Published by
EDP Sciences
EDP Sciences Journals List
Subscriber Authentication Point
Home All issues Volume 459/ 1 Article
Free access
Issue A&A
Volume 459, Number 1, November III 2006
Page(s) L21 - L24
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20066392



A&A 459, L21-L24 (2006)
DOI: 10.1051/0004-6361:20066392

Letter

On the H$\alpha$ emission from the $\beta$ Cephei system

R. S. Schnerr1, H. F. Henrichs1, R. D. Oudmaijer2 and J. H. Telting3

1  Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
    e-mail: rschnerr@science.uva.nl
2  School of Physics and Astronomy, EC Stoner Building, University of Leeds, Leeds LS2 9JT, UK
3  Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain

(Received 13 September 2006 / Accepted 20 September 2006)

Abstract
Context.Be stars, which are characterised by intermittent emission in their hydrogen lines, are known to be fast rotators. This fast rotation is a requirement for the formation of a Keplerian disk, which in turn gives rise to the emission. However, the pulsating, magnetic B1IV star $\beta$ Cephei is a very slow rotator that still shows H$\alpha$ emission episodes like in other Be stars, contradicting current theories.
Aims.We investigate the hypothesis that the H$\alpha$ emission stems from the spectroscopically unresolved companion of $\beta$ Cep.
Methods.Spectra of the two unresolved components have been separated in the 6350-6850 Å range with spectro-astrometric techniques, using 11 longslit spectra obtained with ALFOSC at the Nordic Optical Telescope, La Palma.
Results.We find that the H$\alpha$ emission is not related to the primary in $\beta$ Cep, but is due to its 3.4 mag fainter companion. This companion has been resolved by speckle techniques, but it remains unresolved by traditional spectroscopy. The emission extends from about -400 to +400 km s-1. The companion star in its 90-year orbit is likely to be a classical Be star with a spectral type around B6-8.
Conclusions.By identifying its Be-star companion as the origin of the H$\alpha$ emission behaviour, the enigma behind the Be status of the slow rotator $\beta$ Cep has been resolved.


Key words: stars: emission-line, Be -- stars: individual: $\beta$ Cep -- stars: magnetic fields -- stars: early-type -- stars: activity -- binaries: close



© ESO 2006

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.