EDP Sciences
Free access
Issue A&A
Volume 480, Number 2, March III 2008
Page(s) 481 - 487
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20078596

A&A 480, 481-487 (2008)
DOI: 10.1051/0004-6361:20078596

Cyclical period changes in HT Cassiopeiae: a difference between systems above and below the period gap

B. W. Borges1, R. Baptista1, C. Papadimitriou2, and O. Giannakis2

1  Departamento de Física, Universidade Federal de Santa Catarina, CEP 88040-900, Florianópolis, Brazil
    e-mail: [bernardo;bap]@astro.ufsc.br
2  Institute of Astronomy and Astrophysics, National Observatory of Athens, PO Box 20048, Athens 11810, Greece
    e-mail: [cpap;og]@astro.noa.gr

(Received 31 August 2007 / Accepted 26 December 2007)

Aims.We report identification of cyclical changes in the orbital period of the eclipsing cataclysmic variable HT Cas.
Methods.We measured new white-dwarf mid-eclipse timings and combined them with published measurements to construct an observed-minus-calculated diagram covering 29 years of observations.
Results.The data present a 36 yr period modulation of semi-amplitude ~40 s, with a statistical significance greater than 99.9 percent with respect to a constant period.
Conclusions.We combine our results with those in the literature to revisit the issue of cyclical period changes in cataclysmic variables and their interpretation in terms of a solar-type magnetic activity cycle in the secondary star. A diagram of fractional period change $(\Delta
P/P)$ versus the angular velocity of the active star $(\Omega)$ for cataclysmic variables, RS CVn, W UMa, and Algols, reveal that close binaries with periods above the gap (secondaries with convective envelopes) satisfy a relationship $\Delta P/P \propto \Omega^{-0.7
\pm 0.1}$. Cataclysmic variables below the period gap (with fully convective secondaries) deviate from this relationship by more than 3-$\sigma$, with average fractional period changes $\simeq $6 times smaller than those of the systems above the gap.

Key words: accretion, accretion disks -- stars: dwarf novae -- stars: evolution -- stars: binaries: eclipsing -- stars: individual: HT Cas

© ESO 2008

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.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)