- Form: SECTOR source [RAD=(lin,geo)] [C=(r,c)] [SCALE=f]
[PLOT]
-
- source
- The image buffer
- RAD=
- Describe the isophote spacing. Isophotes are initially spaced
linearly every `lin' pixels in radius. Isophotes further out are
spaced geometrically by `geo' when this step is larger than `lin'.
Defaults: lin=2 pixels, geo=0.15 (increase radius by 15% per
step).
- C=
- Give the object center. Default is to use results from
the AXES or AUTOCEN commands.
- SCALE=
- Give the scale in arcsec/pixel. Default is 0.55.
- PLOT
- Plot the isophotes on the TV.
SECTOR measures the brightness distribution of a star cluster or any other
extended object by adding up the flux in a set of circular isophotal rings.
Errors in brightness in any ring are calculated by dividing the ring into
eight angular sectors and intercomparing the individual sector results.
The final profile is saved in the MULT block, and can be saved or gotten
with the MULT keyword in the SAVE or GET commands, printed in the PRINT
command, or plotted with the PLOT command. The object can also be
reconstructed with the RENUC command.
The center should be found first with the AUTOCEN or AXES command. The C
keyword can be used to override the default center. Isophotes increase
linearly from the center at first, and are spaced by the lin entry with the
RAD keyword. When a geometric increment given by the geo entry gives a
larger spacing, it is used to space the outer isophotes. The radii used
are at the radii at which the area of the isophotal rings is evenly
divided. Pixels can be excluded from the calculation by setting them to
zero.
See Also: PROFILE, ANNULUS, AXES