EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 379/2 Article
Free access article

Issue A&A
Volume 379, Number 2, November IV 2001
Page(s) 496 - 500
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011299



A&A 379, 496-500 (2001)
DOI: 10.1051/0004-6361:20011299

On the post main sequence expansion of stars with contracting helium cores

M. Schrinner and W. Deinzer

Universitäts-Sternwarte Göttingen, Geismarlandstrasse 11, 37083 Göttingen, Germany

(Received 12 July 2001 / Accepted 10 September 2001 )

Abstract
The post main sequence expansion of a \(5 M_{\odot}\)-star is investigated by means of a simple composite configuration: a contracting He-core of Schoenberg-Chandrasekhar mass surrounded by an H-envelope of polytropic index n=3. While the structure of the envelope is immediately obtained by solving the equations of hydrostatic equilibrium, the core requires some further simplification: if the actual non-local gravitational energy release due to contraction is replaced by its constant core-average, the equation of radiative energy transport may be easily integrated. Thus an explicit relation between pressure and temperature is obtained and the equations of hydrostatic equilibrium may be solved. Specifying M,Mcore and T0 (the temperature of the H-burning shell-source at the interface), a sequence of models follows with Lcore, the gravitational energy released from the core per second, and hence with t, the contraction time, as the parameter. The resulting simple models show very rapid expansion, a consequence of the thermostatic action of the shell-source. Its fixed temperature prevents the shell-source from participating in the contraction of the core -thus causing the outer parts of the core and hence the adjoining envelope to decrease in density. Accordingly, the envelope must expand. This consequence of a fixed temperature T0 is clearly demonstrated by the distributions of the specific internal and gravitational energies. This characteristic behaviour is also found in stellar models obtained by elaborate numerical simulations.


Key words: stars: Hertzsprung-Russell diagram -- stars: interiors -- stars: evolution

Offprint request: W. Deinzer, deinzer@uni-sw.gwdg.de




© ESO 2001


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.