Title  D/H in cometary water
Pi     D. Bockelée-Morvan
Time   10 hrs per year

 
1. Name of program and authors 
   D/H in cometary water 
   D. Bockelée-Morvan 
 
2. One short paragraph with science goal(s) 
   The D/H ratio in cometary water is a key parameter to constrain the 
   origin of cometary ices. It complements values measured in other Solar  
   System bodies, proto-planetary disks and star-forming regions for a  
   better understanding of Solar System and planetary formation. It has only 
   been measured in 3 comets coming from the Oort cloud with similar values  
   (~3 E-4). The goal is to obtain measurements in a larger sample of  
   comets, including short-period comets coming from the Kuiper Belt.  
    
     
 
3. Number of sources  
    
   Several. Typically one favourable long-period each year, one short-period 
   every two years. Two interesting short-period comets in 2010 
   (103P/Hartley 2) and  2011 (45P/Honda-Mrkos-Padjusakova). 
 
4. Coordinates: 
 
4.1. Rough RA and DEC  
      
4.2. Moving target: yes 
 
4.3. Time critical: yes  
 
4.4. Scheduling constraints: (optional) 
 
 
5. Spatial scales: 
 
5.1. Angular resolution (arcsec): 0.75" (compact configuration) 
 
5.2. Range of spatial scales/FOV (arcsec): 
      
 
5.3. Required pointing accuracy: (arcsec) 
 
0.5" (ephemeris accuracy will be about 1-2") 
 
6. Observational setup 
 
6.1. Single dish total power data: Possibly sloghtly better sensitivity with 
     54 antennas in total power 
 
     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 only for strong sources (active comets with QH2O > 5 E29 s-1) 
 
6.4. Subarrays of 12m baseline-ALMA antennas: no 
 
 
7. Frequencies:  
 
7.1. Receiver band: 8 
 
7.2. Lines and Frequencies (GHz):  
 
     HDO 465 GHz  
     Methanol lines in the same frequency set-up for reference 
 
7.3. Spectral resolution (km/s): < 0.1 km/s 
 
7.4. Bandwidth or spectral coverage (km/s or GHz): 
 
     Adapted to cover strong methanol lines in signal or image bands. 
 
8. Continuum flux density: 
 
9. Line intensity: 
 
9.1. Typical value (K or Jy): 
 
     From 0.1 K km/s (short-period comet with QH2O=E28 s-1 at 
     Earth distance of 1 AU) to 4 K km/s (long-period comet with 
     QH2O=5E29 s-1 at Earth distance of 1 AU). 
     Typical long-period comet: 0.9 K km/s. Line width is about 1.5 km/s.  
     Angular resolution of 0.75" is assumed. 
 
9.2. Required rms per channel (K or Jy): the value for detection 
     with S/N > 5 ALMA sensitivity estimator gives 0.1 K km/s in 1h 
     for 0.75" angular resolution.   
 
9.3. Spectral dynamic range: 
 
9.4. Calibration requirements: absolute      (5%) 
                               repeatability (10%) 
                               relative      (5%) 
 
10. Polarization: no 
 
11. Integration time for each observing mode/receiver setting (hr): 
    1 to 10 hours depending on the comet 
 
12. Total integration time for program (hr): 
    Say at most 10 h per year 
 
13. Comments on observing strategy : (optional) 
 
    Target of Opportunity 
--------------------------------------------------
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).