Discovery of an Ultracool White Dwarf Companion

Abstract

The discovery of a low luminosity common proper motion companion to the white dwarf GD392 at a wide separation of $46^{\prime \prime }$ is reported. $BVRI$ photometry suggests a low temperature ($T_{\mathrm{eff}}\sim 4000$ K) while $JHK$ data strongly indicate suppressed flux at all near infrared wavelengths. Thus, GD392B is one of the few white dwarfs to show significant collision induced absorption due to the presence of photospheric ${\mathrm{H}}_2$ and the first ultracool white dwarf detected as a companion to another star. Models fail to explain GD392B as a normal mass white dwarf. If correct, the cool companion may be explained as a low mass white dwarf or unresolved double degenerate. The similarities of GD392B to known ultracool degenerates are discussed, including some possible implications for the faint end of the white dwarf luminosity function.

27 pages, 9 figures, 4 tables, re-accepted to ApJ after some revision

References in corpus (3)

• The USNO-B Catalog
• Model Atmosphere Analysis of Two Very Cool White Dwarfs
• A Critical Examination of Halo White Dwarf Candidates

Cited by in corpus (12)

• Low Luminosity Companions to White Dwarfs
• Discovery of New Ultracool White Dwarfs in the Sloan Digital Sky Survey
• The white dwarf luminosity function
• Toward a Spectroscopic Census of White Dwarfs Within 40 parsecs of the Sun
• Additional Ultracool White Dwarfs Found in the Sloan Digital Sky Survey
• A Nearby Old Halo White Dwarf Candidate from the Sloan Digital Sky Survey
• The Mystery Deepens: Spitzer Observations of Cool White Dwarfs
• The ultra-cool white dwarf companion of PSR J0751+1807
• Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample
• Photometric Identification of Cool White Dwarfs
• Common Proper Motion Wide White Dwarf Binaries Selected From The Sloan Digital Sky Survey
• Cool Versus Ultracool White Dwarfs