2004ApJ...600L..71M -
Astrophys. J., 600, L71-L73 (2004/January-1)
A substellar companion to van Maanen 2.
MAKAROV V.V.
Abstract (from CDS):
The Hipparcos data for the nearest white dwarf van Maanen 2 (=HIP 3829; distance of 4.4 pc) indicate astrometric binarity, in that the proper motion has a large first derivative not accounted for as a perspective acceleration due to changing distance. The presence of a companion was suspected, but never demonstrated, from the pre-Hipparcos astrometric measurements of photographic plates. Inspection of a digital position probability chart based on the Hipparcos Intermediate Astrometry Data reveals a pendulum-like motion of the photocenter mostly in the east-west direction with a period of about 1.5 yr. Having this period as an initial constraint, an orbital fit was obtained with the following parameters: a0=27 mas, P=1.57 yr, i=89°, ω=95°, Ω=92°, and T0=1991.26. Assuming a mass of 0.83 M☉for the primary white dwarf, the mass of the secondary is 0.08 M☉. Covariance analysis shows, however, that the uncertainty of the semimajor axis estimate and, subsequently, of the mass estimate is great for this nearly edge-on orbit. A more robust estimate is obtained for the semiminor axis, providing a lower bound mass of the companion of 0.06±0.02 M☉.
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Journal keyword(s):
Astrometry - Stars: Binaries: General - Stars: Individual: Name: van Maanen 2 - Stars: Low-Mass, Brown Dwarfs - Stars: White Dwarfs
Simbad objects:
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