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Effective Area Calculation, version 14-Jan-2008

Derived from PAT_A and PAT_B observations of HZ21

Processed with new spectral flats (newcfg cmdev) on 14-Jan-2008

Data Set: Each of the PAT_A and PAT_B tiles had three visits divided into six subvisits using the particular pattern for a total of 36 individual observations that are analyzed for this EA curve: 2 x 6 x 3 = 36.

Processing: These data were processed using the development pipeline accessed by entering newcfg cmdev. I used two shell scripts to set up and execute the processing:

  1. gx_gdir sets up the grism directories with the apropriate raw and mcat files:
    • calls /home/galex/tab/bin/pipecheck to get paths
    • creates processing directory
    • links raw files and mcat file
    • copies *-scst.fits files
  2. gx_gs does the actual processing:
    • calls galexspac for the FUV and NUV initial processing
    • calls galexspex for the FUV and NUV final processing
    • calls gspcombine to produce combined results

Procedure: The resulting *-ng-xsp.fits and *-fg-xsp.fits files are read in and the counts and errors are dispersion corrected to 1 Ang/px with the IDL routine gx_dc_cnts.pro, which uses the standard wavelength polynomials. These observations are compared individually with STIS calibration spectra with the same wavelength scale to derive an EA curve for each observation. At each wavelength an error-weighted mean EA is calculated from all 36 measurements. The resulting weighted-mean EA curve was then smoothed with a boxcar size of 25 Angstroms (pixels). The calling routine that does the averaging is gx_ea_cal.pro. Click on the <EA> below to retrieve the resulting EA table.

Plots: The top plot shows the average EA curve as the thin lines and the smoothed curves as the thick lines. The standard deviation is indicated by the red lines and the error in the mean is shown by the green lines. The middle plot shows the ratio of each individual curve to the average curve. The bottom plot compares the old (GR3) EA curve with the new (GR4) one. The major difference is in the FUV where saturation was greatest. Click on the image to retrieve a postscript plot.

<EA>
EA/<EA>
EA OLD and NEW