White Dwarfs in Ultrashort Binary Systems
White dwarf binaries are thought to be the most common binaries in the Universe: in our Galaxy their number is estimated to be as high as 108. In addition, most stars are known to be part of binary systems, roughly half of which have orbital periods short enough that the evolution of the two stars is strongly influenced by the presence of a companion. Furthermore, it has become clear from observed close binaries, that a large fraction of binaries that interacted in the past must have lost considerable amounts of angular momentum, thus forming compact binaries, with compact stellar components. The details of the evolution leading to the loss of angular momentum are uncertain, but generally this is interpreted in the framework of the so-called “common-envelope evolution”: the picture that in a mass-transfer phase between a giant and a more compact companion, the companion quickly ends up inside the giant's envelope, after which frictional processes slow down the companion and the core of the giant, causing the “common envelope” to be expelled, as well as the orbital separation to shrink dramatically .
Among the most compact binaries known, often called ultra-compact or ultra-short binaries, are those hosting two white dwarfs and classified into two types: detached binaries, in which the two components are relatively widely separated and interacting binaries, in which mass is transferred from one component to the other. In the latter class a white dwarf is accreting from a white dwarf like object (we often refer to them as AM CVn systems, after the prototype of the class, the variable star AM CVn; [56, 28]).
KeywordsOrbital Period White Dwarf Orbit Coupling Orbital Evolution Common Envelope
Unable to display preview. Download preview PDF.
- 4.V. Burwitz, and K. Reinsch: 2001, X-ray astronomy: stellar endpoints, AGN, and the diffuse X-ray background, Bologna, Italy, eds White, N. E., Malaguti, G., Palumbo, G., AIP conference proceedings, 599, 522 (2001)Google Scholar
- 8.S. Dall'Osso, G. L. Israel & L. Stella: astro-ph/0603795 (2006b)Google Scholar
- 17.G.L. Israel, M.R. Panzera, S. Campana, et al.: Astr. & Astroph. 349, L1 (1999)Google Scholar
- 18.G.L. Israel, L. Stella, W. Hummel, S. Covino and S. Campana, IAU Circ., 7835, (2002a)Google Scholar
- 28.G. Nelemans: ASP Conf. Ser. 330 – The Astrophysics of Cataclysmic Variables and Related Objects, 330, p. 27, (2005), astro-ph/0409676.Google Scholar
- 31.G. Nelemans, & P. G. Jonker: astro-ph/0605722 (2006); to appear in proceedings of “A life with stars” a conference in honour of Ed van den Heuvel's 60th birthday, New Ast. RevGoogle Scholar
- 32.G. Nelemans: AIP Conf. ser. 873 (Ed. S.M. Merkowitz, J.C. LIvas), 873, p. 397 (2007), astro-ph/0703292Google Scholar
- 37.P. Podsiadlowski , P. A. Mazzali , P. Lesaffre , C. Wolf , and F. Forster: astro-ph/0608324Google Scholar
- 43.G. Ramsay et al.: astro-ph/0610357 (2006b), to appear in Proc 15th European White Dwarf Workshop, held in Leicester Aug 7-11th 2006, and to be published by ASPGoogle Scholar
- 44.K. Reinsch, V. Burwitz and R. Schwarz, Revista Mexicana de Astronomia y Astrofisica Conference Series, 2004, 20, pp. 122, see astro-ph/0402458Google Scholar