In this splinter session, participants will take stock of the present state of stellar radio astronomy and chart a course for the field’s future, emphasizing:
Nonthermal radio emission, in the context of cool star radio astronomy, has traditionally encompassed mainly (gyro)synchrotron radiation and centimeter and millimeter wavelengths, i.e., emission from (mildly) relativistic electrons in magnetic fields. But recent years have shown a variety of other ways in which radio observations can deliver astrophysical insight. The discovery of brown dwarf radio emission has rekindled interest in electron cyclotron maser (ECM) emission as just one of several intriguing physical mechanisms in this regime, many of which are stepping stones toward studies of low-frequency exoplanetary radio emission. VLBI observations of stellar radio emission can be used to obtain precision astrometry — and hence precise measurements of fundamental parameters — of ultracool dwarfs or young stellar objects that are not accessible even to Gaia. Broadband, high-time-resolution studies of flares reveal the detailed plasma processes operating in the coronae of other stars.
The world’s best present-day radio observatories — chiefly the VLA and ALMA — launched the stellar radio astronomy renaissance. This is particularly true for constraints on nonthermal emission, which are particularly dependent on continuum sensitivity. Spectral indices, polarization, and variability all require high S/N detections to derive meaningful constraints. The upgraded VLA and VLBA as well as Arecibo now provide such information in the cm wavelength range, ALMA is doing so in the mm wavelength range, and LOFAR, MWA, LWA, HERA, and GMRT are making new forays into the low-frequency range. As a result of these newly feasible measurements, we are obtaining unique information on the role of magnetic fields on various scales and a new and complementary perspective on high-energy processes. These scales now even include outflows/jets from protostars and T Tauri stars, providing initial evidence for magnetic fields in young stellar environments.
The new generation of low-frequency radio observatories promises to figure especially prominently in the upcoming decade of stellar radio astronomy. These observatories can monitor the whole sky nearly continuously, surveying for stellar flares, coronal mass ejections, and other heliospheric phenomena. They are also expected to be the only facilities that will be able to directly probe the magnetic fields of extrasolar planets, through auroral radio bursts, providing unique insight into an essential facet of exoplanetary habitability.
There are important synergies of nonthermal radio emission with other wavelength ranges, and these will also be featured in this splinter session. These are mainly due to the beginning of radio time domain astronomy with the advent of sensitive continuum receivers, as seen for instance in the nearly-complete MeerKAT telescope. It is now possible to systematically study high-energy processes in both the X-ray and the radio time domain, and capabilities for doing so will increase dramatically when eROSITA commences operations. Understanding the correlations between optical and radio variability will be essential in the era of first TESS, then LSST.
While we expect most of the presenters to be astronomers with radio observing experience, our goal is to facilitate a splinter session that is highly relevant to a broad swathe of the Cool Stars community. For radio and non-radio astronomers in the audience alike, it will provide a forum to share the latest developments in areas such as stellar magnetism and stellar plasma physics. Motivated by the timeline of the US Decadal Survey and the suite of new instruments becoming operational in just the next few years, participants will pool their expertise to envision how they can leverage the current and upcoming generation of radio facilities to make the next round of discoveries.