HIRedux TweakArc

HIRES Wavelength Issues

• While a high quality pipeline would provide a non-fail wavelength solution, I fear that is not yet the case. At present I am quite confident about data taken with ECHANGL=0 with HIRESb. Aside from that, I consider the code to be a work in progress. It is improving rapidly however.
• The source of all the trouble is that the resolution actually changes with ECHANGL. This is well understood and expected, but a pain to deal with nevertheless. Basically, it amounts to a stretching or compression of the spectrum relative to the ECHANGL=0 case.
• With HIRESb, I'd say one has very little reason to use an ECHANGL value other than 0 with the 3 CCD mosaic. With HIRESr, however, there is still plenty of reason to do so.
• Anyhow, the obvious source of trouble is that the code yields an RMS for the fit in a given order that exceeds 0.2 pixels. I wouldn't worry for the reddest orders where there are very few lines, but for anywhere else this is a likely problem. I generally check the QA plots for at least one arc in each of my setups. I suggest the same for now.

Running hires_tweakarc

• Minor change :: Most of the problems will be quite minor and hires_tweakarc should be used in this fashion. The code will launch x_identify and the current line identifications. You will then re-identify and re-fit.
      IDL> hires_tweakarc, 'Arcs/Fits/Arc_C####)fit.idl', orders
  --> Here, C is the chip (B,G,R), #### is the frame number, and orders is an array of the echelle order(s) you wish to tweak.
  I now detail the steps to take.
  1. Delete outliers and re-fit
     1. Type 'F' -- This will launch a fitting window and the default will be a 2nd order polynomial. In most cases, there will be a few lines misidentified at the edges of the CCD.
     2. Delete outliers with the RMB (right mouse button)
     3. Type 'R' -- This will show the residuals of the fit
     4. Type 'u' -- This will increase the fit to 3rd order (go no higher)
     5. Type 'q' -- This will quit the fit and apply it
  2. Option 1: The fit was good
     1. Type 'L' -- This will identify all good lines according to the new fit
     2. Type 'F' -- This will launch the Fit window again, but to fit the new set.
        1. Type 'R' -- Examine the residuals
        2. Delete outliers (RMB) -- For now, delete the pink triangles too
        3. Keep the order# at 3 unless you think 4 is much better (toggle with 'u' and 'd')
        4. Type 'q' -- Quit and apply the fit
     3. Type 'q' -- This will quit the re-identify process, save the info to your file and proceed to the next order to tweak as desired.
  3. Option 2: The fit was no good. For now, I suggest you type 'D' to delete all of the lines and start from scratch. Alternatively, read how to do the tweak process below.
• Major change :: If it appears that most of the lines identified are bad, you should reidentify them all. A quick way of doing this is to use one of the archived solutions as guidance. Here is the call to hires_tweakarc
      IDL> hires_tweakarc, 'Arcs/Fits/Arc_C####)fit.idl', orders, 'templatefile'
  --> Here, C is the chip (B,G,R), #### is the frame number, orders is an array of the echelle order(s) you wish to tweak, and 'templatefile' is the name of a good archived solution that includes the echelle orders you wish to tweak. Here is a list of the filenames and info on the orders they cover.
  I now detail the steps to take.
  1. Stretch and shift
     1. The black plot is your arc and the green is the archived arc.
     2. In the top/center you can type in values to shift and stretch the archived data.
     3. When the two overlap closely (within 2-3 pixels everywhere), click on Apply.
  2. Identify and Fit
     1. Type 'L' -- This will identify the arc lines using the archived wavelength solution
     2. Type 'F' -- This will launch a Fit window
        1. Type 'R' -- Examine the residuals
        2. Type 'u' -- Increase the order number to 3 if necessary
        3. Delete outliers (RMB) -- For now, delete the pink triangles too (toggle with 'u' and 'd')
        4. Type 'q' -- Quit and apply the fit
     3. Type 'q' -- This will quit the re-identify process, save the info to your file and proceed to the next order to tweak as desired.

Continuing and Reprocessing

• It is quite likely that you have only noticed the problem to your arcs after running through most or all of the steps.
• WARNING: If you try to restart after tweaking (e.g. buy using the /CLOBBER flag), you will overwrite your tweaked fits.
• To avoid this, run as follows (which will skip the hires_fitarc file:
  • One file
        IDL> print, hires_allarc_sngl('Raw/file.fits', hires, setup, chip, /NOONED, /CLOBBER)
  • All files
        IDL> hires_allarc, hires, setup, [chip], /NOONED, /CLOBBER)

Reporting

• Finally, I'd like to know which orders went wrong and with what setup. I'd also like your fit solution and QA file. Please send me this info.
• It is quite possible I will add your solution to the archive.