PHOTOPT
examines the performance of the three different sky estimators used by PHOTOM on a particular
frame. It does this by performing aperture photometry on random parts of the frame, subtracting the
estimated sky level from a concentric aperture from the level in the central aperture. If the estimator is
good then the expected result is zero, as long as there are no objects in the central aperture. This is
repeated a number of times over the frame to ensure that a fair representation of the frames
characteristics is obtained. The results are shown in graphical form as a set of difference graphs. The
histogram of differences will indicate which is the best suited estimator for the frame.
ANGLE = _REAL (Read)
The orientation of the ellipse defining the aperture. This is
defined in degrees going anti-clockwise from the positive y-axis. This is equivalent to a
position angle.
DEVICE = DEVICE (Read)
The name of the device to receive the graphical
output.
ECCEN = _REAL (Read)
The eccentricity of the ellipse defining the aperture. For
a circular aperture this should be set to 0.0.
IN = IMAGE (Read)
Name of the image
on which the sampling test will be performed.
INNER = _REAL (Read)
The radius of
the inner edge of the annular sky aperture in units of the object aperture size. The actual
dimension in pixels is obtained by multiplying this factor by the object aperture semi-major
axis in pixels.
NP = _INTEGER (Read)
The number of points to sample in the image
up to a maximum of 100. This number is factorised so that a regular grid of samples is
taken. The actual number of samples is restricted to ensure that the central apertures do
not overlap.
OUTER = _REAL (Read)
The radius of the outer edge of the annular sky
aperture in units of the object aperture size. The actual dimension in pixels is obtained by
multiplying this factor by the object aperture semi-major axis in pixels.
PADU = _REAL (Read)
The number of photons for each interval of the data. If the true value is unknown use a
value of 1.
RANGE = _REAL (Read)
The limit of the plot in photon units ( data units
PADU
). This can be used to limit the range of the plot to the interesting region.
SATURE = _REAL (Read)
The saturation level in data units for the image.
SEMIM = _REAL (Read)
The semi-major axis of the
ellipse defining the aperture in pixel units. For a circular aperture this corresponds to the radius in
pixel units.