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HD 41742/41700
HD 41742/41700 is a star system that lies approximately 87 light-years away in the constellation of Puppis. The system consists of two bright stars where the primary is orbited by two fainter stars, making it a quadruple with an unequal hierarchy.
== Component discovery ==
HD 41742 B was discovered early on in the history of visual binaries, due to the brightness of the primary. The earliest measurement in the Washington Double Star Catalog (WDS) dates to 1837 and was made by William Herschel, stating a position angle of 246° and a separation of 1.1" for the companion.〔 Surprisingly, recent measures suggest that the secondary has moved significantly over the two centuries since, with it lying at a position angle of around 215° and a separation increasing between 5.30" in the late 1970s〔 to 5.95" in 2010.〔 This translates to a minimum change in physical separation between 142 and 159 AU over 35 years,〔 which suggests that HD 41742 B is moving quickly away from the primary.
Lying at a considerably wider separation, HD 41700 was first observed relative to HD 41742 later than the tighter binary, despite being much brighter. The first measurement in the WDS dates to 1854 and was again made by Herschel, giving a position angle of 320° and a separation of 174".〔 More recent values agree on the position angle, but suggest a separation closer to 200". The wide separation of this tertiary component means that it has a separate Hipparcos entry to the primary, which confirms that the two stars lie at the same distance and are co-moving. The physical separation between the two is about 0.026 parsecs (0.084 light-years), or approximately 17200 AU.〔 This is comparable to the ~15000 AU separation between Alpha Centauri AB and Proxima Centauri; such wide separations between components are relatively rare, at least for solar-type stars.
Radial velocity observations of HD 41742 A with the HARPS spectrograph detected variations on a level of several km/s over a period of months, indicating that the star is a single-lined spectroscopic binary (SB1).〔 Though an orbital fit was not attempted, A good orbital fit is possible (left), which implies that HD 41742 Ab has a minimum mass of , and is on a high eccentricity ~222-day orbit around the primary. Given that the lines of the secondary are not detected, it must have a significantly lower luminosity than the primary, indicating that it is of late spectral type.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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