Title Unbiased line surveys of high mass star forming regions Pi P. Schilke Time 612 hrs 1. Name: Unbiased line surveys of high mass star forming regions Authors: P. Schilke, E. van Dishoeck, M. Wright, C. Comito, F. Wyrowski ... 2. Science goal: Unbiased line surveys are the only way to get an unbiased view on the chemical composition of sources, which allows, provided the modeling is understood, to reconstruct the evolution history of high mass star forming regions. Since many such regions show pronounced spatial variations of the molecular distribution and excitation conditions, it is necessary to spatially resolve them. This also aids in the finding of new lines and molecules, because it reduces the confusion. In the best studied source so far, Orion-KL, the source intrinsic confusion limit is in the order of 1~K, so that integration down to this level, but not much further down, seems advised. Spanning the survey over the whole frequency range of ALMA allows to cover a large range of excitation conditions for most observed molecules, which is a prerogative for detailed modeling of the temperature, density and FIR field. For high column density sources it seems likely that the dust becomes optically thick at the highest frequencies, which will cause some lines to show up in absorption. This, while it complicates interpretation, permits a modeling of the exitation conditions along the line of sight. The source list should be coordinated with that of HIFI so that complementary information on higher frequencies is also obtained. 3. Number of sources: 10 4. Coordinates: 4.1. 1 source in Orion (RA=05, DEC=-05) 9 sources in Galactic Plane (RA=15, DEC=-54 to RA=19, DEC=15) 4.2. Moving target: no 4.3. Time critical: no 5. Spatial scales: 5.1. Angular resolution: 0.6" for Band 3, 0.3" for Bands 6, 7 and 9 5.2. Range of spatial scales/FOV: 3"x3" 5.3. Single dish: yes, for some sources 5.4. ACA: yes (particularly at higher frequencies) 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 3 Band 6 Band 7 Band 9 6.2. Line: 60 64 95 69 settings 6.3. Spectral resolution (km/s): 0.5 km/s 6.4. Spectral coverage (km/s or GHz): 500 MHz at Band 3, 1 GHz at Bands 6, 7, 2GHz at Band 9 7. Continuum flux density: Band 3 Band 6 Band 7 Band 9 7.1. Typical value: 2-20 2-20 6-100 30-600 Jy (high-mass) 7.2. Continuum peak value: 50 mJy/beam 200 mJy/beam 300 mJy/beam 1 Jy/beam 7.3. Required continuum rms: 0.1 Jy (not relevant for this program) 7.4. Dynamic range in image: >100 8. Line intensity: 8.1. Typical value: 5-500 K 8.2. Required rms per channel: 1 K 8.3. Spectral dynamic range: 3 (for species which are barely detected) >100 (for brightest lines) 9. Polarization: no 10. Integration time per setting: 10 min/Bd 3, 15 min/Bd 6,7, 10 min/Bd 9 11. Total integration time for program: 10 x 60 x 10m : 100 h Band 3 10 x 64 x 15m: 160 h Band 6 10 x 95 x 15m: 237 h Band 7 10 x 69 x 10m: 115 h Band 9 ------------------------------------------- 612 h total Comments: 1) Increasing the spatial resolution for Band 3 to match the others will result in a vast increase of observing time. 2) There are no overheads calculated here. Since the individual settings are only 10-15 min on source, these could be significant, according to Memo 375 in the order 50-100%, depending on frequency. Since some of these overheads apply only once per frequency setting (sideband ratio, bandpass, flux), the best strategy may be to tune to a frequency, observe all the sources, and then retune. Some of the overheads on the other hand apply per source (pointing, phase calibration), so if these dominate the best strategy may be to stay on a source and tune through. 3) Depending on the exact characteristics of the corrlator filters, one would want to decrease the spacing to get some overlap at the edges, increasing the number of correlator settings. This would particularly be the case if the upgraded correlator is used, since there is a lot of aliasing. 4) The correlator upgrade would be very beneficial for this project, but see 3) above. 5) We note that in the current ALMA software there is NO provision to get SSB spectra from single dish observations at least in Band 9, although a deconvolution (as will be done for HIFI) will be possible, using the sideband gain ratios determined in interferometer mode, as noted by Mel Wright. 6) One would want to get even high spatial resolution for selected parts of the survey. **************************************************************************** Review Lee Mundy: OK. -------------------------------------------------- Review v2.0: ok