The application can be operated in two modes; interactive and file.
INTERACTIVE - The user can select whether the radius range used to calculate the scale length values are input via a keyboard (CURSOR=FALSE) or via the mouse/ball (CURSOR=TRUE).
FILE - The user inputs the name of the text file output by ELLPRO, ELLFOU or SECTOR and the radius range over which isophotes will be employed to calculate the galaxy scale length.
In the file mode, graphs are not displayed. Once the input filename has been entered, no further user interaction is required. The input file should contain the contents of a single file output from ELLFOU, ELLPRO, SECTOR, or, alternatively, several such files concatenated together. In both modes, the name of the text file created by GRAPHS to store results in, is supplied by the user.
The X and Y co-ordinates output by SECTOR, ELLFOU and ELLPRO, and hence those plotted by GRAPHS, are in the Base frame coordinate system (units pixels) of the processed NDF images.
Q = quarter power
L = logarithmic
S = square root
R = linear The radius values displayed are the equivalent radius (R) when using ELLPRO/ELLFOU input files and distance from the galaxy origin when using SECTOR derived files.
B = Brightness of the profile in terms of sky i.e. (I-Back)/Sigma
C = Count value of the profile
E = Ellipticity of the profile
FC1 = First cosine Fourier descriptor
FC2 = First sine Fourier descriptor
FC3 = Second cosine Fourier descriptor
FC4 = Second sine Fourier descriptor
FS1 = Third cosine Fourier descriptor
FS2 = Third sine Fourier descriptor
FS3 = Fourth cosine Fourier descriptor
FS4 = Fourth sine Fourier descriptor
P = Position angle of the profile
S = Surface brightness of the profile
X = X co-ordinate (Base frame)
Y = Y co-ordinate (Base frame)
The file RESULTS.DAT is examined and its contents displayed graphically as required. The first display will be of linear radius versus surface brightness and will be shown on device XWINDOWS. The radius range for the isophotes to be employed in the scale length calculation are selected interactively via the mouse/ball.
The results stored in file PROFS.DAT are read one after the. other The profiles and ’fits’ may be observed interactively as graphs on device X2WINDOWS. The first display will be of log(radius) versus position angle. The radius range used when calculating the scale length is 1 to 20 arc seconds. results are output to file LENGTHS.DAT.
Profile data read in from file PROFS.DAT is analysed to determine the scale length using isophotes with a radius in the range 0.5 to 7 arc seconds. The results are output into text file SCALES.DAT.
Within ESP the scale lengths are calculated by assuming an exponential brightness profile for spiral galaxies and an exponential modified by a quarter power law for elliptical galaxies. The scale length value given is derived from the decay constant of the exponential functions.