Symbiotic binary

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Artist's impression of R Aquarii, a symbiotic binary, during an active phase Artists Impression of R Aquarii, A Symbiotic Star.jpg
Artist's impression of R Aquarii, a symbiotic binary, during an active phase

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.

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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.

Variability

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 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]

Nomenclature

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]

Sub-types

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]

Jets

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]

Related Research Articles

Soft X-ray transients (SXTs), also known as X-ray novae and black hole X-ray transients, are composed of a compact object and some type of "normal", low-mass star. These objects show dramatic changes in their X-ray emission, probably produced by variable transfer of mass from the normal star to the compact object, a process called accretion. In effect the compact object "gobbles up" the normal star, and the X-ray emission can provide the best view of how this process occurs. The "soft" name arises because in many cases there is strong soft X-ray emission from an accretion disk close to the compact object, although there are exceptions which are quite hard.

<span class="mw-page-title-main">V603 Aquilae</span> 1918 Nova event in the constellation Aquila

V603 Aquilae was a bright nova first observed in the constellation Aquila in 1918. It was the brightest "new star" to appear in the sky since Kepler's Supernova in 1604. Like all novae, it is a binary system, comprising a white dwarf and donor low-mass star in close orbit to the point of being only semidetached. The white dwarf sucks matter off its companion, which has filled its Roche lobe, onto its accretion disk and surface until the excess material is blown off in a thermonuclear event. This material then forms an expanding shell, which eventually thins out and disappears.

<span class="mw-page-title-main">T Coronae Borealis</span> Recurrent nova in the constellation Corona Borealis

T Coronae Borealis, is a recurring nova in the constellation Corona Borealis. It was first discovered in outburst in 1866 by John Birmingham, although it had been observed earlier as a 10th magnitude star.

Z Andromedae is a binary star system consisting of a red giant and a white dwarf. It is the prototype of a type of cataclysmic variable star known as symbiotic variable stars or simply Z Andromedae variables. The brightness of those stars vary over time, showing a quiescent, more stable phase and then an active one with a more pronounced variability and stronger brightening and/or dimming.

<span class="mw-page-title-main">R Aquarii</span> Star in the constellation of Aquarius

R Aquarii is a variable star in the constellation Aquarius.

An AM Canum Venaticorum star, is a rare type of cataclysmic variable star named after their type star, AM Canum Venaticorum. In these hot blue binary variables, a white dwarf accretes hydrogen-poor matter from a compact companion star.

Symbiotic novae are slow irregular eruptive variable stars with very slow nova-like outbursts with an amplitude of between 9 and 11 magnitudes. The symbiotic nova remains at maximum for one or a few decades, and then declines towards its original luminosity. Variables of this type are double star systems with one red giant, which probably is a Mira variable, and one a hot compact object, with markedly contrasting spectra and whose proximity and mass characteristics indicate it as a symbiotic star. They are divided into D-type (dusty) or S-type (stellar), depending on whether the giant is a Mira variable or not.

<span class="mw-page-title-main">AG Pegasi</span> Star in the constellation Pegasus

AG Pegasi is a symbiotic binary star in the constellation Pegasus. It is a close binary composed of a red giant and white dwarf, estimated to be around 2.5 and 0.6 times the mass of the Sun respectively. It is classified as a symbiotic nova; it has undergone one extremely slow nova outburst and a smaller outburst.

<span class="mw-page-title-main">SY Muscae</span> Star in the constellation Musca

SY Muscae is a binary star system in the constellation Musca composed of a red giant and a white dwarf. Its apparent magnitude varies from 10.2 to 12.7 over a period of 624.5 days. Although the binary is a symbiotic star system, it is unusual in that it does not have an eruptive component. It is an S-type symbiotic system, which means that the light comes from the stars rather than surrounding dust.

<span class="mw-page-title-main">DD Microscopii</span> Star in the constellation Microscopium

DD Microscopii, also known as CD−43°14304, is a binary star system in the constellation Microscopium. The system has a combined average apparent magnitude around 11, making it readily visible in telescopes but not to the naked eye. It is thought to be at a distance of one or two thousand parsecs, although parallax measurements place the system at a distance of around 30,000 light years.

<span class="mw-page-title-main">BV Centauri</span> Star in the constellation Centaurus


BV Centauri is a cataclysmic variable binary star in the constellation Centaurus. It is a dwarf nova, and undergoes rapid increases in brightness that are recurrent with a mean period of 150 days. This period seems to have increased in the last few decades. During quiescence, its visual apparent magnitude is about 13, with variations of a few tenths of magnitude over an orbit due to differences in the star's visible surface area, brightening to a maximum magnitude of 10.7 during outbursts. From its luminosity, it is estimated that the system is about 500 parsecs (1,600 ly) away from Earth. A Gaia parallax of 2.81 mas has been measured, corresponding to about 360 pc.

<span class="mw-page-title-main">SU Ursae Majoris</span> Variable star in the constellation Ursa Major

SU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellation of Ursa Major. It is a periodic cataclysmic variable that varies in magnitude from a peak of 10.8 down to a base of 14.96. The distance to this system, as determined from its annual parallax shift of 4.53 mas, is 719 light-years. It is moving further from the Earth with a heliocentric radial velocity of +27 km/s.

<span class="mw-page-title-main">CH Cygni</span> Variable star in the Cygnus constellation

CH Cygni is a red giant, variable, symbiotic binary in the constellation Cygnus. It is the nearest symbiotic star to Earth, and one of the brightest, making it an ideal candidate for study.

<span class="mw-page-title-main">TU Mensae</span> Star in the constellation Mensa

TU Mensae is a cataclysmic variable star of in the constellation Mensa. A close binary, it consists of a white dwarf and low-mass star orbiting each other in 2 hours 49 minutes. The stars are close enough that the white dwarf strips material off the other star, creating an accretion disc that periodically ignites with a resulting brightening of the system. These result in an increase in brightness lasting around a day every 37 days. Brighter outbursts, known as superhumps, last 5-20 days and take place every 194 days. The properties of TU Mensae have been difficult to calculate, as the calculated mass ratio between the two stars mean there should not be superhumps.

<span class="mw-page-title-main">AR Andromedae</span> Star in the constellation Andromeda

AR Andromedae is a dwarf nova of the SS Cygni type in the constellation Andromeda. Its typical apparent visual magnitude is 17.6, but increases up to 11.0 magnitude during outbursts. The outbursts occur approximately every 23 days.

<span class="mw-page-title-main">DX Andromedae</span> Star in the constellation Andromeda

DX Andromedae is a cataclysmic variable star in the constellation Andromeda. It has a typical apparent visual magnitude of 15.5 during the quiescent phase, but becomes brighter during outbursts recurring with a mean cycle length of 330 days, thus is classified as a dwarf nova of the SS Cygni type.

<span class="mw-page-title-main">EG Andromedae</span> Binary star system in the constellation Andromeda

EG Andromedae is a symbiotic binary in the constellation Andromeda. Its apparent visual magnitude varies between 6.97 and 7.80.

<span class="mw-page-title-main">PX Andromedae</span> Star in the constellation Andromeda

PX Andromedae is an eclipsing cataclysmic variable star in the constellation Andromeda. It has been classified as a SW Sextantis variable, and its apparent visual magnitude varies between 14.04 and 17.

<span class="mw-page-title-main">V455 Andromedae</span> Dwarf nova star in the constellation Andromeda

V455 Andromedae is a dwarf nova in the constellation Andromeda. It has a typical apparent visual magnitude of 16.5, but reached a magnitude of 8.5 during the only observed outburst.

<span class="mw-page-title-main">4 Draconis</span> Variable star in the constellation Draco

4 Draconis, also known as HR 4765 and CQ Draconis, is a star about 570 light years from the Earth, in the constellation Draco. It is a 5th magnitude star, so it will be faintly visible to the naked eye of an observer far from city lights. It is a variable star, whose brightness varies slightly from 4.90 to 5.12 over a period of 4.66 years.

References

  1. ↑ 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.
  2. 1 2 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.
  3. ↑ 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.
  4. ↑ Mikołajewska, Joanna (2002). "Orbital and stellar parameters of symbiotic stars". ASP Conference Series. 303: 9. arXiv: astro-ph/0210489 . Bibcode:2003ASPC..303....9M.
  5. 1 2 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.
  6. ↑ Mikołajewska, J (2007). "Symbiotic Stars: Continually Embarrassing Binaries". Baltic Astronomy. 16: 1. Bibcode:2007BaltA..16....1M.
  7. ↑ 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.
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