Synphot Data User's Guide
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| Synphot Data User's Guide | |||||
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A.4 Use of Kurucz Atlas with SYNPHOT
Synphot tasks now permit the use of spectra selected from one of many columns in a single STSDAS table file. One does this by specifying as the "spectrum" parameter the name of the disk file (as before), and appending the name of the column containing the flux in brackets. Thus, to select any model spectrum characterized by a given metallicity, effective temperature, and gravity, specify a "spectrum" of the form: crgridk93$m_directory/kszz_ttttt.fits[gyy], where m_directory is the name of the subdirectory for a given metallicity. For example, to select the spectrum of a star with a metallicity of +0.1, a temperature of 10,000 K, and log gravity of 3.0, the specification would be: crgridk93$kp01/kp01_10000.fits[g30].
Alternatively, one may select a model spectrum within a synphot expression using the function icat (which interpolates between the nearest matching models) or cat (which simply selects the closest match). The syntax for the Kurucz models is icat(k93models,Teff,metallicity,logG). See Appendix A.4 for an example that includes the use of this function.
The icat task can give incorrect results without warning if it is used at the edges of the defined grid of models. See above for a discussion of the available ranges for these values, and exercise caution when selecting a value near one of the extremes.
Please note that the model spectra in the atlas are in surface flux units. Thus, if the number of counts or the calculated absolute flux is needed, the model spectrum must be renormalized appropriately. One can do this in synphot with the "rn" function.
Since the entire atlas occupies close to 70MB of disk space, many applications could be satisfied by a copy of the solar metallicity spectra, only.
A list of solar metallicity stars of different spectral types and luminosity classes together with their closest Kurucz model spectrum is presented in Table A.6. The physical parameters, T_{eff} and log_g, characterizing each star are taken from Schmidt-Kaler's compilation of physical parameters of stars (Schmidt-Kaler 1982, Landolt-Bornstein VI/2b). The U-B and B-V colors of the closest model agree with the characteristic color of each star (see Schmidt-Kaler 1982) to better than 0.06 magnitude.
Table A.6: Suggested models for specific stellar types
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