Crescent Mercury from MESSENGER

Image credit and detail

It is said that the astronomer Copernicus never saw the elusive planet Mercury, so perhaps it is not so surprising that modern day astronomers had to wait a long time before the first observational confirmation of both brown dwarfs and extrasolar planets in 1995, although while planets around other stars had been postulated for centuries, the idea of a brown dwarf first hit the science stands only in 1963.


Today I want to mention two ongoing research efforts, one using the radial velocity method and the other an unusual direct imaging technique. The MARVELS survey is one of four efforts which form the third phase of the Sloan Digital Sky Survey (SDSS III). This ongoing project will monitor the radial velocities of 11,000 bright stars over six years and be able to detect giant planets in orbits with periods of two years or less. One aim of the project is to investigate the so-called ‘brown dwarf desert’, an apparent paucity of these objects in close binary orbit around main sequence stars when compared to low-mass stellar companions. One brown dwarf companion has a minimum mass around 28 Jupiter masses and orbits a slightly evolved F9 star roughly every six days. A further similar discovery was announced today, a forty Jupiter mass object in an eccentric 13 day orbit around a G0 subgiant.

The Lucky imaging technique exploits extremely short exposure times to ‘freeze’ atmospheric (seeing) disturbances to obtain resolutions near the diffraction limit from ground-based telescopes. In a recent paper new low mass companions have been found in a sample of 451 late K and M stars, constraining the binary fraction in this regime to around 20%.

Those interested in the pre-1995 history of seeking brown dwarfs should refer to this presentation by Rafael Rebolo, one of the leaders in the field, and review articles by Gibor Basri (2000), Oppenheimer et al. (2000) and Kumar (2002).

The Planets around Low Mass Stars (PALMS) collaboration has published two discoveries relevant to the ‘brown dwarf desert’ question, using high contrast adaptive optics imaging on Keck and Subaru. The second is a good candidate for a near-future dynamical mass measurement.

Update: MARVELS-6b is a newly discovered 32 Jupiter mass object in a 47 day orbit around a solar-type star with an age less than 6 Gyr.


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