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The procedure described here calculates the heliocentric motion of the Earth at the time of observation. This procedure does not correct for the small effect (at FOS dispersions) of HST orbital motion.
The IRAF task rvcorrect is used to compute radial velocity corrections. rvcorrect is in the IRAF astutil package and it calls on task observatory, which is also found in astutil. The following steps are an example of its use for an HST dataset where the HST velocity around the Earth is ignored (maximum residual: +/- ~7.8 km/s):
cl> unlearn rvcorrectUse the default observatory task parameters except the following, which must be set to prevent rvcorrect from calculating an unwanted diurnal velocity correction based on the observatory position with respect to the Earth's center.
as> lpar observatory
command = "list" Command (set|list|images)
obsid = "obspars" Observatory to set, list, or image default
images = List of images
override = Observatory identification
(verbose = no) Verbose output?\n
(observatory = "obspars") Observatory identification
(name = " ") Observatory name
(longitude = 0.) Observatory longitude (degrees)
(latitude = 0.) Observatory latitude (degrees)
(altitude = -6378204.8) Observatory altitude (meters)
(timezone = 0.) Observatory time zone
93 01 21 18:50:07 0.2974443291667E+03 0.4896100000000E+02 2000 0
93 01 21 20:05:09 0.2974443291667E+03 0.4896100000000E+02 2000 0
cl>rvcorrect f=rvcor.in > outputfileThe above example produced the following output file. VHELIO contains the (very small, in this case) correction for the heliocentric velocity of the telescope with respect to the target.
HJD VOBS VHELIO VLSR VDIURNAL VLUNAR VANNUAL VSOLAR
2449009.81098 0.00 2.38 2.72 0.000 0.001 2.381 0.342
2449009.88335 0.00 2.35 2.69 0.000 0.001 2.349 0.342