Spitzer Documentation & Tools
IRS Instrument Handbook

5.7.4             IRS_TUNE

The IRS_TUNE module converts the extracted spectrum from units of electron/sec to flux density (Jy). This module is for point source extractions. The conversion is only valid for the standard extraction width (specified in psf_fov.tbl for low resolution, or the full width used in EXTRACT for high resolution). The module takes as input extract.tbl.

This module applies absolute flux calibration to the 1-dimensional spectral output file from EXTRACT. For each separate spectral order in SL and LL and each Echelle order in SH and LH, POINT SOURCE TUNE applies adjustments to the shape of the order and corrects by a scaling constant, in units of electrons/sec/Jy, to convert the spectrum to units of Jy. The scaling and shape adjustments are contained in an input calibration file, fluxcon.tbl. This file contains the coefficients calculated by fitting an nth-order polynomial, where , to the EXTRACT output of one or more calibration stars so that their observed IRS spectra are forced to match a model spectrum taken as truth. The ASCII table spect.tbl is the output from IRS_TUNE. It contains five columns listing the order number, wavelength in microns, flux in units of Jy, uncertainty in the flux density measurement in Jy (not suited to derive signal-to-noise ratios), and cumulative pixel status flag (copied from the output of EXTRACT). The corresponding output in the case of 2-dimensional coadder input is tune.tbl, and in the case of background subtraction input is bksub.tbl, as shown in Figure 5.1.