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HD 53705/53706/53680 is a star system that lies approximately 54 light-years away in the constellation of Puppis. The system consists of four stars in two binaries, making it one of the nearest quadruple star systems. ==Component discovery== HD 53705 was discovered to be a visual binary very early on, owing to the brightness of the two components. The earliest observation in the Washington Double Star Catalog (WDS) dates to 1826 and was made by James Dunlop, stating a position angle of 119 degrees and a separation of 21.5 arcseconds for the companion.〔 The two stars have moved very little relative to each other since, with the most recent measurement from 1999 stating a position angle of 126 degrees and a separation of 20.9 arcseconds. This is related to the nearby location of the system: a separation of 21 arcseconds translates to a physical separation perpendicular to the line of sight of approximately 480 AU,〔 so the orbit of the stars lasts somewhere on the order of millennia. The companionship of HD 53680 to the closer binary was recognised later, with the first measurement in the WDS dating to 1900.〔 With a position angle of 337 degrees and a separation of 185.7 arcseconds, HD 53680 lies on the opposite side of HD 53705 when compared to B, and is about nine times more distant. This separation results in a physical separation perpendicular to the line of sight of 4390 AU,〔 which is atypically distant for a stellar companion but still close enough to be strongly gravitationally bound. While all three components have similar proper motion, HD 53680's proper motion as measured by HIPPARCOS is sizeably discrepant from the proper motions of the other two components. A clue to the cause of this is that HD 53680's Tycho-2 proper motion is different from the HIPPARCOS values, which indicates that the star is being perturbed by a close companion.〔 A fit of the HIPPARCOS astrometric data found a weakly constrained fit found a period of 1500 days, an inclination of 180 degrees (a face-on orbit) and a semimajor axis of 30.6 milliarcseconds.〔 The fit is weakly constrained because HIPPARCOS observations do not span the full orbit of the companion, but the fit does adjust HD 53680's proper motion to be consistent with the proper motion of HD 53705/53706. The low inclination of HD 53680 B's orbit reduces the amplitude of the radial velocity variation that it caused on HD 53680 A. In this case, the effect reduced the minimum mass of the companion into the brown dwarf regime as deduced from observations with the CORALIE spectrograph.〔 The spectroscopic orbit produces far stronger constraint compared to the astrometry-only orbit. 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 53705/53706/53680」の詳細全文を読む スポンサード リンク
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