Paper: astro-ph/0509165
Date: Wed, 7 Sep 2005 12:17:56 GMT (55kb)

Title: Low Mass Companions to White Dwarfs

Authors: J. Farihi, B. Zuckerman, & E.E. Becklin

Comments: 4 pages with figures, accepted as part of a special issue of AN
dedicated to the proceedings of the workshop "Ultralow Mass Star Formation
and Evolution" held in La Palma, Spain during June/July 2005
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This paper summarizes the results of over 17 years of work searching for low
mass stellar and substellar companions to more than 370 nearby white dwarfs.
Roughly 60 low mass, unevolved companions were found and studied all together,
with over 20 discovered in the last few years, including the first unambiguous
brown dwarf companion to a white dwarf, GD 1400B. The resulting spectral type
distributions for companions to white dwarfs and nearby cool field dwarfs are
compared, and the implications for binary star formation are discussed. A brief
analysis of GD 1400B, including new data, is also presented

\\ ( http://arXiv.org/abs/astro-ph/0509165 , 55kb)

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Paper: astro-ph/0509188
Date: Wed, 7 Sep 2005 18:10:45 GMT (35kb)

Title: Excess Infrared Radiation from a Massive DAZ White Dwarf: GD362 - a
Debris Disk?

Authors: Mukremin Kilic, Ted von Hippel (Texas), S. K. Leggett (JAC), and D. E.
Winget (Texas)

Comments: Accepted for publication in ApJ Letters
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We report the discovery of excess K-band radiation from a massive DAZ white
dwarf star, GD362. Combining infrared photometric and spectroscopic
observations, we show that the excess radiation cannot be explained by a
stellar or substellar companion, and is likely to be caused by a debris disk.
This would be only the second such system known, discovered 18 years after
G29-38, the only single white dwarf currently known to be orbited by
circumstellar dust. Both of these systems favor a model with accretion from a
surrounding debris disk to explain the metal abundances observed in DAZ white
dwarfs. Nevertheless, observations of more DAZs in the mid-infrared are
required to test if this model can explain all DAZs.

\\ ( http://arXiv.org/abs/astro-ph/0509188 , 35kb)

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Paper: astro-ph/0509193
Date: Wed, 7 Sep 2005 18:50:12 GMT (20kb)

Title: A Dusty Disk Around GD 362, a White Dwarf With a Uniquely High
Photospheric Metal Abundance

Authors: E.E. Becklin, J. Farihi, M. Jura, Inseok Song, A. J. Weinberger, B.
Zuckerman

Comments: 12 pages, 2 figures. ApJ Letters, in press
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Eighteen years after an infrared excess was discovered associated with the
white dwarf G29-38, we report ground-based measurements (JHKL'N') with
mJy-level sensitivity of GD 362 that show it to be a second single white dwarf
with an infrared excess. As a first approximation, the excess around GD 362,
which amounts to about 3% of the total stellar luminosity, can be explained by
emission from a passive, flat, opaque dust disk that lies within the Roche
radius of the white dwarf. The dust may have been produced by the tidal
disruption of a large parent body such as an asteroid. Accretion from this
circumstellar disk could account for the remarkably high abundance of metals in
the star's photosphere.

\\ ( http://arXiv.org/abs/astro-ph/0509193 , 20kb)