Delta Use Case for EVLA Observing - Spectral Line

Bryan Butler


As described in the main use case document, subsequent use cases from 
that one will be presented as "delta" use cases - only providing 
steps that are different from those in the main use case.  This is the 
second of these delta use cases, describing spectral line observing.

  I. Proposal Preparation and Submission
        4. necessary resources, including configuration, frontend(s),
           backend (correlator) setup.  Some detail on backend setup
           will be required here, to be sure that the desired 
           observation is possible with the WIDAR correlator.  This
           will include line width, total observing bandwidth, and 
           required spectral resolution (all in km/s or MHz, e.g.).  
           Rest frequency of the line must be input - common lines (HI, 
           OH, NH3, etc...) should be provided as defaults.
        5. source information: position, flux density, size, velocity
           (in km/s, or redshift), peak (in a single channel) and total 
           integrated line flux density
        7. time needed
           a) in order to figure out how much time is needed, the user 
              may do one of:
              (1) specify an rms, from which the tool automatically 
                  calculates the necessary time.  For spectral line
                  observations, the ability to specify an rms per 
                  channel must be provided.
              (2) specify a dynamic range, then given the source flux 
                  density the tool figures out the needed rms and then 
                  the time.  For spectral line observations, this
                  dynamic range is at the peak of the line, and the rms 
                  is per channel.
              (3) for spectral line observations, the observer must 
                  input a required bandpass accuracy, e.g., .1%.  This 
                  may drive the required observing time, along with 
                  necessary calibrations and accuracy.

 II. Observation Preparation
     C. the user then specifies the following:
        2. a source list, containing all of the sources of interest
           d) a hardware setup for each source (including frontend and 
              backend details), including integration time, correlator 
              setup, etc...  For spectral line observations, some 
              detail on backend setup will be required here, to set up 
              the WIDAR correlator:
              (1) rest frequency of the line - common lines (HI, OH, 
                  NH3, etc...) should be provided as defaults.
              (2) source velocity
              (3) total observing bandwidth
              (4) spectral resolution
              units of velocity, frequency, or redshift should all be 
              allowed where sensible.
           g) a sequence of observations - including the cycle time 
              between source and phase calibrators, and when to observe 
              the flux density and, if needed, bandpass calibrators.  
              Note that sensible defaults should be provided, of course.
           i) for spectral line observations, associated bandpass
              calibrators (might be the same for many sources)

III. During Observing

     nothing beyond the default use case, except it should be noted
     that the user will be interested in seeing the instrumental 
     bandpass (from TelCal, probably) and spectrum of target sources 
     (from the Quick Look Pipeline).

 IV. After Observing (Data Access)

     nothing beyond the default use case...