Ephemeris Computation Utility
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This tool can be used to check whether an ephemeris is available for a particular pulsar at a particular moment in time. This is accomplished by setting parameter strict=yes, which causes gtephem to consider only ephemerides whose interval of validity includes the given time. If an ephemeris is available, the tool will compute and display an extrapolated ephemeris for that given moment in time, in a manner similar to that shown in the next section. If no ephemeris is available, the tool will produce output similar to the following:
To find an ephemeris for a particular pulsar at a particular time, ignoring the interval of validity of the candidate ephemerides, gtephem can be invoked with parameter strict=no. (This option can be omitted because no is the default value.)
If orbital parameters for a binary orbit of a pulsar of interest are included in an ephemerides database file, the tool will use them to compute orbital effects on photon arrival times (light-travel time, gravitational time dilation, etc.), apply them when it estimates a spin ephemeris at a given moment in time, as shown in the following example. Unlike spin parameters there is no validity interval associated with orbital parameters, so the strict=yes option does not have any effect on search and computation of orbital parameters.
If gtephem is invoked with chatter parameter set to 4 or larger, it will display a brief summary of loaded ephemerides, and spin and orbital ephemerides that are used to compute an extrapolated spin ephemeris at a particular moment in time, together with an extrapolated ephemeris at the given time. This feature shows you additional information on computations being performed, which may help you understand the tool. Also, the extra information printed may contain a clue to diagnose certain types of problem. So, try a high chatter when you are unsure on the tool's behavior.
Owned by: | Masaharu Hirayama hirayama@jca.umbc.edu |
James Peachey James.Peachey-1@nasa.gov |
Last updated by: Masaharu Hirayama 2/24/2009 |