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Cataclysmic variable star
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<h2 id="classification">Classification</h2> <p>Cataclysmic variables are subdivided into several smaller groups, often named after a bright prototype star characteristic of the class. In some cases the <a href="/facts/Magnetic_field/Ta8Ev588">magnetic field</a> 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 <a href="/facts/Polarization_(waves)/fP33m0eD">polarization</a> in their optical light, and are therefore sometimes called <a href="/facts/Polar_(cataclysmic_variable)/zqgWhIR3">polars</a>; these often exhibit small-amplitude brightness fluctuations at what is presumed to be the white dwarf's period of rotation. </p> <table><tbody><tr><td><a href="/facts/Supernova/Pfo2J23l">Supernovae</a></td><td>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.</td></tr><tr><td>(Classical) <a href="/facts/Nova/H1GcmKXT">novae</a></td><td>These cataclysmic variables have very large outbursts, of 6 to 19 magnitudes, caused by thermonuclear fusion of material accreted onto the white dwarf.</td></tr><tr><td>Recurrent novae</td><td>These have outbursts of about 4 to 9 magnitudes, repeating every 10 to 80 years.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> Examples include <a href="/facts/T_Pyxidis/xFpd5E8R">T Pyxidis</a> and <a href="/facts/RS_Ophiuchi/6DXle64S">RS Ophiuchi</a>.</td></tr><tr><td><a href="/facts/Dwarf_nova/Kk8Q9hIH">Dwarf novae</a></td><td>Dwarf novae, or <a href="/facts/U_Geminorum_star/Kk8Q9hIH">U Geminorum stars</a>, are cataclysmic variables which are observed to brighten repeatedly, though by a smaller amount than classical novae.<table><tbody><tr><td><a href="/facts/Z_Camelopardalis_star/Kk8Q9hIH">Z Camelopardalis stars</a></td><td>Temporarily "halt" at a particular brightness below their peak</td></tr><tr><td><a href="/facts/SU_Ursae_Majoris_star/Kk8Q9hIH">SU Ursae Majoris stars</a></td><td>Have "<a href="/facts/Superoutburst/4jU8BPw2">superoutbursts</a>" which are brighter than the average</td></tr><tr><td><a href="/facts/SS_Cygni_star/Kk8Q9hIH">SS Cygni stars</a></td><td>Have outbursts of two distinct lengths</td></tr></tbody></table></td></tr><tr><td><a href="/facts/Luminous_red_nova/7L9Lvg7k">Luminous red novae</a></td><td>These are stellar mergers that become very red after outburst.</td></tr><tr><td><a href="/facts/Polar_(cataclysmic_variable)/zqgWhIR3">Polars</a></td><td><table><tbody><tr><td><a href="/facts/AM_Herculis_variable/zqgWhIR3">AM Herculis</a> 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.</td></tr><tr><td><a href="/facts/DQ_Herculis_variable/1InW0Kdm">DQ Herculis</a>, also called 'intermediate polars', have a slightly weaker magnetic field than <a href="/facts/AM_Herculis/FwHm2j1Q">AM Herculis</a> stars; there is an accretion disc, but substructure in it is created by the field.</td></tr></tbody></table></td></tr><tr><td><a href="/facts/VY_Sculptoris_variable/5L893Ysy">VY Sculptoris</a></td><td>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.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></td></tr><tr><td><a href="/facts/AM_Canum_Venaticorum_variable/jFfM9SyM">AM Canum Venaticorum</a></td><td>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 <a href="/facts/Gravitational_waves/4XWN3NtG">gravitational waves</a>.</td></tr><tr><td><a href="/facts/SW_Sextantis_variable/7w3rMJTj">SW Sextantis</a></td><td>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 <a href="/facts/Eclipsing_variable/TYlDe1bD">eclipsing variables</a>, though this appears to be a <a href="/facts/Selection_artefact/XmeLAXBF">selection artefact</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></td></tr><tr><td><a href="/facts/Z_Andromedae/EqrsGMy0">Z Andromedae</a> (symbiotic variables)</td><td>These are close binaries with a large cool component losing mass to a hotter compact component and accretion disc.</td></tr></tbody></table> <p>There are over 1600 known CV systems.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The catalog was frozen as of 1 February 2006 though more are discovered each year. </p> <h2 id="discovery">Discovery</h2> <p>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 <a href="/facts/Asteroids/g7Ulr1VB">asteroids</a> whose movement from night to night is clear. </p><p>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 <a href="/facts/Emission_line/HuI4Bj5f">emission lines</a>. They emit in the <a href="/facts/Ultraviolet/kncBUqn5">ultraviolet</a> and <a href="/facts/X-ray/wseP79cN">X-ray</a> 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.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p><p>Around six <a href="/facts/Galactic_astronomy/DswSfrtT">galactic</a> novae (i.e. in <a href="/facts/Milky_Way/ulF6lccN">our own galaxy</a>) 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;<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> 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 <a href="/facts/Full_moon/NRMWFPh2">full moon</a>. </p> <h2 id="superhumps">Superhumps</h2> <p class="note">Main article: <a href="/facts/Superhump/4jU8BPw2">Superhump</a></p> <p>Some cataclysmic variables experience periodic brightenings caused by deformations of the <a href="/facts/Accretion_disk/8zJXshat">accretion disk</a> when its rotation is in resonance with the orbital period of the binary. </p> <h2 id="external-links">External links</h2> <ul><li><a href="http://archive.stsci.edu/prepds/cvcat/index.html">A Catalog and Atlas of Cataclysmic Variables (Archival Edition)</a></li> <li><a href="https://wwwmpa.mpa-garching.mpg.de/RKcat/">Catalogue of Cataclysmic Binaries, Low-Mass X-Ray Binaries and Related Objects (RKcat Edition 7.24, 31 Dec 2015 – The Final Edition)</a></li> <li><a href="https://sites.google.com/site/aavsocvsection/">CVnet, a website and community for CV enthusiasts and researchers</a> – features announcements of new discoveries</li> <li><a href="http://www.mssl.ucl.ac.uk/www_astro/gal/cv_beginners.html">A Beginner's Guide to Cataclysmic Variables</a> – features a very good categorisation of the different classes of stars</li> <li><a href="https://heasarc.gsfc.nasa.gov/docs/objects/cvs/cvstext.html">Cataclysmic Variables</a>, NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) page</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Lavalle, Mimi; University, Louisiana State. "Binary star V Sagittae to explode as very bright nova by century's end". phys.org. Retrieved 2024-07-14. <a href="https://phys.org/news/2020-01-binary-star-sagittae-bright-nova.html" target="_blank">https://phys.org/news/2020-01-binary-star-sagittae-bright-nova.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>NASA (2017-12-11). "Introduction to Cataclysmic Variables (CVs)". heasarc.gsfc.nasa.gov. Retrieved 2024-10-06. <a href="https://heasarc.gsfc.nasa.gov/docs/objects/cvs/cvstext.html" target="_blank">https://heasarc.gsfc.nasa.gov/docs/objects/cvs/cvstext.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Astronomers Discover 'Cataclysmic' Star Pair, Confirming Decades-Old Prediction". CNET. Retrieved 2023-11-06. <a href="https://www.cnet.com/science/space/astronomers-discover-cataclysmic-star-pair-confirming-decades-old-prediction/" target="_blank">https://www.cnet.com/science/space/astronomers-discover-cataclysmic-star-pair-confirming-decades-old-prediction/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Mobberley, Martin (2009). Cataclysmic Cosmic Events and How to Observe Them. New York: Springer. p. 59. ISBN 978-0-387-79945-2. <a href="978-0-387-79945-2" target="_blank">978-0-387-79945-2</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>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. <a href="/wiki/Astronomy_and_Astrophysics" target="_blank">/wiki/Astronomy_and_Astrophysics</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"Defining Characteristics of the SW Sextantis Stars". Archived from the original on 2007-11-19. <a href="https://web.archive.org/web/20071119022732/http://spider.ipac.caltech.edu/staff/hoard/research/swsex/characteristics.html" target="_blank">https://web.archive.org/web/20071119022732/http://spider.ipac.caltech.edu/staff/hoard/research/swsex/characteristics.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Downes, Ronald; et al. "A Catalog and Atlas of Cataclysmic Variables". <a href="http://archive.stsci.edu/prepds/cvcat/index.html" target="_blank">http://archive.stsci.edu/prepds/cvcat/index.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>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. <a href="/wiki/Astronomy_and_Astrophysics" target="_blank">/wiki/Astronomy_and_Astrophysics</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>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. <a href="https://doi.org/10.1111%2Fj.1365-2966.2006.10297.x" target="_blank">https://doi.org/10.1111%2Fj.1365-2966.2006.10297.x</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> </ol>