Volume 480, Number 2, March III 2008
|Page(s)||481 - 487|
|Section||Stellar structure and evolution|
|Published online||09 January 2008|
Cyclical period changes in HT Cassiopeiae: a difference between systems above and below the period gap*
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
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 versus the angular velocity of the active star 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 . Cataclysmic variables below the period gap (with fully convective secondaries) deviate from this relationship by more than 3-σ, with average fractional period changes 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
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