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On the Evolutionary History of Progenitors of EHBs and Related Binary Systems from their Observed Properties

Published online by Cambridge University Press:  09 August 2007

V.V. Pustynski
Affiliation:
Tallinn Technical University, Ehitajate tee 5, 19086, Tallinn, Estonia; Tartu Observatory, Tõravere, 61602 Estonia, e-mail: vladislav@aai.ee
I. Pustylnik
Affiliation:
Tartu Observatory, Tõravere, 61602Estonia, e-mail: izold@aai.ee
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Abstract

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It has been shown quite recently (Morales-Rueda et al. 2003) that dB stars, extreme horizontal branch (EHB) objects in high probability all belong to binary systems. We study in detail the mass and angular momentum loss from the giant progenitors of sdB stars in an attempt to clarify why binarity must be a crucial factor in producing EHB objects. Assuming that the progenitors of EHB objects belong to binaries with initial separations of a roughly a hundred solar radii and fill in their critical Roche lobes while close to the tip of red giant branch, we have found that considerable shrinkage of the orbit can be achieved due to a combined effect of angular momentum loss from the red giant and appreciable accretion on its low mass companion on the hydrodynamical timescale of the donor, resulting in formation of helium WD with masses roughly equal to a half solar mass and thus evading the common envelope stage. A simple approximative analytical formula for mass loss rate from Roche lobe filling giant donor has been proposed depending on mass, luminosity and radius of donor.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2007

References

Eggleton, P.P., 1983, ApJ 268, 368369 CrossRefGoogle Scholar
Hurley, J.R., Pols, O.R. & Tout, C.A., 2000, MNRAS 315, 543569 CrossRefGoogle Scholar
Morales-Rueda, L., Maxted, P.F.L., Marsh, T.R., North, R.C. & Heber, U., 2003, MNRAS 338, 752764 CrossRefGoogle Scholar
Pustynski, V.V. & Pustylnik, I., 2006, Acta Astronomica 56, 8495 Google Scholar
Tout, C.A. & Hall, D.S., 1991, MNRAS 253, 918 CrossRefGoogle Scholar