Evolutionary Processes in Binary and Multiple Stars (Cambridge Astrophysics)

Evolutionary Processes in Binary and Multiple Stars (Cambridge Astrophysics)

Language: English

Pages: 332

ISBN: 1107403421

Format: PDF / Kindle (mobi) / ePub


Binary systems of stars are as common as single stars. Stars evolve primarily by nuclear reactions in their interiors, but a star with a binary companion can also have its evolution influenced by the companion. Multiple star systems can exist in a stable state for millions of years, but can ultimately become unstable as one star grows in radius until it engulfs another. This volume discusses the statistics of binary stars; the evolution of single stars; and several of the most important kinds of interaction between two (and even three or more) stars. A series of mathematical appendices provides a concise but complete account of the mathematics of these processes.

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with a fairly rapid drop in numbers to lower mass in the range 0.3–0.07 M , a low plateau in the brown-dwarf region 0.07–0.01 M , and then a peak for major planetary masses 14 Introduction below ∼0.01 M (Marcy and Butler 1998). This is consistent with the likely hypothesis that the formation mechanism of binary stars is very different from that of planetary systems. The two processes are not exclusive, however. Some systems are known to have both a planetary companion and a stellar companion:

surface temperature; the latter is plotted backwards, for traditional reasons. Our theoretical understanding of the internal structure and evolution of single stars is based on the concepts of hydrostatic equilibrium, thermodynamic equilibrium and the consumption of nuclear fuel, mainly hydrogen. In hydrostatic equilibrium, the inward force of gravity is balanced by the outward push of a pressure gradient. In thermodynamic equilibrium, the heating or cooling of a spherical layer of material is

discussed in more detail below (Section 2.3.1). RHT is the largest radius that a star of given luminosity and mass can have (in hydrostatic equilibrium, but not necessarily in thermal equilibrium), and is reached if the star is fully, or at least very largely, convective. R/RHT is also a function – Eq. (2.49) – of only global quantities L , R and M. R < RHT if the star is partly radiative: R ∼ 0.55 RHT for the Sun. A rough empirical fit to both low-mass ZAMS stars and to red giants, as well as to

in the oldest stars. From Schr¨oder et al. (2000). On the horizontal branch is a fairly narrow range of colour or temperature in which the atmosphere is unstable to radial pulsations. The RR Lyr pulsating variables are found there, with pulsation periods of ∼0.25–0.75 days. The pulsation is a relaxation cycle driven primarily by the second ionisation of He. The zone in the interior where this occurs is at about 105 K. In hot stars, this zone is too near the surface to contain sufficient mass to

hence local minima of neutron capture cross-section. The convection in the outer envelope extends intermittently down into the region which is occupied by C-rich and s-processed material from a slightly earlier episode of shell flash and deeper mixing, and so can bring the heavy elements, and accompanying carbon, to the surface. Such elements are observed to be enhanced in a proportion of red supergiants (main sequence stars, S stars, C stars). Although C stars as a fraction of all giants amount

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