Preparation for Data Monitoring

• In a terminal, start up an IDL session on one of the fast linux machines (e.g. fusion00,aolc1,2,3,4).
        ssh -X a2010@remote.naic.edu
        ssh -X a2010@fusion00 (or aolc1, etc)
        lbwdata   This alias puts you into the directory/share/a2010-2/lbwdata
        idl
        @corinit   This loads all the procedures we will need for the following steps
• You can find documentation of the idl routines we will be using on Phil's idl page.

Load the correlator file.

• We need to open the correlator file so that can manipulate it to display our data
        openr, lun, '/share/olcor/corfile.16jan12.a2669.1', /get_lun
  
• Make sure to choose the correct file.

Do the (ON-OFF)/OFF

• In order to remove the bandpass shape imposed by the instrumentation, we want subtract the OFF observation from the ON, and then divide by the OFF spectrum. See the explanation of LBW observing page for an explanation of why we do this.
• We will use Phil's corposonoff routine.
        io=corposonoff(lun, b, /han, /scly)
  
• This routine returns the (ON-OFF)/OFF to the structure b. There are four substructures - b.b1, b.b2, b.b3, b.b4 - one for each board of the correlator. For now, we only care about the data in the first two boards.
• The keyword /scljy scales the ouptput to Jy using information from the calibrator.
• The keyword /han applies Hanning smoothing.
• Since we have a single ON-OFF pair in each file, we do NOT need to set the scan number - the routine defaults to the first scan.

Average the Polarizations

• We want to take advantage of the fact that we took data in two separate polarizations, and average the polarizations together to increase our sensitivity.
• We will use the routine coravg to do this.
        bavg = coravg(b, /pol)
  
• The keyword /pol tells the routine to average polarizations.
• The returned structure, bavg will have fewer boards than the original structure, b. Since boards 1&2 have the same set-up but are different polarizations, the routine averages the two boards together and returns them to a single board, bavg.b1. The remaining number of boards in the bavg structure will depend on whether the observations are in low- or high-velocity mode. For now, we don't need to worry about those other boards.

Smooth the Data

• Now we smooth the spectral data to increase our sensitivity slightly.
        corsmo, bavg, smo=3
  
• The output structure bsm contains the smoothed spectral data.
• For now we set smo=3 to boxcar smooth the data over 3 channels. The smoothing value can be increased to more channels as appropriate.

Plot the Data

• Time to plot the data to look for a detection!
        corplot, bsm, brdlist=1, xtitle='Frequency', ytitle='Flux'
  
• The keyword brdlist allows us to plot just the first board of bsm. Remember, this board contains the average of the original two boards, as they were separate polarizations.
• The default behavior of corplot is to plot flux as a function of the topocentric frequency. This is what we need for low-velocity mode as we take data in the topocentric frame! For the high-velocity mode, we center on the velocity of our source, and you can set the keyword /vel.
• If you're observing in low-velocity mode you may want to rescale the y-axis manually to see signals that have low fluxes compared to the Galactic HI.
        ver, y_low, y_high   Scale the y-axis between y_low & y_high
  

Clean Up

• We want to close the files we have opened and free the lun - there are a limited number of luns in IDL and we don't want to run out.
        close, lun
        free_lun, lun
  
• Now you're ready to go back to the top for the next source!