Date : Aug, 01 2012 Observing Application Proposal ID : VLA/13A-471 Legacy ID : AH1104 PI : Gregg Hallinan Type : Regular Category : Solar System, Stars, Planetary Systems Total Time : 36.0 The Thermal Atmospheres of Nearby Solar-type Stars Abstract: We request 36 hours of shared risk observing with the JVLA to observe 5 nearby solar type stars (F8V - K2V) with levels of magnetic activity expected to be similar to that of the Sun. The goal of our survey is the detection of quiescent gyroresonance emission from above active regions at the base of the coronae. Any detection would constitute the first radio detection of a star of similar magnetic activity levels to the Sun, and provide the first insight into coronal field strengths and plasma temperatures for other solar-type stars. The total time request is 36 hours. Authors: Name Institution Email Status Gregg Hallinan California Institute of [email protected] Graduating: N/A Technology Thesis: false Jackie Villadsen California Institute of [email protected] Graduating: N/A Technology Thesis: false Stephen Bourke California Institute of [email protected] Technology Principal Investigator: Gregg Hallinan Contact: Gregg Hallinan Telephone: 5104092840 Email: [email protected] Related proposals: Joint: Not a Joint Proposal Observing type(s): Continuum, Single Pointing(s) VLA Resources Name Conf. Frontend & Backend Setup Ku Band Any Ku Band 2 cm 12000 - 18000 MHz Catalog ID: 12542 Shared Risk Observing ResourceName: 12581 Resource ID: Ku band 1 Name Conf. Frontend & Backend Setup X band Any X Band 3.6 cm 8000 - 12000 MHz Catalog ID: 12542 Shared Risk Observing ResourceName: X band Resource ID: 12543 Testing Resource Images Sources: Name Position Velocity Group Coordinate System Equatorial Convention Radio Equinox J2000 03:32:55.84 epsilon Eridani Right Ascension Ref. Frame LSRK EpsEri 00:00:00.0 -9:27:29.7 Declination Velocity 0.00 00:00:00.0 Coordinate System Equatorial Convention Radio Equinox J2000 01:44:04.8 tau Ceti Right Ascension Ref. Frame LSRK Tau Ceti 00:00:00.0 -15:56:15.0 Declination Velocity 0.00 00:00:00.0 Coordinate System Equatorial Convention Radio Equinox J2000 04:15:16.32 40 Eridani Right Ascension Ref. Frame LSRK 40Eri 00:00:00.0 -7:39:10.3 Declination Velocity 0.00 00:00:00.0 Coordinate System Equatorial Convention Radio Equinox J2000 00:49:06.29 eta Cassiopeiae Right Ascension Ref. Frame LSRK EtaCass 00:00:00.0 +57:48:54.67 Declination Velocity 0.00 00:00:00.0 Coordinate System Equatorial Convention Radio Equinox J2000 03:19:55.6505 82 Eridani Right Ascension Ref. Frame LSRK 82Eri 00:00:00.0 -43:04:11.221 Declination Velocity 0.00 00:00:00.0 Coordinate System Equatorial Convention Radio Equinox J2000 00:00:00.0 OneSource Right Ascension Ref. Frame LSRK FollowUp 00:00:00.0 +00:00:00.0 Declination Velocity 0.00 00:00:00.0 Sessions: Name Session Time Repeat Separation LST minimum LST maximum Elevation (hours) Minimum EpsEri 3.00 1 0 day 00:00:00 24:00:00 0 EpsEri 3.00 1 0 day 00:00:00 24:00:00 0 TauCet 3.00 1 0 day 00:00:00 24:00:00 0 TauCet 3.00 1 0 day 00:00:00 24:00:00 0 40Eri 3.00 1 0 day 00:00:00 24:00:00 0 40Eri 3.00 1 0 day 00:00:00 24:00:00 0 EtaCass 3.00 1 0 day 00:00:00 24:00:00 0 EtaCass 3.00 1 0 day 00:00:00 24:00:00 0 2 Name Session Time Repeat Separation LST minimum LST maximum Elevation (hours) Minimum 82Eri 3.00 1 0 day 00:00:00 24:00:00 0 82Eri 3.00 1 0 day 00:00:00 24:00:00 0 Follow-up 3.00 1 0 day 00:00:00 24:00:00 0 Follow-up 3.00 1 0 day 00:00:00 24:00:00 0 Session Constraints: Name Constraints Comments Session Source/Resource Pairs: Session Name Source Resource Time Figure of Merit Subarray EpsEri epsilon Eridani Ku Band 3.0 hour 0.003 mJy/bm EpsEri epsilon Eridani X band 3.0 hour 0.003 mJy/bm TauCet tau Ceti X band 3.0 hour 0.003 mJy/bm TauCet epsilon Eridani Ku Band 3.0 hour 0.003 mJy/bm 40Eri 40 Eridani X band 3.0 hour 0.003 mJy/bm 40Eri epsilon Eridani Ku Band 3.0 hour 0.003 mJy/bm EtaCass eta Cassiopeiae X band 3.0 hour 0.003 mJy/bm EtaCass eta Cassiopeiae Ku Band 3.0 hour 0.003 mJy/bm 82Eri 82 Eridani X band 3.0 hour 0.003 mJy/bm 82Eri 82 Eridani X band 3.0 hour 0.003 mJy/bm Follow-up OneSource Ku Band 3.0 hour 0.003 mJy/bm Follow-up OneSource Ku Band 3.0 hour 0.003 mJy/bm Present for observation: yes Staff support: None Plan of Dissertation: no 3 Detecting the Thermal Atmospheres of Nearby Solar-Type Stars Abstract We request 36 hours of shared risk observing with the JVLA to observe 5 nearby solar type stars (F8V - K2V) with levels of magnetic activity expected to be similar to that of the Sun. The goal of our survey is the detection of quiescent gyroresonance emission from above active regions at the base of the coronae. Any detection would constitute the first radio detection of a star of similar magnetic activity levels to the Sun, and provide the first insight into coronal field strengths and plasma temperatures for other solar-type stars. The total time request is 36 hours. Introduction The detection of quiescent radio emission from the coronae of a wide range of main sequence dwarf stars was one of the major breakthroughs with the advent of the VLA and completely revolutionized the field of stellar radio astronomy (Gary & Linsky 1981ApJ...250..284G). The implied luminosities and hence brightness temperatures associated with this quiescent emission confirmed that such stars have non-thermal coronae, where large populations of electrons are continuously accelerated to high energies, a totally unexpected result as there is simply no solar counterpart. Quiescent microwave radio emission detected from the sun is typically due to thermal bremsstrahlung emission from the chromosphere (typically at ν < 3 GHz) and gyroresonance (cyclotron) emission above active regions (best observed from ν = 3 − 20 GHz), with a luminosity ∼ 1011 erg s−1 Hz−1. The much brighter quiescent radio emission from nearby active dwarf stars, on the other hand, is thought to be due to gyrosynchrotron emission from the population of continuously accelerated electrons that constitute the non-thermal corona. Invariably such radio detected dwarf stars are also bright x-ray sources and rapid rotators, and thus represent extreme levels of magnetic activity. To date, no star with magnetic activity levels similar to the Sun has ever been detected at radio frequencies. The EVLA: A New Era in Stellar Radio Astronomy The unprecedented sensitivity and spectral resolution of the EVLA opens entirely new avenues into the study of the radio emission from main sequence stars. Whereas the VLA was only sensitive to the most luminous, and hence active, members of the nearby stellar population, the EVLA can probe entire populations of nearby stars and investigate radio luminosity as a function of parameters such as age, mass and rotation rate as well as enabling correlation with other activity tracers such as X-ray luminosity. In particular, for the first time, nearby solar analogs (spectral type F8V-K2V) of similar age, mass and magnetic activity level to the Sun, can be detected producing quiescent radio emission of the same nature as that detected from the Sun. Figure 1 shows the flux of the Sun at various bands of the EVLA at a distance of 1.3 pc. The thermal blackbody photosphere of the Sun would be detectable at the higher bands of K and Ka out to a distance of 6 pc in a single 4 hour observation. However, although the detection of the photosphere of a solar-type star would be a landmark achievement for the EVLA, a result of higher scientific merit would be the detection of thermal bremmstrahlung (free-free) emission from the stellar chromosphere and gyroresonance (cyclotron) emission above active regions at the base of stellar coronae. In particular, we will focus on the latter mechanism which can potentially provide excellent diagnostic information on the magnetic field strengths, filling factors and plasma temperatures at the base of stellar coronae. 1 Furthermore, monitoring such emission can reveal rotational modulation as compact active regions rotate in and out of view on the stellar disk and longer term monitoring can reveal the presence of magnetic cycles, similar to the well characterized solar cycle. The Diagnostic Power of Gyroresonance Emission from Stellar Active Regions Gyroresonance emission produced above active regions at the base of the solar corona is the most powerful diagnostic tool used in the study of the radio Sun. Similar diagnostic potential is available for stellar coronae with the advent of the EVLA. Gyroresonance emission is produced through reso- nance between electromagnetic waves and electrons spiraling in magnetic fields at the local electron 6 cyclotron frequency, νc = 2:8 × 10 B Hz, where B is measured in Gauss. The radio emission is pro- duced at low harmonics (s=1,2,3,4) with the opacity in a given electromagnetic mode of the plasma decreasing by two orders of magnitude for each increase in harmonic number. For solar coronal conditions, the x mode radiation is typically optically thick for the gyroresonant layer corresponding to s=3, whereas the o mode is typically optically thick for the gyroresonant layer s=2.