Fits a galaxy profile using simple intensity analysis. The routine fits a series of ellipses to the galaxy, at
varying intensity values, and displays the position, size and angle of these ellipses, as well as the
azimuthally-averaged intensity around them. It plots these intensities as a function of
The position of the centre of the galaxy (and a number of other parameters) may be specified
interactively (using cursor or keyboard) or the location within the image of several galaxies may be
specified using an ASCII text file.
A number of options allow the user to determine criteria for; when profiling should end, whether an
ARD file is to be used to mask out bad areas of the image, whether the initial galaxy centre
value is to be fixed throughout profiling and also whether or not the initial galaxy centre
co-ordinates provided by the user may be refined by the application before the first profile is
The position of the centre of the galaxy in question may be input interactively, MODE=TRUE), or (if
there are many galaxies to be considered) may be read in from a text file (MODE=FALSE). In addition,
when in MODE=TRUE the galaxy can be identified using a cursor (CURSOR=TRUE) as opposed to a
keyboard entry of its co-ordinates.
ELLPRO MODE BACK SIGMA PSIZE ZEROP ARDFIL
DEVICE OUT (OUTCAT)
AUTOL AUTOLT FRZORI [CURSOR] [IN] [ORIGIN] (FAST)
(FINE) [RLIM] (LIM1) (LIM2) (LIM3) (FRACT) [SAME]
[AGAIN] [INFILE) [IMGDEV] (COLOUR) (ANGCON) (ANGOFF)
Allows the user to elect to repeat the profiling operation on the current
Angle rotation convention. Defines if clockwise or
anticlockwise is considered positive. TRUE=Clockwise.
for position angles generated. Units degrees.
The name of an ARD file to
be used to mask out regions of the image that are not to be used.
true, then the application attempts to find a better initial estimate of the galaxy centre. See also
the AUTOLT parameter for further control of this, and contrast the FRZORI parameter.
Controls the method used when improving the estimate
of the galaxy centre (see parameter AUTOL). If autolt=true, the application refines the
initial galaxy centre by taking the centroid of the points in a small region around the given
location. If autolt=false, it uses an alternative weighted-mean method.
The background count value for the image. Units counts.
COLOUR = _INTEGER
Colour of the pen used to mark galaxy centres.
Whether the galaxy locations are to be identified using the graphics cursor or the keyboard.
Name of the graphics device on
which the results graph should be displayed.
Is the faster
method of profiling to be used? Default value is true. The slower version should yield better
values at low radii values since surface interpolation (rather than bi-linear) is used. The
surface generated by the slow method to model the galaxy near its centre is a 8x8 bi-cubic
spline, so considerable calculation is involved.
A factor modifying
the default separation of ellipses profiled. The default value is 1. Decreasing this value
increases the number of profiles generated for a given object. Increasing this value above
2.0 is not recommended.
The minimum fraction of the points
round the ellipse for which no value was available due to either image pixels set to the
bad value or parts of the ellipse being beyond the bounds of the image. If the fraction of
points available for a given ellipse drops below this value the results for that radius are not
If FRZORI is true, then the initial galaxy position,
after any initial refinement if the AUTOL parameter is true, will be frozen for the rest of
the calculation. If FRZORI is false, then the initial estimate will be allowed to drift if that
improves an ellipse fit.
Name of the graphics device displaying
Name of a text file containing the co-ordinates of
galaxies to be profiled. (Only used in file mode i.e. MODE=FALSE) Co-ordinates are in the
Current coordinate system of the WCS component of IN.
The name of
the source NDF data structure/file.
The maximum ratio that is
permitted between the average mean count value of the two preceeding radii profiled
and that of the current radius. If this value is exceeded, the profiling operation stops.
The lower limit for mean profile count value (above sky). If the
mean count value for the current profile drops below this value the profiling operation
stops. Units are standard deviations.
The distance from the galaxy
origin at which the profile is assumed to maintain a constant position angle, origin and
ellipticity. At radii beyond these, parameters are no longer modified. The position angle, origin
and ellipticity are not frozen if a value of zero or less than zero is suggested. Units are
Which type of ellipse-residual minimisation is to be
The type of residual to be calculated is specified as 0, 1 or 2. It’s not completely clear what is the best
type of residual to use. The original one – a weighted standard error, selected by giving this parameter
the option 0 – is rational, but not obviously ideal. As alternatives, you can use the range and the
squared-differences, selectable by options 1 and 2 respectively. This also controls which
type of statistic is returned in the final column of the ELLPRO output file: this statistic is
the mean, median and mean (including background) in the three cases, but you should
not regard this as useful information. You are advised not to play with this unless you
particularly wish to experiment. If this parameter makes much of a difference, the ESP
maintainer would be interested to hear about it.
application is to run in file input mode or interactively. Interactive MODE=TRUE. File
Image co-ordinates for the origin point to be
used. Co-ordinates are in the Current co-ordinate system of the WCS component of IN.
File name for the output text file containing the profile data.
File name for an output file which is written using the CAT library. See
SUN/181. The type of catalogue which is written depends on the file extension to the filename
presented here. A file ending .txt will be written as a STL (Small Text List) file, and one
ending .fits will be written as a FITS file.
The size of each pixel in
arc seconds. If the image contains a SKY co-ordinate frame this value will be determined
Radius at which the profiling will be stopped. Units pixels.
Is the results graph to be displayed on the device currently
displaying the input image? Only valid if CURSOR is true. If SAME is set to true then
the user is prompted to identify the quadrant of the input device in which graph will be
The standard deviation of the background value. Units
Zero point of the scale for surface brightness plots. Units
magnitudes per arc seconds.
Parameters surrounded by curved brackets may
only be modified via the command line.