Quantifying the Contribution of the ngVLA to Exo-Space Weather A Community Studies Report Rachel Osten STScI ngVLA workshop June 28, 2017

Forward-looking Facility, Forward-looking Science Characterizing the atmospheres and environments of potentially habitable exoplanets will be a major focus of the astronomical community in the next 10-20 years Filled-out exoplanet demographics from RV, transits, direct imaging Detailed correlations of planet properties vs. stellar properties Many (potentially) habitable worlds Stellar activity can create false positives in biomarkers (Tian et al. 2014) The conditions stars create around them is a major factor in the space weather environments of these exoplanets: Steady stellar wind Flaring and associated coronal mass ejections Star-planet magnetospheric interactions }Focus of study

The Importance of Being Magnetic Garaffo et al. (2016, 2017): stellar magnetosphere influences inner edge of the traditional habitable zone. Orbits crossing the Alfven surface (all but 2 of the TRAPPIST-1 planets) experience severe space weather

Detecting Stellar Winds Winds affect where planets are formed, migration/evaporation. Important for stellar rotational evolution, influences planetary dynamos Right now we have only indirect measures of cool stellar mass loss Radio emission from an ionized stellar wind is the workhorse of characterizing winds on hot stars. . . Cool stellar mass loss is feeble (Msun ~ 2x10-14 Msun/yr), has escaped detection at radio wavelengths

Detecting Stellar Winds Lyman alpha astrospheric absorption is currently the only game in town Can only be done with high-res spectrograph from space (STIS on HST) Does not detect the wind, detects the bow shock created when the wind interacts with the local ISM Non-detections do not provide upper limits to stellar mass loss Wood et al. (2004)

Detecting Stellar Winds Lyman alpha astrospheric absorption is currently the only game in town Can only be done with high-res spectrograph from space (STIS on HST) Does not detect the wind, detects the bow shock created when the wind interacts with the local ISM Non-detections do not provide upper limits to stellar mass loss Wood et al. (2014) Evidence for a weak wind from the young Sun from astrospheric detection towards π1 UMa

Detecting Stellar Winds Lyman alpha astrospheric absorption is currently the only game in town Can only be done with high-res spectrograph from space (STIS on HST) Does not detect the wind, detects the bow shock created when the wind interacts with the local ISM Non-detections do not provide upper limits to stellar mass loss Wood et al. (2014) Evidence for a weak wind from the young Sun from astrospheric detection towards π1 UMa

Detecting Stellar Winds Power-law relationship between mass loss and surface X-ray flux, with a cliff The most active stars do not appear to have strong winds Can’t constrain the mass-loss history, using analogues, of the Sun further back in time than a stellar age of ~700 MY Wood et al. (2014) Evidence for a weak wind from the young Sun from astrospheric detection towards π1 UMa

Detecting Stellar Winds There is a gap between current radio upper limits on cool stellar mass loss and Lyman alpha astrospheric constraints The rotational wind model of Johnstone et al. (2015) requires higher wind mass loss rate than astrospheric constraints to explain the observed spin-down rate for solar-like stars Current solar mass loss rate Fichtinger et al. (2017) constraints from JVLA and ALMA observations of solar analogs

Detecting Stellar Winds Constraints on stellar winds from X-ray halo arising from charge exchange between highly charged ions in stellar wind & surrounding ISM (Wargelin & Drake 2001) Wargelin & Drake (2002) upper limits to Prox Cen mass loss of 3x10-13 Msun/yr (14 Ṁsun) factor of ~3 uncertainty in model Thousands of times weaker than coronal emission, need to look in the wings of PSF Possible complementarity: Lynx mission concept under study by NASA (50x Chandra sensitivity, ~Chandra-like angular resolution) may be competitive for stars within ~5 pc

Detecting Stellar Winds – what can the ngVLA do? Parametric study of constraints on the winds of nearby stars Optically thick emission goes as ν0.6, favoring higher frequencies Twind=104, 105,106 for different stellar parameters (coronal wind is most favorable) Analytic expressions for radio flux density adapted from Wright & Barlow (1975): assumes spherically symmetric mass outflow

Detecting Stellar Winds – what can the ngVLA do? →Cover a quite wide array of parameter space in wind velocity, mass loss rate for nearby solar-like stars (τ Ceti, ξ Boo A)

Detecting Stellar Winds – what can the ngVLA do? ngVLA constraints on Ṁ dot for wind speed=escape speed Current solar mass loss rate →Increase the “look-back time” for studying the wind evolution of the young Sun

Detecting Stellar Winds – what can the ngVLA do? →Constrain stellar wind properties of a fair fraction of the ~270 M dwarfs within 10 pc

Detecting Stellar Winds – what can the ngVLA do Detecting Stellar Winds – what can the ngVLA do? Interpretation of radio emission is complicated ν0.6 optically thick regime, ν-0.1 if optically thin Time-averaged mass loss from CMEs can not be higher than a steady spherically symmetric stellar wind; Drake et al. (2013), Osten & Wolk (2015) have argued for a high flare-associated transient mass loss from active stars Gyrosynchrotron emission: νpeak ~10 GHz, flat/slightly negative above; νpeak is a function of activity Chromospheric emission at even higher frequencies (as seen with ALMA) Stellar wind must be optically thin nonthermal radio emission originating closer to the stellar surface Need large BW to disentangle different contributions to SED, mitigate variability Circular polarization to rule out nonthermal emission

Particles and Fields: Exo-Space Weather Habitability studies are interested in the outward- directed accelerated particles; the most energetic ones are the most impactful Studying the population of accelerated particles near the stellar surface can provide details of the particle spectrum, compare to well-studied solar events, explore any systematics to scalings/extrapolations used for solar/stellar/space weather calculations Segura et al. (2010) impact on ozone layer of a superflare from an M dwarf, scaling flare UV photons only

Particles and Fields: Exo-Space Weather Energetic particles can deplete the ozone layer of a planet in the habitable zone of an Earthlike planet around an M dwarf experiencing a superflare (Segura et al. 2010) Induces non-steady state atmospheric chemistry; effects are detectable with e.g. JWST spectra (Venot et al. 2016)

Particles and Fields: Exo-Space Weather Optically thin gyrosynchrotron emission (>νpeak) constrains index of accelerated particles, also enables constraint on magnetic field strengths Flux Density Frequency νpeak ~ 10 GHz, varies with activity level

Particles and Fields: Exo-Space Weather Optically thin gyrosynchrotron emission (>νpeak) constrains index of accelerated particles, also enables constraint on magnetic field strengths Osten et al. (2016)

Particles and Fields: Exo-Space Weather Can also investigate details of particle injection and trapping, which give constraints on anisotropy of accelerated particles (e.g. work of Lee & Gary 2000 on solar microwave bursts) Need to be confident about observing optically thin emission: large BW to explore frequency- time variations

Particles and Fields: Exo-Space Weather Probabilistic approach to radio luminosities of classes of radio-active stars Using time domain information (8 GHz) on specific objects, assuming homogeneity of source population

Particles and Fields: Exo-Space Weather Probabilistic approach to radio luminosities of classes of radio- active stars Using time domain information on specific objects, assuming homogeneity of source population Sensitivity enables detection down to much lower levels; essentially ALL of these sources in the galaxy will be detectable.

Summary ngVLA will enable stellar wind detections/robust constraints on upper limits; primarily tuned to the nearest stars (within about 10 pc) Sensitivity will enable detection and characterization of essentially all classes of radio-active cool stars in the galaxy, opening up new fields of study, contribute to understanding of stellar contribution to exo- space weather Key requirement is instantaneous BW Good connection to some of the key science topics (cradle of life): stars continue to be interesting after the primary stage of star & planet formation has occurred!