ASTR 3520 Spectral Flatfielding


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Spectral flatfielding using IRAF.
  1. standard [VEGA_SPEC] [VEGA_SPEC]_std star_name="hr7001" airmass=1.0 exptime=90.0 mag=0.0 magband=V teff=A0 caldir="/usr/local/iraf/iraf/noao/lib/onedstds/bstdscal/"
  2. sensfunc [VEGA_SPEC]_std [VEGA_SPEC]_sens interactive=yes
  3. calibrate [SCIENCE_SPEC] [SCIENCE_SPEC]_calibrated sensitivity=[VEGA_SPEC]_sens extinct=no flux=yes exptime=240 airmass=1.0 fnu=yes

The above are:
SCIENCE_SPEC: aperture-extracted, dispersion-corrected science spectrum
VEGA_SPEC: aperture-extracted, dispersion-corrected standard star spectrum

Variables:
  • exptime: the exposure time in the standard spectrum (for the standard command) or the science spectrum (for the calibrate command)
  • starname: the name of the star that corresponds to a name in the spectrophotometric standards catalog. HR 7001 = Vega


Details:
  1. standard [interactive]
    The standard function compares your spectrum of a known standard star to the NOAO database version of that spectrum. Your goal in this interactive code is to select smooth regions of the spectrum across the spectrum to fit with a curve. You should draw many small boxes and carefully avoid absorption lines.
  2. sensfunc [interactive]
    Uses the fit you made in standard to create a sensitivity calibration. Necessary to get your flux into real flux units.
  3. calibrate
    Applies the calibrations you computed with standard and sensfunc.


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