A symbiotic binary is a type of binary star system, often simply called a symbiotic star. They usually contain a white dwarf with a companion red giant. The cool giant star loses material via Roche lobe overflow or through its stellar wind, which flows onto the hot compact star, usually via an accretion disk.

Symbiotic binaries 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 because of the unique interstellar dynamics present within the system.


Many symbiotic binaries show brightness changes and are classified as variable stars. The star Z Andromedae is often considered the prototype of the symbiotic binary class of stars. More commonly it is considered as the prototype of only a subset of symbiotic stars with irregular variations up to about 4 magnitudes in amplitude. Even the Z Andromedae variable stars are thought to be an inhomogeneous group. The so-called symbiotic novae are a closely related class of symbiotic binaries, more formally known as type NC novae. They appear similar to classical novae but have extremely slow outbursts that can remain near maximum brightness for years.[1]

The typical behaviour of symbiotic binaries can be divided into two phases, based on the rate of accretion to the compact component. The two phases have very different luminosities, but the systems are often also variable in each phase.
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.[2] 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 emission 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 state. Others, however, such as AG Draconis enter active phases on a regular and cyclical basis.[2]

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]

Symbiotic stars are all binaries and so the term symbiotic binary is synonymous. Many are variable and the term symbiotic variable or symbiotic variable star is sometimes also used synonymously, but more commonly is used only for Z Andromedae variable stars.[5]

Symbiotic binaries are often divided into two sub-types based on the nature of the continuum in their spectra. S-type systems have a stellar continuum since the giant component is not obscured.[5] D-type systems are surrounded by optically thick dusty nebulosity and the star itself is not directly visible. D-type systems tend to contain a Mira variable or other long period variable star.[6]

Some symbiotic stars have jets which are a collimated outflow of material. These typically are bi-polar and extend from both poles of the white dwarf. Jets are most commonly observed on stars which are currently in active phase or outburst. Once the outburst has ended, the jet fades and the ejected emissions dissipate. It has been argued that the jets present in symbiotic stars could help further the understanding of jets in other systems, such as in active galactic nuclei.[7]

Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
Skopal, Augustin (8 May 2008). "How to understand the light curves of symbiotic stars". Journal of the American Association of Variable Star Observers. 36 (1): 9.arXiv:0805.1222. Bibcode:2008JAVSO..36....9S.
Tomokazu Kogure; Kam-Ching Leung (5 May 2010). The Astrophysics of Emission-Line Stars. Springer Science & Business Media. pp. 5–. ISBN 978-0-387-68995-1.
Mikołajewska, Joanna (2002). "Orbital and stellar parameters of symbiotic stars". ASP Conference Series. 303: 9.arXiv:astro-ph/0210489. Bibcode:2003ASPC..303....9M.
Skopal, A (2005). "Disentangling the composite continuum of symbiotic binaries. I. S-type systems". Astronomy and Astrophysics. 440 (3): 995–1031.arXiv:astro-ph/0507272. Bibcode:2005A&A...440..995S. doi:10.1051/0004-6361:20034262. S2CID 15292910.
Mikołajewska, J (2007). "Symbiotic Stars: Continually Embarrassing Binaries". Baltic Astronomy. 16: 1. Bibcode:2007BaltA..16....1M.

Sokoloski, J. L. (June 20, 2003). "Symbiotic Stars as Laboratories for the Study of Accretion and Jets: A Call for Optical Monitoring". Journal of the American Association of Variable Star Observers. 31 (2): 89–102.arXiv:astro-ph/0403004. Bibcode:2003JAVSO..31...89S.

External links

List of symbiotic stars discovered by IPHAS
Symbiotic binaries Astrophysics Group, University of Exeter



Accretion Molecular cloud Bok globule Young stellar object
Protostar Pre-main-sequence Herbig Ae/Be T Tauri FU Orionis Herbig–Haro object Hayashi track Henyey track


Main sequence Red-giant branch Horizontal branch
Red clump Asymptotic giant branch
super-AGB Blue loop Protoplanetary nebula Planetary nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Blue straggler Stellar population Supernova Superluminous supernova / Hypernova

Spectral classification

Early Late Main sequence
O B A F G K M Brown dwarf WR OB Subdwarf
O B Subgiant Giant
Blue Red Yellow Bright giant Supergiant
Blue Red Yellow Hypergiant
Yellow Carbon
S CN CH White dwarf Chemically peculiar
Am Ap/Bp HgMn Helium-weak Barium Extreme helium Lambda Boötis Lead Technetium Be
Shell B[e]


White dwarf
Helium planet Black dwarf Neutron
Radio-quiet Pulsar
Binary X-ray Magnetar Stellar black hole X-ray binary


Blue dwarf Green Black dwarf Exotic
Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Gravastar Frozen Quasi-star Thorne–Żytkow object Iron Blitzar

Stellar nucleosynthesis

Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova
Symbiotic Remnant Luminous red nova


Core Convection zone
Microturbulence Oscillations Radiation zone Atmosphere
Photosphere Starspot Chromosphere Stellar corona Stellar wind
Bubble Bipolar outflow Accretion disk Asteroseismology
Helioseismology Eddington luminosity Kelvin–Helmholtz mechanism


Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram

Star systems

Contact Common envelope Eclipsing Symbiotic Multiple Cluster
Open Globular Super Planetary system


Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude
Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard


Proper names
Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest
Historical Most luminous Nearest
Nearest bright With exoplanets Brown dwarfs White dwarfs Milky Way novae Supernovae
Candidates Remnants Planetary nebulae Timeline of stellar astronomy

Related articles

Substellar object
Brown dwarf Sub-brown dwarf Planet Galactic year Galaxy Guest Gravity Intergalactic Planet-hosting stars Tidal disruption event

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