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HD 168625 (V4030 Sgr) is a blue hypergiant and candidate luminous blue variable located in the constellation of Sagittarius easy to see with amateur telescopes. It forms a visual pair with the also blue hypergiant (and luminous blue variable) HD 168607 and is located to the south-east of M17, the Omega Nebula. Its distance and association with that nebula and the mentioned star is dubious; while some authors think both stars are physically associated and belong to the stellar association Serpens OB1,〔 〕 at a distance to the Sun of 2.2 kiloparsecs (7.200 light years),〔 〕 others think HD 168625 is farther, at a distance estimated to be 2.8 kiloparsecs (9,100 light years) and unrelated to the former objects.〔 〕 == Physical characteristics == Assuming a distance of 2.2 kiloparsecs, HD 168625 is 220,000 times brighter than the Sun, having a surface temperature of 12,000 K.〔 It is losing mass through a very strong stellar wind at a rate of roughly 1.46×10−6 solar masses per year〔 and observations realized in 2012 with the help of the VLT show it's actually a binary star.〔 〕 However, its most notable characteristic is the presence of a nebula surrounding it that was discovered in 1994〔 〕 and that has been studied with the help of several instruments and observatories and telescopes that include among others the Hubble Space Telescope〔 and the VLT.〔 〕 Said studies show that HD 168625 is actually surrounded by two nebulae: an inner one that has an elliptical shape and a very complex structure that includes arcs and filaments,〔 and a much larger outer one discovered with the help of the Spitzer Space Telescope that has a bipolar shape and that looks like a clone of the one surrounding Sanduleak -69° 202, the progenitor of the supernova 1987A in the Large Magellanic Cloud.〔 〕 This suggests Sanduleak -69° 202 was also a luminous blue variable as well as the possibility of HD 168625 exploding as a Type II supernova in the near future.〔 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「HD 168625」の詳細全文を読む スポンサード リンク
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