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AB7, also known as SMC WR7, is a binary star in the Small Magellanic Cloud. A Wolf-Rayet star and a supergiant companion of spectral type O orbit in a period of 19.56 days. The system is surrounded by a ring-shaped nebula known as a ''bubble nebula''. ==Nebula== AB7 lies at the centre of a bubble nebula shaped and ionised by powerful stellar winds from the stars within it. The nebula was first catalogued as the N76 and N76A Hα emission line nebulae. N76A is the brighter portion of the larger round N76 nebula towards bottom left in the images and N76B is the detached knot at bottom right. N76 lies between two other prominent HII region The nebula was catalogued at radio wavelengths as SMC DEM 123 and 124, corresponding to N76A and N76 respectively. DEM 124 is described as a shell surrounding DEM 123. N76 is an HII region about 5 arc-minutes wide, 40-50 parsec N76 is described as containing the open cluster NGC 371, although the reverse may be more accurate. The stars of NGC 371 are scattered over twice the diameter of N76, around 100 parsecs, and might better be described as a stellar association than an open cluster. They can be seen as the higher density of stars in the lower half of the images. Hodge catalogued stellar associations in the SMC and Hodge 53 was defined to include NGC 371. AB7 is sometimes described as being within N76A, but this is incorrect. N76A is the small dense HII region SE of AB7, part of the "ring", while AB7 lies at the centre of the less dense nebulosity within the ring.〔〔 It may already be the home of a new generation of stars; N76A hosts at least five hot young stars including a probable O9 main sequence star at its centre.〔 A nearby unusual oxygen-rich supernova remnant has been intensively studied. It is visible as the knot of filaments growing green from ionised oxygen emission. 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「AB7」の詳細全文を読む スポンサード リンク
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