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Giclas 29-38 is a variable white dwarf star of the DAV, or ZZ Ceti, whose variability is due to large-amplitude, non-radial pulsations, known as gravity waves. It was first reported to be variable by Shulov and Kopatskaya in 1974.〔O. S. Shulov and E. N. Kopatskaya, ''Astrofizika'' 10, #1 (January–March, 1974), pp. 117–120. Translated into English as (Variability of the white dwarf G 29-38 ), ''Astrophysics'', 10, #1 (January, 1974), pp. 72–74. DOI 10.1007/BF01005183.〕〔(G 29-38 and G 38-29: two new large-amplitude variable white dwarfs ), J. T. McGraw and E. L. Robinson, ''Astrophysical Journal'' 200 (September 1975), pp. L89–L93.〕 DAV stars are like normal white dwarfs but have luminosity variations with amplitudes as high as 30%, arising from a superposition of vibrational modes with periods from 100 to 1,000 seconds. Large-amplitude DAVs generally differ from lower-amplitude DAVs by having lower temperatures, longer primary periodicities, and many peaks in their vibrational spectra with frequencies which are sums of other vibrational modes.〔(Observational limits on companions to G29-38 ), S. J. Kleinman, R. E. Nather, D. E. Winget, J. C. Clemens, P. A. Bradley, A. Kanaan, J. L. Provencal, C. F. Claver, T. K. Watson, K. Yanagida, J. S. Dixson, M. A. Wood, D. J. Sullivan, E. Meistas, E. M. Leibowitz, P. Moskalik, S. Zola, G. Pajdosz, J. Krzesinski, J.-E. Solheim, A. Bruvold, D. O'Donoghue, M. Katz, G. Vauclair, N. Dolez, M. Chevreton, M. A. Barstow, S. O. Kepler, O. Giovannini, C. J. Hansen, and S. D. Kawaler, ''Astrophysical Journal'' 436, #2 (December 1994), pp. 875–884.〕 G29-38, like other complex, large-amplitude DAV variables, has proven difficult to understand. The power spectrum or periodogram of the light curve varies over times which range from weeks to years. Usually, one strong mode dominates, although many smaller-amplitude modes are often observed. The larger-amplitude modes, however, fluctuate in and out of observability; some low-power areas show more stability. Asteroseismology uses the observed spectrum of pulsations from stars like G29-38 to infer the structure of their interiors.〔 ==Debris disk== The circumstellar environment of G29-38 first attracted attention in the late 1980s during a near-infrared survey of 200 white dwarfs conducted by Ben Zuckerman and Eric Becklin to search for low mass companion stars and brown dwarfs.〔(A low-temperature companion to a white dwarf star ), E. E. Becklin & B. Zuckerman, ''Nature'' 336 (Dec. 15, 1988), pp. 656-658〕 G29-38 was shown to radiate substantial emission between 2 and 5 micrometres, far in excess of that expected from extrapolation of the visual and near infrared spectrum of the star.〔(Excess infrared radiation from a white dwarf - an orbiting brown dwarf? ) B. Zuckerman & E. E. Becklin, ''Nature'' 330, (Nov. 12, 1987), pp. 138-140〕 Like other young, hot white dwarfs, G29-38 is thought to have formed relatively recently (600 million years ago) from its AGB progenitor, and therefore the excess was naturally explained by emission from a Jupiter-like brown dwarf with a temperature of 1200 K and a radius of 0.15 solar radius.〔〔 However, later observations, including speckle interferometry, failed to detect a brown dwarf.〔Keck Speckle Imaging of the White Dwarf G29-38: No Brown Dwarf Companion Detected, Marc J. Kuchner, Christopher D. Koresko, and Michael E. Brown, ''The Astrophysical Journal'' 508, #1 (November 20, 1998), pp. L81–L83. . .〕 Infrared observations made in 2004 by NASA's Spitzer Space Telescope indicated the presence of a dust cloud around G29-38, which may have been created by tidal disruption of a comet passing close to the white dwarf.〔(The Dust Cloud around the White Dwarf G29-38 ), William T. Reach, Marc J. Kuchner, Ted von Hippel, Adam Burrows, Fergal Mullally, Mukremin Kilic, and D. E. Winget, ''Astrophysical Journal'' 635, #2 (December 2005), pp. L161–L164.〕 This may mean that G29-38 is still orbited by a ring of surviving comets and, possibly, outer planets. This is the first observation supporting the idea that comets persist to the white dwarf stage of stellar evolution.〔(NASA's Spitzer Finds Possible Comet Dust Around Dead Star ), NASA press release, January 11, 2006.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「G 29-38」の詳細全文を読む スポンサード リンク
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