the galactic chemical evolution models.
science theme: Post main sequence cool stars
schedule: Thu, 13:00 (haiku)
Michele Trabucchi (1,2); Peter R. Wood (3); Nami Mowlavi (1); Giada Pastorelli (2,4); Paola Marigo (2); Leo Girardi (5); Thomas Lebzelter (6)
(1) Department of Astronomy, University of Geneva, Ch. des Maillettes 51, CH-1290 Versoix, Switzerland; (2) Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo dell’Osservatorio 2, I-35122 Padova, Italy; (3) 3Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia; (4) STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA; (5) Osservatorio Astronomico di Padova – INAF, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy; (6) Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, A-1180 Vienna, Austria
I present the results of the first systematic analysis of nonlinear pulsation as a function of stellar mass, luminosity and temperature in 1D hydrodynamic models of the envelopes of O-rich Asymptotic Giant Branch stars. It is found that large-amplitude fundamental mode pulsation induces a structural readjustment of the oscillating resulting in a shorter variability period with respect to linear predictions, leading to a substantial improvement in the agreement with observations. The grid of nonlinear pulsation models presented here is the first to allow for an accurate description of the fundamental mode period of Miras and related variable stars, and of their period-luminosity relation. I will also discuss the dependence of pulsational stability on physical and model parameters, and present exploratory analysis of the effects of varying chemical composition.
science theme: Post main sequence cool stars
schedule: Thu, 13:00 (haiku)
Jamie Tayar; the TESS-Subgiant collaboration
(1) Institute for Astronomy, University of Hawaii; (2) various
There are still significant uncertainties in our understand of convection and rotation in evolved low-mass stars. To address this, we have spectroscopically, photometrically, and asteroseismically characterized a set of subgiant and lower red giant stars in the TESS southern continuous viewing zone, and combined them with previous samples from Kepler. I will show that when quantitatively compared, these stars can identify inaccuracies in the temperature and gravity evolution of currently used grids of models. They also show a coherent evolution of the internal rotation rate from the main sequence to the red giant branch and a significant contrast between the core and envelope rotation rates that is incompatible with several proposed theories of angular momentum transport in stellar interiors. Finally, I will end with a discussion of how we can continue to improve our understanding and what these changes mean for future studies of stellar evolution.
science theme: Post main sequence cool stars
schedule: Thu, 13:00 (haiku)
Thomas Granzer (1); Klaus G. Strassmeier (1); Michael Weber (1); Andrea Dupree (2)
(1) Leibniz Institute for Astrophysics, Potsdam; (2) Harvard–Smithsonian Center for Astrophysics
Since more than a decade, the AIP is monitoring $\alpha$ Ori with its robotic spectroscopic facility STELLA/SES in Teide observatory, Tenerife along with its automated photoelectric telescope T7 in Fairborn observatory, Az. Additionally, we were awarded with exclusive two-band photometric data on Betelgeuse from the BRITE satellite consortium, covering the last seven seasons. In late 2019, Betelgeuse showed a rapid brightness decline, reaching an all-time low in Feb. 2020, followed by a quick re-brightening.
In this talk, I want to investigate the question whether this recent dip can be traced back to semi-periodic variability behavior or if it has been an outstanding event. In particular, I will show that periods and cycles found in the radial velocity data have a close match to Betelgeuse's photometric cycles.
science theme: Post main sequence cool stars
schedule: Thu, 13:00 (haiku)
Samuel Grunblatt
(1) American Museum of Natural History; (2) Center for Computational Astrophysics, Simons Foundation
Despite the discovery of thousands of planets orbiting various stars thoughout our Galaxy, star-planet interaction remain poorly understood. In particular, late-stage star-planet interaction has remained particularly elusive, largely due to the difficulties in detecting planets around evolved stars. However, the Full Frame Image data from the TESS mission has provided 30-min cadence light curves of hundreds of thousands of evolved stars across the sky. Here I will introduce the newest planet discoveries around these evolved stars, including the shortest-period planet ever discovered around a red giant star. These particularly short period systems have been predicted to decay quickly, but the timescale of orbital decay is strongly dependent on the stellar structure in these subgiant and low-luminosity red giant stars, which has not yet been accurately modeled. We introduce new constraints on tidally driven period decay in these systems, tidal qualities of the evolved host stars studied here and provide updated boundaries between convective and radiative cores in subgiant and red giant stars. Finally, we consider additional constraints on star and planet structure and evolution that can be deduced from the larger population of planet candidates around evolved stars observed by TESS.
science theme: The Sun and the Heliosphere
schedule: Thu, 13:00 (haiku)
Surajit Mondal (1); Divya Oberoi (1); Ayan Biswas (1); Shabbir Bawaji (2); Ujjaini Alam (2); Arpit Behera (1); Devojyoti Kansabanik (1) ; Federico Fraschetti (3); Kathy Reeves(4)
(1) National Centre for Radio Astrophysics, Tata Institute of Fundamental Research; (2) ThoughtWorks; (3) University of Arizona; (4) Smithsonian Astrophysical Observatory
It has a long standing problem as to how the solar corona can maintain its million K temperature, while the photosphere, which is the lowest layer of the solar atmosphere, is only at a temperature of 5800 K. A very promising theory to explain this is the “nanoflare” hypothesis. However, detecting these nanoflares directly is challenging with the current instrumentation as they are hypothesised to occur at very small spatial, temporal and energy scales. These nanoflares are expected to produce nonthermal electrons, which is expected to emit in the radio band. Due to its importance a lot of searches for these nonthermal emissions has been done, but they were only limited to active regions. The quiet corona is also hot, and so it is equally important to understand the physical processes which maintain this medium at MK temperatures. This presentation will describe the results from our effort to use the data from the Murchison Widefield Array (MWA) to search for impulsive radio emissions in the quiet solar corona. We have uncovered ubiquitous very impulsive nonthermal emissions from the quiet sun. We now refer to these emissions as Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs). We have done independent observations spanning very different solar conditions and proved that WINQSEs are present throughout the quiet corona at all times. Their occurrence rate lies in the range of many hundreds to a $\sim$thousand per minute, implying that on average $\sim$10 WINQSEs in every 0.5 s MWA image. Preliminary estimates suggest that WINQSEs have a bandwidth of $\sim$2 MHz. Due to the importance of WINQSEs and their possible connection to the hypothesised “nanoflares”, we are pursuing several projects to characterise their spectro-temporal structure and their energetics. In this talk, I will present these results.
science theme: Post main sequence cool stars
schedule: Thu, 13:00 (haiku)
Patrick Gaulme (1,2); Federico Spada (1); Jason Jackiewicz (2)
(1) Max Planck Institute for Solar System Research, Goettingen, Germany; (2) Department of Astronomy, New Mexico State University, Las Cruces, NM, USA
According to dynamo theory, stars with convective envelopes efficiently generate surface magnetic fields (which manifest as magnetic activity: starspots, faculae, flares) when their rotation period is shorter than their convective turnover time. Most red giants (RG), having undergone significant spin down while expanding, have slow rotation and no spots. However, Gaulme et al. (2020) showed that out of a sample of 4500 RGs observed by the NASA Kepler space telescope, about 8% display spots. They also detected solar-like oscillations in 99.3% of the sample, and determined the evolutionary stage (hydrogen-shell or helium-core burning) of 76% of them. From complementary high-resolution spectroscopic observations of 85 targets, the active RGs can be categorized as: 1) RGs in close binary systems spun up by tidal forces; 2) solar-mass RGs that gained angular momentum by engulfing stellar or substellar companions; 3) intermediate-mass RGs that were fast rotators in the late main sequence before entering the red giant phase. In this presentation, we report new insights on the active RGs that may have engulfed a companion based on spectroscopic observations of the entire active solar-mass RGs identified by Gaulme et al. (2020).
Gaulme et al. (2020) A&A 639, A63
science theme: The Sun among stars
schedule: Thu, 13:00 (haiku)
Jorge Meléndez; Jhon Yana Galarza
Departamento de Astronomia, IAG-USP
The abundance patterns observed in the Sun and in metal-poor stars show a clear odd-even effect. An important question is whether the odd-even effect in solar-metallicity stars is similar to the Sun, or if there are variations that can tell us about different chemical enrichment histories. We report for the first time observational evidence of a differential odd-even effect in the solar twin HIP 11915, relative to the solar odd-even abundance pattern. We analysed high resolving power (R = 140 000) and high S/N ratio (∼400) VLT/ESPRESSO spectra, obtaining precise chemical abundances (∼0.01 dex). The differential abundances relative to the Sun, show a non-solar odd-even effect even after performing Galactic Chemical Evolution corrections. This suggest a supernova enrichment history different to the Sun's.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
Katja Poppenhaeger
(1) Leibniz Institute for Astrophysics Potsdam; (2) University of Potsdam, Institute for Physics and Astronomy
Transit observations in the helium lines near 10830 Angstrom are a new successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionization and recombination of helium in the exoplanetary atmosphere. This ionization is caused by stellar photons in the extreme UV (EUV); however, no currently active telescopes can observe this part of the stellar spectrum. The stellar spectrum close to the helium ionization threshold consists of individual emission lines, many of which are formed by iron at coronal temperatures. Coronal elemental abundances exhibit distinct patterns related to the first ionization potential (FIP) of those elements, with elements like iron being strongly depleted for high-activity low-mass stars. I show that stars with high versus low coronal iron abundances follow different scaling laws that tie together their X-ray emission and the EUV flux close to the helium ionization threshold. I also show that the currently observed large scatter in the relationship of EUV irradiation with exoplanetary helium transit depths can be reduced by taking coronal iron abundances into account, allowing us to target exoplanets with well-observable helium signatures with much higher confidence.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
J. R. Callingham (1,2); H. Vedantham (2,3); T. Shimwell (2,1); B. J. S. Pope (4); and LoTSS team
(1) Leiden University; (2) ASTRON, Netherlands Institute for Radio Astronomy; (3) Groningen University; (4) Sagan Fellow, New York University
For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With the Dutch radio telescope LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf - the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star. I will also discuss how our LOFAR observations represents the most comprehensive survey of stellar systems at low frequencies, and the implications of this new population we have detected in understanding the magnetosphere of M dwarfs and exoplanetary magnetic fields.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
Adam S Jermyn (1); Jamie Tayar (2,3); Jim Fuller (4)
(1) Center for Computational Astrophysics, Flatiron Institute, New York, NY 10010, USA; (2) Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA; (3) Hubble Fellow; (4) TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125, USA
Over time, tides synchronize the rotation periods of stars in a binary system to the orbital period. However, if the star exhibits differential rotation then only a portion of it can rotate at the orbital period, so the rotation period at the surface may not match the orbital period. The difference between the rotation and orbital periods can therefore be used to infer the extent of the differential rotation. We use a simple parameterization of differential rotation in stars with convective envelopes in circular orbits to predict the difference between the surface rotation period and the orbital period. Comparing this parameterization to observed eclipsing binary systems, we find that in the surface convection zones of solar-like stars in short-period binaries there is very little radial differential rotation, with $|r\partial_r \ln \Omega| < 0.02$. This holds even for longer orbital periods, though it is harder to say which systems are synchronized at long periods, and larger differential rotation is degenerate with asynchronous rotation.
science theme: Stellar flares and activity
schedule: Thu, 15:00 (haiku)
Maximilian N. Günther
Massachusetts Institute of Technology (MIT)
On our search for habitable worlds, we have to account for explosive stellar flaring and coronal mass ejections (CMEs) impacting exoplanets’ surface (or cloud) habitability. These stellar outbursts are a double-edged sword. On the one hand, flares and CMEs are capable of stripping off atmospheres and extinguishing existing biology. On the other hand, flares might be the (only) means to deliver the trigger energy for prebiotic chemistry and initiate life. In this talk, I will highlight our TESS study of all stellar flares from Years 1 & 2 of the mission, driven by the "stella" convolutional neural network. Where manual vetting would have taken a lifetime, and conventional outlier detection would have missed the smallest flares, state-of-the-art machine learning approaches allow us a fast, efficient, and probabilistic characterization of flares. I will also discuss flaring as a function of stellar type, age, rotation, spot coverage, and other factors. Finally, I will link our findings to prebiotic chemistry and ozone sterilization, identifying which worlds might lie just in the right regime between too much and too little flaring. With the TESS extended mission and increased cadences (20s, 2min and 10min), stellar flare studies and new exoplanet discoveries will ultimately aid in defining criteria for exoplanet habitability.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
M. Deal (1); O. Richard (2); S. Vauclair (3)
(1) Instituto de Astrofísica e Ciências do Espaço (IA), Porto, Portugal; (2) LUPM, Montpellier, France; (3) IRAP, Toulouse, France
The formation and evolution of light elements in the Universe act as important cosmological constraints. The oldest stars of the Galaxy have long been assumed to display in their outer layers the primordial lithium abundance, although all studies of stellar physics proved that this abundance must have decreased with time. The primordial Li abundance deduced from the observations of the Cosmological Background is indeed larger than the maximum one observed in these stars. Recent observations gave evidence of a large Li abundance dispersion in very metal poor stars.
During this presentation, we address the general question of the lithium abundance dispersion obtained from observations of metal-poor stars, and how the interplay of atomic diffusion and accretion of matter modifies the element abundances in these metal-poor stars. In particular, we focus on the hydrodynamic processes that could take place after accretion. We consider initial metallicities from [Fe/H]=-2.31 down to [Fe/H]=-5.45.
We show that the observations of lithium dispersion, associated or not with carbon enrichment, are well accounted for in terms of accretion onto the metal-poor stars, with accreted masses smaller than a few Jupiter masses, when using a lithium initial abundance in accordance with the primordial lithium abundance obtained from latest BBN results.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
Sam Morrell; Tim Naylor
University of Exeter
There has been growing evidence in the literature that M-dwarf stars suffer radius inflation compared to theoretical models, suggesting that models are missing some key physics required to completely describe stars at effective temperatures less than about 4000K. We presented evidence at the previous Cool Stars meeting that this problem is evident in pre-main sequence populations within stellar clusters. With the advent of Gaia DR2, we have been able to generalise our novel SED fitting methodology, which relies only upon multiband photometry and geometric distances, to measure the radii of >15,000 nearby main-sequence field M-dwarf stars, and show that radius inflation persists onto the main sequence.
From this sample, we have determined that M-dwarfs show an inflation of 3 - 7 per cent from the purely theoretical models, with no more than 1 - 2 per cent intrinsic spread in the inflated sequence. We show that this measurement technique is able to measure M-dwarf radii to an accuracy of 2.4 per cent, however we determined that this is limited by the precision of metallicity measurements; which contribute 1.7 per cent to measurement uncertainty. We also present evidence that stellar magnetism is currently unable to explain the radius inflation in M-dwarfs.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
Oliver J. Hall (1,2,3); Guy R. Davies (2,3); Jennifer van Saders (4); Martin B. Nielsen (2,3); Mikkel N. Lund (3); William J. Chaplin (2,3); Rafael A. Garcia (5,6); Louis Amard (7); Angela A. Breimann (7); Saniya Khan (2,3); Victor See (7); Jamie Tayar (4,8)
(1) European Space Agency (ESA), European Space Research and ; (2) Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The ; (3) Netherlands; (4) School of Physics and Astronomy, University of ; (5) Birmingham, Edgbaston, Birmingham, B15 2TT, UK; (6) Stellar ; (7) Astrophysics Centre, Department of Physics and Astronomy, Aarhus ; (8) University, Ny Munkegade 120, 8000 Aarhus C, Denmark; (9) Institute ; (10) for Astronomy, University of Hawai'i, Honolulu, HI 96822; (11) IRFU, ; (12) CEA, Universite Paris-Saclay, F-91191 Gif-sur-Yvette, France; (13) AIM, CEA, CNRS, Universite Paris-Saclay, Universite Paris Diderot, ; (14) Sorbonne Paris Cite, F-91191 Gif-sur-Yvette, France; (15) University ; (16) of Exeter Department of Physics and Astronomy, Stocker Road, Devon, ; (17) Exeter, EX4 4QL, UK; (18) Hubble Fellow
Studies using asteroseismic ages and rotation rates from star-spot rotation have indicated that standard age-rotation relations may break down roughly half-way through the main sequence lifetime, a phenomenon referred to as weakened magnetic braking. While rotation rates from spots can be difficult to determine for older, less active stars, rotational splitting of asteroseismic oscillation frequencies can provide rotation rates for both active and quiescent stars, and so can confirm whether this effect really takes place on the main sequence.
In this talk, I’ll show how we obtained asteroseismic rotation rates of 91 main sequence stars showing high signal-to-noise modes of oscillation. Using these new rotation rates, along with effective temperatures, metallicities and seismic masses and ages, we built a hierarchical Bayesian mixture model that showed that our new ensemble more closely agreed with weakened magnetic braking, over a standard rotational evolution scenario.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
E. M. Amazo-Gómez (1) ; J. D. Alvarado-Gómez (1) ; G. A. J. Hussain (2) ; K. Poppenhäger (1) ; P. C. König (3); J. F. Donati (4); B. E. Wood (5); J. J. Drake (6); J. Do Nascimento (6); F. Del Sordo (7); M. Damasso (7); Jorge Sanz-Forcada (8); Beate Stelzer (9)
(1) Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany; (2) European Spatial Agency, Keplerlaan 1, 2201 AZ Noordwijk, Netherlands; (3) European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany; (4) CNRS-IRAP, 14, avenue Edouard Belin, F-31400 Toulouse, France; (5) Naval Research Laboratory, Space Sciences Division, Washington, DC 20375, USA; (6) Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge MA 02138, USA; (7) Osservatorio di Torino, INAF, Via Osservatorio, 20, 10025 Pino Torinese TO, Italy; (8) Centro de Astrobiología (CSIC-INTA), ESAC Campus, Camino Bajo del Castillo, E-28692 Villanueva de la Cañada, Madrid, Spain; (9) Eberhard Karls Universität, Institut für Astronomie und Astrophysik, Sand 1, 72076 Tübingen, Germany
A simultaneous and revealing stellar analysis has been performed on the young Sun-like star iota-Horologii. The star has one the shortest reported magnetic cycle, of about 1.4 years. That short period, in comparison with the 22 years solar magnetic cycle, allowed a faster activity analysis of a young Sun. We compiled a long-term spectropolarimetric follow-up under the "Far beyond the Sun" campaign of about 6 observational semesters. During the last semester of observation, we combined simultaneous observations of the star by TESS and HST satellites. Those observations let us compare the stellar activity for different atmospheric stratifications. By using the GPS method combined, for the first time, with Zeeman Doppler Imaging (ZDI) mapping technique we constrained the faculae to spot driver ratio. Such combined information helps us to better interpret the stellar surface. We found that the stellar surface is spot dominated, with a facular to spot ratio $(S_{fac}/S_{spot})$ of about 0.74. For reference, the Sun displays a roughly constant $(S_{fac}/S_{spot})$ about 3, faculae dominated surface along its activity cycle. We retrieved diagnostics of the coronal transition region, derived from the $O_{ \rm iv}$ and $S_{ \rm iv}$ inter-combination lines observed by HST. We describe and place our results in the context of the correlations between the different observables, which improves the magnetic activity characterization for the different atmospheric layers.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
Diego Godoy-Rivera (1); Marc H. Pinsonneault (1); Luisa M. Rebull (2)
(1) The Ohio State University; (2) Infrared Science Archive (IRSA), IPAC
The period versus mass diagrams (i.e., rotational sequences) of open clusters provide crucial constraints for angular momentum evolution studies. However, their memberships are often heavily contaminated by field stars, which could potentially bias the interpretations. In this work, we use data from Gaia DR2 to re-assess the memberships of seven open clusters with rotational data, and present an updated view of stellar rotation as a function of mass and age. We use the Gaia astrometry to identify the cluster members in phase-space, and applying our membership analysis to the rotational sequences reveals that: 1) the contamination in clusters observed from the ground can reach up to $\sim$ 35\%; 2) the overall fraction of rotational outliers decreases substantially when the field contaminants are removed, but some outliers still persist; 3) there is a sharp upper edge in the rotation periods at young ages; 4) stars in the 1.0–0.6 $M_{\odot}$ range inhabit a global maximum in terms of rotation periods, potentially providing an optimal window for habitable planets. Additionally, we see clear evidence for a strongly mass-dependent spin-down process. In the regime where rapid rotators are leaving the saturated domain, the rotational distributions broaden (in contradiction with popular models), which we interpret as evidence that the torque must be lower for rapid rotators than for intermediate ones. The cleaned rotational sequences from ground-based observations can be as constraining as those obtained from space.
science theme: Cool Stars on the main sequence
schedule: Thu, 15:00 (haiku)
David Wilson; Mega-MUSCLES Collaboration
UT Austin
M dwarf stars have emerged as ideal targets for exoplanet observations. Their small radii aids planetary discovery, their close-in habitable zones allow short observing campaigns, and their red spectra provide opportunities for transit spectroscopy with JWST. The potential of M dwarfs has been underlined by remarkable systems such as the seven Earth-sized planets orbiting TRAPPIST-1 and the habitable-zone planet around Proxima Centauri.
Assessing the characteristics of such planets requires a firm understanding of how M dwarfs differ from the Sun, beyond just their smaller size and mass. Of particular importance are the time-variable, high-energy ultraviolet and x-ray regions of the M dwarf spectral energy distribution (SED), which can influence the chemistry and lifetime of exoplanet atmospheres, as well as their surface radiation environments. Unfortunately, those wavebands are extremely faint for most M dwarfs, requiring too large an investment of telescope time to obtain data at most stars.
The Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (Mega-MUSCLES) Treasury project, together with the precursor MUSCLES project, will produce full SEDs of a representative sample of M dwarfs, covering a wide range of stellar mass, age, and planetary system architecture. We have obtained x-ray and ultraviolet data for 12 stars using the Hubble, Chandra and XMM space telescopes, along with state-of-the-art DEM modelling to fill in the unobservable extreme ultraviolet regions. Our completed SEDs will be available as a community resource, with the aim that a close MUSCLES analogue should exist for most M dwarfs of interest.
In this presentation I will overview the Mega-MUSCLES project, describing our choice of targets, observation strategy and SED production methodology. I will also discuss notable targets such as the TRAPPIST-1 host star, comparing our observations with previous data and model predictions.
Posters are listed on the poster page (with images like on a poster board) and on zenodo (in list form).