Gamma Cassiopeiae Analog
Gamma-Cassiopeiae-Analogs or sometimes also Gamma-Cassiopeiae-like-Objects are a subgroup of the Be stars with unusual X-ray luminosities between those of normal Be stars and the X-ray binary stars with a Be star as a mass donor. They are named after the prototype Gamma Cassiopeiae , as are the Gamma Cassiopeiae stars , a group of eruptive variables .
properties
The Gamma Cassiopeiae Analogs have the following characteristics:
- Their X-ray luminosity is between 10 32 and 10 33 erg / s , while in the case of X-ray binary stars with a Be star, this does not drop below 10 34 erg / s even in rest phases . Inconspicuous Be stars do not exceed 10 30 erg / s, whereby the X-rays arise as bremsstrahlung in shocks of the stellar wind .
- The soft part of the X-ray radiation is thermal in nature, while the hard part is similar to a cataclysmic variable .
- No signs of a close companion to the Be stars have been found in either the optical or X-ray light.
- Periodic brightness fluctuations in both spectral ranges on the order of one day are interpreted as a rotation modulation.
- In addition, eruptions occur in the X-ray range within seconds to minutes, which are referred to as flares. Furthermore, semi-periodic modulations on the order of months to years have been assumed.
- The Gamma-Cassiopeiae-Analogs do not differ in the radio range and the gamma radiation from other Be stars.
- If the Gamma Cassiopeiae analogs occur in an open star cluster , they are blue stragglers above average .
interpretation
Two hypotheses have been put forward for the unusual X-ray radiation. Accordingly, the high-energy radiation arises when matter falls from a circumstellar ring on a white dwarf , similar to X-ray binary stars on a neutron star . Due to the lower gravitational potential of the white dwarf, the X-ray radiation is softer and shows a lower luminosity. The second hypothesis allows the X-rays to arise as a result of an interaction between the magnetic field of the Be star and a circumstellar disk , whereby the disk could also have an embedded magnetic field.
Examples
- Gamma Cassiopeiae
- HD 45314
- HD 119682
- HD 110432
- HD 161103
literature
- Myron A. Smith, Raimundo Lopes de Oliveira, Christian Motch: The X-ray emission of the gamma Cassiopeiae stars . In: Astrophysics. Solar and Stellar Astrophysics . 2015, arxiv : 1512.06446 (English).
- CR Shrader, K. Hamaguchi, SJ Sturner, LM Oskinova, T. Almeyda, R. Petre: High-Energy Properties of the Enigmatic Be Star gamma Cassiopeiae . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1410.4050v1 (English).
- G. Rauw, Y. Naze, M. Spano, T. Morel, A. ud-Doula: HD45314: a new gamma Cas analog among Oe stars . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1306.6520v1 (English).
- Myron A. Smith, Raimundo Lopes de Oliveira, Christian Motch: Characterization of the X-ray light curve of the gamma Cas-like B1e star HD110432 . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1206.1377v1 (English).
- Raimundo Lopes de Oliveira, Christian Motch: A hard and variable X-ray emission from the massive emission line star HD 157832 . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1102.4625v1 (English).