Title  Observations of the great comet of the decade
Pi     D. Bockelee-Morvan
Time   200 hrs

1. Name of program and authors 
   Observations of the great comet of the decade 
   Authors: D. Bockelee-Morvan, N. Biver, J. Crovisier, J. Boissier 
 
2. One short paragraph with science goal(s) 
   Bright new comets (here referred as comets A), with water  
   production rates ~5E29 molecules/s at perihelion (q~1AU), can be observed  
   statistically once every decade at geocentric distances of typically 1 AU.  
   Active comets (QH2O~1E29 molecules/s) coming close to Earth (~0.1 AU)  
   might be as well expected (comets B) during the first years of operation 
   of ALMA. Observations with ALMA will allow: 
   1) to characterize their molecular and isotopic composition. New isotopic 
   and molecular species will be searched for. 
   2) to map the spatial distribution of dust and molecular species  
   with ALMA with unprecedented spatial resolution (specially for comets B),  
   and study its evolution with nucleus rotation. 
   3) for the most productive comets (comets A), to monitor their dust and  
   gaseous activity as a function of heliocentric distance.  
 
3. Number of sources  
   One of each of type A & B comets might be observed over a 3 year period  
   (plus monitoring).  These will be truly TOO observations, occurring at 
   a completely unpredictable time. 
    
4. Coordinates: 
 
4.1. Rough RA and DEC  
 
4.2. Moving target: yes 
 
4.3. Time critical: yes 
 
4.4. Scheduling constraints:  
 
5. Spatial scales: 
 
5.1. Angular resolution (arcsec): 
       
     -Compact configuration (1-2 arcsec)for lines 
     -Typically 5 km baselines for nucleus continuum observations 
      (for nucleus/coma contrast > 10)  
     - For weak lines, auto-correlation measurements may be more sensitive     
 
5.2. Range of spatial scales/FOV (arcsec): 
  
5.3. Required pointing accuracy: (arcsec) 
     0.5" 
 
6. Observational setup 
 
6.1. Single dish total power data: beneficial 
 
     Observing modes for single dish total power:  
     frequency switch 
 
6.2. Stand-alone ACA: no 
 
6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas:  
     beneficial 
 
6.4. Subarrays of 12m baseline-ALMA antennas: no 
 
 
7. Frequencies: 
 
7.1. Receiver band: Band 3, 4, 5, 6, 7, 8  
 
7.2. Lines and Frequencies (GHz):  
      
     multi-line observations  
      
 
7.3. Spectral resolution (km/s): < 0.1 km/s 
 
7.4. Bandwidth or spectral coverage (km/s or GHz): 
     8 GHz in continuum mode 
     depends upon frequency setup in spectroscopic range  
     (e.g. large coverage for covering many lines at the same time) 
 
8. Continuum flux density:  
 
8.1. Typical value (Jy) 
     nucleus : ~2 mJy for 10 km size comet nucleus at 1 AU from Earth 
 
8.2. Required continuum rms (Jy or K):  
 
8.3. Dynamic range within image: 
 
8.4. Calibration requirements: absolute      ( 10% ) 
                               repeatability ( 10% ) 
                               relative      ( 10% ) 
 
9. Line intensity 
 
9.1. Typical value (K or Jy): 
     depends upon line 
     At perihelion: 0.1 to 50 K km/s for compact configuration in 2 km/s 
     velocity range.       
 
9.2. Required rms per channel (K or Jy): depends upon line 
 
9.3. Spectral dynamic range: 
 
9.4. Calibration requirements: absolute      (10%) 
                               repeatability (10%) 
                               relative      (10%) 
 
 
10. Polarization: no  
 
 
11. Integration time for each observing mode/receiver setting (hr): 
    several frequency setup, with different integration times 
 
12. Total integration time for program (hr): 200 h 
 
 
13. Comments on observing strategy :  
     Target of Opportunity 
     Line mapping requires ALMA to be in compact  
     configuration. Nucleus investigation requires more extended 
     configurations. So the observing strategy will depend upon Alma 
     configuration at time of comet perihelion. 
     Line monitoring : can be done in single-dish mode  
 
 
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Review v2.0:
 
Review of 4.3.1-4.3.9

These projects have all been updated to v2.0 and a new, timely project
on D/H has been added.

One issue that all projects share is their use of the ACA in
crosscorrelation with the ALMA-12m antennas. Are the common baselines
really essential, or would *simultaneous* (but standalone) ACA
observations also work? This might be much easier on the system
(slewing times; correlator; ...). Fully standalone (and therefore
separate in time) ACA observations for comets obviously make little
sense (...although, one could think of cases where some large-scale
monitoring could be useful). 

Comment: the integration times do not seem to be worked out in much
detail, although the total times listed seem of the correct
magnitude. This may be the best that is currently feasible. (cf. v1.1
where more detailed estimates are given).