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Sakurai's Object (V4334 Sgr) is a star in the constellation of Sagittarius named after Yukio Sakurai, a Japanese amateur astronomer, who discovered it in 1996. It is a star which has undergone a Very Late Thermal Pulse. Sakurai's Object is thought to be a red giant star that was previously a white dwarf; a Very Late Thermal Pulse occurred during the white dwarf phase and caused it to swell back to a giant configuration. These types of objects, of which only a handful have been observed, become hydrogen deficient and enriched in helium and other metals.〔 It is expected that these stars will end up as helium rich white dwarves after retracing their evolution track from the "born-again" giant phase back to the white dwarf cooling track. Sakurai's Object is one of only two stars observed during the high luminosity phase of a Very Late Thermal Pulse, the other being V605 Aquilae which was discovered in 1919. There are few other suspected "born-again" objects; one example being FG Sagittae. ==Observation history== An International Astronomical Union Circular sent on February 23, 1996 announced the discovery of a “possible ’slow’ nova” of magnitude 11.4 by Yukio Sakurai, an amateur astronomer.〔(THE ING NEWSLETTER No. 2, March 2000, Don Pollacco, QUB )〕 Japanese astronomer Syuichi Nakano reported the discovery, drawing attention to the fact that the object had not been visible in images from 1993 nor in Harvard–Smithsonian Center for Astrophysics records for the years 1930-1951 despite it appearing to slowly brighten over the previous year. Nakano wrote that “While the outburst () a slow or symbiotic nova, the lack of obvious emission lines one year after brightening is very unusual.” Following the initial announcement, Hilmar Duerbeck et al. published a study investigating the ‘possible final helium flash’ seen by Sakurai. In it, they noted that the location of Sakurai’s Object corresponded to a faint object detected in 1976 of magnitude 21, and discussed other observations in the years 1994–1996, by which time the magnitude had increased to around 11–15. By investigating the measured fluxes, angular diameter, and mass of the nebula, a distance of 5.5kpc and luminosity of was determined. The researchers noted that this was in agreement with appearance and model predictions and that the outburst luminosity was in the area of 3100 solar luminosities; lower than predicted by a factor of 3. The first infrared observations were published in 1998, in which both near and far infrared spectroscopy was presented. The collected data showed Sakurai's Object brightening over the year of observations as expected and the researchers found that circumstellar dust was present at a temperature of ~680K. Further infrared data, taken using the United Kingdom Infrared Telescope, was published in 2000 in which findings of the changing absorption lines were discussed. 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「Sakurai's Object」の詳細全文を読む スポンサード リンク
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