脈動白矮星

脈動白矮星是一種光度變化是由自身內部非徑向的引力波脈動造成的白矮星，已經知道的脈動白矮星包括DAV，或鯨魚座ZZ(這是大氣層以氫為主，光譜為DA型的白矮星)^[1]^{, pp. 891, 895}、DBV，或 武仙座V777(這是大氣層以氦為主，光譜為DB型的白矮星)^[2]^{, p. 3525}、和室女座GW(這是大氣層以氦、碳和氧為主，光譜為PG 1159型的白矮星。有些作者會將非PG 1159星的也包括在室女GW型內)。室女GW型可以再分為DOV和PNNV星^[3]^{, §1.1, 1.2;}^[4]。嚴格來說，它們還不是白矮星，因為在赫羅圖上還沒有抵達白矮星的位置，但可以算是前白矮星^[3]^{, § 1.1;}^[5]。大氣層以碳為主的次分類DQV星，也被建議屬於這一類^[6]。

由於有許多週期在數百秒至數千秒的變化模式疊加，使它們輸出的光度變化不會很大(1%-30%)。對這些變化的觀測提供了白矮星內部星震的證據^[7]。

DAV星

脈動白矮星的類型^[8]^[3]^{, §1.1, 1.2;}^[6]
DAV (GCVS：ZZA)	光譜類型DA，在光譜中只有氫的吸收線
DBV (GCVS: ZZB)	光譜類型DB，在光譜中只有氦的吸收線
室女座GW (GCVS: ZZO)	大氣層中大部分是C、He和O；或許可再分為DOV和PNNV星
DQV	光譜類型DQ；高溫、大氣層以碳為主

早期的計算建議白矮星的變光週期約為10秒鐘，但迄1960年代都未能找到^[1]^{, § 7.1.1;}^[9]。第一顆被發現的變光白矮星是HL金牛座76， Arlo U. Landolt在1965和1966年觀測到他的變光週期是12.5分^[10]。週期遠遠超過預測的原因是HL金牛座76像所知的其它脈動白矮星一樣，是由非徑向的引力波脈動造成的^[1]^{, § 7.}。在1970年，其它的白矮星，羅斯548 (Ross 548)，也被發現有和HL金牛座76相同型式的變化^[11]；在1972年，被冠上變星的標示，為鯨魚座ZZ^[12]。鯨魚座ZZ這個名稱也是脈動白矮星變星的一種類型，他是大氣層以氫為主的白矮星，也稱為DAV^[1]^{, pp. 891, 895.}。這種恆星的變光週期在30秒至25分鐘之間，有很狹窄的表面溫度，範圍大約在11,100至12,500K^[13]。測量鯨魚座ZZ 引力波脈動周期相對於時間變化的速率，可以直接測量DA白矮星冷卻的時間尺度，反過來可以獨立測量星系盤的年齡^[14]。

DBV星

在1982年，D. E. Winget和他同事的計算建議大氣層以氦為主，表面溫度大約在19,000的DB白矮星也是脈動白矮星^[15]^{, p. L67.}。Winget然後在搜尋中發現這樣的恆星GD 358，它是一顆變光的DB或DBV白矮星^[16]，這是第一種在被發現之前就已經預側到它們存在的變星^[17]^{, p. 89.}。在1985年，這顆變星被標示為武仙座V777，這也是這一種變星的另一個名稱^[18]^;^[2]^{, p. 3525}。這種恆星的有效溫度大約是25,000K^[1]^{, p. 895.}。

室女座GW星

第三種已知的脈動白矮星是室女座GW 星，經常再DOV和PNNV星，它們的原型是PG 1159-035^[3]^{, §1.1.}。這種變化的恆星(它的原型有時也稱為PG 1159星)是在1979年發現的^[19]，並且在1985年被以室女座GW標示為變星^[18]，並作為這一類變星的名稱。嚴格來說，這種恆星還不是白矮星，相反的，它們在赫羅圖上的位置介於漸近巨星分支和白矮星之間，它們應該稱為前白矮星^[3]^{, § 1.1;}^[5]。它們是高溫的，表面溫度在75,000 K至200,000 K，並且有著以氦、碳和氧為主的大氣層。它們可能有相對較低的表面重力(log g ≤ 6.5.)^[3]^{, Table 1}，一般認為這類的恆星在冷卻後會成為DO白矮星^[3]^{, § 1.1.}。

室女座GW的變光模式週期範圍在大約300秒至5,000秒^[3]^{, Table 1}，對室女座GW脈動是如何變化的研究，最早開始於1980年代^[20]，但仍然困擾了將近20年^[21]。一開始，激發的機制被認為是所謂的κ-機制與光球層下面被電離的碳和氧的包層共同的作用，但是，如過氦也存在於這些包層中，這種機制將不會發生作用。但是，現在認為即使有氦的存在，這種機制依然可以激發^[22]^{, §1.}。

DQV星

一種新類型白矮星，有著高溫、以碳為主的大氣層，光譜類型為DQ，是Patrick Dufour、James Liebert和他們的同事在最近發現的^[23]。理論上，這種白矮星在它們在有一部分大氣層被電離的溫度下就會發生脈動變化。麥克唐納天文臺的觀測認為SDSS J142625.71 + 575218.3就是這一種白矮星；若真是如此，它將是這種新類型脈動白矮星，DQV，的第一個成員。但是，它也可能是有碳-氧吸積盤的聯星系^[6]。

參考資料

^ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 Physics of white dwarf stars （页面存档备份，存于互联网档案馆）, D. Koester and G. Chanmugam, Reports on Progress in Physics 53 (1990), pp. 837–915.
^ ^2.0 ^2.1 White dwarfs, Gilles Fontaine and François Wesemael, in Encyclopedia of Astronomy and Astrophysics, ed. Paul Murdin, Bristol and Philadelphia: Institute of Physics Publishing and London, New York and Tokyo: Nature Publishing Group, 2001. ISBN 0333750888.
^ ^3.0 ^3.1 ^3.2 ^3.3 ^3.4 ^3.5 ^3.6 ^3.7 Mapping the Instability Domains of GW Vir Stars in the Effective Temperature-Surface Gravity Diagram （页面存档备份，存于互联网档案馆）, Quirion, P.-O., Fontaine, G., Brassard, P., Astrophysical Journal Supplement Series 171 (2007), pp. 219–248.
^ §1, Detection of non-radial g-mode pulsations in the newly discovered PG 1159 star HE 1429-1209 （页面存档备份，存于互联网档案馆）, T. Nagel and K. Werner, Astronomy and Astrophysics 426 (2004), pp. L45–L48.
^ ^5.0 ^5.1 The Extent and Cause of the Pre-White Dwarf Instability Strip （页面存档备份，存于互联网档案馆）, M. S. O'Brien, Astrophysical Journal 532, #2 (April 2000), pp. 1078–1088.
^ ^6.0 ^6.1 ^6.2 SDSS J142625.71+575218.3: A Prototype for a New Class of Variable White Dwarf, M. H. Montgomery et al., Astrophysical Journal 678, #1 (May 2008), pp. L51–L54, Bibcode：2008ApJ...678L..51M, doi:10.1086/588286.
^ Asteroseismology of white dwarf stars, D. E. Winget, Journal of Physics: Condensed Matter 10, #49 (December 14, 1998), pp. 11247–11261. DOI 10.1088/0953-8984/10/49/014.
^ Association Française des Observateurs d'Etoiles Variables. ZZ Ceti variables. Centre de Données astronomiques de Strasbourg. [2007-06-06]. （原始内容存档于2007-02-05）.
^ Ultrashort-Period Stellar Oscillations. I. Results from White Dwarfs, Old Novae, Central Stars of Planetary Nebulae, 3C 273, and Scorpius XR-1 （页面存档备份，存于互联网档案馆）, George M. Lawrence, Jeremiah P. Ostriker, and James E. Hesser, Astrophysical Journal 148, #3 (June 1967), pp. L161–L163.
^ A New Short-Period Blue Variable （页面存档备份，存于互联网档案馆）, Arlo U. Landolt, Astrophysical Journal 153, #1 (July 1968), pp. 151–164.
^ High-Frequency Stellar Oscillations. VI. R548, a Periodically Variable White Dwarf, Barry M. Lasker and James E. Hesser, Astrophysical Journal 163 (February 1971), pp. L89–L93.
^ 58th Name-List of Variable Stars, B. V. Kukarkin, P. N. Kholopov, N. P. Kukarkina, N. B. Perova, Information Bulletin on Variable Stars, #717, September 21, 1972.
^ Bergeron, P.; Fontaine, G. On the Purity of the ZZ Ceti Instability Strip: Discovery of More Pulsating DA White Dwarfs on the Basis of Optical Spectroscopy. The Astrophysical Journal. [2007-06-06]. （原始内容存档于2012-06-20）.
^ Kepler, S.O.; G. Vauclair, R. E. Nather, D. E. Winget, and E. L. Robinson. G117-B15A - How is it evolving?. White dwarfs; Proceedings of IAU Colloquium 114th, Hanover, NH, Aug. 15-19, 1988 (A90-32719 13-90). Berlin and New York: Springer-Verlag. 1989 [2007-06-07]. （原始内容存档于2012-06-20）.
^ Hydrogen-driving and the blue edge of compositionally stratified ZZ Ceti star models, D. E. Winget, H. M. van Horn, M. Tassoul, G. Fontaine, C. J. Hansen, and B. W. Carroll, Astrophysical Journal 252 (January 15, 1982), pp. L65–L68.
^ Photometric observations of GD 358: DB white dwarfs do pulsate, D. E. Winget, E. L. Robinson, R. D. Nather, and G. Fontaine, Astrophysical Journal 262 (November 1, 1982), pp. L11–L15.
^ White Dwarf Stars, Steven D. Kawaler, in Stellar remnants, S. D. Kawaler, I. Novikov, and G. Srinivasan, edited by Georges Meynet and Daniel Schaerer, Berlin: Springer, 1997. Lecture notes for Saas-Fee advanced course number 25. ISBN 3540615202.
^ ^18.0 ^18.1 The 67th Name-List of Variable Stars, P. N. Kholopov, N. N. Samus, E. V. Kazarovets, and N. B. Perova, Information Bulletin on Variable Stars, #2681, March 8, 1985.
^ PG1159-035: A new, hot, non-DA pulsating degenerate, J. T. McGraw, S. G. Starrfield, J. Liebert, and R. F. Green, pp. 377–381 in White Dwarfs and Variable Degenerate Stars, IAU Colloquium #53, ed. H. M. van Horn and V. Weidemann, Rochester: University of Rochester Press, 1979.
^ A Pulsation Mechanism for GW Virginis Variables, Arthur N. Cox, Astrophysical Journal 585, #2 (March 2003), pp. 975–982.
^ An Instability Mechanism for GW Vir Variables, A. N. Cox, p. 786, American Astronomical Society, 200th AAS Meeting, #85.07, in Bulletin of the American Astronomical Society 34 (May 2002).
^ New nonadiabatic pulsation computations on full PG 1159 evolutionary models: the theoretical GW Virginis instability strip revisited, A. H. Córsico, L. G. Althaus, and M. M. Miller Bertolami, Astronomy and Astrophysics 458, #1 (October 2006), pp. 259–267.
^ White dwarf stars with carbon atmospheres, Patrick Dufour, James Liebert, G. Fontaine, and N. Behara, Nature 450, #7169 (November 2007), pp. 522–524, Bibcode：2007Natur.450..522D, doi:10.1038/nature06318

外部連結和延伸讀物

Variable White Dwarf Data Tables （页面存档备份，存于互联网档案馆）, 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 Matter 10, #49 (December 14, 1998), pp. 11247–11261. DOI 10.1088/0953-8984/10/49/014.

[physrev-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 Physics of white dwarf stars （页面存档备份，存于互联网档案馆）, D. Koester and G. Chanmugam, Reports on Progress in Physics 53 (1990), pp. 837–915.

[wden-2] 2.0 ^2.1 White dwarfs, Gilles Fontaine and François Wesemael, in Encyclopedia of Astronomy and Astrophysics, ed. Paul Murdin, Bristol and Philadelphia: Institute of Physics Publishing and London, New York and Tokyo: Nature Publishing Group, 2001. ISBN 0333750888.

[quirion-3] 3.0 ^3.1 ^3.2 ^3.3 ^3.4 ^3.5 ^3.6 ^3.7 Mapping the Instability Domains of GW Vir Stars in the Effective Temperature-Surface Gravity Diagram （页面存档备份，存于互联网档案馆）, Quirion, P.-O., Fontaine, G., Brassard, P., Astrophysical Journal Supplement Series 171 (2007), pp. 219–248.

[4] §1, Detection of non-radial g-mode pulsations in the newly discovered PG 1159 star HE 1429-1209 （页面存档备份，存于互联网档案馆）, T. Nagel and K. Werner, Astronomy and Astrophysics 426 (2004), pp. L45–L48.

[obrien-5] 5.0 ^5.1 The Extent and Cause of the Pre-White Dwarf Instability Strip （页面存档备份，存于互联网档案馆）, M. S. O'Brien, Astrophysical Journal 532, #2 (April 2000), pp. 1078–1088.

[dqv-6] 6.0 ^6.1 ^6.2 SDSS J142625.71+575218.3: A Prototype for a New Class of Variable White Dwarf, M. H. Montgomery et al., Astrophysical Journal 678, #1 (May 2008), pp. L51–L54, Bibcode：2008ApJ...678L..51M, doi:10.1086/588286.

[7] Asteroseismology of white dwarf stars, D. E. Winget, Journal of Physics: Condensed Matter 10, #49 (December 14, 1998), pp. 11247–11261. DOI 10.1088/0953-8984/10/49/014.

[8] Association Française des Observateurs d'Etoiles Variables. ZZ Ceti variables. Centre de Données astronomiques de Strasbourg. [2007-06-06]. （原始内容存档于2007-02-05）.

[9] Ultrashort-Period Stellar Oscillations. I. Results from White Dwarfs, Old Novae, Central Stars of Planetary Nebulae, 3C 273, and Scorpius XR-1 （页面存档备份，存于互联网档案馆）, George M. Lawrence, Jeremiah P. Ostriker, and James E. Hesser, Astrophysical Journal 148, #3 (June 1967), pp. L161–L163.

[10] A New Short-Period Blue Variable （页面存档备份，存于互联网档案馆）, Arlo U. Landolt, Astrophysical Journal 153, #1 (July 1968), pp. 151–164.

[11] High-Frequency Stellar Oscillations. VI. R548, a Periodically Variable White Dwarf, Barry M. Lasker and James E. Hesser, Astrophysical Journal 163 (February 1971), pp. L89–L93.

[12] 58th Name-List of Variable Stars, B. V. Kukarkin, P. N. Kholopov, N. P. Kukarkina, N. B. Perova, Information Bulletin on Variable Stars, #717, September 21, 1972.

[13] Bergeron, P.; Fontaine, G. On the Purity of the ZZ Ceti Instability Strip: Discovery of More Pulsating DA White Dwarfs on the Basis of Optical Spectroscopy. The Astrophysical Journal. [2007-06-06]. （原始内容存档于2012-06-20）.

[14] Kepler, S.O.; G. Vauclair, R. E. Nather, D. E. Winget, and E. L. Robinson. G117-B15A - How is it evolving?. White dwarfs; Proceedings of IAU Colloquium 114th, Hanover, NH, Aug. 15-19, 1988 (A90-32719 13-90). Berlin and New York: Springer-Verlag. 1989 [2007-06-07]. （原始内容存档于2012-06-20）.

[15] Hydrogen-driving and the blue edge of compositionally stratified ZZ Ceti star models, D. E. Winget, H. M. van Horn, M. Tassoul, G. Fontaine, C. J. Hansen, and B. W. Carroll, Astrophysical Journal 252 (January 15, 1982), pp. L65–L68.

[16] Photometric observations of GD 358: DB white dwarfs do pulsate, D. E. Winget, E. L. Robinson, R. D. Nather, and G. Fontaine, Astrophysical Journal 262 (November 1, 1982), pp. L11–L15.

[kawaler-17] White Dwarf Stars, Steven D. Kawaler, in Stellar remnants, S. D. Kawaler, I. Novikov, and G. Srinivasan, edited by Georges Meynet and Daniel Schaerer, Berlin: Springer, 1997. Lecture notes for Saas-Fee advanced course number 25. ISBN 3540615202.

[namelist67-18] 18.0 ^18.1 The 67th Name-List of Variable Stars, P. N. Kholopov, N. N. Samus, E. V. Kazarovets, and N. B. Perova, Information Bulletin on Variable Stars, #2681, March 8, 1985.

[19] PG1159-035: A new, hot, non-DA pulsating degenerate, J. T. McGraw, S. G. Starrfield, J. Liebert, and R. F. Green, pp. 377–381 in White Dwarfs and Variable Degenerate Stars, IAU Colloquium #53, ed. H. M. van Horn and V. Weidemann, Rochester: University of Rochester Press, 1979.

[20] A Pulsation Mechanism for GW Virginis Variables, Arthur N. Cox, Astrophysical Journal 585, #2 (March 2003), pp. 975–982.

[21] An Instability Mechanism for GW Vir Variables, A. N. Cox, p. 786, American Astronomical Society, 200th AAS Meeting, #85.07, in Bulletin of the American Astronomical Society 34 (May 2002).

[newnon-22] New nonadiabatic pulsation computations on full PG 1159 evolutionary models: the theoretical GW Virginis instability strip revisited, A. H. Córsico, L. G. Althaus, and M. M. Miller Bertolami, Astronomy and Astrophysics 458, #1 (October 2006), pp. 259–267.

[23] White dwarf stars with carbon atmospheres, Patrick Dufour, James Liebert, G. Fontaine, and N. Behara, Nature 450, #7169 (November 2007), pp. 522–524, Bibcode：2007Natur.450..522D, doi:10.1038/nature06318

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