| Parameters : | PSFPhot : int
Type of photometry to be run. Options are
- 0 (aperture),
- 1 (standard PSF-fit)
- 2 (PSF-fit weighted for central pixels).
Option 1 is suggested for most photometric needs, but option 0 can
provide superior photometry if the signal-to- noise is high and the
field is uncrowded.
FitSky : int
Sky-fitting setting. Options are
- 0 (use the sky map from calcsky)
- 1 (fit the sky normally prior to each photometry measurement)
- 2 (fit the sky inside the PSF region but outside the photometry
aperture),
- 3 (fit the sky within the photometry aperture as a
2-parameter PSF fit), and
- 4 (fit the sky within the photometry
aperture as a 4-parameter PSF fit).
Options 1 and 3 are the suggested settings. Option 0 should be used
only if the field is very uncrowded; option 2 can be used in extremely
crowded fields; option 4 can help in fields with strong background
gradients (though I have yet to see this be useful).
RCentroid : int
The centroid used for obtaining initial positions of stars is a
square of size 2RCentroid + 1 on each side.
SigFind : real
Sigma detection threshold. Stars above this limit will be kept in the
photometry until the final output.
SigFindMult : real
Multiple for sigma detection threshold in initial finding algorithm.
This should be close to one for larger PSFs, and as low as 0.75 for
badly undersampled PSFs.
SigFinal : real
Sigma threshold for a star to be listed in the final photometry list.
To get all stars, set SigFinal equal to SigFind.
MaxIT : int
Maximum number of photometry iterations.
FSPS : str
The functional form of the analytic PSF. Allowable options are “Gauss”
(Gaussian), “Lorentz” (Lorentzian), “Lorentz2” (a squared Lorentzian),
and “G+L” (sum of Gaussian and Lorentzian).
SkipSky : int
Sampling of sky annulus; set to a number higher than 1 to gain speed at
the expense of precision. This is only used if FitSky is set to 1.
In general, this should never be larger than the FWHM of the PSF.
SkySig : real
Sigma rejection threshold for sky fit; only used if FitSky is set to 1.
NoiseMult : real
To allow for imperfect PSFs, the noise is increased by this value
times the star brightness in the pixel when computing chi values.
FSat : real
Fraction of nominal saturation for which pixesl are considered
saturated.
Zero : real
Zero point for a star of brightness 1 DN per second.
PosStep : real
Typical stepsize in x and y during photometry iterations. Should be set
to a factor of a few smaller than the PSF FHWM.
dPosMax : real
Maximum position change of a star during a single photometry iteration.
Note that this parameter is currently ignored.
RCombine : real
Minimum separation of two stars (they will be combined if they become
closer than this value). This value can generally be about 2/3 of the
PSF FWHM, but no less than 1.42.
sigPSF : real
Minimum signal-to-noise for a PSF solution to be attempted on a star.
Fainter detections are assigned type 2.
PSFStep : real
Typical stepsize of FWHM during photometry iterations. Setting to zero
will replace PSF solution with three-state solution in which a star
will be very small, fit the stellar PSF, or very large.
MinS : real
Minimum FWHM for a good star (type 1). This should be set to something
like half the PSF FWHM.
MaxS : real
Maximum FWHM for a good star (type 1). This needs to be set to
something larger than the FWHM of the PSF.
MaxE : real
Maximum ellipticity for a good star (type 1).
UseWCS : int
Use WCS header information for alignment? Allowed values are 0 (no),
1 (use to estimate shift, scale, and rotation), or 2 (use to estimate
a full distortion solution). Note that any shifts or rotations selected
by img shift and img xform are applied in addition to what is
determined by the WCS solution. If reducing HST data, selecting
UseWCS=1 can eliminate the need for running the fitdistort utilities.
UseWCS=2 generally is not recommended for HST data since the
distortion coefficients provided with DOLPHOT provide higher-order
corrections than do the WCS headers.
Align : int
Align images to reference? Allowed values are 0 (no),
1 (x/y offsets only), 2 (x/y offsets plus scale difference),
and 3 (x/y offsets plus distortion).
Rotate : int
Correct for rotation in alignment? Allowed values are 0 (no) and
1 (yes).
SecondPass : int
Number of additional passes when finding stars to locate stars in the
wings of brighter stars. Must be a non-negative value.
SearchMode : int
Sets the minimization used to determine star positions. Allowed values
are 0 (chi divided by SNR) and 1 (chi only). A value of one appear
safe for all applications. A value of zero has been seen to fail if
images of very different exposure times are used together.
Force1 : int
Force all objects to be of class 1 or 2? Allowed values are 0 (no) and
1 (yes). For crowded stellar fields, this should be set to 1 and the
chiand sharpness values used to discard extended objects.
EPSF : int
Allow elliptical PSFs in parameter fits? Allowed values are 0 (no) and
1 (yes).
PSFsol : int
Make analytic PSF solution? Allowed values are -1 (no),
0 (constant PSF), 1 (linear PSF variation), and
2 (quadratic PSF variation).
PSFres : int
Solve for PSF residual image? Allowed values are 0 (no) and 1 (yes).
Turning this feature off can create nonlinearities in the photometry
unless PSFphot is also set to zero.
psfstars : str or None
Specify coordinates of PSF stars. The file must contain extension,
chip, X, and Y (the first four columns of DOLPHOT output).
psfoff : real
Coordinate offset of PSF star list. Values equal the list coordinates
minus the DOLPHOT coordinates, and would thus be 0.5 if using a DAOPHOT
or IRAF star list.
ApCor : int
Make aperture corrections? Allowed values are 0 (no) and 1 (yes).
Default aperture corrections always have the potential for error, so
it is strongly recommended that you manually examine the raw output
from this process.
SubPixel : int
The number of PSF calculations made per dimension per pixel. For
Nyquist-sampled images, this can be set to 1, but very small PSFs
require the extra precision.
FakeStars : str or None
Run DOLPHOT in artificial star mode. The FakeStars parameter is the
name of the text file containing the artificial star data. The file
should contain the following information for each star, one star per
line: extension (0 = main image), chip (usually 1), X, Y, and the
number of counts on each image. If the warmstart option is being used,
one also needs to specify the recovered X, Y, and object type values
before the counts. Note that photometry must be run first; the
photometry list, PSFs, etc. from DOLPHOT are used as inputs in the
fake star routine.
FakeMatch : real
Maximum allowable distance between input and recovered artificial star.
FakePSF : real
Approximate FWHM of the image, used to determine which of two input
stars a recovered star should be matched with.
FakeStarPSF : int
Use PSF residual from initial photometry run. This should be left at
zero, unless the PSF residuals are small and well-measured.
RandomFake : int
Apply Poisson noise to fake stars when adding them. This should always
be used, unless running fake star tests twice (once with and once
without) to quantify photometric errors from crowding and background
independently of the errors due to photon noise.
xytfile : str or None
star list filename for warmstart
xytpsf : str or None
PSF solution for the reference image for difference image photomtry.
photsec : list or None
Optinally, specify a subset fo the image to be photometered (relative
to first image, or referene image). Pass a list of six integer values:
extension (usually 0), Z (usually 1), minimum X, minimum Y, maximum X,
maximum Y.
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