Brown Dwarf Science Problem Ideas Expanded

TonyLinde, AnitaRichards, and ElizabethAuden spoke with Roy Williams, Bob Mann, and Sean Bechhofer about constructing a "narrow slice" ontology for the Brown Dwarf science problem. These are the ideas that came out of the discussion based on Elizabeth's notes, expanded by Anita:

Catalogues / Archives to include:

  • 2MASS
  • SDSS
  • USNO-B1.0
for initial selection, plus catalogues/nDim datasets e.g. images for further measurements

1. Query Registry for potential Brown Dwarfs located in Galactic Clusters: (i.e. compare metadata about coverage etc. of entire catalogues/nDim data sets)

If catalogues of clusters are not yet directly accessible by AstroGrid, use preselected list of clusters and go straight to 3.

User INPUT: catalogues contain measurements of

  • Explicitly identified Galactic Stellar CLUSTERS (e.g. open clusters, but not globular clusters nor clusters of galaxies).
  • DISTANCE (or could this selection be applied at stage 2.?)

OUTPUT: List of catalogues

2. Query Catalogues (i.e. compare metadata about contents of each column in a catalogue(which might include info inherited from header), and evaluate contents of columns) INPUT: List of catalogues from 1. and criteria:

OUTPUT: MySpace list of:

  • within DISTANCE of (e.g.) 1 kpc (optional at this stage)
  • ANGULAR or SPATIAL SIZE of cluster, where given
  • CLUSTER/member VELOCITY, if given
  • ERRORS in above quantities, where given

3. Query Registry to enable colour-colour selection:

Criteria: catalogues or datasets (INPUT: MySpace list from 1.) containing

  • Data on stars or mixed or unspecified objects (i.e. catalogue is not restricted to galaxies)
  • Data at POSITIONS of CLUSTER LIST extracted from 2.

Some objects may have already catalogued COLOURs or proper motions which could also be fed into workflow? Might catalogues contain colours but not direct photometry?

OUTPUT: list of catalogues

4. Query Catalogues/datasets from 3.:

INPUT catalogues from 3. and MySpace list of cluster parameters

and selection criteria below:

Some astrometric and photometric alignment required in order to get secure IDs and sufficinetly accurate colours - ADD any required metadata after consultation. For example, if some objects alrady have catalogued proper motion?

Also how do we select between duplicate information?

  • Exclude objects classified as galaxies in mixed catalogues, or which can be identified as galaxies in nDim images (How? Just 'extended'? Or do we rely on them falling out of the later colour selection or proper motion selection?)
  • Cone search on basis of POSITIONS from 2.; use ANGULAR SIZE of cluster (based on SPATIAL SIZE/DISTANCE if necessary) and/or POSITION ERRORS or DEFAULT.
  • Extract I R and K flux density measurements - reject object if all three not available
  • Extract date of observation if available
  • Extract errors in all above quantities if available
  • Extract VELOCITY/DISTANCE information if available

VELOCITY can mean along line of sight, proper motion, or full 3D velocity estimates.

ID - If use position-based need search cone due to proper motion.

OUTPUT MySpace catalogue of values of parameters for each candidate

5. Sample Selection from list of objects and measurements from 4.:

INPUT MySpace catalogue of objects from 4.

  • Select objects which have measurements in all 3 bands above (use POSITION VELOCITY and DISTANCE information to aid in identification.)

Call library function to make colour-colour plot from flux density measurements and select objects which are in user-defined Brown Dwarf region (eventually could be VO definition?). This is known as a ColourCut (maybe an expert can define please?) and provides a list of Brown Dwarf candidates.

OUTPUT MySpace list of candidates meeting colour cut criteria

6. Query Registry to enable Proper Motion measurement

INPUT: MySpace list of candidates from 5. and catalogues according to:

Criteria: catalogues or datasets (starting with selection from 1. and 3.) contain

  • Data on stars or mixed or unspecified objects (i.e. catalogue is not restricted to galaxies)
  • Data at POSITIONS of Brown Dwarf CANDIDATE LIST


  • Proper motion measurements if they exist May not initially be in catalogue directly accessed by AstroGrid


  • POSITION measurements
  • DATE of observation
  • ERRORs or ranges in above, or some means of assigning errors (e.g. from characteristics of telescope catalogues elsewhere).
  • FREQUENCY BAND of observation is specified

(question - BD are not resolved so does it actually matter for measuring proper motion what the wavelength is? Is this required so that a particular BD can be identified even if it has moved, by assuming that it will still have the same brightness at a given wavelength?)

OUTPUT: list of catalogues containing parameters for candidates as specified above. MySpace catalogue of candidates with ready-made proper motions added.

7. Query catalogues/datasets from 6.

INPUT catalogues from 6. and MySpace list of candidates plus criteria:

  • Measurements exist at at least 2 EPOCHS (? in same FREQUENCY BAND?)
  • ERRORS in the above

ERRORs must be in specified ranges, but this might be decided dynamically, e.g. worse errors could be tolerated for 3 observations 20 yr apart than for two observations 2 yr apart.

OUTPUT MySpace catalogue of candidate Brown Dwarf identifiers (position with cone due to error and proper motion) and lists of positions at multiple epochs where extracted as above.

8. Sample Selection from data from 7.

INPUT catalogue from 7. and MySpace list of candidates

If no ready-made proper motion: compare positions of objects at 2 or more epochs and measure proper motions. Objects with proper motions exceeding an a priori value (depending on distance or expressed in absolute units) are selected as strong Brown Dwarf candidates. Does the proper motion have to be compared with the overall cluster proper motion, if known?

OUTPUT MySpace List of objects with proper motion measurements

9. Query Registry for information about composition of sample:

INPUT MySpace Lists of candidate brown dwarfs


  • Catalogues/Datasets contain data at positions of lists.
  • Catalogues/Datasets contain measurements or detections of Li, CH4 or other Brown Dwarf diagnostics

OUTPUT catalogues meeting above criteria

10. Query catalogues/datasets from 9.

INPUT catalogues from 9, MySpace catalogue of candidates

  • Extract measurements of ABUNDANCE/DETECTION at positions of candidates
  • Extract errors in above
  • Extract POSITION ACCURACY, RESOLUTION and DATE information if present
  • Extract VELOCITY or DISTANCE information if present

OUTPUT MySpace catalogue of Brown Dwarf candidates with additional information on Li, CH4 etc.

This may involve exporting list to query catalogues not initially directly accessible to AstroGrid

11. Sample ranking based on results from 10.

INPUT MySpace catalogue from 10

Mark objects which are associated with e.g. an Li detection within a priori limits. Use POSITION/DATE and VELOCITY/DISTANCE information to asses how secure the association is.

OUTPUT Return list of Brown Dwarf candidates with probabilities that each object is a Brown Dwarf...

Many things contribute to the accuracy of this list:

  • Accuracy of identifying the same object at different wavebands/epochs
  • Accuracy of photometry
  • Accuracy of position measurements
  • Accuracy of model
    • how unique are Brown Dwarf colours?
    • not all Brown Dwarfs have a high proper motion?

etc. etc.

Tests of accuracy:

  • Compare with list of well-identified brown dwarfs.
  • User plots properties of candidates and investigates any outliers or suspicious IDs

Thus AstroGrid must enable these, in particular that there should be full access to the history of catalogues queried etc.

I imagine that until the VO gets some very clever library functions, the crossIDing of objects at different epochs with high proper motions will have to be confirmed by the user - this will affect stage 7. and possibly even stage 4.

-- AnitaRichards - 28 Oct 2002

Topic revision: r4 - 2002-11-13 - 15:34:00 - AnitaRichards
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