iraf.net

I've been using sinterp and rspectext to convert a spectrum in ascii format into a fits one for more time that i care to remember. Lately, several times I wanted the output FITS file to have a log-linear instead of linear wavelength dispersion. As far as I know, sinterp and rspectext interpolate to linear dispersion only (or?).

How can I read a 2-columns ascii file (wavelength, flux) and interpolate the spectrum into a FITS spectrum where the dispersion is log-linear? (given that I provide the desired CRVAL1 and CDELT1 of the output FITS in log).

thanks in advance.
paula

The DISPCOR task is what's normally used to rebin spectra to a log dispersion, so the brute force approach is to use something like RSPECTEXT to convert your ascii tables and then DISPCOR toset the desired log dispersion, e.g. by wrapping this up in a small CL script command. There is, however, a new SPTABLE package that allows you to deal with tabular spectra directly -- I haven't tried it but the package does include a modified ONEDSPEC package and so the DISPCOR task in there might be able to do the conversion directly.