WD0837+185: THE FORMATION AND EVOLUTION OF AN EXTREME MASS-RATIO WHITE-DWARF-BROWN-DWARF BINARY IN PRAESEPE

Journal Article · Sat Nov 10 04:00:00 EST 2012 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/759/2/L34· OSTI ID:22078442

Casewell, S L; Burleigh, M R; Wynn, G A; Alexander, R D; Lawrie, K A; Jameson, R F ^[1]; Napiwotzki, R ^[2]; Dobbie, P D ^[3]

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1. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)
2. Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom)
3. School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania 7001 (Australia)

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 {approx}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{sub Sun} (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 {approx}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 ({alpha}) and binding energy parameters ({lambda}) for the AGB star to {alpha}{lambda} {approx} 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.

• OSTI ID: 22078442
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 759; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASYMPTOTIC SOLUTIONS
BINARY STARS
BINDING ENERGY
GALACTIC EVOLUTION
MASS
ORBITS
STAR CLUSTERS
SUN
WHITE DWARF STARS