Photom -- programs to perform photometric calibration of stellar photometry

Version 0.8: March 27, 2005

Version 0.8 has one big enhancement and one small fix:

The user can now request that stars detected in only a single passband be retained and included in output. They will have no color corrections made, only zero-point and extinction shifts.
A minor big in initializing memory has been fixed; it caused the selftest script to fail on some machines.

Added March 25, 2006: Version 0.8 (and all earlier versions) have one important bug.

The code requires the names of the filters for which data will be reduced to be "V" and "I". It turns out these are the filters used in the TASS Mark IV project, for which this software was written. I was just too lazy to create the proper routines to handle arbitrary filter names.
So, whatever filters you are using, you'll have to supply "V=" and "I=" as the arguments on the command line, even if the data of interest are, e.g., "B" and "V".

Thanks very much to Andisheh Mahdavi for pointing this out. I ought to fix it in a future release ....

Added Sep 7, 2007: If the code compiles and links, and passes some of the self-tests -- but fails on others -- try editing the Makefile to change

        CFLAGS = -g -O2

        CFLAGS = -g

These programs are designed to take raw, instrumental measurements of stellar brightness and convert them to calibrated magnitudes on some standard system. They were written as part of the TASS Mark IV pipeline , but may work on other datasets.

This package creates two executables:

collate, which matches up measurements of the same star in images taken through different passbands
photom, which compares multi-passband measurements of stars to magnitudes in a catalog, determines the coefficients of a simple photometric solution, and applies it to the raw measurements

The photom program tries to fit the raw measurements from N frames to the catalog magnitudes with in one of three modes:

if given command-line option mode=noextinct, an equation of N + 1 free parameters and no extinction
```
   calibrated mag  =   raw mag  +  a   +   b * (raw color)
                                    i
```
if given command-line option mode=noextinct and fixk=, an equation of N + 1 free parameters and differential extinction within each frame with user-supplied coefficient
```
   calibrated mag  =   raw mag  +  a   +   b * (raw color)  -  k*X
                                    i
```
if given command-line option mode=extinct, an equation with just 3 free parameters
```
   calibrated mag  =   raw mag  +  a   +   b * (raw color)  -  k * airmass
```

where

a_i is the magnitude zero-point for frame i, or, in the last case, a is the single magnitude zero point shared by all frames
b is a first-order color term
k is a first-order extinction coefficient

There is no default; the user must specify the mode in the command line. If no values for fixk are given, then no differential extinction is included in the solution.

Requirements

The source code is vanilla ANSI C. It links against the standard math library, and also against the GNU Scientific Library (GSL). It works off the command line, with no user-friendly GUI. The package includes a self-test is written in Perl, but it's not necessary for the operation of the programs. The GSL will take about 75 MB of disk space to download, compile and install, but much of that is needed only temporarily. The photom code itself requires only a few tens of MB.

Read the README for latest version.
Read the collate HTML manual.
Read the photom HTML manual.
Download latest tar.gz (143056 bytes)

Older version is photom 0.7, last modified Aug 2, 2003.

Read the README for version 0.7.
Read the collate HTML manual for version 0.7.
Read the photom HTML manual for version 0.7.
Download photom-0.7.tar.gz (131033 bytes)

Last modified March 27, 2005 by Michael Richmond