palFk524
palFk524
- Convert J2000.0 FK5 star data to B1950.0 FK4
- Description:
- This function converts stars from the IAU 1976, FK5, Fricke
system, to the Bessel-Newcomb, FK4 system. The precepts
of Smith et al (Ref 1) are followed, using the implementation
by Yallop et al (Ref 2) of a matrix method due to Standish.
Kinoshita's development of Andoyer's post-Newcomb precession is
used. The numerical constants from Seidelmann et al (Ref 3) are
used canonically.
- Invocation:
- palFk524( double r2000, double d2000, double dr2000, double dd2000,
double p2000, double v2000, double
r1950, double
d1950,
double
dr1950, double
dd1950, double
p1950, double
v1950 )
- Arguments:
-
-
r2000 = double (Given)
-
J2000.0 FK5 RA (radians).
-
d2000 = double (Given)
-
J2000.0 FK5 Dec (radians).
-
dr2000 = double (Given)
-
J2000.0 FK5 RA proper motion (rad/Jul.yr)
-
dd2000 = double (Given)
-
J2000.0 FK5 Dec proper motion (rad/Jul.yr)
-
p2000 = double (Given)
-
J2000.0 FK5 parallax (arcsec)
-
v2000 = double (Given)
-
J2000.0 FK5 radial velocity (km/s,
ve = moving away)
-
r1950 = double
(Returned)
-
B1950.0 FK4 RA (radians).
-
d1950 = double
(Returned)
-
B1950.0 FK4 Dec (radians).
-
dr1950 = double
(Returned)
-
B1950.0 FK4 RA proper motion (rad/Jul.yr)
-
dd1950 = double
(Returned)
-
B1950.0 FK4 Dec proper motion (rad/Jul.yr)
-
p1950 = double
(Returned)
-
B1950.0 FK4 parallax (arcsec)
-
v1950 = double
(Returned)
-
B1950.0 FK4 radial velocity (km/s,
ve = moving away)
- Notes:
- The proper motions in RA are dRA/dt rather than
cos(Dec)
dRA/dt, and are per year rather than per century.
- Note that conversion from Julian epoch 2000.0 to Besselian
epoch 1950.0 only is provided for. Conversions involving
other epochs will require use of the appropriate precession,
proper motion, and E-terms routines before and/or after
FK524 is called.
- In the FK4 catalogue the proper motions of stars within
10 degrees of the poles do not embody the differential
E-term effect and should, strictly speaking, be handled
in a different manner from stars outside these regions.
However, given the general lack of homogeneity of the star
data available for routine astrometry, the difficulties of
handling positions that may have been determined from
astrometric fields spanning the polar and non-polar regions,
the likelihood that the differential E-terms effect was not
taken into account when allowing for proper motion in past
astrometry, and the undesirability of a discontinuity in
the algorithm, the decision has been made in this routine to
include the effect of differential E-terms on the proper
motions for all stars, whether polar or not. At epoch 2000,
and measuring on the sky rather than in terms of dRA, the
errors resulting from this simplification are less than
1 milliarcsecond in position and 1 milliarcsecond per
century in proper motion.
-
References
- Smith, C.A. et al, 1989. "The transformation of astrometric
catalog systems to the equinox J2000.0". Astron.J. 97, 265.
- Yallop, B.D. et al, 1989. "Transformation of mean star places
from FK4 B1950.0 to FK5 J2000.0 using matrices in 6-space".
Astron.J. 97, 274.
- Seidelmann, P.K. (ed), 1992. "Explanatory Supplement to
the Astronomical Almanac", ISBN 0-935702-68-7.