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Astrometric detection and characterization of brown dwarfs

Published online by Cambridge University Press:  01 October 2007

R.-D. Scholz ,
M. J. McCaughrean ,
S. Röser  and
E. Schilbach
R.-D. Scholz
Affiliation:
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D–14482 Potsdam, Germany email: [email protected]
M. J. McCaughrean
Affiliation:
University of Exeter, School of Physics, Stocker Road, Exeter EX4 4QL, UK email: [email protected]
S. Röser
Affiliation:
Astronomisches Rechen-Institut, Mönchhofstraße 12-14, D–69120 Heidelberg, Germany email: [email protected], [email protected]
E. Schilbach
Affiliation:
Astronomisches Rechen-Institut, Mönchhofstraße 12-14, D–69120 Heidelberg, Germany email: [email protected], [email protected]
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Abstract

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As a result of failed star formation, brown dwarfs (BDs) do not reach the critical mass to ignite the fusion of hydrogen in their cores. Different from their low-mass stellar brothers, the red dwarfs, BDs cool down with their lifetime to very faint magnitudes. Therefore, it was only about 10 to 20 years ago that such ultracool objects began to be detected. Accurate astrometry can be used to detect them indirectly as companions to stars by the signature of the so-called astrometric wobble. Resolved faint BD companions of nearby stars can be identified by their common proper motion (CPM). A direct astrometric detection of the hidden isolated BDs in the Solar neighborhood is possible with deep high proper motion (HPM) surveys. This technique led to the discovery of the first free-floating BD, Kelu 1, and of the nearest BD, ε Indi B. Both were meanwhile found to be binary BDs. The astrometric orbital monitoring of ε Indi Ba+Bb, for which we know an accurate distance from the Hipparcos measurement of its primary, ε Indi A, will allow the determination of individual masses of two low-mass BDs. Hundreds of BDs have been identified for the last decade. Deep optical sky survey (SDSS) and near-infrared sky surveys (DENIS, 2MASS), played a major role in the search mainly based on colours, since BDs emit most of their light at longer wavelengths. However, alternative deep optical HPM surveys based on archival photographic data are not only sensitive enough to detect some of the nearest representatives, they do also uncover many of the rare class of ultracool halo objects crossing the Solar neighborhood at large velocities. SSSPM 1444, with the extremely large proper motion of 3.5 arcsec/yr, is one of the nearest among these subdwarfs with masses at the substellar boundary. We present preliminary parallax results for this and two other ultracool subdwarfs (USDs) from the Calar Alto Omega 2000 parallax program.

Keywords

astrometrysurveysstars: low-massbrown dwarfsbinaries: generalstars: distancesstars: kinematicssubdwarfssolar neighborhoodGalaxy: halo
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S248: A Giant Step: from Milli- to Micro-arcsecond Astrometry , October 2007 , pp. 30 - 35
Copyright
Copyright © International Astronomical Union 2008

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