-- ElizabethAuden - 30 May 2002

Brown Dwarf Science Problem


An astronomer exploring the lower end of the stellar mass function wants to conduct a census of brown dwarfs. The census population will be determined by colour, proper motion, and location (such as all brown dwarfs within some radius around the sun). New brown dwarf candidates have been successfully identified by conducting a proper motion survey of Galactic clusters (clusters of Stars in the Milky Way).

This use case is based on the paper "Brown Dwarfs in the Pleiades and the initial mass function across the stellar/substellar boundary" by Hambley, et al, MNRAS 303, 835. Their calculation for relative proper motion should probably be accessed via user code, a web service, or possibly a library function. Their procedure for calculating proper motion has been summarized:

For each 'image' (defined by Hambly, et al as an area of 5 or more connected pixels) in the dataset, the mean position of the image is calculated over all datasets. Then the relative shift of each image from an individual dataset is determined with respect to the mean position. Finally a weighted linear least-squares fit as a function of time is applied to the relative shifts; this determines the image's relative proper motion. A vector-point diagram of the images' proper motion is produced.

Flow of Events

1. The astronomer searches the resource catalogue for catalogues containing Galactic clusters via PerformRegistrySearch.

2. A list of cluster catalogues is returned via MySpaceStoreResults, and the astronomer selects one or more cluster catalogues via SelectCatalogue.

3. Next, the astronomer searches the selected catalogues for cluster locations via PerformCatalogueSearch.

4. A list of locations, defined by right ascension, declination, radius, and distance, is returned via MySpaceStoreResults.

5. The astronomer then returns to the resource catalogue and executes a complex query for catalogues with coverage of I, K, or R wavelengths over each cluster location via ComplexQuery.

6. A list of catalogues with I, K, or R coverage of the cluster location is returned via MySpaceStoreResults.

7. The astronomer selects 1 or more catalogues via SelectCatalogue and searches them for 2 or more datasets covering the cluster location in the same wavelength (either all datasets with I coverage or all with K coverage) via PerformCatalogueSearch.

8. The datasets are stored to MySpace via MySpaceStoreResults.

9. Now the astronomer can prepare the data for the proper motion survey. The datasets are astrometrically aligned using a library function, a web service, or user code via DetermineProgram.

10. Next, the proper motion can be applied to the datasets by user code, a web service, or a library function via DetermineProgram.

11. The program calculates a proper motion vector-point diagram of objects in the dataset. The diagram is stored on MySpace via MySpacePublishDerivedData and returned to the astronomer.

Sequence Diagram

Revised "simple" sequence diagram:

Old Sequence diagram:

  • Revised sequence diagram from Together: -- DavidGiaretta - 08 Aug 2002


These use cases are the ones that will be needed to deliver this case.

  1. PerformRegistrySearch
  2. PerformCatalogueSearch
  3. MySpaceStoreResults
  4. ComplexQuery
  5. DetermineProgram
  6. MySpacePublishDerivedData
  7. SelectCatalogue

The diagrams above are based on the conceptual model of the AstroGrid project. Developed by ElizabethAuden, DavidGiaretta and AnitaRichards with contributions from various focus meetings and other people, it looked at the concepts within the VO.VirtualObservatory domain space. This was an excellent start to the project and allowed participants to scope the AstroGrid project within the VO domain (ie, what VO bits AstroGrid would and would not do).

A later focus meeting (ArchitectureMeeting20020819) concentrated on the Services (or components) that AG would deliver (see GridServiceList). Future development of the architecture will be driven from that point of view (see ServicesModel).

-- TonyLinde - 04 Sep 2002

Topic attachments
I Attachment Action Size Date Who Comment
gifgif BrownDwarfSelection.gif manage 49.8 K 2002-08-08 - 12:30 DavidGiaretta Sequence diagram from Together
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Topic revision: r10 - 2002-10-23 - 16:19:30 - ElizabethAuden
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