starfind

NAME

starfind -- locate stars and measure their parameters


USAGE

starfind [flags] image(s)

beta b 0.1, 50.0
bin false
center false
const c 12345.0
fwhm f 1.2, 15.0
gain g 0.0
kbox k 3
nan n 0.0
neg false
outputtab o sf.tab
psf_image p
star s 0:0,0:0
tresh t 8.0
verbose v 0
wep e false


PARAMETERS

beta = 0.1, 50.0
Beta exponent range of the moffat PSF-profile fit. Use two identical numbers in order to fix the exponent to e certain value.
bin = false
Using this flag, a cross binning is made before detection. All valid pixels (not having the value nan) are replaced by an average of the value of the pixel itself and the values of all valid neighbouring pixels (left, right, upper, lower).
center = false
If true, a Gaussian PSF-fit is made to each of detected stars in order to determine the (non-integer) center of the PSF. If false only the integer pixel number is written to "sf.tab".
const = -1e100
If not "-1e100", use fixed background value during the PSF-profile fitting.
fwhm = 1.2, 15.0
Seeing full width half maximum range of the moffat PSF-profile fit. Use two identical numbers in order to fix the fwhm to e certain value.
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.
kbox = 3
Box size. Only to be used in combination with the star- or the psf_image-flag. If a reference star region is specified, a reference PSF is measured. The amplitude of each detected star is measured using a linear fit to this reference PSF. The kbox-parameter specifies the size of a box in which the fit to the reference PSF is made.
nan = 0.0
Input not a number value. These pixels are not taken into account.
neg = false
Search also for negative sources. If used, the task inverts the input image(s) and searchs for maxima in the inverted image.
outputtab = sf.tab
Output table filename. This file contains the parameters of the detected stars (position, FWHM, background, amplitude). If center = false, the positions are only integer pixel values. If true, the center of each star is measured using a Gaussian fit and written to the output table.
psf_image = ""
Reference image filename. If used in combination with the star-flag, the reference PSF is fitted around the maximum within the specified region. If star "is 0:0,0:0", the region is set to the whole reference image size.
star = 0:0,0:0
Region of the PSF-profile reference star. The reference PSF is fitted around the maximum within this region. If star is "0:0,0:0" no refernce PSF is used and all parameters are fitted to each of the detected stars. If a refernce image is given (specified by the psf_image-flag) the referenve PSF is measured in the whole refernce image if star is "0:0,0:0" or in the specified region.
tresh = 8.0
Detection threshold. All stars with amplitude a >= background(x,y) + tresh * sigma(x,y) result in a detection where (x,y) is the position of the local maximum. The sigma is the pixel value taken from the corresponding error image (remember, sigma(x,y) is "1" if wep = false and gain = 0.0).
verbose = 0
Verbose level. If verbose >= 1, three additional output images are written.
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. Otherwise the error is assumed to be "1" and all pixel values are equally weighted.
image(s)
Input image(s).

DESCRIPTION

The task starfind detects stars in one ore more input image(s), measures their parameters and writes them to an output table. First the program searches for local maxima within a 3x3 box around each pixel. Then for each of the local maxima the amplitude is measured by PSF-profile fitting. In principle for this step there are two different ways. One way is to use a reference PSF measured on a refernce star (the region of the reference star has to be specified using the star-flag). The other way is to fit an individual moffat PSF-profile to each of the local maxima (star = "0:0,0:0"). The region of the reference star can also be specified in an optional input reference image specified by the psf_image-flag. Here, leaving star at "0:0,0:0" means taking the whole image as reference star region. For the individual moffat PSF-profile fit (and also the PSF-fit of the reference star), a region of valid full width half maximums (fwhm) and moffat beta parameters can be specified. After the amplitude of each star is determined the task checks if it is higher than a treshold specified by tresh. If so, the local maximum is concerned to be a detection.
For the use of errorweighting there are two ways. If the wep-flag is true, an error image is used and the individual pixel errors are taken into account. If the flag is false, a gain can be specified and an error map is created based on photon noise calculations. If wep is false and gain is "0.0", all pixels are assumed to have an error of "1".
The task has some optional parameters: If bin is set true, a cross binning is made before the local maxima detection. All valid pixels (not having the value nan) are replaced by an average of the value of the pixel itself and the values of all valid neighbouring pixels (left, right, upper, lower). Another optional parameter is the neg-flag. Using this also negative sources are detected. If center is used, a Gaussian PSF-fit is made to each of detected stars in order to determine the (non-integer) center of the PSF.
The output of starfind is a table "sf.tab" containing the parameters of the stars found (position, FWHM, background, amplitude). If verbose >= 1, three additional output images are written (see OUTPUT).


OUTPUT

sf.tab
Output table containing the parameters of the stars found (position, FWHM, background, amplitude). If center = false, the positions are only integer pixel values. If true, the center of each star is measured using a Gaussian fit and written to the output table.

If verbose >= 1:
sf_maxi.fits
Output image which shows the positions of all detected local maxima (value = "1").
sf_shomof.fits
Output image which shows the positions of all detected stars (value = "1").
sf_psfmof.fits
Output image which shows the moffat profiles of all detected stars.

EXAMPLE

starfind --center -b 2.5,2.5 -e -t 75 -f 1.2,6.0 -k 2 -o starfind_75.tab reference.fits


Task index
This task was implemented by A. Riffeser
Dokumentation maintained by J. Koppenhöfer
This file was last time updated on 31 Mar 2005