GLOSSARY

AOT - Astronomical Observation Template:

Representation of an observing mode in the proposal generation software (PGA).

Background:

Sky emission towards the direction of the source. The contributors are: high energy particles, Zodiacal light, diffuse galactic emission and local diffuse emission in the vicinity of the source.

Chopper:

Mirror inside the ISOPHOT instrument that switches between the source position and an adjacent position such that alternatingly the emission from the source and background together and background alone is measured.

Instrument mode:

A mode in which the instrument can be operated.

Exposure time:

Time during which the target is observed plus, in the case of chopped observations, the time for measurements at reference positions.

Integration time:

The time during which the target is observed. Time for chopping is not included (cf. Exposure time).

Micro scan:

A scan which involves short spacecraft slews, within a raster map or a scan.

Mission Data Base:

The data base of proposals and observations.

Mission planning:

Generation of a sequence of observations, from the mission data base, for each revolution of the ISO satellite.

Observation:

A combination of target and specific observing parameters.

Observing mode:

An instrument mode dedicated to a specific type of astronomical observation. The representation of an observing mode vis-a-vis the observer is an AOT.

Orientation:

Angular distance of direction of a scan line. Counted in degrees from North through East.

Overhead:

Time to prepare the spacecraft and instrument for an observation, e.g.\ detector heating, wheel positioning and spacecraft slews.

Oversampling factor:

A factor that indicates how many celestial positions are used to cover the diameter of the aperture or the detector arrays, projected on the sky.

Phase 1:

First phase of proposal submission.

Phase 2:

Second phase of proposal submission.

Point spread function:

The flux distribution due to diffraction in the image of an ideal point-like source as seen by the telescope optics at a specific wavelength.

Pointing:

Positioning of spacecraft at a required sky position.

Pointing constraint:

An area of the sky where pointing of the satellite is forbidden. A constraint may not be violated (e.g. the Sun constraint).

Pointing restriction:

An area of the sky where satellite pointing is not allowed (e.g. the Jupiter restriction). If necessary, a restriction may be overridden (e.g. in the case of observation of Jupiter).

Proposal Generation Aids - PGA:

The ISO software system to enter proposals in submission Phase 2. It consists of a data base management system with a user interface.

Proposal Handling:

Processing proposals at the Science Operations Centre, which includes checking formal validity of proposals and their technical feasibility and entering proposals into the Mission Data Base.

Raster map:

A series of regularly spaced pointed observations, where at each position the observation is repeated. It is defined by the centre position, the step sizes in Right Ascension and Declination and its orientation.

Revolution:

The time during which the ISO satellite orbits around the Earth once (=24 hrs).

Reference beam or Reference field:

A position adjacent to the source usually selected to determine the background emission.

Scan, Scan line or Scan leg:

A series of spacecraft pointings in one dimension.

Sky bin:

A portion of the sky which is 10 by 10 degrees. The division of the sky in bins facilitates the calculation of visibility of the sky.

Sparse map:

For PHT only. Irregularly spaced map, where the individual points are defined by their positions i.e. Right Ascension and Declination and not by the step sizes, as is the case for a raster map. All positions have to be within an area of 3 degrees diameter.

Staring observations:

Pointed observations without chopping.

Step scanning:

To obtain a scan or a map the chopper is used to observe the positions between two adjacent spacecraft pointings. By these means the number of spacecraft slews is reduced. This type of observation is used for oversampled maps and scans for PHT only.

Step size:

Distance between two points in a map and between scan lines to define the size of the map.

Target dedicated time:

The time spent for the observation of a source in an observing mode including integration time and overhead times.