Title Resolving the Molspheres of M supergiants Pi G. Harper Time 18,4 hrs 29 September 2006 1. Name of program and authors Resolving the Molspheres of M supergiants Graham Harper Colorado gmh@casa.colorado.edu Alexander Brown Colorado ab@casa.colorado.edu Matthew Richter California richter@physics.ucdavis.edu Nils Ryde Uppsala ryde@astro.uu.se Takashi Tsuji Tokyo ttsuji@ioa.s.u-tokyo.ac.jp Keiichi Ohnaka Bonn kohnaka@mpifr-bonn.mpg.de Rachel Osten GSFC rosten@milkyway.gsfc.nasa.gov 2. One short paragraph with science goal(s) Multi-wavelength and very high spatial-resolution continuum observations with ALMA will resolve nearby M supergiant MOLspheres, the quasi-static dynamically detached molecular envelopes that may be the formation site for nascent dust. These observations will map the temperature and density structure in the MOLspheres and thereby provide constraints on unknown mechanisms that control the atmospheric energy and momentum balance. These observations will also empirically constrain the wavelength dependence of silicate dust emissivity by separating the stellar and optically thin envelope contributions. ALMA will make a unique contribution to the study atmospheres surpassing the spatial resolution of HST UV observations that sample the same spatial regions. 3. Number of sources 3 stellar systems with a field of view < 25''x25'' 4. Coordinates: 4.1. Rough RA and DEC RA DEC Betelgeuse (M2 Iab) 05 55 10 +07 24 25 Antares (M1 Iab + B4 V) 16 29 25 -26 25 55 alpha Her (M5 II + ) 17 14 39 +14 23 25 4.2. Moving target: no 4.3. Time critical: no (unless we coordinate with other observatories) 4.4. Scheduling constraints: The different frequency bands should be observed as close together in time as possible to avoid interpretation complications resulting from stellar variability 5. Spatial scales: 5.1. Angular resolution (arcsec): 0.006-0.090 5.2. Range of spatial scales/FOV (arcsec): 0.006 - 25.000 scales reflect highest possible resolution of stellar source optional: single-field 5.3. Required pointing accuracy: 0.6 (arcsec) 6. Observational setup 6.1. Single dish total power data: required Observing modes for single dish total power: on-the-fly mapping 6.2. Stand-alone ACA: beneficial 6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: no 6.4. Subarrays of 12m baseline-ALMA antennas: no 7. Frequencies: 7.1. Receiver band: Band 3, 4, 6, 7, 8, and 9 7.2. Lines and Frequencies (GHz): maximum transmission for each band - see highest continuum sensitivity 7.3. Spectral resolution (km/s): N/A 7.4. Bandwidth or spectral coverage (km/s or GHz): 8 GHz 8. Continuum flux density: 8.1. Typical value (Jy): Average total system fluxes (unresolved) 350 GHz 0.3 Jy 666 GHz 0.9 Jy 8.2. Required continuum rms (Jy or K): Criterion S/N of 10 at 2nd peak in visibility. Use model of Harper, Brown and Lim (2001 ApJ 551, 1073) For Betelgeuse 0.1*(2nd vis. peak) are mJy GHz Band 3: 1.4 100 Band 4: 2.2 150 Band 6: 3.2 250 Band 7: 5.1 350 Band 8: 7.1 400 Band 9: 15.1 660 8.3. Dynamic range within image: weakly resolved source in clear field (from 7.1 and 7.2, but also indicate whether, e.g., weak objects next to bright objects) 8.4. Calibration requirements: absolute ( 5%) repeatability ( 1-3%) relative ( 1-3%) 9. Line intensity: N/A 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: No 10.1. Required Stokes parameters: 10.2. Total polarized flux density (Jy): 10.3. Required polarization rms and/or dynamic range: 10.4. Polarization fidelity: 10.5. Required calibration accuracy: 11. Integration time for each observing mode/receiver setting (hr): Assumes a factor of two overhead for fast switching. GHz hrs Band 3: 100 0.8 + 1.0 Band 4: 150 0.8 + 1.0 Band 6: 250 2.0 + 1.0 Band 7: 350 2.4 + 1.0 Band 8: 400 2.4 + 1.0 Band 9: 660 4.0 + 1.0 For the on-the-fly mapping we assume 20 min per star, per band, for one telescope. 12. Total integration time for program (hr): 18.4 hours 13. Comments on observing strategy : (optional) To obtain the highest spatial resolution with as wide a range of observing frequencies as possible, and to obtain the total system flux on spatial scales larger than the array FOV. Use maximum bandwidth to observe the stellar thermal continuum emission for maximum sensitivity. Each source should be observed at as many frequencies as possible at the same time to avoid interpretation problems causes by source variability. In addition to observing the highest frequencies in "best weather", this will/may require that the lower frequencies also be observed under "best weather" conditions. Preferably the observations should be obtained within a couple of days, and not more than a week. We will make preparatory observations with CARMA and APEX to examine the dust structure outside the narrow ALMA interferometer FOV, which will lead to more reliable time estimates for the on-the-fly mapping. -------------------------------------------------- Review v2.0: Resolving the Molspheres of M supergiants Graham Harper Colorado gmh@casa.colorado.edu Alexander Brown Colorado ab@casa.colorado.edu Matthew Richter California richter@physics.ucdavis.edu Nils Ryde Uppsala ryde@astro.uu.se Takashi Tsuji Tokyo ttsuji@ioa.s.u-tokyo.ac.jp Keiichi Ohnaka Bonn kohnaka@mpifr-bonn.mpg.de Rachel Osten GSFC rosten@milkyway.gsfc.nasa.gov DRSP 2.0 Review Leonardo Testi: I am not familiar with this science, so it is difficult for me to figure out exactly what is needed here. So it is not clear to me why all frequencies are required and why for all of them the full range of resolutions is necessary. At the low frequencies t will not be possible to obtain the 0.006 arcsec resolution, thus it will not be possible to obtain temperature and density maps at this resolution. If the goal is to compute these maps, then one should probably limit to a lower resolution (which will also be less demanding at the highest frequencies). Presumably OTF total power mapping will be required only for band 8 and 9 (given the primary beam size at lower frequencies). It is not clear to me whether the correct range of configurations (to cover the range of resolutions) have been considered in the computation of the observing times. I have some problems in figuring out the computation for the integration times. If the sensitivity is to be computed for individual (u,v) points (2 antennas) at the second visibility peak as mentioned, then in 1hr (with no overheads) at 660 GHz I only get a S/N=3 (sort of) for 15 mJy. ...There is something I did not understand. R.: The proposed observations of M supergiants make major demands on the proposed capabilities of ALMA, both in terms of available bandwidth and spatial resolution, and this is why we have submitted this DRSP2.0. Below we provide supplemental text to help clarify the project for the reviewers. Note on the exposure times (last comment in review): The thermal continuum emitting source of the M supergiant can be characterized as a disk with diffuse edges because the density scale heights are small compared to the stellar radius, and the visibilities reflect this. We require for each relevant antenna pair a S/N of 10 at the 2nd peak of the visibility curve. In section 8.2 we listed the flux at 1/10 of the 2nd peak, i.e. the required 1 sigma. For the example given by the reviewer: at 660 GHz the 2nd peak has a estimated flux of 150 mJy and 1/10 of this is 15 mJy. Using the ALMA Sensitivity Calculator it takes 600 sec (10 mins) to achieve a 1 sigma (with default parameters) of 15.1 mJy. This is 1/10 of the 2nd Peak, and so a S/N=10. If this interpretation of the sensitivity tool is incorrect please let us know and we will modify accordingly.