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Kappa Fornacis (κ For) is a star system that lies approximately 72 light-years away. The system consists of a somewhat evolved primary orbited by a massive, 'dark' secondary that is actually itself a close red dwarf binary, making a hierarchal triple system. == Multiplicity == Kappa Fornacis was found to be 0.23 arcseconds north of an X-ray and Radio source in 1995, a distance so close that it is most likely associated with the star.〔 While this would indicate that the star is active and therefore young, private communication indicated that Kappa Fornacis was a spectroscopic binary, leaving the possibility that a companion star was the source of the excess emission. The Hipparcos mission detected a large 19.4 mas/year acceleration in the proper motion of Kappa Fornacis, suggesting that part of an orbit was being observed. Combining this with other proper motion data spanning approximately half a century indicated a periodic variation of 26.5 ± 2 years, confirming that the star is an astrometric binary.〔〔 The amplitude of the variation indicated a mass sum of ; with a primary of approximately , it was evident that the two components must have approximately equal masses. However, as the companion's light or spectrum was not observed, it was clear that it was fainter than a main sequence star. This was interpreted as the companion being a white dwarf. Apparently unaware of the indication of binarity, Kappa Fornacis was included in several radial velocity-based planet searches that began towards the end of the century. A long-period variability was obvious; a linear trend of -1.73 ± 0.02 m/s/d was found by the CCPS,〔 while the longer time series of the ESO-CES survey, non-linearity in the trend was apparent and a preliminary orbit was presented, considerably shorter than the astrometric one.〔 Abt et al. 2006 expanded upon this with new and historical data to find a more precise orbit, again shorter than the astrometric one.〔 More recently, a continuation of the ESO-CES survey to the HARPS spectrograph indicates that the companion's orbital period is somewhat longer, more consistent with the astrometric period.〔 Kappa Fornacis B was first resolved independently by Lafrenière et al. (2007) and Tokovinin and Cantarutti (2008),〔〔 both finding a separation of about 0.5 arcseconds that is consistent with the astrometric orbit. The difference in brightness between the two components confirmed that the secondary is overly faint for its mass; The latter paper ascribes this to it being a massive white dwarf or a close M-dwarf binary, but could not discriminate between the two possibilities. The companion has been resolved several times since, allowing for a preliminary visual orbit to be made by 2012.〔 Tokovinin (2013) combined spectroscopic and visual data on the system to find the most accurate determination of the binary orbit thus far.〔 While the photometric colours of the secondary are consistent with an early M-dwarf (), it lies above the main sequence, meaning that its luminosity is too high to be a single star. This means that the secondary must actually be two close stars of similar spectral type, themselves orbiting the more massive primary. Two faint absorption lines were weakly detected in the Hα line, varying by about 80 km/s over a period of a few days; these are consistent with two M-dwarfs orbiting each other, confirming that the secondary is a close binary. The subsystem consists of two approximately equal-mass red dwarfs orbiting each other every ~3.7 days. Binaries with such close orbits typically maintain high levels of activity for their lifetimes due to their rotational periods being synchronised to their orbital period, so the components of the secondary are the source of the excess energy in the system. 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「Kappa Fornacis」の詳細全文を読む スポンサード リンク
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