starphot

NAME

starphot -- photometry tool


USAGE

starphot [flags] reference_image image(s)

beta b 1.0, 10.0
const c -1e10
fwhm f 1.2, 15.0, 1.0
gain g 0.0
header h false
inputtab i
mag m false
neg n false
outputtab o sp.tab
radiusbox k 10
sort r 0
star s 0:0,0:0
tresh t 0.0
variable v 0.0
verbose 0
wep e false
zentrum z false
zeropoint 25.0


PARAMETERS

beta = 1.0, 10.0
Beta exponent range of the moffat PSF-profile fit. Use two identical numbers in order to fix the exponent to e certain value.
const = -1e10
If not "-1e10", use fixed background value during the PSF-profile fitting.
fwhm = 1.2, 15.0, 1.0
The first two values set the valid seeing full width half maximum (fwhm) range of the moffat PSF-profile fit. If the third value is "0", the x- and y-fwhm are fixed to the first and the second value respectively.
gain = 0.0
This parameter has an effect only if no error files are used (wep-flag is false). If the gain is not "0.0", error image(s) are created based on photon noise calculations. Otherwise the error is assumed to be "1" and all pixel values are equally weighted.
header = false
If true, the measured parameters of the first star in the input table are written to the header of the input image(s).
inputtab = ""
Input table filename. This file contains a list with the x- and y-positions (column one and two) and the seeing full widths half maximum in x- and y-direction (column three and four) of all the stars to be measured.
mag = false
If true, an additional column with the stellar brightness in magnitudes is added to the output table. A zeropoint can be added. If a gain is specified(gain is not 0.0), the counts are multiplied in order to get photon fluxes which are then transformed to magnitudes.
neg = false
Measure negative sources also. If used, the task inverts the input image(s) and measures a PSF at each of the positions in the inverted image.
outputtab = sf.tab
Output table filename. This file contains the positions and parameters of the measured stars.
radiusbox = 10
Boxsize for PSF-profile fitting.
sort = 0
If true and the input table is containing more than one star, the output list is sorted according to this column. "1" means sorting by x-value, "2" sorting by y-value, and so on. Don't count the magnitude column if mag is used (to sort by magnitude, simply sort by flux).
star = 0:0,0:0
If the position of a PSF-profile reference star is given, the parameters fwhm, angle and beta are measured on this star and kept fixed for all of the other stars.
tresh = 0.0
Threshold kappa value. The fit is rejected if the measured amplitude of a star is less than tresh * e(x,y) where e(x,y) is the star's center pixel value in the error frame. (remember that e(x,y) is "1" if wep = false and gain = 0.0).
variable = 0.0
Use variable box size for PSF-profile fitting. The size will be variable times the seeing full width half maximum taken from the input table.
verbose = 0
Verbose level. If verbose >= 1, two additional output images are written. One image ("sp_...") is showing the measured PSF-profiles of the positive sources and one image is showing the measured PSF-profiles of the positive sources plus the inverted measured PSF-profiles of the negative sources. If neg = false the two images are identical.
wep = false
Use error image(s) also. If false, a gain can be specified in order to create error image(s) based on photon noise calculations. If gain is "0.0", the error is assumed to be "1" everywhere and all pixel values are equally weighted.
zentrum = false
If true, the center position of the PSF is kept fixed (to the value specified in inputtab) during the PSF-profile fitting.
zeropoint = 25.0
Magnitude zeropoint. If the mag-flag is used the stellar flux is transfomed into a brightness magnitude using this value. An additional magnitude-column is added to the output table.
reference_image
Input reference image.
image(s)
Input image(s).

DESCRIPTION

The task starphot is doing PSF-photometry on a set of input image(s). To each of the positions given in inputtab an analytic moffat PSF is fitted using the pixels in a box with the size of radiusbox. If the variable-flag is beeing set a variable box size is used. If the neg-flag is used, the task inverts the input image(s) and measures a PSF at each of the positions in the inverted image also.
There are ten free parameters in the fit, namely x- and y-position, amplitude, full width half maximum (fwhm) in x- and y-direction, angle, beta and three parameters for sky surface( const1 + const2 * x + const3 * y ). Some of the parameters can be limited to a certain range or fixed to certain value (fwhm, beta, const and zentrum). There is also a possibility to specify a reference star region (star) in either the images itself or in an additional reference_image. If so, the parameters fwhm, angle and beta are measured using this star and kept fixed for all of the other stars.
If the wep-flag is used, for each input image an error image is beeing read and the error of each pixel is taken into account for the photometry. If wep is false, a gain can be specified in order to create error images based on photon noise calculations. If gain is "0.0", the error is assumed to be "1" everywhere and all pixel values are equally weighted.
The output of the task starphot is a table (outputtab) containing the determined parameters of all the stars. If header is true, the measured parameters of the first star in the input table are written to the header of the input image(s).
If the mag-flag is used the stellar flux is transfomed into a brightness magnitude using zeropoint. In this case an additional magnitude-column is added to the output table.


OUTPUT

sp.tab
Output table containing the determined parameters of all the stars (position, FWHM, background, amplitude, etc.).

If verbose >= 1:
sp_...
Output image which shows the measured PSF-profiles of the positive sources.
sp_all.fits
Output image which shows the measured PSF-profiles of the positive sources plus the inverted measured PSF-profiles of the negative sources. If neg = false the image is identical to "sp_...".

EXAMPLE

starphot


Task index
This task was implemented by A. Riffeser
Dokumentation maintained by J. Koppenhöfer
This file was last time updated on 1 Apr 2005