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pmpar.doc
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PMPAR v 1.5
A proper motion / parallax fitting program
Walter Brisken, Princeton University, Dec. 19, 2000
How to use
~~~~~~~~~~
pmpar has 5 main modes. The first thing pmpar does, no matter which mode it is
in, is to use a least squares fitting to generate an internal model. Several
iterations are done since it is slightly non-linear, but quickly converging.
The limitations of the model are due to the limited precision of double
precision floating point and will introduce an error up to about 5 microarcsecs.
All calculations are done in equinox 2000.0 coordinates.
The input file used to generate the model has two sections -- the fixed
parameter section and the data section. Both are not required, but if not
enough information is included, the program will probably produce obviously
erronious or ill-defined results. Any line starting with a # sign is ignored.
Here is a sample input file (example.pmpar included with pmpar):
# This is an example file for pmpar. This is actual vlba data that was
# published Oct 1, 2000 in Astrophysical Journal.
name = B0950+08
ref = J0946+1017
dm = 2.9702
epoch = 2000.0
# Positions
1998.331 09:53:09.30708 0.00003 07:55:36.0994 0.0003 # bf040a
1998.337 09:53:09.30709 0.00003 07:55:36.0996 0.0003 # bf040b
1998.874 09:53:09.30750 0.00002 07:55:36.1133 0.0002 # bf046
1999.373 09:53:09.30696 0.00002 07:55:36.1301 0.0002 # bb106
Possible parameters are:
name : The name of the object
ref : The name of the reference source
epoch : The epoch to be used when a date is needed. default = 2000.0
RA : The object's RA at the given epoch
Dec : The object's Dec at the given epoch
mu_a : The object's RA proper motion in mas/yr (mu_ra*cos(dec))
mu_d : The object's Dec proper motion in mas/yr
pi : The object's parallax
dm : The dispersion measure (for pulsars)
non-standard parameters:
break : Specify an epoch when a change in coordinates happened
sh_x : Fix the coordinate offsets in x for the break
sh_y : Fix the coordinate offsets in y for the break
dmu_x : Fix relative motions of coordinate systems in x for the break
dmu_y : Fix relative motions of coordinate systems in y for the break
An optional equal sign can appear between these names and their values.
The parameters not fixed are fitted for with the constraints of the given
parameters.
Below describes how each of the 5 modes are used and examples:
MODE 0 Printing the model
~~~~~~~~~~~~~~~~~~~~~~~~~~
pmpar <file> [-c] [date1 [date2 [date3 ... ]]]
This will simply print the model parameters and their uncertainties.
Derived parameters such as distance and electron density are also shown
when appropriate. Using the -c option will also print the normalized
covariance matrix. Appending the dates to the command line will print
the objects position on the dates given.
MODE 1 Predicting path of object as seen from earth
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pmpar <file> -z start_epoch [stop_epoch delta_epoch [sigx sigy]]
Produces an ephemeris for the position of the object as seen from earth. With
the sigx and sigy, an output that can be used as input is produced. This is
useful for predicting the final errors before doing an experiment. For
example, the following command can be used:
pmpar <file> -z 1999.635 2000.635 0.25 0.0001 0.001 | pmpar -
where the final - means take input from standard in, not a file.
MODE 2 Predicting path of object as seen from sun
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pmpar <file> -s start_epoch [stop_epoch delta_epoch]
Same as above without inclusion of parallax
MODE 3 Determine when parallax extrema are
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pmpar <file> -m [center_epoch]
The last two lines are usually the important ones. Expect +-1 day error on
these values since the observer's location on earth is not known and leapdays
are not handled perfectly.
MODE 4 Produce plot files
~~~~~~~~~~~~~~~~~~~~~~~~~~
pmpar <file> -o[p][m][s]
pmpar <file> -o output model and raw data
pmpar <file> -op output model and raw data with parallax removed
pmpar <file> -om output model and raw data with pm removed
pmpar <file> -os output model and raw data with break(shift) removed
pmpar <file> -omp remove both
pmpar <file> -opm remove both
Two files are generated : pmpar_e and pmpar_t containing the raw data and
theoretical model. Outputs have these formats:
pmpar_e : epoch ra[mas] sigra[mas] dec[mas] sigdec[mas]
pmpar_t : epoch ra[mas] dec[mas]
When using the non-standard parameters, an additional option of using s in the
-o command, eg -oms, will remove the break from the first coordinate system.
MODE 5 Save data to .psr file
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pmpar <file> -p
This produces output that is useful for other astrometry code.