Journal Article

Discovery of a widely separated ultracool dwarf–white dwarf binary

A. C. Day-Jones, D. J. Pinfield, R. Napiwotzki, B. Burningham, J. S. Jenkins, H. R. A. Jones, S. L. Folkes, D. J. Weights and J. R. A. Clarke

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 388, issue 2, pages 838-848
Published in print August 2008 | ISSN: 0035-8711
Published online July 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13455.x
Discovery of a widely separated ultracool dwarf–white dwarf binary

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We present the discovery of the widest known ultracool dwarf–white dwarf binary. This binary is the first spectroscopically confirmed widely separated system from our target sample. We have used the Two-Micron All-Sky Survey (2MASS) and SuperCOSMOS archives in the southern hemisphere, searching for very widely separated ultracool dwarf–white dwarf binaries, and find one common proper motion system, with a separation of 3650–5250 au at an estimated distance of 41–59 pc, making it the widest known system of this type. Spectroscopy reveals 2MASS J0030−3740 is a DA white dwarf with Teff= 7600 ± 100 K, log(g) = 7.79–8.09 and MWD= 0.48–0.65 M. We spectroscopically type the ultracool dwarf companion (2MASS J0030−3739) as M9 ± 1 and estimate a mass of 0.07–0.08 M, Teff= 2000–2400 K and log(g) = 5.30–5.35, placing it near the mass limit for brown dwarfs. We estimate the age of the system to be >1.94 Gyr (from the white dwarf cooling age and the likely length of the main-sequence lifetime of the progenitor) and suggest that this system and other such wide binaries can be used as benchmark ultracool dwarfs.

Keywords: binaries: general; stars: low-mass, brown dwarfs; white dwarfs

Journal Article.  7499 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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