Compute Barycentric Velocity Correction Using Only Task Parameters
bcvcorr will compute the barycentric velocity correction and
heliocentric Julian date for an observation based on time, position,
and observatory information in the parameter file. The spectra
parameter must be set to a null string.
bcvcorr Task Parameters
The values of the needed information are
set in the parameter file:
spectra = "" List of input spectra
...
(ra = 4.6993444444444) Right ascension of observation
(dec = 5.6095277777778) Declination of observation
(equinox = "2000") Coordinate equinox header keyword
...
(hjd = 0.) Heliocentric Julian Date of observation
(gjd = 2450678.6448) Julian Date of observation
(year = INDEF) UT year of observation
(month = INDEF) UT month of observation
(day = INDEF) UT day of month of observation
(ut = INDEF) Universal Time of observation
(obsname = "test") Observatory name--file to read from image heade
...
(obslong = 155.46666666667) Observatory longitude
(obslat = 19.816666666667) Observatory latitude
(obsalt = 41000.) Observatory altitude in meters
...
Results
The results are summarized to standard output as follows:
rv> bcvcorr
List of input spectra:
test lat 19:49:00.0 , long 155:28:00.0, alt 41000.0
Julian date is 2450678.64480 at 1997-Aug-18 3:28:30.7 UT
Object at ra 4:41:57.640 dec 5:36:34.30 eq 2000
Heliocentric Julian date: 2450678.64340
gbcvel = 27.3759 ghcvel = 27.3902 geovel = -0.2008
bcv = 27.1751 hcv = 27.1894 computed
rv>
In this example, the date and UT are computed from the Geocentric Julian
Date of the observation, gjd. Because the observatory position
is given in the parameter list and there is no image from which to read
it, no attempt is made to read it from the
observatory database.
The heliocentric Julian date is the time which the measured
light from the observed object passes the sun. A correction from the center
of the earth to the observatory site (geovel) is added to the
geocentric barycentric (gbcvel) and heliocentric (ghcvel)
velocity corrections to give the topocentric barycentric (bcv) and
heliocentric (hcv corrections.
[rvsao]
[bcvcorr]