Assign wavelengths to HST/STIS TIME_TAG event files
It is necessary to retrieve the ephemeris of HST to correct the time stamp of each photon to the solar-system barycenter. This will correct for (from ODELAYTIME help)
- general relativistic effects (up to 2 milliseconds),
- displacement of the telescope from the center of the Earth (up to 20 milliseconds),
- and displacement of the Earth from the solar-system barycenter (up to 500 seconds).
Go directly to HST Starview. On the left hand side, choose >ALL>ENGINEERING. In the search form, choose in the ARchive class: ORB, to search for orbital ephemeris. Click search and look for the files that contain your observations (every ORB file usually contains three days worth of ephemeris). From the dataset than you retrieve within the HST archive, the one we need is the FIT file.
Once in iraf/pyraf, load >stdas/hst_cal/stis. In there, there will be a routine called ODELAYTIME. To correct each tag.fits, simply run the routine as an example:
odelay odfa01030_tag.fits obs_ephem=p6d0000r.fit
This will overwrite the original file (I usually keep a raw copy of these files just in case.)
import stis_photons fln_tag = 'o4oj01020_tag.fits' ## TAG-TIME file fln_x1d = 'o4oj01020_x1d.fits' ## Spectra associated with TIME-TAG File fln_moc = 'h4s1350io_moc.fits' ## MOC file used in the data reduction fln_dsp = 'm7p16110o_dsp.fits' ## DSP file used in the data reduction output = 'stis_timetag20' ## Output numpy and text file stis_photons.localise(fln_tag,fln_x1d,fln_dsp,fln_moc, output=output, verbose=True, plot_diagnostics=False)
If you have already the fits file with wavelengths, you can also plot the diagnostics: