Prepping for Daophot and Allstar
The calm before the storm?
December 03, 2007
Before beginning daophot, we must prepare a series of files.
1. The Image Files
Luckily, we have updated daophot and it now acccepts fits images!
Please note that during the course of the photometry, we will make a
series of potentially large ascii files as well as making at least 2 copies of the
original fits image. Please make sure you have enough free disk space to do this.
The errors output by the program when the disk is full are quite difficult
to interpret correctly.
2. The OPTions Files
Daophot and Allstar each require a file that contains a series of image specific parameters.
These files can be automatically generated with an IDL program written by David Nidever.
However, the headers for the Fan Mountain data contain none of the required information.
So, we're going to do this the old fashioned way.
Tony Sohn wrote a Fortran script,
mkopt.f , that will create the opt files for
daophot and allstar. This code requires a very specific preparation file that we nominally
call night#.log. In this file you will collect a series of image parameters that will be complied
into the opt files by mkopt.f .
The file has a very specific format :
Image exptime gain rdnoise FWHM Hi-limit Filters
Name (s) (e/ADU) (e) (pixels) (ADU)
obj516_1 5.000 1.30 5.4 5.20 60000. V
obj516_2 5.000 1.40 5.5 5.20 60000. V
obj516_3 5.000 1.50 5.5 5.20 60000. V
obj516_4 5.000 1.40 5.3 5.20 60000. V
There are a few things to note.
A CAVEAT: It is very tempting to take the saturation limit to be the actual limiting count of the amplifier.
In practice, however, this is not the actual saturation limit of the stars.
- The image name can only be 8 characters.
- The exposure time can be found in the logs.
- The read noise and gain of the detector should be available in the Fan Moutain User's Manual.
- The fwhm can be computed as the average of a series of stars using the 'r' task in iraf's imexam.
- The High Limit is the saturation limit of the chip. The best way to estimate this is by examining the radial profile
of a saturated star and determining the point at which it becomes saturated.
- The Filter should be available in the log.
Once this file is put together you can compile and run mkopt.f:
Log file ?
Now you will have a obj????.opt and obj????.als.opt files for each image in your file.
Daophot and Allstar look for these files as daophot.opt and allstar.opt respectively.
Thus you will need to change the name of the file for each run in daophot.
The obj????.opt file is for Daophot. You should recognize some of your inputs in the .log file for mkopt:
RE = 3.79
GA = 1.40
LO = 7.00
HI = 60000.00
FW = 2.70
TH = 3.50
LS = 0.20
HS = 1.00
LR = -1.00
HR = 1.00
WA = -2.00
FI = 2.70
PS = 10.80
VA = 2.00
AN = -6.00
EX = 5.00
PE = 0.75
PR = 5.00
The key fields to note are:
The obj????.als.opt files are for Allstar:
- REead noise
- HIgh limit, i.e. the saturation limit in data counts
- FWhm, in pixels
- THreshold for detection in sigmas
FI = 2.70
IS = 1.70
OS = 11.80
RE = 1.00
WA = 0.00
PE = 0.75
PR = 5.00
CR = 2.50
CE = 6.00
MA = 50.00
3. The photo.opt file
The photo.opt file is a list of apertures for aperture photometry to be performed in daophot.
Daophot will read in this file automatically if it has the name photo.opt.
The default file is adequate for our purposes here:
A1 = 3.0000
A2 = 3.7965
A3 = 4.8046
A4 = 6.0803
A5 = 7.6947
A6 = 9.7377
A7 = 12.3232
A8 = 15.5952
A9 = 19.7360
AA = 24.9762
AB = 31.6077
AC = 40.0000
IS = 45.0000
OS = 50.0000