In addition to the observing parameters for multifilter observations the observer has to specify the fraction of flux in the extended component and the signal-to-noise ratio required for measuring the extended component.
For each AOT request the observer has to specify the following parameters:
FILTER: specify the central wavelength of the filter requested
POINT OR EXTENDED SOURCE: specification of source type; this
parameter defines whether the EXPECTED SOURCE FLUX is given in Jy or
MJy
STARING OR CHOPPING MODE: definition of the observing mode
if CHOPPING MODE is selected (see Sect. 3.1 and
6.2 for details):
CHOPPER MODE: rectangular, triangular or sawtooth chopping
CHOPPER THROW: angular separation (in arcsec) between target and
reference position
CHOPPER AVOIDANCE DIRECTION: direction to be avoided by the
chopper
FULL AVOIDANCE ANGLE: angular region to be avoided by the chopper
EXPECTED SOURCE FLUX: best available estimate of source flux
(see Sect. 6.2)
EXTENDED COMPONENT: flux of the extended component to be
specified as fraction of point source flux (in percent)
UNCERTAINTY IN SOURCE FLUX: uncertainty of source flux estimate
MAXIMUM BACKGROUND FLUX: expected background flux at source
position including all components (see Sect. 6.2)
PEAKING UP REQUEST: for small apertures and high pointing
accuracies peaking-up on the source is necessary (see ISO OBSERVER'S
MANUAL)
INTEGRATION TIME or S/N: the integration
time requested or, alternatively, the signal-to-noise ratio required for
the detection of the extended component have to be specified
NUMBER OF APERTURES: total number of apertures requested
APERTURE: list of individual apertures required. The
smallest selectable aperture is the
diffraction limited one of the respective filter band.
Although the main purpose of this observing mode is the detection of extended components around point sources, it can also be used for multi-aperture photometry of EXTENDED SOURCES. In this case the parameter EXTENDED COMPONENT must be set to zero.
The observer should be warned that if diffraction limited apertures are required, a non-negligible part of the point spread function ( 30%) is truncated by the aperture. In order to detect faint extended components around point sources the largest selected aperture should be at least twice the diffraction limited aperture size. Tab. 2 should be consulted for fractions of the point spread function in different apertures for given filters.
The observer should determine the extent and contrast of the source to be observed from sky flux maps. For each aperture the expected flux should be estimated, and the appropriate apertures chosen.