UseCase: GetFluxOrUpperLimitAtPosition

PrimaryActor:

Research astronomer (or software agent running this UseCase as part of a higher-level task)

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EndResult:

Astronomer gets flux or upper limit in given band at particular source position, or has that passed to another VO operation or analysis tool, together with an estimate of the uncertainty on that quantity, and sufficient information about its origin and derivation.

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OtherActors:

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PreConditions:

Astronomer is interested in given object: this UseCase could be run interactively by the astronomer, or by an agent running some higher-level task, such as in the ScienceProblem SpectralEnergyDistributions, where an astronomer asks for the SED of a given object.

Astronomer (or agent) knows what size aperture to use: e.g. if running this UseCase as part of ScienceProblem SpectralEnergyDistributions then might choose to select aperture size matching that of existing catalogue data in other bands.

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FlowOfEvents:

1. astronomer (or agent) asks for flux in given band at particular sky position
2. databases including data from band are searched for objects at sky position
3. if record exists in photometric catalogue for named object and/or source sufficiently close to sky position then flux is returned to astronomer
4. if no such record exists, but there is appropriate calibrated imaging data, then a flux or upper limit is measured at the sky position by an appropriate method.
5. the astronomer (or agent) is presented with the flux or upper limit, together with an error estimate and information on where the flux/upper limit came from and how it was computed (either from catalogue, or noting algorithm used here)

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PostCondition:

Astronomer (or agent) has a photometric data point (plus uncertainty) that can be used in a variety of analyses.

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BasicAssumptions:

The passband required can be readily specified: this may be implemented in several different ways - e.g. astronomer after a near-infrared magnitude for a source could check 'J', 'H' and 'K' in a list of standard photometric bands, or could check 'near-infrared' and could then be returned data for any of those three bands (or, indeed, other passbands in the near-infrared measured from space, and therefore not defined by the same atmospheric windows).

It is assumed that sufficient information exists to compute a sensible error bar for any flux measurement made within this UseCase.

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AlternativeFlows:

In Step 1, the astronomer might supply an object name, which is resolved into a sky position.

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Discussion:

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Links to ScienceProblems:

This UseCase is a possible constituent part of SpectralEnergyDistributions.

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KeyReferences:

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GoodStyle: Please add comments below. This area should be used for refinement of the above document. If you want to ask questions or start a dialogue with the author, please use (or create) a topic in the Use Cases Forum.
Author: Once the refinements here and comments in the forum die down, perhaps you could rewrite the problem, incorporating the comments and refinements.

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-- BobMann - 12 Feb 2002

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Some possible modifications to make this more general (or you might prefer a separate use case?):

EndResult - in addition, provide exact position/size of source/uncertainty of data extracted from image

PreConditions - selection of aperture size by astronomer (ie seach box?) should also take into account input uncertainties or source structure (e.g. for ComplexObjectIdentification). AG should then add the relevant allowance for error in the data being searched.

FlowOfEvents

1. Astronomer asks for any object (i.e. not just flux) in given frequency range within search box as defined in PreConditions.

4. - 'calibrated imaging data' should be any suitable calibrated data - e.g. interferometer visibility data which can be mapped on the fly; spectral data taken with a suitable spatial resolution.

PostCondition - astronomer also known position of counterpart source, useful for everything from AstrometryBootstrap to the Science Cases e.g. AGBstarCandidates, UnusualStarsInGalacticPlane and in ComplexObjectIdentification

BasicAssumptions - passband should be in unambiguous units e.g. observing wavelength range.

Also, this assumes AG has access to the required data processing software to invert interferometry data, measure spectra etc., and knows what the footprint/resolution of its data is (which may be a function of the desired accuracy).

-- AnitaRichards - 02 Mar 2002