Brown Dwarf Science Problem Ideas Revised

TonyLinde, AnitaRichards, and ElizabethAuden spoke with Roy Williams, Bob Mann, and Sean Bechhofer about constructing a "narrow slice" ontology for the BrownDwarf science problem. These are the ideas that came out of the discussion based on Elizabeth's notes, expanded by Anita. Updated Mar 2003 to support Registry discussion.

Each step is either a RegistryQuery, a DataSetQuery/Evaluation or DataProcessing. User could mean human issuing explicit instructions, or agent using library criteria for identifying Brown Dwarfs or performing components of the process e.g. calculating proper motions.

Catalogues / Archives to include:

• 2MASS
• APMCAT
• SDSS
• USNO-B1.0

for initial selection. It may be essential at some stages of the query to access catalogues not held by AstroGrid (presumably via Vizier) and to access the SIMBAD name resolver, and if this is not possible such stages should initially be omitted or user-supplied data used. E.g., if catalogues of clusters are not yet directly accessible by AstroGrid, at step 1., use preselected list of clusters and go straight to 3. Eventually some stages could also use nDim data (e.g. spectra, images) but that is not essential to the operation of any stage (although few results may be returned from caalogues alone).

1. RegistryQuery for potential Brown Dwarfs located in Galactic Clusters:

   INPUT: User Criteria.
   Select catalogues containing measurements of:

   • Explicitly identified Galactic Stellar CLUSTERS (e.g. open clusters, but not globular clusters nor clusters of galaxies) and/or MEMBERs of such clusters.
   • IDENTIFIER for each cluster or member object (this would probably be a position or region but might be any ID which SIMBAD can translate into a position e.g. Gleise number?).
   also separately
   • All catalogues listing STELLAR TYPE or possibly more fine-grained category covering BROWN DWARF
   OUTPUT: List of catalogues

2. DataSetQuery/Evaluation to select Galactic Stellar Clusters and known Brown Dwarfs

   INPUT: List of catalogues from 1. and user list of data to be extracted:

   • POSITIONs or other ID of CLUSTERs or MEMBERS
   • EPOCH of position measurement, where given
     • Information used to find solid angle for CONE SEARCH
       • ERROR in position, where given - if not, adopt default.
       • ANGULAR or SPATIAL SIZE of cluster, where given
   • MEMBERS or objects lying within CLUSTERs already classified as BROWN DWARFs. These might be removed from further investigation (to save time) or left in to act as a control sample.
   OUTPUT: MySpace list of the above data:

3. RegistryQuery for existing proper motion and distance measurements

   INPUT: Catalogues already selected in 1. and those with entries meeting these criteria:

   • SKY COVERAGE overlapping positions from 2.
   • and DATA ON STARS or mixed or unspecified objects (i.e. catalogue is not restricted to galaxies);
   and within these:
   • Stellar ID or positions;
   • Proper motion
   • and/or Distance (NB this may be parallax or Distance Modulus).
   OUTPUT: List of catalogues

4. DataSetQuery/Evaluation to get definative list of cones:

   INPUT: Catalogues selected from 3. and list from 2.

   Use list from 2. to find catalogue entries with matching IDs or perform CONE SEARCH around position of CLUSTER/OBJECT/ID, or position of stellar ID, angular size of cone derived using Cluster Size or Object Position Uncertainty where given, or AstroGrid defaults, plus crude and generous proper motion allowance default (**check using Hipparcos cata?). Also extract

   • DISTANCE plus uncertainty if given
   • PROPER MOTION plus uncertainty if given
   Initially these may not be in catalogue directly accessed by AstroGrid.
   
   • If distance but not proper motion is available a typical upper limit of proper motion as a function of distance is adopted. The upper limits to proper motions - as above or measurement plus uncertainty - are then used to reduce the size of the cone for each object and reduce ambiguous matches.
   • Where there are unambiguous matches extract position errors, if higher accuracy is available use to improve position accuracy/search cone size.
   The user may, now or later, choose to reject all objects which are too distant using either or both of these criteria - either setting a priori limits or deriving them using results from later stages:
   • Too distant to obtain proper motion measurement (the converse does not apply, some nearby Brown Dwarfs may have negligible proper motions);
   • Too distant to be detected if they were Brown Dwarfs.
   OUTPUT: MySpace list of objects within Galactic Stellar Clusters with a position (direct or via ID) for each object, and additional information (distance etc. as listed above). In addition calculate a cone search radius (for later steps) which is a combination of the position measurement uncertainty and a time-dependent proper motion allowance if available at this stage. In addition the user may retain the regions covering Clusters/Members without catalogued distances/proper motions.

5. RegistryQuery to enable colour-colour selection:

   INPUT: Catalogues in MySpace list from 4. and possibly additional image or other DataSets containing

   • Sky Coverage covering position or stellar ID within cones from 4. and in both cases
     • PHOTOMETRY in I R or K optical/uv WAVELENGTH BANDS or COLOUR

   OUTPUT: list of catalogues/DataSets meeting 1st criterion and meeting both criteria, and photometry measurements etc for each candidate.

6. DataSetQuery/Evaluation to perform ColourCut

   INPUT DataSets meeting both criteria from 5. and cone search parameters from 4.

   and selection criteria below: (how do we select between duplicate information?)

   • Select objects meeting cone search parameters from 4.
   • 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?)
   • Extract I R and K flux density measurements (and uncertainties if possible) - reject object if all three not available (not necessarily in same catalogue but need information to make comparisons between different photometric systems - filter characteristics (bandpasses), zero-points etc. or defaults)
   • Extract date or possible range of dates of observation
   • Extract PROPER MOTION/DOPPLER VELOCITY/DISTANCE information if in photometric catalogue.

   OUTPUT MySpace catalogue of values of parameters for each candidate

7. DataProcessing for Sample Selection:

   INPUT MySpace catalogue of objects from 4. and cone search parameters from 6.

   • Possibly exclude objects which are too bright for given distance to be Brown Dwarfs
   • Select objects which have measurements in all 3 bands above (use POSITION, PROPER MOTION, DOPPLER 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

8. RegistryQuery to enable Proper Motion measurement

   INPUT: MySpace list of candidates from 7. and catalogues according to:

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

   User might want to exclude objects with existing catalogued proper motions (found at stage ?) or keep these in as a control, or keep in proper motion measurments with large errors to improve accuracy.

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

9. DataSetQuery/Evaluation to obtain proper motions

   INPUT catalogues from 8. and MySpace list of candidates from 7. plus criteria:

   • Measurements exist at at least 2 EPOCHS (? in same FREQUENCY BAND?)
   • POSITION on DATE
   • 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

10. DataProcessing for sample selection based on proper motions

    INPUT data from 9. in MySpace list of candidates

    Compare positions of objects at 2 or more epochs and measure proper motions. Use photometry, Doppler velocity etc. to resolve ambiguous matched. Merge with list of catalogued proper motions (fount at step 4.). 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 colours and proper motion measurements meeting Brown Dwarf criteria.

11. RegistryQuery for information about composition of sample:

    INPUT MySpace Lists of candidate brown dwarfs from 10.

    Criteria:

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

    OUTPUT catalogues meeting above criteria

12. DataSetQuery/Evaluation to select on basis of chemical composition

    INPUT DataSets from 11, MySpace catalogue of candidates, possibly Chemical Spectral Templates if spectra are used.

    • Extract measurements of ABUNDANCE/DETECTION at positions of candidates
    • Extract errors in above
    • Extract POSITION ACCURACY, RESOLUTION and DATE information if present
    • Extract PROPER MOTION, DOPPLER 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

13. DataProcessing sample ranking based on results so far

    INPUT MySpace catalogue from 6, 10, 12

    Mark objects which are associated with e.g. an Li detection within a priori limits. Use POSITION/DATE and DOPPLER VELOCITY and PROPER MOTION/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.

-- AnitaRichards - 03 Mar 2003