Makee: Flux Calibration

Special notes (July 2018): I have made a few changes to the flux calibration programs in order to produce better results with ESI data. If you intend to flux calibrate your ESI data, you should use the '-atm' option (atmospheric extinction correction is not automatic for ESI). The following steps are recommended for ESI data: 

  starzero Flux-###.fits Flux-###-zero.fits  
  star2resp Flux-###-zero.fits Resp-###.fits -E17
  csmthresp Resp-###.fits Resp-###-smooth.fits
  opim mul Resp-242-smooth.fits Flux-242.fits F-242.fits
Note the new 'C' program 'csmthresp'.

The following comments refer to HIRES data reductions. I have not yet (November 2000) made serious attempts to flux calibrate ESI data, although I am hopeful the ESI spectra may flux calibrate more successfully than has been my experience so far with HIRES data.

The Flux-###.fits 2D spectrum files produced by makee are not flux calibrated. The values are in counts divided by the flat field spectrum. It is possible to do an approximate flux calibration using a standard star , however since the response function across echelle orders varies as a function of telescope position in a (as of now) unpredictable manner, the response function derived from the standard star will often not correctly flux calibrate the object. Furthermore, with respect to the shape of the spectrum and alignment between orders, flux calibration can sometimes make things worse.

Nevertheless, the following programs can be used to (approximately) flux calibrate your object spectrum. This process has been divided into four steps so you can inspect the spectra at each stage.

starzero
The program " starzero " is used to "zero out" or "mask" wavelength regions in your standard star spectrum. These regions contain absorption lines which hinder the computation of the correct response function.

Look in ./makee/StanStarDataBase/ to find the FITS file of your standard star. If your star is not in this directory you cannot use these programs to flux calibrate. Look for the ".bwr" (bad wavelength regions) file which gives the sections to be masked in the response function. This file is used by starzero to mask bad regions. You can edit this file if too many bad features appear in your response spectrum. You can give these filenames in the program arguments, or the program will be search for these files using the OBJECT name in the FITS header. (See fix note .)

EXAMPLE: starzero Flux-###.fits Flux-###-zero.fits

star2resp
The program " star2resp " can be used to create a response function 2D spectrum which can be multiplied by your object spectrum to get a flux calibrated object spectrum.

EXAMPLE: star2resp Flux-###-zero.fits Resp-###.fits

smthresp
Once you have created a response spectrum (say, Resp-###.fits), you can smooth and interpolate over the masked (bad) areas using " smthresp ".

EXAMPLE: smthresp Resp-###.fits Resp-###-smooth.fits

opim
Once you are happy with your response function, you can apply it to your standard star or any observation taken with the same setup using " opim ".

EXAMPLE: opim mul Resp-###-smooth.fits Flux-###.fits F-###.fits

Your flux calibrated spectrum will be in F-###.fits.

(Note: opim is a general image operation tool for multiplying, dividing, adding, etc. any FITS image(s).)

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