Apply barycentric corrections to event times, GTIs, and header values.
axbary infile orbitfile outfile [ra] [dec] [refframe] [clobber]
axbary is a multi-mission tool that applies barycenter corrections
to HEASARC-compliant FITS files.
It currently recognizes the missions CHANDRA (or AXAF),
XTE, and Geocenter.
The script copies the infile to the outfile, applying barycenter corrections
to all times in the process. In all tables, the values in the
TIME (case-insensitive) column will be corrected, as will the
START and STOP columns in the GTI blocks. Time-related header
keywords are also corrected (see list below).
The correction is based on either of the JPL solar system
ephemerides -- DE200 and DE405. DE405 is consistent with
the ICRS reference system (as are Chandra coordinates) and is
more accurate. However, many pulsar timing ephemerides
are based on DE200 (which uses FK5). If your results are to be
compared with data derived with DE200, this must be specified
in the refFrame parameter.
axbary searches for the principal HDU in the input FITS file to determine the
conversion parameters and then updates the following keywords in all HDUs:
|
TIMESYS
|
"TDB"
|
|
TIMEREF
|
"SOLARSYSTEM"
|
|
RA_NOM
|
Right Ascension used for barycentering
|
|
DEC_NOM
|
Declination used for barycentering
|
|
RADECSYS
|
Reference frame used ("FK5" or "ICRS")
|
|
PLEPHEM
|
JPL ephemeris used
|
|
TSTART
|
barycenter-corrected
|
|
TSTOP
|
barycenter-corrected
|
|
DATE-OBS
|
barycenter-corrected
|
|
DATE-END
|
barycenter-corrected
|
|
TIERRELA
|
relative clock error
|
|
TIERABSO
|
absolute clock error
|
|
TIMEZERO
|
set to 0.0; previous value will be incorporated in times
|
|
CREATOR
|
"axbary;"
|
|
DATE
|
creation date (UTC)
|
If needed, axbary applies the best clock correction available, provided
that it is defined for the mission. The decision is based on the value
of TIERABSO (Currently, this is only the case for RXTE data).
The code in axbary is the same as used in the Ftool faxbary.
axbary event.fits orbit.fits corrected.fits
Applies barycenter correction to times in event.fits, using orbit.fits
as orbit ephemeris file, and writing output in corrected.fits. RA_NOM
and DEC_NOM will be used for the reference position.
axbary event_1.fits orbit_file_1.fits barycentered.fits ra=278.132
dec=-10.586
Uses orbit_file_1.fits to apply barycenter correction to
times in event_1.fits. Output is written to
barycentered.fits. The RA and DEC for the
correction are defined explicitly.
axbary events.fits orbit_file.fits test_out.fits refframe=FK5
Applies barycenter correction to times in events.fits, using
orbit_file.fits as the orbit ephemeris file, and writing output in
test_out.fits. The FK5 (DE200) solar system ephemeris is
used.
Input event file
The input event file should already have any desired GTI/time
filtering completed. If you correct the times and then use a GTI
filter from the pipeline, you will be filtering out the wrong
intervals since those times are not barycentered.
Input orbit ephemeris file
The Chandra orbit ephemeris file is of the form
"orbitf051004864N002_eph1.fits."
A complete collection of orbit ephemeris files are available
via FTP at ftp://cda.harvard.edu/pub/arcftp/bary/ephem.
If you can't find a level=1 orbit ephemeris file on the
server, the level=0 one may be used. The L1 files are the
definitive orbit ephemeris files which
become available about a week after the dates they cover. In
addition to that information, the L0 files contain an
extrapolation into the future and are thus always available
when the data become available. The file with the the latest
start time that is still earlier than the start time of the
observation should be used.
Output file
The correction can be done in situ by setting the outfile to
the same name as the infile and specifying clobber=yes.
RA in decimal degrees to be used for barycenter corrections.
Values must be J2000 coordinates.
If set to INDEF, axbary looks for the value in the header of
infile; if the RA_NOM keyword is unavailable, RA_PNT is used.
The user is strongly encouraged to provide this value explicitly.
DEC in decimal degrees to be used for barycenter corrections.
Values must be J2000 coordinates.
If set to INDEF, axbary looks for the value in the header of
infile; if the DEC_NOM keyword is unavailable, DEC_PNT is used.
The user is strongly encouraged to provide this value explicitly.
Reference frame to be used for barycenter corrections.
The allowed values for refframe are "FK5" (DE200) or "ICRS"
(DE405). If set to INDEF, axbary uses the value
of the RADECSYS keyword in the header of infile.
As Chandra files have RADECSYS equal to "ICRS",
the JPL DE405 solar system ephemeris would then be used.
However, if the results are to be compared with data
derived with the DE200 ephemeris, the user is advised
to specify "FK5."
If clobber=no, the tool exits instead of overwriting the existing file.
Must be set to "yes" for in situ corrections.
Two parameter names were changed to match parameter naming
conventions: orbitfile (was orbitFile) and refframe (was
refFrame).
|
![[CIAO Logo]](../imgs/ciao_logo_navbar.gif){kind=logo}