PHOTISO

Name

photiso

Purpose (one Line Only)

Compute aperture photometry and grade sources for field contamination

Description

This program takes a list of sources on an astronomical image and the
image and categorizes the sources into two types. The two types are
sources that are isolated and those that are not isolated. Isolated
means that a source does not have anything nearby that affects its
brightness as measured with the aperture radius provided. This is
used most often with somewhat crowded fields where you want to measure
object brightnesses of only those that can be directly measured with
aperture photometry.

Calling Sequence

photiso,gain,image,exptime,xloc,yloc,radius,sky1,sky2,ngood,zgood

Inputs

gain - Gain of the CCD. Photons per count (DN).
image - CCD image array.
exptime - Exposure time for the image in seconds.
xloc, yloc - Current location of the cursor in image coordinates.
radius - Current aperture radius in pixels.
sky1 - Inner radius of the sky annulus (in pixels).
sky2 - Outer radius of the sky annulus (in pixels).
If sky2<0 then sky1 is taken to be the actual sky signal
in DN/pixel and |sky2| is the error on the sky.
Note: these inputs work exactly the same as for basphote.pro

Optional Input Parameters

Keyword Input Parameters

BOXMRAD - Size of the box to look for local max in. Default=radius.
If boxmrad is negative, then the call to BOXM that finds the
local max is suppressed. In effect, basphote assumes that
the input location is already the maximum. You still need
to provide a non-zero number for boxmrad so that a local
area is defined for the fwhm calculation.
PSCALE - Plate scale in arc-sec per pixel (default=1.0).
RDNOISE - Optional CCD readout noise in (e-/pixel). Default=10 e-,
default is also used if RDNOISE is given as a negative number.
VERBOSE - Flag, if set will generate some diagnostic printed output and
a bunch of histograms.

Outputs

ngood - This is the number of input sources that are considered to be
isolated. This value can be zero and you must test for this
possibility.
zgood - Vector of indicies into the input position array for those sources
considered to be isolated. The value of this variable is
ill-defined if ngood=0.

Keyword Output Parameters

ERR - Optional return of the magnitude error.
FLERR - Uncertainty (1 sigma) of object flux.
FLUX - Object flux (photons per second)
FWHM - FWHM of object image(s), in arcsec if PSCALE provided, otherwise
returned in pixels
MAG - Optional return of the instrumental magnitude.
XCEN - Optional output of centroid x-position(s).
YCEN - Optional output of centroid y-position(s).
SKYMEAN - Sky signal computed for each source (DN/pixel).
SKYERR - Uncertainty on the sky signal.

Common Blocks

Side Effects

Restrictions

Procedure

This program uses multiple aperture sizes to measure fluxes and positions
of all the sources. The ensemble of these measurements is used to
find those that are well behaved in both position as a function of
aperture and magnitude as a function of aperture. Everything that is
isolated will act the same. Robust statistics are performed on quite
a few metrics to whittle the list down to the good ones.

Modification History

2010/12/28 - Written by Marc W. Buie, Southwest Research Institute
2012/03/08 - MWB, fixed a problem with the first cleanup cut. It was much
too agressive, letting far too few sources survive to the end