In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (from Latin 'new'), since ones with an outburst brightness visible to the naked eye and an invisible quiescent brightness appeared as new stars in the sky.
A non-magnetic cataclysmic variable. A white dwarf accretes matter from its Roche lobe-filling companion.
Cataclysmic variable stars are binary stars that consist of two components; a white dwarf primary, and a mass transferring secondary. The stars are so close to each other that the gravity of the white dwarf distorts the secondary, and the white dwarf accretes matter from the companion. The tightest currently observed orbit in a hydrogen-rich system is 51 minutes in ZTF J1813+4251. Therefore, the secondary is often referred to as the donor star. The infalling matter, which is usually rich in hydrogen, forms in most cases an accretion disk around the white dwarf. Strong UV and X-ray emission is often seen from the accretion disc, powered by the loss of gravitational potential energy from the infalling material.[citation needed]
Material at the inner edge of disc falls onto the surface of the white dwarf primary. A classical nova outburst occurs when the density and temperature at the bottom of the accumulated hydrogen layer rise high enough to ignite runawayhydrogen fusion reactions, which rapidly convert the hydrogen layer to helium. If the accretion process continues long enough to bring the white dwarf close to the Chandrasekhar limit, the increasing interior density may ignite runaway carbon fusion and trigger a Type Ia supernova explosion, which would completely destroy the white dwarf.
The accretion disc may be prone to an instability leading to dwarf nova outbursts, when the outer portion of the disc changes from a cool, dull mode to a hotter, brighter mode for a time, before reverting to the cool mode. Dwarf novae can recur on a timescale of days to decades.
Cataclysmic variables are subdivided into several smaller groups, often named after a bright prototype star characteristic of the class. In some cases the magnetic field of the white dwarf is strong enough to disrupt the inner accretion disk or even prevent disk formation altogether. Magnetic systems often show strong and variable polarization in their optical light, and are therefore sometimes called polars; these often exhibit small-amplitude brightness fluctuations at what is presumed to be the white dwarf's period of rotation.
These are classed as cataclysmic variables and have extremely large outbursts that destroy the progenitor star. Some result from white dwarfs in binary systems but others are very massive stars.
These cataclysmic variables have very large outbursts, of 6 to 19 magnitudes, caused by thermonuclear fusion of material accreted onto the white dwarf.
Recurrent novae
These have outbursts of about 4 to 9 magnitudes, repeating every 10 to 80 years.[1] Examples include T Pyxidis and RS Ophiuchi.
Dwarf novae, or U Geminorum stars, are cataclysmic variables which are observed to brighten repeatedly, though by a smaller amount than classical novae.
AM Herculis stars are binaries in which the magnetic field of the white dwarf has synchronized the latter's rotational period with the binary orbital period. Matter from the donor star is magnetically channeled onto the white dwarf rather than forming a disc.
DQ Herculis, also called 'intermediate polars', have a slightly weaker magnetic field than AM Herculis stars; there is an accretion disc, but substructure in it is created by the field.
These are stars which occasionally drop in brightness by more than one magnitude, with very occasional dwarf-nova-type outbursts during the dim state. They may be a subclass of polars.[2]
These are cataclysmic variables both of whose components are white dwarfs; the accretion disc is composed primarily of helium, and they are of interest as sources of gravitational waves.
These are like dwarf novae but have the accretion disc in a steady state, so do not show outbursts; the disc emits non-uniformly. They are usually also eclipsing variables, though this appears to be a selection artefact.[3]
These are close binaries with a large cool component losing mass to a hotter compact component and accretion disc.
There are over 1600 known CV systems.[4] The catalog was frozen as of 1 February 2006 though more are discovered each year.
Discovery
Cataclysmic variables are among the classes of astronomical objects most commonly found by amateurs, since a cataclysmic variable in its outburst phase is bright enough to be detectable with very modest instruments, and the only celestial objects easily confused with them are bright asteroids whose movement from night to night is clear.
Verifying that an object is a cataclysmic variable is also fairly straightforward: they are usually quite blue objects, they exhibit rapid and strong variability, and they tend to have peculiar emission lines. They emit in the ultraviolet and X-ray ranges; they are expected also to emit gamma rays, from annihilation of positrons from proton-rich nuclei produced in the fusion explosion, but this has not yet been detected.[5]
Around six galactic novae (i.e. in our own galaxy) are discovered each year, whilst models based on observations in other galaxies suggest that the rate of occurrence ought to be between 20 and 50;[6] this discrepancy is due partly to obscuration by interstellar dust, and partly to a lack of observers in the southern hemisphere and to the difficulties of observing while the Sun is up and at full moon.
Some cataclysmic variables experience periodic brightenings caused by deformations of the accretion disk when its rotation is in resonance with the orbital period of the binary.
References
^Mobberley, Martin (2009). Cataclysmic Cosmic Events and How to Observe Them. New York: Springer. p. 59. ISBN978-0-387-79945-2.
^Hameury, Jean-Marie; Lasota, Jean-Pierre (October 4, 2002). "VY Sculptoris stars as magnetic CVs". Astronomy and Astrophysics. 394 (1): 231–239. arXiv:astro-ph/0207084. Bibcode:2002A&A...394..231H. doi:10.1051/0004-6361:20021136. S2CID 5498393.
^Downes, Ronald; et al. "A Catalog and Atlas of Cataclysmic Variables".
^Senziani, F; Skinner, G.K.; Jean, P.; Hernanz, M. (2008). "Detectability of gamma-ray emission from classical novae with Swift/BAT". Astronomy and Astrophysics. 485 (1): 223–231. arXiv:0804.4791. Bibcode:2008A&A...485..223S. doi:10.1051/0004-6361:200809863. S2CID 16650963.
^Darnley, M. J.; Bode, M. F.; Kerins, E.; Newsam, A. M.; An, J.; Baillon, P.; Belokurov, V.; Calchi Novati, S.; Carr, B. J.; Creze, M.; Evans, N. W.; Giraud-Heraud, Y.; Gould, A.; Hewett, P.; Jetzer, Ph.; Kaplan, J.; Paulin-Henriksson, S.; Smartt, S. J.; Tsapras, Y.; Weston, M. (2006). "Classical novae from the POINT-AGAPE microlensing survey of M31 -- II. Rate and statistical characteristics of the nova population". Monthly Notices of the Royal Astronomical Society. 369 (1): 257–271. arXiv:astro-ph/0509493. Bibcode:2006MNRAS.369..257D. doi:10.1111/j.1365-2966.2006.10297.x. S2CID 85510790.
External links
A Catalog and Atlas of Cataclysmic Variables (Archival Edition)
Catalogue of Cataclysmic Binaries, Low-Mass X-Ray Binaries and Related Objects (RKcat Edition 7.24, 31 Dec 2015 – The Final Edition)
CVnet, a website and community for CV enthusiasts and researchers – features announcements of new discoveries
A Beginner's Guide to Cataclysmic Variables – features a very good categorisation of the different classes of stars
Cataclysmic Variables, NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) page
January 26, 2023
cataclysmic, variable, star, astronomy, cataclysmic, variable, stars, stars, which, irregularly, increase, brightness, large, factor, then, drop, back, down, quiescent, state, they, were, initially, called, novae, from, latin, since, ones, with, outburst, brig. In astronomy cataclysmic variable stars CVs are stars which irregularly increase in brightness by a large factor then drop back down to a quiescent state They were initially called novae from Latin new since ones with an outburst brightness visible to the naked eye and an invisible quiescent brightness appeared as new stars in the sky A non magnetic cataclysmic variable A white dwarf accretes matter from its Roche lobe filling companion Cataclysmic variable stars are binary stars that consist of two components a white dwarf primary and a mass transferring secondary The stars are so close to each other that the gravity of the white dwarf distorts the secondary and the white dwarf accretes matter from the companion The tightest currently observed orbit in a hydrogen rich system is 51 minutes in ZTF J1813 4251 Therefore the secondary is often referred to as the donor star The infalling matter which is usually rich in hydrogen forms in most cases an accretion disk around the white dwarf Strong UV and X ray emission is often seen from the accretion disc powered by the loss of gravitational potential energy from the infalling material citation needed Material at the inner edge of disc falls onto the surface of the white dwarf primary A classical nova outburst occurs when the density and temperature at the bottom of the accumulated hydrogen layer rise high enough to ignite runaway hydrogen fusion reactions which rapidly convert the hydrogen layer to helium If the accretion process continues long enough to bring the white dwarf close to the Chandrasekhar limit the increasing interior density may ignite runaway carbon fusion and trigger a Type Ia supernova explosion which would completely destroy the white dwarf The accretion disc may be prone to an instability leading to dwarf nova outbursts when the outer portion of the disc changes from a cool dull mode to a hotter brighter mode for a time before reverting to the cool mode Dwarf novae can recur on a timescale of days to decades Contents 1 Classification 2 Discovery 3 Superhumps 4 References 5 External linksClassification EditCataclysmic variables are subdivided into several smaller groups often named after a bright prototype star characteristic of the class In some cases the magnetic field of the white dwarf is strong enough to disrupt the inner accretion disk or even prevent disk formation altogether Magnetic systems often show strong and variable polarization in their optical light and are therefore sometimes called polars these often exhibit small amplitude brightness fluctuations at what is presumed to be the white dwarf s period of rotation Supernovae These are classed as cataclysmic variables and have extremely large outbursts that destroy the progenitor star Some result from white dwarfs in binary systems but others are very massive stars Classical novae These cataclysmic variables have very large outbursts of 6 to 19 magnitudes caused by thermonuclear fusion of material accreted onto the white dwarf Recurrent novae These have outbursts of about 4 to 9 magnitudes repeating every 10 to 80 years 1 Examples include T Pyxidis and RS Ophiuchi Dwarf novae Dwarf novae or U Geminorum stars are cataclysmic variables which are observed to brighten repeatedly though by a smaller amount than classical novae Z Camelopardalis stars Temporarily halt at a particular brightness below their peakSU Ursae Majoris stars Have superoutbursts which are brighter than the averageSS Cygni stars Have outbursts of two distinct lengthsLuminous red novae These are stellar mergers that become very red after outburst Polars AM Herculis stars are binaries in which the magnetic field of the white dwarf has synchronized the latter s rotational period with the binary orbital period Matter from the donor star is magnetically channeled onto the white dwarf rather than forming a disc DQ Herculis also called intermediate polars have a slightly weaker magnetic field than AM Herculis stars there is an accretion disc but substructure in it is created by the field VY Sculptoris These are stars which occasionally drop in brightness by more than one magnitude with very occasional dwarf nova type outbursts during the dim state They may be a subclass of polars 2 AM Canum Venaticorum These are cataclysmic variables both of whose components are white dwarfs the accretion disc is composed primarily of helium and they are of interest as sources of gravitational waves SW Sextantis These are like dwarf novae but have the accretion disc in a steady state so do not show outbursts the disc emits non uniformly They are usually also eclipsing variables though this appears to be a selection artefact 3 Z Andromedae symbiotic variables These are close binaries with a large cool component losing mass to a hotter compact component and accretion disc There are over 1600 known CV systems 4 The catalog was frozen as of 1 February 2006 though more are discovered each year Discovery EditCataclysmic variables are among the classes of astronomical objects most commonly found by amateurs since a cataclysmic variable in its outburst phase is bright enough to be detectable with very modest instruments and the only celestial objects easily confused with them are bright asteroids whose movement from night to night is clear Verifying that an object is a cataclysmic variable is also fairly straightforward they are usually quite blue objects they exhibit rapid and strong variability and they tend to have peculiar emission lines They emit in the ultraviolet and X ray ranges they are expected also to emit gamma rays from annihilation of positrons from proton rich nuclei produced in the fusion explosion but this has not yet been detected 5 Around six galactic novae i e in our own galaxy are discovered each year whilst models based on observations in other galaxies suggest that the rate of occurrence ought to be between 20 and 50 6 this discrepancy is due partly to obscuration by interstellar dust and partly to a lack of observers in the southern hemisphere and to the difficulties of observing while the Sun is up and at full moon Superhumps EditMain article Superhump Some cataclysmic variables experience periodic brightenings caused by deformations of the accretion disk when its rotation is in resonance with the orbital period of the binary References Edit Mobberley Martin 2009 Cataclysmic Cosmic Events and How to Observe Them New York Springer p 59 ISBN 978 0 387 79945 2 Hameury Jean Marie Lasota Jean Pierre October 4 2002 VY Sculptoris stars as magnetic CVs Astronomy and Astrophysics 394 1 231 239 arXiv astro ph 0207084 Bibcode 2002A amp A 394 231H doi 10 1051 0004 6361 20021136 S2CID 5498393 Defining Characteristics of the SW Sextantis Stars Archived from the original on 2007 11 19 Downes Ronald et al A Catalog and Atlas of Cataclysmic Variables Senziani F Skinner G K Jean P Hernanz M 2008 Detectability of gamma ray emission from classical novae with Swift BAT Astronomy and Astrophysics 485 1 223 231 arXiv 0804 4791 Bibcode 2008A amp A 485 223S doi 10 1051 0004 6361 200809863 S2CID 16650963 Darnley M J Bode M F Kerins E Newsam A M An J Baillon P Belokurov V Calchi Novati S Carr B J Creze M Evans N W Giraud Heraud Y Gould A Hewett P Jetzer Ph Kaplan J Paulin Henriksson S Smartt S J Tsapras Y Weston M 2006 Classical novae from the POINT AGAPE microlensing survey of M31 II Rate and statistical characteristics of the nova population Monthly Notices of the Royal Astronomical Society 369 1 257 271 arXiv astro ph 0509493 Bibcode 2006MNRAS 369 257D doi 10 1111 j 1365 2966 2006 10297 x S2CID 85510790 External links EditA Catalog and Atlas of Cataclysmic Variables Archival Edition Catalogue of Cataclysmic Binaries Low Mass X Ray Binaries and Related Objects RKcat Edition 7 24 31 Dec 2015 The Final Edition CVnet a website and community for CV enthusiasts and researchers features announcements of new discoveries A Beginner s Guide to Cataclysmic Variables features a very good categorisation of the different classes of stars Cataclysmic Variables NASA s High Energy Astrophysics Science Archive Research Center HEASARC page Retrieved from https en wikipedia org w index php title Cataclysmic variable star amp oldid 1124057068, wikipedia, wiki, book, books, library,
