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Authors: Casewell, Sarah L.
Burleigh, M. R.
Wynn, G. A.
Alexander, R. D.
Napiwotzki, R.
Lawrie, K. A.
Dobbie, P. D.
Jameson, R. F.
Hodgkin, S. T.
First Published: 23-Oct-2012
Publisher: IOP Publishing LTD
Citation: Astrophysical Journal Letters, 2012, 759 (2), L34
Abstract: 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 ~0.006 AU) 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 ~2 AU, 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.
DOI Link: 10.1088/2041-8205/759/2/L34
ISSN: 2041-8205
eISSN: 2041-8213
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2012. The American Astronomical Society. All rights reserved. The file associated with this record is distributed under the Creative Commons “Attribution Non-Commercial No Derivatives” licence, further details of which can be found via the following link:
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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