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WD0837+185: The formation and evolution of an extreme mass-ratio white-dwarf-brown-dwarf binary in praesepe


Casewell, SL and Burleigh, MR and Wynn, GA and Alexander, RD and Napiwotzki, R and Lawrie, KA and Dobbie, PD and Jameson, RF and Hodgkin, ST, WD0837+185: The formation and evolution of an extreme mass-ratio white-dwarf-brown-dwarf binary in praesepe, Astrophysical Journal Letters, 759, (2) Article L34. ISSN 2041-8205 (2012) [Refereed Article]

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Copyright Statement

Copyright 2012 The American Astronomical Society.

DOI: doi:10.1088/2041-8205/759/2/L34


There is a striking and unexplained dearth of brown dwarf companions in close orbits (<3 AU) around stars more massive than the Sun, in stark contrast to the frequency of stellar and planetary companions. Although rare and relatively short-lived, these systems leave detectable evolutionary end points in the form of white-dwarf-brown-dwarf binaries and these remnants can offer unique insights into the births and deaths of their parent systems. We present the discovery of a close (orbital separation ~0.006AU) substellar companion to a massive white dwarf member of the Praesepe star cluster. Using the cluster age and the mass of the white dwarf, we constrain the mass of the white dwarf progenitor star to lie in the range 3.5-3.7 M⊙ (B9). The high mass of the white dwarf means the substellar companion must have been engulfed by the B star's envelope while it was on the late asymptotic giant branch (AGB). Hence, the initial separation of the system was ~2AU, with common envelope evolution reducing the separation to its current value. The initial and final orbital separations allow us to constrain the combination of the common envelope efficiency (α) and binding energy parameters (λ) for the AGB star to αλ ~ 3. We examine the various formation scenarios and conclude that the substellar object was most likely captured by the white dwarf progenitor early in the life of the cluster, rather than forming in situ.

Item Details

Item Type:Refereed Article
Keywords:binaries: close; brown dwarfs; white dwarfs
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Stellar astronomy and planetary systems
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Dobbie, PD (Dr Paul Dobbie)
ID Code:80973
Year Published:2012
Web of Science® Times Cited:25
Deposited By:Mathematics and Physics
Deposited On:2012-11-19
Last Modified:2013-06-28

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