Title Surveys of interstellar molecular absorption
Pi    R. Lucas 
Time   57 hrs
   1. Name of program and authors

      Surveys of interstellar molecular absorption
      R. Lucas, H. Liszt

   2. One short paragraph with science goal(s)

     Absorption measurement in front of background sources is the
 preferred method to detect unexcited interstellar molecules. Low
 density environments (diffuse and translucent clouds) are sites of a
 remarkable complex chemistry, despite their unprotected exposition to
 photodissociating radiation from stars. Relative abundances of the
 molecules are grossly similar to those of dark clouds, but with
 several notable differences. Moreover the small observed scatter in
 some of the abundance ratios clearly indicates that these low density
 regions are a choice laboratory for the study of the basic physical
 and chemical processes of the interstellar medium.

 We propose to do a systematic frequency survey of band 3 for a few
 (~ 3) sources, selected for high molecular content (estimated from HCO+
 column density and/or visual extinction). Each source requires 64
 settings to cover all band 3. 

 
   3. Number of sources (e.g., 1 deep field of 4'x4', 50 YSO's,
                              300 T Tauri stars with disks, ...; do NOT
                              list individual sources or your "pet object",
                              except in special cases like LMC, Cen A, HDFS)

      About 3 sources with flux in range 0.3-2 Jy.

   

   4. Coordinates:

      4.1. Rough RA and DEC (e.g., 30 sources in Taurus, 30 in Oph, 20 in Cha, 
                             30 in Lupus)
 
      Sources coordinates are not known at this time.
     
     Indicate if there is significant clustering in a particular RA/DEC range
     (e.g. if objects in one particular RA range take 90% of the time)

     Sources are in galactic plane.

      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):

      These are point sources. The angular resolution does not really
      matter. 

      5.2. Range of spatial scales/FOV (arcsec):           
           (optional: indicate whether single-field, small mosaic, 
            wide-field mosaic...)

      These are point sources.

      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: Band 3, 6, 7, or 9

      Band 3

      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)

	   32 settings in band 3,  spaced by 1.0 GHz.
 
      6.3. Spectral resolution (km/s):

	   0.5 km/s

      6.4. Bandwidth or spectral coverage (km/s or GHz):

	   1.0 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)

	   Minimum 0.3 Jy
           
      7.2. Required continuum rms (Jy or K):

          .04 mJy  is expected but not required.

      7.3. Dynamic range within image:                  
           (from 7.1 and 7.2, but also indicate whether e.g. weak objects 
            next to bright objects)

	    100, but no imaging is needed.

   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)

	   typical 0.03 Jy (10% absorption).

      8.2. Required rms per channel (K or Jy):

	   1% of flux density (.003 Jy for weakest sources)

      8.3. Spectral dynamic range: 

           100             


   9. Polarization:  yes/no  (optional)

           no

      9.1. Required Stokes

           total intensity only
   
      9.2. Total polarized flux density (Jy)

           N/A

      9.3. Required polarization rms and/or dynamic range

           N/A

      9.4. Polarization fidelity

           N/A

   10. Integration time for each observing mode/receiver setting (hr):

           time 19.2 hr per source (0.6 hr per setting) assuming a
           0.3Jy source flux

   11. Total integration time for program (hr):

           total time 57 hr

   12. Comments on observing strategy (e.g. line surveys, Target of
       Opportunity, Sun, ...): (optional)

           This is a line survey. The observations are essentially
	   self calibrated, so there is NO requirement on phase
	   stability. The data are usable provided that the pointing
	   accuracy is better than, say, 5" and the 3mm optical depth
	   smaller than 0.5. This means the stringency is probably
	   very low (close to 1).

************************************************************************

Review Lee Mundy: OK.
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Review v2.0:
 
ok