Title Thermal Emission from Red Giant and Supergiant Stars Pi K.M. Menten Time 100 hrs 13.2.1: Single DRSP Project: Thermal Emission from Red Giant and Supergiant Stars ================================================================== 1. Name of program and authors Thermal Emission from Red Giant and Supergiant Stars Authors Karl M. Menten 2. Science goal(s) As found by Reid & Menten (1997, ApJ, 476, 327 ; hereafter RM97) from multi-wavelength (8 - 22 GHz) VLA observations, red giant stars form a "radio photosphere" which is characterized by a (1) a size of ~2 times the (line free) optical photosphere, (2) temperature ~1500 K (lower than the 2000 - 2500 K stellar temperature), a thermal spectrum rising with the square of the frequency, and (3) little variability. Their technique involved (at 22 and 43 GHz) to observe simultaneously strong H2O (or, resp., SiO) masers in one narrow IF band and line-free continuum in another broad IF band. The maser emission was self-calibrated and the selfcal solutions were transferred to the continuum data, yielding perfect calibration for it, which otherwise, due to its weakness (a few mJy at 22 Jy) would have been impossible to image. RM97 successfully modeled this radiophotospheric continuum emission as due to free-free interactions of electrons released from low-ionization metals with neutral hydrogen atoms and molecules. In particular, they derived a spectrum that rises as frequency^1.9 from the lowest radio frequencies to mid-IR wavelengths until it peaks at 100 THz (3 microns) and turns over beyond. The existence of this radio photosphere also explains the lack of variations in the radio flux with stellar cycle. Observational data below 50 GHz, at 250 GHz, and above 10 THz are very well reproduced by this relationship (see, e.g. their Fig. 2). The size determinations, only marginally possible with the initial 22 GHz work, were later confirmed and refined by 43 GHz observations. The continuum emission from the radio photosphere will be of CENTRAL importance for ALL (continuum, molecular, and atomic) high resolution (better than 0.1") observations of circumstellar envelopes. This is because it will be possible to self-calibrate the continuum emission with itself at ALL ALMA frequencies. This is quite the opposite to radio frequencies, were maser observations are used to calibrate continuum data. Another important "use" of red giant continuum emission, will be (as already pointed out by MR9) that, given their well-determined spectra they will be excellent, maybe the best, point-like, absolute flux calibrators for ALMA. Finally, for all line observation, the continuum position will mark the position of the central star, whose knowledge is crucial, e.g. for model calculations, and frequently not will determinable given the often complicated, fragmented distributions of the line emission. 3. Number of sources: (see below for justifi cation of volume) Numbers of stars per kpc^3 (Jura & Kleinmann 1992, ApJS, 79, 105 All carbon 100 "Very dusty carbon" 30 S-type 30 O-rich miras (300 < P < 400 d) 210 O-rich miras (P<300 d) 35-60 "very dusty oxygen 30 This numbers should be regarded as strict lower limits of objects for which selfcal is easily possible. 4. Coordinates and expected fluxes (examples with measured radio data): (a) Stars with measured 22 GHz flux densities Star RA(J2000) Dec(J2000) D S(22.4 GHz) S(350 GHz) S(680 GHz) (pc) (mJy) (Jy) (Jy) o Cet 02 18 20.8 -02 58 37.4 128 2.6 0.48 2.4 normalized to D=100 pc: - 4.3 R Leo 09 47 33.5 +11 25 44 101 1.5 0.28 1.4 normalized to D=100 pc: - 1.5 W Hya 13 49 02.0 -28 22 03 115 3.0 0.56 2.8 normalized to D=100 pc: - 4.0 R Aql 19 06 22.3 +08 13 49 211 0.8 0.15 0.7 normalized to D=100 pc: - 3.5 chi Cyg 19 50 33.9 +32 54 51 106 1.6 0.30 1.5 normalized to D=100 pc: - 1.8 R Cas 23 58 24.7 +51 23 20 107 0.8 0.15 0.7 * normalized to D=100 pc: - 0.9 ---------------------------------------------------------------------------- adopt for D=100 pc: - 2.7 0.66 2.5 ALMA rms cont. sensitivity (in 10 s): - - 0.0005 0.003 Distance out to which star could be detected at 5 sigma (kpc): 1.6 1.3 * outside of ALMA declination range 4.2. Moving target: yes/no (e.g. comet, planet, ...) no 4.3. Time critical: yes/no (e.g. SN, GRB, ...) no 5. Spatial scales: 5.1. Angular resolution (arcsec): 0.010-0.020 for resolution of emission, any for detection/selfcal 5.2. Range of spatial scales/FOV (arcsec): (optional: indicate whether single-field, small mosaic, wide-field mosaic...) continuum only: <1", any for simultaneous line emission 5.3. Single dish total power data: yes/no no 5.4. ACA: yes/no no 5.5. Subarrays: yes/no no 6. Frequencies: 6.1. Receiver band: all 6.2. 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) any 6.3. Spectral resolution (km/s): N/A 6.4. Bandwidth or spectral coverage (km/s or GHz): 7. Continuum flux density: 7.1. Typical value (Jy): (take average value of set of objects) (optional: provide range of fluxes for set of objects) 30-50 uJy for G and M dwarfs (5-10 pc) at 100 GHz 300-500 uJy for G and M dwarfs (5-10 pc) at `300 GHz 7.2. Required continuum rms (Jy or K): e.g. 0.5 mJy at 350 GHz 3 mJy at 680 GHz both in 10 s to allow selfcal 7.3. Dynamic range within image: (from 7.1 and 7.2, but also indicate whether e.g. weak objects next to bright objects) N/A; no nearby weaker objects expected 8. Line intensity: 8.1. Typical value (K or Jy): (take average value of set of objects) (optional: provide range of values for set of objects) 8.2. Required rms per channel (K or Jy): 8.3. Spectral dynamic range: 9. Polarization: no 10. Integration time for each observing mode/receiver setting (hr): Dictated by simultaneous line observations 11. Total integration time for program (hr): 100 12. Comments on observing strategy (e.g. line surveys, Target of Opportunity, Sun, ...): (optional) ************************************************************************* Review Leonardo Testi: The project is interesting, but the estimate of the required time is obscure. The continuum does not require long integrations, but the time is set by lines, which are TBD. We can probably buy the quoted 100hrs with the idea that if more time is needed only a fraction of the sample will be done in the 3yrs covered by the DRSP. Priority: High -------------------------------------------------- Review v2.0: Project: Thermal Emission from Red Giant and Supergiant Stars ================================================================== 1. Name of program and authors Thermal Emission from Red Giant and Supergiant Stars Authors Karl M. Menten DRSP2.0 Review Leonardo Testi: It would be great to have some ideas on the lines/correlator setups... or to know that this is going to be a continuum only project.