ScienceProblem: BrownDwarfSelection

PrimaryActor:

Astronomer

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ScienceGoal:

Learn about the lower end to the stellar mass function by conducting a census of all brown dwarfs within, say, 1kpc of the sun, selected on the basis of their colours and their proper motions.

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DataSets:

Currently, using near-infrared data from 2MASS and optical data from APMCAT (Schmidt telescope photographic plates scanned by the APM machine at Cambridge). This is now being supplemented by optical data from the Sloan Digital Sky Survey, and, in a few years, much deeper near-infrared data from the UKIDSS survey will be available for use. VISTA programmes will also address this issue.

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ProblemDescription:

A key question in the area of star formation is the form of the stellar mass function at the lower end - i.e. what is the contribution of brown dwarfs to the stellar mass budget?

Brown dwarfs are intrinsically faint and rare objects, so their detection is not straightforward. It can be done, however, through a combination of selection criteria using colour and proper motion information. Colour selection is the more important, because brown dwarfs populate a well-defined photospheric temperature range (although the coolest brown dwarfs have unusual spectral energy distributions, peaking around 1 micron, due to the absorption of near-infrared continuum flux by water and methane), but proper motion selection can help, too, since any detectable brown dwarfs must be nearby and, so, on average, they will have relatively high proper motions.

The use of wide field optical/near-IR survey's to localise Brown Dwarfs is discussed by Basri, 2000, his Figure 7 shows the colour magnitude diagram for low mass Pleiades members.

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CurrentSolution:

Currently, running the relatively complex colour/motion selection criteria required here is only possible for those with local access to some of the relevant databases and with the patience to download significant quantities of data from other datasets to a local workstation. This is neither very democratic, nor scalable to the next generation of relevant datasets (e.g. the full Sloan Digital Sky Survey and UKIDSS).

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VOSolution:

This is a very generic VO problem (see the HaloWhiteDwarfs ScienceProblem for an analogous application), since it requires the ability to make queries combining attributes of astronomical objects stored in different databases. In fact, this is all that is required: the result-sets from such queries will be quite small (probably only thousands of objects), so their analysis can be performed on the user's own workstation, once the brown dwarfs have been found.

One slight complication here is the requirement for proper motion selection, which means that the database federations must be queryable on time and position together, in some manner, rather than simply on position.

The resulting brown dwarf sample data sets can then be used as input into spectrscopic conformation programmes, confirming the nature of the objects by means of tests such as the 'Lithium Test' (see Martin et al, 2000).

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Iteration Breakdown:

• BrownDwarfRoughNotes

-- AnitaRichards - 12 Jan 2004

• Astrogrid.Itn04BrownDwarfSelection - science workflow for case in Iteration 04
• Astrogrid.Itn06BrownDwarfSelection - science workflow for case in Iteration 06
• Astrogrid.Itn08BrownDwarfSelection - science workflow for case in Iteration 08

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KeyReferences:

Basri, G, 2000 ARA&A, 38, 485, 'Observations of Brown Dwarfs'

Nigel Hambly (IfA, Edinburgh), private communication

Hambly N.C., Hodgkin S.T., Cossburn M.R., Jameson R.F., 1999, MNRAS, 303, 835

Martin et al, 2000, 543, 299, 'Membership and Multiplicity among Very Low Mass Stars and Brown Dwarfs in the Pleiades Cluster'

Interesting reference about identifying brown dwarfs through lithium and methane lines: http://clavius.as.arizona.edu/ssn/ssn29.txt (Search for "Background" in the text).

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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 Science Problems Forum. For other ScienceProblems, refer to the ScienceProblemList.
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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This will be a key AG science driver - most data sets exist and are held at core UK sites. Science is still likely to be topical in 3 years.

-- NicholasWalton - 17 Apr 2002

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UseCaseDesign:

BrownDwarfSelectionSD sequence diagramme

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-- NicholasWalton - 24 Jan 2002