Title Millimeter observations of nonthermal emission from active stars Pi R. A. Osten Time 36 hrs 1. Name of program and authors "Millimeter observations of nonthermal emission from active stars" R. A. Osten 2. One short paragraph with science goal(s) This is a project to investigate the high frequency (86--116 GHz) end of the nonthermal electron distribution which manifests itself at centimeter wavelengths. These high frequencies will probe the most energetic electrons, where optically thin coronal conditions are expected. There will be a search for time variability, from minute timescales to longer. Previous observations of energetic flares from 5--40 GHz with the VLA (Bastian, unpublished) have shown a rising spectrum up to 40 GHz (with flux densities of order a few hundred mJys). Recently (Brown & Brown 2006, ApJ 638, L37) reported a large mm flare on an active binary at a frequency of 99 GHz with OVRO. Solar flare observations at mm wavelengths have cemented the relationship between these energetic particles and nonthermal hard X-ray emissions; stellar radio (cm and mm wavelengths) remain the most sensitive means of detecting these particles, and studying their dynamics. Observations at two frequencies, both of which are optically thin to gyrosynchrotron emission (86 and 116 GHz), can cement the index of the power-law electron distribution, a key component to beginning to understand the energetics of particle acceleration in non-solar stellar flares. The sample has been chosen to contain both active evolved stars and active dwarf stars; their properties at cm-wavelengths and X-ray wavelengths appear to be similar, implying a similarity in some fundamentals of coronal heating and nonthermal emission; this investigation will extend to the highest energy electrons currently detectable. In a sense this proposal could be split into two parts: a first one concentrating on detections (which can be done quickly given ALMA's sensivities) and a second one focussing on the detected objects to look for variability. 3. Number of sources (e.g., 1 deep field of 4'x4', 50 YSO's, 300 T Tauri stars with disks, ...; do NOT list individual sources or your "pet object", except in special cases like LMC, Cen A, HDFS) Radio bright, active stars distributed among three classes: (1) active binary systems with at least one evolved component (HR 1099, UX Ari, II Peg, sigma Gem), (2) single active dwarf stars (AD Leo, UV Cet, YZ CMi), and (3) single active evolved stars (FK Com, HD 32918). Total of 9. 4. Coordinates: 4.1. Rough RA and DEC (e.g., 30 sources in Taurus, 30 in Oph, 20 in Cha, 30 in Lupus) Indicate if there is significant clustering in a particular RA/DEC range (e.g., if objects in one particular RA range take 90% of the time) HR 1099: 03 34 +00 25 UX Ari: 03 23 +28 32 II Peg: 23 55 +28 38 sigma Gem: 07 43 +28 53 AD Leo: 10 16 +20 07 UV Cet: 01 36 -18 12 YZ CMi: 07 42 +03 40 FK Com: 13 30 +24 13 HD 32918: 04 58 -75 16 4.2. Moving target: yes/no (e.g. comet, planet, ...) no 4.3. Time critical: yes/no (e.g. SN, GRB, ...) yes, need accompanying cm-wavelength observations. 4.4. Scheduling constraints: (optional) 5. Spatial scales: 5.1. Angular resolution (arcsec): pt. src. 5.2. Range of spatial scales/FOV (arcsec): (optional: indicate whether single-field, small mosaic, wide-field mosaic...) 5.3. Required pointing accuracy: (arcsec) 1 6. Observational setup 6.1. Single dish total power data: no/beneficial/required no Observing modes for single dish total power: (e.g., nutator switch; frequency switch; position switch; on-the-fly mapping; and combinations of the above) 6.2. Stand-alone ACA: no/beneficial/required no 6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: no/beneficial/required no 6.4. Subarrays of 12m baseline-ALMA antennas: yes/no no 7. Frequencies: 7.1. Receiver band: Band 3, 4, 5, 6, 7, 8, or 9 3, would like to be able to sample the low and high ends of this band simultaneously 7.2. Lines and Frequencies (GHz): (approximate; do _not_ go into detail of correlator set-up but indicate whether multi-line or single line; apply redshift correction yourself; for multi-line observations in a single band requiring different frequency settings, indicate e.g. "3 frequency settings in Band 7" without specifying each frequency (or give dummies: 340., 350., 360. GHz). For projects of high-z sources with a range of redshifts, specify, e.g., "6 frequency settings in Band 3". Apply redshift correction yourself.) 7.3. Spectral resolution (km/s): n/a 7.4. Bandwidth or spectral coverage (km/s or GHz): few GHz 8. Continuum flux density: 8.1. Typical value (Jy): We expect a range from the tens of microJys to $>$ 100 mJy during major flares depending on the variability seen. As an example, extrapolating from the 15 GHz detection of EV Lac (dM3e; similar spectral type to the flare stars listed above) of Osten et al. (2006 ApJ 647, 1349) to 86 GHz using alpha=-0.55 gives an expected 86/116 GHz flux of 130/110 microJy. (take average value of set of objects) (optional: provide range of fluxes for set of objects) 8.2. Required continuum rms (Jy or K): To establish detections at the 8 sigma level, need 1 sigma rms of 15 microJy for the example given above. This can be achieved in 600 seconds. To establish variations of spectral index within flaring events, need 1 sigma rms of 50 (120) microJy, which can be achieved in 60 s at 86 (116) GHz. Note the observation will be longer than this. 8.3. Dynamic range within image: (from 7.1 and 7.2, but also indicate whether, e.g., weak objects next to bright objects) >8 8.4. Calibration requirements: absolute ( 10% ) repeatability ( 5% ) relative ( 1-3% ) 9. Line intensity: 9.1. Typical value (K or Jy): (take average value of set of objects) (optional: provide range of values for set of objects) 9.2. Required rms per channel (K or Jy): 9.3. Spectral dynamic range: 9.4. Calibration requirements: absolute ( 1-3% / 5% / 10% / n/a ) repeatability ( 1-3% / 5% / 10% / n/a ) relative ( 1-3% / 5% / 10% / n/a ) 10. Polarization: yes/no (optional) yes 10.1. Required Stokes parameters: I,V 10.2. Total polarized flux density (Jy): Expected Stokes V flux varies; percent circular polarization probably low, <10%. 10.3. Required polarization rms and/or dynamic range: Using example above, to detect 10% circular polarization with flux density (I) of 130 microJy requires 1 sigma rms of 4 microJy for a 3 sigma detection. This can be done in 2 hours. 10.4. Polarization fidelity: 10.5. Required calibration accuracy: 11. Integration time for each observing mode/receiver setting (hr): for detections in total intensity: 0.17 hour (10 min.) for detections of circular polarization: 2 hours 12. Total integration time for program (hr): For detection phase of program, 2hrs x 9 sources = 18 hours. Additional time will be requested to pursue variability of detected sources. Assume four of the sources show strong (>20 sigma) detections, and follow each source for 5 hours. 4 x 5 = 20 hours. Total time =18+20 =36 hours. 13. Comments on observing strategy : (optional) For monitoring variability, we would observe in two sub-arrays, one using frequencies near 86 GHz and the other with frequencies near 116 GHz. (e.g. line surveys, Target of Opportunity, Sun, ...): -------------------------------------------------- Review v2.0: 1. Name of program and authors "Millimeter observations of nonthermal emission from active stars" R. A. Osten DRSP2.0 Review Leonardo Testi: ok with main driver for time from variability. Are there requirements for the time separation between observations at 86 and 115 GHz (cannot be observed simultaneously)? Why is single dish and ACA required? Which are the angular resolution and maximum angular scales requested for this programme? Reply: The 86 and 115 GHz observations should be performed simultaneously. ACA and single dish data are not required. These are point sources, in fields which are not confused, so there are no stringent constraints on angular resolution or maximum angular scale. For the active binaries, the orbital separation is only a few mas.