Content of the results files

The results of the parameterisation analysis are written into two files.

The first file name is defined by the RESULTS parameter. There are eleven columns in the output file containing the following information :-

Column	Name	Description
1	INDEX	Index number of object.
2	XPOS	X position of object in pixels.
3	YPOS	Y position of object in pixels.
4	INTENSITY	Integrated intensity of object.
5	NPIX	Number of pixels above threshold.
6	PEAK	Peak intensity of object in one pixel.
7	ELLIPT	Ellipticity of object.
8	ANGLE	Orientation of object, anti-clockwise from y-axis.
9	SXX	Second moment of data in x.
10	SYY	Second moment of data in y.
11	SXY	Cross moment of data in x and y.

The SXX, SYY and SXY moments are defined as:

$$SXX = \frac{\sum{x^{2}I_{i}}}{\sum{I_{i}}}, SYY = \fra... ...}}{\sum{I_{i}}}, SXY = \frac{\sum{xyI_{i}}}{\sum{I_{i}}}$$

Where $x$ and $y$ are offsets from the centre of the object (determined by the centroid) and $I_{i}$ is the intensity in a pixel, corrected for the background contribution.

The ellipticity is defined by the equation:

$$ell = \frac{a-b}{a}$$

Where $a$ and $b$ are the semimajor and semiminor axes:

$$a^{2} = 2 (SXX + SYY) +2 \sqrt{(SXX - SYY)^{2} +4 SXY^{2}}$$

$$b^{2} = 2 (SXX + SYY) -2 \sqrt{(SXX - SYY)^{2} +4 SXY^{2}}$$

Note that these are intensity weighted rms-like distances. If you want to calculate values that go out to say the detection isophote then you should use the geometric formulae:

$$a = \sqrt{\frac{NPIX}{(\pi (1-ELLIPT))}}$$

$$b = a (1-ELLIPT)$$

The results of the areal thresholding analysis are written to the file whose name is given by the SIZES parameter. There are nine columns in the output file, the last seven contain the number of pixels within the intensity thresholds : -

$$I_{i} = I_{t} * 2^{(i+2)},\; i=2,8$$

where $I_{t}$ is the threshold intensity and $I_{i}$ is the object intensity above the threshold :-

Column	Name	Description
1	INDEX	Index number of object.
2	A1	Number of object pixels within threshold.
3	A2	Number of object pixels within i=2 threshold.
4	A3	Number of object pixels within i=3 threshold.
5	A4	Number of object pixels within i=4 threshold.
6	A5	Number of object pixels within i=5 threshold.
7	A6	Number of object pixels within i=6 threshold.
8	A7	Number of object pixels within i=7 threshold.
9	A8	Number of object pixels within i=8 threshold.

The RESULTS output of PISAFIND can be used as input to the aperture photometry program PHOTOM [4]. This could be exploited to automate the photometry of standard stars on CCD frames.