ScienceProblem: HaloWhiteDwarfs

PrimaryActor:

Research astronomer

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ScienceGoal:

Determine the contribution of stellar remnants to the 'missing mass' on Galactic scales.

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DataSets:

Large optical survey databases, providing multi-colour and multi-epoch information for fields at high Galactic latitude. Currently work centres on the SuperCOSMOS Sky Survey, but future work will use the Sloan Digital Sky Survey and, eventually, VISTA.

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ProblemDescription:

The rotational characteristics of the Galactic disk suggest that the Milky Way contains a hitherto-unidentified spheroidal mass component. One suggestion is that a significant fraction of this 'missing mass' might be in the form of remnants of earlier generations of stars, and one subset of such objects that might be detectable relatively easily would be a population of cool white dwarfs in the Galactic halo: in conventional models for the evolution of the Milky Way, the halo population is the oldest stellar population, and any white dwarfs that remain from such a population must be cool, on account of their age and lack of energy generation processes.

Cool white dwarfs in the Galactic halo can be found on the basis of selection criteria combining colour and proper motion information. This is similar to the case of BrownDwarfSelection but it is the proper motion selection that is more important here: being in the halo, these stars are expected to have high space velocities, which will translate (on average) to high proper motions, while colour information will help select objects with the appropriate range of photospheric temperatures (a slight complication here is that the coolest white dwarfs have unusual optical/near-infrared spectral energy distributions, as their near-infrared continuum flux can be absorbed by helium or molecular hydrogen in their atmospheres).

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CurrentSolution:

Since very large photometric catalogues have to be searched to find even a few of these rare objects, this analysis is currently pretty much restricted to those with local access to the archive data, which is not very democratic.

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VOSolution:

As with BrownDwarfSelection, the VO solution to this problem is to enable the average astronomer (i.e. not just those located at major data centres) to run complicated queries (combining colour and proper motion criteria) on large optical databases.

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KeyReferences:

Nigel Hambly (IfA, Edinburgh), private communication

Oppenheimer B.R., Hambly N.C., Digby A.P., Hodgkin S.T., Saumon D., 2001, Science, 292, 698

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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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Similar to the VO.BrownDwarfSelection case - so will be an AG driver ...

-- NicholasWalton - 17 Apr 2002

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-- BobMann - 09 Feb 2002