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

journal contribution
posted on 2023-05-17, 14:25 authored by Casewell, SL, Burleigh, MR, Wynn, GA, Alexander, RD, Napiwotzki, R, Lawrie, KA, Dobbie, PD, Jameson, RF, Hodgkin, ST
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.

History

Publication title

Astrophysical Journal Letters

Volume

759

Article number

L34

Number

L34

Pagination

1-5

ISSN

2041-8205

Department/School

School of Natural Sciences

Publisher

Institute of Physics Publishing Ltd.

Place of publication

United Kingdom

Rights statement

Copyright 2012 The American Astronomical Society.

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the physical sciences

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