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FG Sagittae, in the constellation Sagitta, is a supergiant star in the constellation Sagitta at a distance of 8000 light-years. When first noted in 1943, it was noticed to be a variable star, and its spectrum was registered as of B4Ieq ("blue") in 1955. Since then it has expanded and reddened to G ("yellow") in 1991,〔(Newscientist: Life and times of a chameleon star )〕 and then further to about K〔(VizieR data on FG Sge ), search for Catalogue of Stellar Spectral Classifications (Skiff, 2007)〕 ("orange"). FG started to pulsate when becoming an A-type star (soon after being registered as B4Ieq) with a period of 15 days, now the period has increased to over 100 days. FG Sagittae is the central star of the planetary nebula ''Henize 1-5''. Since 1992 the star has exhibited fadings and recoveries similar to that of a R Coronae Borealis variable star, and this behavior is emphasized by a hydrogen deficiency typical for this class of stars.〔(NASA ADS: "Sakurai's Object, V605 Aquilae, and FG Sagittae: An Evolutionary Sequence Revealed", by Lawlor, T. M.; MacDonald, J. )〕 It has been proposed that this star has undergone a ''late thermal pulse'' (LTP) of helium fusion after having left the asymptotic giant branch (AGB) to move towards the hottest end of the ''white dwarf cooling track''. This thermal pulse is believed to have revived this aged star to once again, for a short time, behave as an AGB star.〔 == See also == * Sakurai's Object, also known as V4334 Sgr, another presumed late thermal pulsing object. * V605 Aquilae. 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「FG Sagittae」の詳細全文を読む スポンサード リンク
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