The Extended Source Tune module converts the extracted spectrum of extended sources from units of electrons per second to flux density (Jy). Point Source Tune is used for point sources. The calibration assumes that the flux is measured over a 28-pixel straight edge aperture in the low-res modules and over the full slit in the high-res ones. These are the default parameters of the Extract module with Extended Source extraction. The resulting calibration is only strictly valid for cases in which the extended source is uniformly bright and covers an area much larger than the slit. In practice, the calibration will be approximately correct for sources that are uniform over the width of the slit plus several PSF widths (~6 pixels) on either side.
INPUTS
There are no user inputs for Extended Source Tune.
OUTPUTS
ReTune Results (*.aploss_spect.tbl, *.extsrc.tbl): The output of the module is two spectra. The first (aploss_spect.tbl) is the flux tuned spectrum (in Jy). The spectrum is derived assuming a point source extracted with the full aperture (aploss correction). The second (extsrc.tbl) is the spectrum in aploss_spect.tbl multiplied by the slit loss correction (slitloss correction). The slitloss correction assumes that at a given wavelength the source is infinite in extent and it has a constant surface brightness. In practice, the correction should be valid for sources that are uniform over an area slightly larger than the slit (by a few PSF widths). Both spectra are written to the output directory, and the second one is displayed in the plot window.
DISCUSSION
The module applies photometric “tuning” and flux conversion coefficients to the extracted full slit 1-D spectrum from Extract, and converts it to Jy. The module corrects the slope and curvature of each order and takes into account the effects of the extended source extraction. This is done in two steps. First, the flux calibration appropriate for the large aperture is applied (producing aploss_spect.tbl). Secondly, the module applies the correction for slit losses (producing extsrc.tbl). See extended source extraction for more details.
