PISAPEAK - Transforms the PISAFIND parameterisations so that the variables are intensity invariant

Description:

PISAPEAK reads in the object parameterisations file produced by PISAFIND. Using the PISA profiling function it then transforms certain of the variables into values which are intensity invariant for a radial stellar profile. Two of the output variables may have values of around 1.0 for objects which are well represented by the given PISA profiling parameters. The variables produced are the ratio of the semi-major axis of the object fit to the radius of an object whose peak intensity is the same, but whose size is determined by the PISA profiling function (a peakedness measure). The ratio of the integrated intensity to the peak intensity and the model object ratio. The ellipticity (unmodified) and the absolute value of the intensity weighted cross moment (ABS(SXY)).

The output from PISAPEAK can be used in star-galaxy separation, either by applying direct cuts in variable values or by discrimination analysis routines such as PISAKNN.

Usage:

PISAPEAK IN FINDDATA RESULTS GSIGM CROSS COMIX BACKGROUND THRESH

Parameters:

BACKGROUND = _REAL (Read)

The frame background value (sky) as used by PISAFIND. [Global]

COMIX = _REAL (Read)

The mixture coefficient, as a fraction of the Gaussian peak, of a Lorentzian function used to model the wings of the stellar profile. At each point in the analytical profile the Lorentzian function is added to the Gaussian/exponential core scaled by the mixture coefficient. [Global]

CROSS = _REAL (Read)

The crossover point, as a percentage of the Gaussian peak, where an exponential fall-off in the analytical stellar profile takes over from the Gaussian core. The exponential function is joined on smoothly to the Gaussian. [Global]

FINDDATA = FILENAME (Read)

Name of the file containing the PISAFIND parameterisations. [PISAFIND.DAT]

GSIGM = _REAL (Read)

The standard deviation, in pixels, of the Gaussian core of the analytical stellar profile. [Global]

IN = NDF (Read)

The NDF containing the objects which have been parameterised by PISAFIND.

RESULTS = FILENAME (Write)

Name of a file to contain the PISAPEAK results. [PISAPEAK.DAT]

THRESH = _REAL (Read)

The detection threshold as used by PISAFIND. [Global]

Examples:

PISAPEAK IN=FRAME FINDDATA=PISAFIND.DAT RESULTS=PISAPEAK.DAT BACKGROUND=255 THRESH=12

This example shows PISAPEAK using the objects found in NDF FRAME with parameters stored in file PISAFIND.DAT. The results are stored in file PISAPEAK.DAT. Note that the model parameters GSIGM CROSS and COMIX are defaulted to those which have been stored in GLOBAL. These values were probably written by the routine PISAFIT which uses a list of stars to fit the PISA profiling function. The background value and threshold are those used by PISAFIND when detecting and parameterising the objects.

Notes:

• The model profile is used to scale the object values to those around unity. This only works well if the PISA profiling function is a good fit to the stars on your frame. If it is not a good fit or you cannot determine the model parameters then inaccurate values can be used, the only criterion being that the GSIGM value is about the FWHM seeing of your data. The results file will now contain values 'normalised' to this 'imaginary' object. The stars will still form a group of objects with similar values, although they will not be as tightly clustered as with a good fit.