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Published May 1, 2008 | Published
Journal Article Open

The 'DODO' survey - I. Limits on ultra-cool substellar and planetary-mass companions to van Maanen's star (vMa2)

Abstract

We report limits in the planetary-mass regime for companions around the nearest single white dwarf to the Sun, van Maanen's star (vMa2), from deep J-band imaging with Gemini North and Spitzer Infrared Array Camera (IRAC) mid-IR photometry. We find no resolved common proper motion companions to vMa2 at separations from 3 to 45 arcsec, at a limiting magnitude of J≈ 23. Assuming a total age for the system of 4.1 ± 1 Gyr, and utilizing the latest evolutionary models for substellar objects, this limit is equivalent to companion masses >7 ± 1 MJup(Teff≈ 300 K). Taking into account the likely orbital evolution of very low mass companions in the post-main-sequence phase, these J-band observations effectively survey orbits around the white dwarf progenitor from 3 to 50 au. There is no flux excess detected in any of the complimentary Spitzer IRAC mid-IR filters. We fit a white dwarf model atmosphere to the optical BVRI, JHK and IRAC photometry. The best solution gives Teff= 6030 ± 240 K, log g= 8.10 ± 0.04 and, hence, M= 0.633 ± 0.022 M⊙. We then place a 3σ upper limit of 10 ± 2 MJup on the mass of any unresolved companion in the 4.5 μm band.

Additional Information

© 2008 The Authors. Journal compilation © 2008 RAS. Accepted 2008 January 21. Received 2008 January 18; in original form 2007 December 19. Published Online: 5 March 2008. MB acknowledges receipt of a STFC Advanced Fellowship. EH acknowledges the support of a STFC Postgraduate Studentship. This work is supported in part by the NSERC Canada. PB is a Cottrell Scholar of Research Corporation. Based in part on observations obtained at the Gemini Observatory. We thank Isabelle Baraffe and Jay Farihi for their enlightening thoughts and comments.

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