Carma Ephemeris :
The Carma ephemeris uses the USNO/NOVAS library for various calculations. The
ephemeris data are either from (ASCII) tables in $CARMA/conf/catalogs
(or cedarflat:/opt/array/rt/catalogs for user supplied ones)
or tables prepared by JPL, via the Horizons systems:
Although all major planets are by default present, transient
objects like asteroids and comets are not, and you will need to
provide an ephemeris for the period around your observation.
We are also providing support to track a stationary object
on the surface of a solar system object, though this also
requires more detailed software that knows about the (optionally
differentially rotating) body in question. An implementation for the Sun is
available (sept 2008).
- JPL HORIZONS
(web interface to ephemeris)
(software library with which CARMA interfaces for RA/DEC and AZ/EL computations)
Generating your own solar system ephemeris
There are a number of ways to generate the VECTORS Ephemeris file for solar
system targets (all major planet have been predefined).
The resulting file should look something like this:
- edit the template in
$CARMA/conf/catalogs/horizons.job and modify the following lines
to suit your needs. Some examples of the ones you need to change:
EMAIL_ADDR = 'firstname.lastname@example.org'
COMMAND = 'C/2007 N3' (a comet)
COMMAND = 'DES=73P-B;NOFRAG;CAP' (a comet)
COMMAND = '4;' (the asteroid Vesta)
COMMAND = 4 (the planet Mars, barycenter)
COMMAND = 499 (the planet Mars, bodycenter; you want this one)
COMMAND = ''g: 310.9, -84.7, 0.0 @ 301' (LCROSS impact 9-oct-2009)
START_TIME = '2009-FEB-15 00:00'
STOP_TIME = '2009-JUN-25 00:00'
STEP_SIZE = '30 minutes'
This template file has plenty
comments to guide you through the relevant parameters, but obviously
a number of them should not be modified or the CARMA ephemeris
software will get confused or may even crash your observing script.
Most likely you should only need to change the 5 listed above.
One additional piece of advice, choosing the correct syntax for COMMAND=
can be challenging. Best perhaps is to use the
web interfaceand search
for the correct incantation using the Target Body [change] button.
No need to generate the ephemeris here, but
use the show "batch-file" data link on the result page what the
correct syntax for COMMAND= is.
Send this template as an email with the subject line JOB to JPL. For
example in Unix the following command probably works:
mail -s JOB email@example.com < horizons.job
You will get an email back (this can take several minutes,
and on bad days many hours)
with the ephem file embedded. Use awk (as per instructions in the template)
or an editor to get the data lines.
If you don't know the object name, use either the query in the web
interface below, or guess the object (e.g. Lulin in the example
above would have helped) and the returned email will contain a list
of matches (in this case there were two).
For moons of planets it is useful to know when the moon is too close to the
parent planet, either in front, or behind. The CARMA program "distance" can
be used for this, e.g.
/opt/rt/bin/distance ref=jupiter source=io
# Time jupiter : az/el io : az/el angular distance
2013-05-23T17:01:40.2 85.90794867 34.67951883 85.91386128 34.68498299 0.007314143047
where the distance in degrees is printed in the last column.
- (experienced users only) use the web
interface, save the output and edit out the non-data lines.
This is tricky, since the default settings for the output
format and solar system viewpoint and parameters are not what
we need for our ephemeris files.
Make sure you see something like the following settings:
Ephemeris Type [change] : VECTORS
Target Body [change] : Io (JI) 
Coordinate Origin [change] : Solar System Barycenter (SSB) [500@0]
Time Span [change] : Start=2013-06-01, Stop=2013-09-01, Step=30 m
Table Settings [change] : quantities code=2; reference plane=FRAME; CSV format=YES
Display/Output [change] : download/save (plain text file)
and the file should look the same as the email version.
- (black belts only) a telnet interface, as described on horizons web page
- (experimental) using CARMA's checkephem program. It can actually also generate ephem files
for the major solar system objects using a version of JPL's DE405 database, it is mainly
used for tracking objects such as sunspots on the solar surface using a simple model
of a uniformly rotating (but dependant on latitude on the body) spot.
# Example 1: simply reproducing the sun
% checkephem source=sun mjd=54728 nsteps=10 step=1 spot=f | grep ^24 > sun1.ephem
% checksource source=sun1 mjd=54230.2
# Defining a sunspot by giving the proper MJD and Latitude/Longitude.
% checkephem source=sun mjd=54728.123874332 nsteps=10 step=0.1 latitude=22 longitude=21 | grep ^24 > ss_32.ephem
# JD date X Y Z VX VY VZ
2453870.500000000, A.D. 2006-May-15 00:00:00.0000,-5.465227102812747E-01, -7.833548627966440E-01,-2.894963713205840E-01, 2.040779775667518E-02,-5.228213740077321E-03, -7.051900383075237E-03,
2453870.583333333, A.D. 2006-May-15 02:00:00.0000,-5.448215004089416E-01, -7.837897446353480E-01,-2.900837333555622E-01, 2.042123503452728E-02,-5.208944593118194E-03, -7.044784550018225E-03,
2453870.666666667, A.D. 2006-May-15 04:00:00.0000,-5.431191718016970E-01, -7.842230192634879E-01,-2.906705014276759E-01, 2.043464737011887E-02,-5.189640693874762E-03, -7.037645272212271E-03,
2453870.750000000, A.D. 2006-May-15 06:00:00.0000,-5.414157265442097E-01, -7.846546837868722E-01,-2.912566735826597E-01, 2.044803461546170E-02,-5.170302086300463E-03, -7.030482536695162E-03,
where X,Y,Z are in AU and VX,VY,VZ in AU/day. The frame of reference for XYZ is
the Earth Mean Equator and Equinox of Reference Epoch (usually ICRF/J2000.0)
Once you have this file, copy it to
/arrayt/rt/catalogs/SOURCE.ephem, in upper case (until this bug
is fixed around Nov 1, 2008)
Test it by trying
checksource source=source mjd=53870.1
Please note that ephem table filename need to be stored in UPPER CASE!, and remember mjd = jd - 2400000.5.
Generating your own catalog
The ucat command (from $CARMA//scripts/python/subarrayCommands.py) is used
to set an alternative catalog of sources to be searched before the system
catalog. They must be placed in
/arrayt/rt/catalogs/catalog.cat, in matching case.
checksource source=N3870 catalog=/array/rt/catalogs/kartik.cat
The corresponding entry in the catalog file looks as follows:
# Kartik's catalog
# NOTE: SOURCE NAMES MAY NOT EXCEED 8 CHARACTERS
#| Source | RA | DEC | Parallax | Velocity | VelFrame | VelDef | PMRA | PMDEC | ID | PntType | Comments |
#| s | hms | dms | r | r | s | s | r | r | i | s | s |
#| | | | arcsec | km/s | | | asec/cent| asec/cent| | | |
N3870 11:45:56.6 50:11:59.10 0.0 756.0 LSR RADIO 0.000 0.000 1 RADIO
NGC5194 12:00:00 10:00:00 0.0 1000.0 LSR RADIO 0.000 0.000 1 RADIO
Within sac the command would be:
Please note that specifying doppler velocities in CARMA is limited. See the discussion on doppler.
Last updated: 23-may-2013 PJT