Symbiotic binary
A symbiotic star is a type of binary star.[1] They are usually a white dwarf with a companion late sequence red giant. They are indicated by the exhibition of spectral lines of the highly contrasting temperatures of the red giant(~3000°K) and the white dwarf(~20 000°K). The white dwarf gains mass from stellar wind from the red giant or gravitational streaming.
Symbiotic stars are of particular interest to astronomers as they can be used to learn about stellar evolution. They are also vital in the study of stellar wind, ionized nebulae, and accretion[2] because of the unique interstellar dynamics present within the system.
Discovery
The term 'symbiotic star' was first used in 1958 in a publication about 'stars of composite spectra'.[3] However, the distinct category of symbiotic stars had been previously known. They were first recognized as a class of stars with unique spectroscopic qualities by Annie Cannon near the beginning of the 20th century. Their binary nature was made clear by the simultaneous existence of the spectral lines indicative of a red giant and of a white dwarf or neutron star.[4]
Phases
One of the requisite conditions for a star to be defined as symbiotic is an interaction between stars. This is typically a transfer of mass from the larger, giant star to the dwarf star. Depending on the rate of the emissions from the giant to the dwarf, the system can be divided into two phases.
Quiescent phase
When the accretion, mass-loss and ionization processes are all in equilibrium between the stars, the system is said to be in quiescence. At this point, the system will continue to release energy at an approximately average rate.[5] This can be observed through the spectral energy distribution(SED) of the star which will be remain relatively constant.
Active phase
If the equilibrium of a quiescent symbiotic star is disturbed, it will transition into an active phase. This phase is shown through a large change in both the nature of the radiation from the star, and a brightening of the optical of the star by several magnitudes. The transitions between phases are poorly understood, and it is currently difficult to predict when a star will transition into an active phase from quiescence, or when it will return to quiescence. Many systems have not yet been observed to enter an active states. Others, however, such as AG Dra enter active phases on a regular and cyclical basis.[5]
References
- ^ Sokoloski, J. L. (June 20, 2003). "Symbiotic Stars as Laboratories for the Study of Accretion and Jets: A Call for Optical Monitoring". AAVSO. 31.
{{cite journal}}:|access-date=requires|url=(help) - ^ "Symbiotic binaries". Astrophysics Group. University of Exeter.
- ^ Tomakazu, Kogure; Kam-Ching, Leung. "The Astrophysics of Emission-Line Stars". Springer Science & Business Media. p. 397.
{{cite web}}: Missing or empty|url=(help) - ^ Joanna, Mikołajewska (2002). "Orbital and stellar parameters of symbiotic stars". ASP Conference Series. xxx.
- ^ a b Skopal, Augustin (8 May 2008). "How to understand the light curves of symbiotic stars". The Journal of the American Association of Variable Star Observers. 36 (1): 9.
External links
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