It was noticed that the MJD in the header (not in the data) of de200.fits, the file describing the Earth's ephemeris, is off by 0.5 days. This causes an error in the barycentric correction to the time stamps, when using "odelaytime" with the STIS timetag data. The error introduced in this step can be a few seconds.
We are fixing the header in the de200.fits so that 'odelaytime' will work correctly in the next release of STSDAS. In the meantime, here are the IRAF commands that you can use to fix the de200.fits file, leaving the corrected copy in your default directory.
cl> copy stsdas$data/fits/de200.fits . cl> thedit de200.fits firstmjd 33264.0 cl> thedit de200.fits lastmjd 69808.0 cl> odelaytime.earth_ephem = "de200.fits"You should get correct answer if you use this corrected copy of de200.fits.
[N.B. The problem described above was fixed in the 2001 June 20 release of STSDAS version 2.3 (containing Calstis version 2.10). Any data processed with odelaytime from earlier versions of STSDAS will be subject to errors of a few seconds, as described above.]