The COCO program can be used to convert between various coordinate systems (for
example, celestial to galactic) or different equinoxes and epochs. COCO is a
STARLINK program written by Pat Wallace. Its commands are as follows:
I p specify input coordinate system (p defined below)
O p specify output coordinate system ( " )
F x specify RA mode: x = H or D (hours,degrees)
R y select report resolution: y = H, M or L (high,medium,low)
S display current settings
<coords> perform conversion (or = to repeat last coordinates)
? show format of <coords>
/<file> switch to secondary input file <file>
H list the commands
E exit
Parameters p for I and O commands:
4 [eq] [ep] equatorial, FK4
B [eq] [ep] like FK4 but without E-terms
5 [eq] [ep] equatorial, FK5
A ep equatorial, geocentric apparent
E ep ecliptic
G [ep] galactic
eq equinox, such as 1950 (optional B or J prefix)
ep epoch, such as 1984.53 or 1983 2 26.4
Input format:
RA Dec PM Px RV
h m s d ' " [s/y "/y [" [km/s]]]
or
h m s d '
or
h m d '
or
h d
(proper motions default to zero in FK5)
Notes:
COCO is for use only with sources well outside the solar system.
Three report resolutions are provided: L (low), M (medium), and H (high).
The computations are the same irrespective of the report resolution selected.
The accuracy is more than adequate for report resolution 'M', and is good
enough for all practical purposes at present. Resolution 'H' is provided
mainly to allow comparison with other predictions and to decrease rounding
errors where differences are taken.
The raw output file consists only of positions expressed to a fixed but
high resolution. It is free from extraneous prompting, logging, and error
messages in order to facilitate subsequent processing by other programs.
COCO is not intended for the conversion of catalog data, and reports
positions only - updated proper motions etc are not reported. Full conversion
of catalog data is possible using some of COCO's component subprograms.
Example:
<- 12 -62 ! convert from b1950 to j2000 (the default mode)
= 12 00 00.000 -62 00 00.00 B1950.00 B1950.00 FK4 0.000 0.0
-> 12 02 34.461 -62 16 42.53 J2000.00 J2000.00 FK5
<- 12 23 -62 23 ! convert from b1950 to j2000 (the default mode)
= 12 23 00.000 -62 23 00.00 B1950.00 B1950.00 FK4 0.000 0.0
-> 12 25 47.406 -62 39 36.88 J2000.00 J2000.00 FK5
<- o g ! convert from b1950 celestial to galactic
Conversion is to:
Galactic, epoch B1950.00
<- 12 23 -62 00
= 12 23 00.000 -62 00 00.00 B1950.00 B1950.00 FK4 0.000 0.0
-> 299.95345 0.44640 B1950.00 galactic (II)
<-
The NH program, written by P. Giommi provides, for a specified right ascension
and declination. He gives a value for galactic HI hydrogen column density.
The NH program uses the data contained in the ``Bell Laboratories H I Survey"
(A.A. Stark, et al., 1990, privately distributed tape) and interpolates for a
given sky position. To run the NH program from within the XRAY account,
simply type:
HEASARC> nh
Give an RA and Dec as prompted and the program will
return a value for galactic NH.
Note that the Bell Lab 21-cm survey data only cover regions of the sky north of
declination -40 degrees.
PIMMS (Portable, Interactive, Multi-Mission Simulator) is a simulation program
initially tuned for ASCA but written in a general enough way as to be useful
for other missions. PIMMS can perform flux conversion to and from count rate
or count rate to count rate conversion, given a spectral model. The current
version of PIMMS can also simulate simple ASCA SIS images.
The name PIMMS reflects three crucial design goals.
Portability: The program must be portable enough that the majority (if not
all) of astronomers can take a copy to their own home institutions and run it
there. At the same time, use of PIMMS via remote login to a central location
is supported. PIMMS is being developed in OGIP standard Fortran for this
purpose.
Interactive design: few users of PIMMS are expected to be content to find one
number at the end of a run. More likely, users will want to repeat nearly
identical calculations for different parameter values (such as NH). This is
most readily accommodated in a command-driven approach, in which parameter
values are preserved for successive calculations unless explicitly changed.
Multi-Mission nature: It is often the case that one wants to predict, for
example, the ASCA count rate of a source given the known Einstein IPC (or some
other experiment) count rate. Such conversion presents a problem to the users
of many existing utilities, each of which typically deals with only one
instrument (or at most one satellite). One has to run two separate programs, or
trust a given value of a conversion to a physical flux unit. By providing a
single step conversion between various missions, PIMMS guarantees that exactly
the same model was used for both instruments and asks only for the observed
count rate. PIMMS still provides flux to count rate conversion, for the more
theoretically inclined.
Complex spectral simulation has not been included within PIMMS. That would
require a rather extensive effort, not only initially but also to keep up with
the ever increasing set of theoretical models. PIMMS is currently limited to
three analytical models (blackbody, power law, and Bremsstrahlung) and a
limited grid of Raymond-Smith models, each with a simple cold absorber. More
complex spectral model can be imported to PIMMS by way of an ASCII file that
can be generated using XSPEC or by users' own programs.
When planning a time-critical observation, it may be necessary to know when a
satellite can observe a particular target. Viewing is a stand-alone utility
program which calculates sun angle constraint and outputs the visibility window
(i.e., times of year when the satellite can point at the target).
Viewing does not have information on up-to-date orbital elements of satellites;
thus it is impossible to predict a detailed viewing pattern (Earth
occultations, SAA passages etc.) or the efficiency of observation with this
program. Some satellites may have additional constraints (e.g., thermal) that
Viewing does not take into account. However, in the case of ASCA, for instance,
there are currently no factors which can make the observation of a target on
a given date impossible, as long as the Sun angle constraint is satisfied. For
other missions, consult respective mission description documents.
PIMMS and Viewing are available as part of the HEASARC Online Service and may
be used from the xray account. PIMMS and Viewing can also be obtained by
anonymous ftp from ``heasarc.gsfc.nasa.gov" under the directory
asca/nra_info/pimms. This directory includes a README file and several
compressed tar files. Help files and an up-to-date user's guide, as well as the
source code and data files, are also provided by anonymous ftp.