Astronomical Applications Department, U.S. Naval Observatory novas c 2 doc Page 26
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4.12
TRANSFORM_HIP
void transform_hip (cat_entry *hipparcos,
cat_entry *fk5)
PURPOSE:
To convert Hipparcos data at epoch J1991.25 to epoch J2000.0 and
FK5-style units. To be used only for Hipparcos or Tycho stars
with linear space motion.
INPUT
ARGUMENTS:
*hipparcos (struct cat_entry)
An entry from the Hipparcos catalog, at epoch J1991.25, with
all members having Hipparcos catalog units. See Note 1
below (struct defined in novas.h).
OUTPUT
ARGUMENTS:
*fk5 (struct cat_entry)
The transformed input entry, at epoch J2000.0, with all
members having FK5 catalog units. See Note 2 below (struct
defined in novas.h).
RETURNED
VALUE:
None.
Discussion:
This function takes Hipparcos catalog data, which is given for epoch J1991.25, and
transforms it to epoch J2000.0 for use in NOVAS-C functions such as app_star. The
appropriate units conversion is also performed. Function transform_cat is called to
perform the epoch transformation.
This subroutine should be used only for Hipparcos or Tycho stars with linear space
motion.
Note that radial velocity is not given in the Hipparcos catalog. If a value is not
known, set it to zero in the input
hipparcos
structure.
