UseCase: SyntheticSpectra




Spectrum of desired object(s) is (are) returned covering the broadest wavelength range for which data is available


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Input list of objects with positional (plus position error) information.


  1. User has list of objects for which the spectral energy distribution is desired over a complete a wavelength range as possible.
  2. User is returned a list of all data that could match query, taking into account position, error, size of target source, size of aperture on sky of the instrument.
  3. User selects data sets of interest, or accepts default best set of data, or accepts all possible data.
  4. Data is extracted and coverted to a common flux scale.
  5. Data for which no flux information is available is normalised to 'best fluxed' data
  6. Data is returned in the form of an energy vs wavelength distribution, with an indication of the provenance of each data point.


  1. All data will be on a common flux scale
  2. It should be possible to zoom in on certain wavelength regions where data of high spectral resolution might be available.


  1. Both spectral and photometric data points should be gathered.
  2. Data flagged as of photometric quality should be used when normalising the fluxes of non-photomtric or un-fluxed data

"Extracts spectral plots" in conjunction with "browses" suggests that there's some general browsing tool that (a) can detect and correlate records that match by position and (b) knows how to do the plots. This won't work well unless each survey returns its spectophotometry in a standard format. If the optical results are in magnitudes, the radio results in janskies and the X-ray results in counts per square arcsecond per second for survey X and Wm-2 for survey Y, then correlating the data will be hard.


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Adapted and expanded from GTR's use case: synthetic spectra

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.

What does "normalised to best-fluxed data" (step 5 of the flow of events) mean? GuyRixon - 08 Feb 2002

This is for cases where the photometry on the spectrum is suspect (because of non photometric conditions etc) and thus is scaled to well calibrated spectra or indeed matched to photometry. Non fluxed spectrum won't help in building up an absolutely fluxed wide wavelength range SED. But they would be of use in giving spectral line information, so the shape of the distribution at higher resolution, that is important. NicholasWalton - 19 Mar 2002

At step 3, should there not be an option to refine the selection criteria? This would be something other than simply selecting data-sets from a list; more like adding constraints on, say, epoch of observation.

-- GuyRixon - 26 Mar 2002

-- NicholasWalton - 31 Jan 2002

Topic revision: r5 - 2002-03-26 - 14:32:57 - GuyRixon
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