Apulsating white dwarf is awhite dwarfstar whoseluminosityvaries due to non-radialgravity wave pulsations within itself. Known types of pulsating white dwarfs includeDAV, orZZ Ceti, stars, withhydrogen-dominated atmospheres and the spectral type DA;^[1]DBV, orV777 Her, stars, withhelium-dominated atmospheres and the spectral type DB;^[2] andGW Vir stars, with atmospheres dominated by helium,carbon, andoxygen, and the spectral typePG 1159. (Some authors also include non-PG 1159 stars in the class of GW Vir stars.) GW Vir stars may be subdivided intoDOV andPNNV stars;^[3][4] they are not, strictly speaking, white dwarfs butpre-white dwarfs which have not yet reached the white dwarf region on theHertzsprung–Russell diagram.^[5][6] A subtype ofDQV stars, withcarbon-dominated atmospheres, has also been proposed,^[7] and in May 2012, the first extremely low mass variable (ELMV) white dwarf was reported.^[8]

These variables all exhibit small (1%–30%) variations in light output, arising from a superposition of vibrational modes with periods of hundreds to thousands of seconds. Observation of these variations givesasteroseismological evidence about the interiors of white dwarfs.^[9]

Types of pulsating white dwarf[4][7][8][10]
DAV (GCVS:ZZA)	DAspectral type, having onlyhydrogenabsorption lines in its spectrum
DBV (GCVS:ZZB)	DB spectral type, having onlyhelium absorption lines in its spectrum
GW Vir (GCVS:ZZO)	Atmosphere mostly C, He and O; may be divided intoDOV andPNNV stars
DQV	DQ spectral type; hot,carbon-dominated atmosphere
ELMV	DA spectral type;${\displaystyle \lesssim 0.2M_{\odot }}$

Early calculations suggested that white dwarfs should vary with periods around 10 seconds, but searches in the 1960s failed to observe this.^[11][12] The first variable white dwarf found wasHL Tau 76; in 1965 and 1966,Arlo U. Landolt observed it to vary with a period of approximately 12.5 minutes.^[13] The reason for this period being longer than predicted is that the variability of HL Tau 76, like that of the other pulsating variable white dwarfs known, arises from non-radialgravity wave pulsations.^[14] In 1970, another white dwarf,Ross 548, was found to have the same type of variability as HL Tau 76;^[15] in 1972, it was given thevariable star designationZZ Ceti.^[16] The nameZZ Ceti also refers to this class of pulsating variable white dwarfs, which, as it consists of white dwarfs with hydrogen atmospheres, is also calledDAV.^[17] These stars have periods between 30 seconds and 25 minutes and are found in a rather narrow range ofeffective temperatures between about 12,500 and 11,100K.^[18] The measurement of the rate of change of period with time for thegravity wave pulsations in ZZ Ceti stars is a direct measurement of the cooling timescale for aDA white dwarf, which in turn can give an independent measurement of the age of thegalactic disk.^[19]

In 1982, calculations byDon Winget and his coworkers suggested that helium-atmosphere DB white dwarfs with surface temperatures around 19,000 K should also pulsate.^[21] Winget then searched for such stars and found thatGD 358 was a variable DB, orDBV, white dwarf.^[20] This was the first prediction of a class of variable stars before their observation.^[22] In 1985, this star was given the designationV777 Her, which is also another name for this class of variable stars.^[2][23] These stars have effective temperatures around 25,000K.^[24]

The third known class of pulsating variable white dwarfs is theGW Vir stars, sometimes subdivided intoDOV andPNNV stars. Their prototype isPG 1159-035.^[5] This star (also the prototype for the class ofPG 1159 stars) was observed to vary in 1979,^[26] and was given the variable star designationGW Vir in 1985,^[23] giving its name to the class. These stars are not, strictly speaking, white dwarfs; rather, they are stars which are in a position on theHertzsprung–Russell diagram between theasymptotic giant branch and the white dwarf region. They may be calledpre-white dwarfs.^[5][6] They are hot, withsurface temperatures between 75,000 K and 200,000 K, and have atmospheres dominated byhelium,carbon, andoxygen. They may have relatively low surface gravities (logg ≤ 6.5).^[27] It is believed that these stars will eventually cool and become DO white dwarfs.^[5]

The periods of thevibrational modes of GW Vir stars range from about 300 to about 5,000seconds.^[27] How pulsations are excited in GW Vir stars was first studied in the 1980s^[28] but remained puzzling for almost twenty years.^[29] From the beginning, the excitation mechanism was thought to be caused by the so-calledκ-mechanism associated with ionizedcarbon andoxygen in the envelope below the photosphere, but it was thought this mechanism would not function if helium was present in the envelope. However, it now appears that instability can exist even in the presence of helium.^[30]

A new class of white dwarfs, with spectral type DQ and hot, carbon-dominated atmospheres, has recently been discovered by Patrick Dufour, James Liebert and their coworkers.^[31] Theoretically, such white dwarfs should pulsate at temperatures where their atmospheres are partially ionized. Observations made atMcDonald Observatory suggest thatSDSS J142625.71+575218.3 is such a white dwarf; if so, it would be the first member of a new,DQV, class, of pulsating white dwarfs. However, it is also possible that it is a white dwarfbinary system with acarbon-oxygenaccretion disk.^[7]

• G 117-B15A
• Instability strip
• Stellar pulsation

• Koester, D.; Chanmugam, G. (1990)."REVIEW: Physics of white dwarf stars"(PDF).Reports on Progress in Physics.53 (7):837–915.Bibcode:1990RPPh...53..837K.doi:10.1088/0034-4885/53/7/001.ISSN 0034-4885.S2CID 250915046.
• Quirion, P.O.; Fontaine, G.; Brassard, P. (1 July 2007)."Mapping the Instability Domains of GW Vir Stars in the Effective Temperature-Surface Gravity Diagram".The Astrophysical Journal Supplement Series.171 (1):219–248.Bibcode:2007ApJS..171..219Q.doi:10.1086/513870.ISSN 0067-0049.

• Variable White Dwarf Data Tables, Paul A. Bradley, 22 March 2005 version. Accessed online June 7, 2007.
• A Progress Report on the Empirical Determination of the ZZ Ceti Instability Strip, A. Gianninas, P. Bergeron, and G. Fontaine, arXiv:astro-ph/0612043.
• Asteroseismology of white dwarf stars, D. E. Winget,Journal of Physics: Condensed Matter10, #49 (December 14, 1998), pp. 11247–11261. DOI 10.1088/0953-8984/10/49/014.

• Pulsating white dwarfs
• Star types

• Articles with short description
• Short description is different from Wikidata