Beta Cephei star

As a Beta Cephei stars ( GCVS -Systematikkürzel: BCEp ) refers to a class pulsationsveränderlicher stars , named after their prototype β Cephei . Some of the brightest stars in the night sky belong to this massive class of stars .

properties

spectrum

Beta Cephei stars are stars with spectral types between B0.5 and B2 and are on or slightly above the main sequence . The classified luminosity classes range from I to V, most stars are in luminosity classes IV and III (sub-giants and giants). They belong to population I and have a mass in the range of 8 to 18 solar masses .

Pulsations

As a first approximation, the apparent brightness of the Beta Cephei stars fluctuates sinusoidally with an amplitude of up to 0.2 magnitudes with a period between 3 and 7 hours. The vibrations of the stellar atmosphere are excited by the kappa mechanism , as in many other pulsation-variable stars . In the case of Beta Cephei stars, it is the ionization zone of iron and not of hydrogen as in most other pulsating variable stars. The restoring force of the vibrations is both gravitation and pressure.

Until a few years ago, it was assumed that most Beta Cephei stars only pulsate radially. When observing satellites such as MOST (satellite) , Kepler and COROT , all Beta Cephei stars also showed non-radial pulsation, i.e. wave peaks and valleys orbiting the star in addition to the radial oscillations. Satellite observations avoid the problematic separation of vibrations with only slightly different frequencies , since interruptions during the day and due to the weather are irrelevant from space. If non-radial and / or radial pulsation frequencies that are close to one another are superimposed, only the beating of the frequencies is visible in the overall light of the star . Typical beat periods range from days to weeks.

There is also the term Beta-Canis-Majoris-Stars, which is interpreted differently. Sometimes it is equated with the Beta Cephei stars and sometimes it is used exclusively for multiperiodic Beta Cephei stars. However, since all Beta Cephei stars seem to be multiperiodic, this class is hardly used anymore.

Occurrence in star catalogs

The General Catalog of Variable Stars currently lists around 120 stars with the abbreviations BCEP or BCEPS , which means that a little over 0.2% of all stars in this catalog are classified as Beta Cephei stars.

Well-known Beta Cephei stars

• β Cephei
• β Canis Majoris
• γ pegasi
• β Centauri
• Becrux

See also

• Variable star
• Pulsation-variable star
• Cepheids

literature

• Cuno Hoffmeister , G. Richter, W. Wenzel: Variable stars . JA Barth Verlag, Leipzig 1990, ISBN 3-335-00224-5 .
• John R. Percy: Understanding Variable Stars . Cambridge University Press, Cambridge 2007, ISBN 978-0-521-23253-1 .
• C. Ulusoy, E. Niemczura, B. Ula, T. Gulmez: New β Cephei variable in the Southern open cluster NGC 6200: ALS 3728 . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1302.5313v1 .

Individual evidence

1. ↑ Variability types General Catalog of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Retrieved May 12, 2019 .