Glossary

AOT - Astronomical Observation Template:

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

Central Programme:

The co-ordinated observing programme to be carried out in the guaranteed time of the four Principal Investigator teams that built the instruments, the five Mission Scientists and the Science Operations Team.

Discretionary Time:

An average of 30 minutes observing time per day will be kept available for observations that could not have been foreseen at the time of proposal submission.

Duplication:

Two or more identical observations, i.e. combinations of target and observing parameters.

Exposure time:

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

Grade:

One of the elements used by the mission planning system in choosing observations for scheduling is their grade. The Observer enters a grade for each observation into PGA at the time of Phase 2 data entry. This grade is based on the scientific priority set either by the guaranteed time holder (for the guaranteed time) or by the OTAC (for the open time). Guaranteed time priorities 1, 2 and 3 ``map'' to grades 9, 7 and 4, in PGA. Open time priorities 1 and 2 map to grades 8 and 6, respectively, in PGA. Open time priority 3 maps to grade 3 in general and to grade 2 for a specific filler programme. (See also Priority in this glossary).

Guaranteed Time:

Observing time on ISO reserved for those involved in building and operating the facility.

Instrument mode:

A mode in which the instrument can be operated.

Integration time:

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

IRPSS - ISO Remote Proposal Submission Software:

Software to prepare and format Phase 1 proposals.

Mission Data Base:

The data base of details of observations.

Mission planning:

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

Observing Time Allocation Committee, OTAC:

The committee, appointed by the ESA Director of Science, that is responsible for reviewing the proposals and recommending those observations that should be carried out.

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.

Open Time:

Observing time on ISO that is distributed via a Call for Observing Proposals and peer review.

Overhead:

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

Phase 1:

First phase of proposal submission. Proposers use the IRPSS to prepare and format proposals. The formatted proposals are submitted via electronic mail and in 12 paper copies (print-outs). Proposers submit the abstract, scientific justification and the requested targets and observing modes.

Phase 2:

Second phase of proposal submission, after OTAC review. Full details of recommended observations are entered by the proposer with the PGA software at the Proposal Data Entry Centre at ESTEC or (for US Observers, at IPAC). The purpose is to build up the Mission Data Base for operations.

Pointing:

Positioning of spacecraft (i.e. telescope/instrument) towards the required sky position.

Principal Investigator:

Depending on context may refer either to the leader of one of the four consortia that built the ISO instruments or to the lead author of a proposal, sometimes referred to as ``Guest Observer''.

Priority:

Within the Guaranteed Time programme, the top 40% has been designated as priority 1, the next 30% as priority 2 and the remaining 30% as priority 3. The overall programme has been sized so that it is expected that most of all three priorities will be carried out during ISO's lifetime. For the Open Time programmes, observations that were to be entered into the Phase 2 data base were given a priority of 1, 2 or 3 by the OTAC. Priority 1 open time corresponds to about one-third of the time expected to be available for Open Time and the SOC will try to execute all these observations, even if it entails a loss of operating efficiency. Priority 2 open time corresponds to the remaining two-thirds of the time expected to be available for Open Time. Priority 3 open time exists to provide an ``oversubscription'' of approximately a factor of 2 in the observations available to the mission planning system so as to improve the efficiency of the observing timelines. Only a relatively-small fraction of these Priority 3 observations will be executed, mainly to fill gaps in the schedule. As observers enter their observations into the PGA software, they have to enter ``grades'' not priorities (see Grade in this glossary).

Proposal Data Entry Centre:

The centre located at ESTEC in Noordwijk (The Netherlands) where the PGA software will run during Phase 2. Proposers visit this centre to enter full details of recommended observations using the PGA software. (US and Japanese proposers will follow alternative instructions for Phase 2 data entry).

Proposal Generation Aids - PGA:

The ISO software system to enter full details of observations during 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:

A rectangular grid of 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 by its orientation on the sky.

Revolution:

The time (just under 24 hrs) in which the ISO satellite orbits the Earth once, from perigee to perigee.

Reference beam or Reference position:

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

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.

Sky Coverage:

Portion of the sky that can be seen by ISO, either at a given time or over a specific time interval.

Slew:

A movement of the satellite to point from one target to another.

Staring observations:

Pointed observations without chopping.

Step size:

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

Target dedicated time (TDT):

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

Target of Opportunity, ToO:

An astronomical phenomenon which may be anticipated but cannot be predicted in detail.