Subject: JPL DE200 and DE405 in FITS; Barycenter Code

From: Arnold Rots <[email-masked]>
Date: Tue, 2 Dec 1997 14:54:45 -0500 (EST)

This is the announcement of the release of a FITS version of
the JPL DE200 and DE405 solar system ephemerides, and an ANSI-C
software package to access these ephemerides and calculate
barycenter corrections.  The package was developed for the
RXTE mission, but written in such a way that, where necssary,
mission-dependent functions can be plugged in for other space
missions, as well as for ground-based observatories.

I would like to emphasize that the FITS versions contain the
full DE ephemeris data (i.e., all planets) and use the original
Chebyshev polynomials.

This summer, the new JPL DE405 solar system ephemeris was
released.  That seemed a good reason to revamp XTE's barycenter
correction code and make it fully generic.  It would be good if
the astronomical community were to switch over to DE405 and I
hope that making this code available will further that cause.

In order to distinguish which planetary ephemeris (if any) has
been used to create a particular FITS file, I have adopted a
convention using the existing FITS keyword RADECSYS and the
new keyword PLEPHEM.
  DE200 is indicated by:
    RADECSYS= 'FK5'
    PLEPHEM = 'JPL-DE200'
  DE405 is indicated by:
    RADECSYS= 'ICRS'
    PLEPHEM = 'JPL-DE405'
In addition, the TIMESYS keyword, as defined in the Appendix
to the FITS Year-2000 resolution, is used.

The package may be obtained from:

    ftp://heasarc.gsfc.nasa.gov/xte/calib_data/clock/bary

This directory contains a 00README and a gzipped tar file.
Appended below is the introduction of the 00README file.
The package requires the HEASARC's cfitsio library.

  - Arnold Rots
    NASA/GSFC - USRA    [email-masked]

    XTE-GOF
    Code 660.2
    GSFC
    Greenbelt, MD 20771

--------------------------------------------------------------

BARY
$Id: 00README,v 2.0 1997/11/25 14:56:24 arots Exp arots $

Arnold Rots
USRA
25 November 1997

A package containing:
  - the JPL DE200 and DE405 ephemerides (full Chebyshev polynomials)
    in FITS format;
  - ANSI standard C code to access those ephemerides;
  - new barycenter correction code that can use either ephemeris and
    starts from any of these time systems: UTC, ET, TT, TCG, TAI;
  - a phase binner that bins photon events in absolute phase, using
    the Princeton radio pulsar database (format);
  - a utility, baryFase, that calculates barycenter corrections and
    (optionally) absolute phase for any time and celestial position.

One should be aware that the JPL ephemeris, as distributed in "Unix"
format, are really IEEE; hence, those files will work just fine on,
say, a Sparc station, but will cause trouble on Alphas and Intel
machines.  The FITS format circumvents this problem.

Although the application is for barycenter corrections, the dpleph
version distributed as part of this package will allow retrieval
of positions for all members of the solar system contained in the
JPL DE ephemerides.

The barycenter package is geared toward space missions and detects
the identity of the mission through the TELESCOP or MISSION keywords
in the FITS headers.  However, it will be easy to include ground-based
observatories by inserting an appropriate geographic position function
for the "orbit ephemeris".  Indeed, the currently supported "missions"
are XTE and the Geocenter.

This directory contains the following files:

00README       This file
JPLEPH.200     FITS version of the JPL DE200 lunar and planetary
               ephemeris for 1950-2050
JPLEPH.405     FITS version of the JPL DE405 lunar and planetary
               ephemeris for 1950-2050
JPLEPH         Symbolic link to the default ephemeris
dpleph.c       Functions to access the JPL ephemeris
bary.c         General utilities and functions to calculate barycenter
               corrections
ctatv.c        Function to calculate TDB - TT
baryFase.c     Utility to calculate individual barycenter corrections
               and phase
phaseHist.c    Phase binner function: bins events in energy and
               absolute phase according to timing ephemeris
faseBin.c      The phase binner main function, or wrapper, for
               phaseHist
bary.h         Header file required by all
xCC.c          XTE clock correction function
bineph2fits.c  Utility to convert ephemerides to FITS