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HD 120987 (''y Cen'' or ''y Centauri'') is a star located in the constellation Centaurus. HD 120987 is a quintuple star system located 50 pc (163 light years) from the Sun. The system is located at RA 13h 53m 32.8s, and Dec -35 deg 39 arcmin 51 arcsec. The entire system has an apparent visual magnitude of +5.54, and an absolute magnitude of +2.03. The system is both a visual and spectroscopic binary. The system is centered on the AB component, which contains two F4V dwarf stars, with 3 other stars further out. HD 120987 A is the primary, an F4V dwarf of apparent visual magnitude +6.2, and absolute visual magnitude of +2.7. The star has an effective temperature of 6900 Kelvin and is 1.5 solar masses. HD 120987 B is an F4V dwarf of apparent visual magnitude +6.4, and absolute visual magnitude of +2.9. The star has a mass of 1.5 solar masses, and effective temperature 6900 Kelvin. The star is a spectroscopic binary with HD 120987 A, and was first discovered by AH Howe, in 1889. The angular separation is less than one arcsec. HD 120987 AB orbit each other with a true separation of approximately 0.8 AU. HD 120987 C is a white dwarf of apparent visual magnitude of +12.5. HD 120987 AC orbits the AB pair with angular separation of 27.5 arcsec. The star was first discovered by SW Burnham. HD 120987 AC orbits the AB pair at a distance of 24 AUs, less than the distance of Uranus from the Sun. HD 120987 D is a white dwarf of apparent visual magnitude of +14.5. y Centuari AD orbits the AB pair with angular separation of 30 arcsec. The star was first discovered by Robert T.A. Innes. HD 120987 AD orbits the AB pair at a distance of about 26 AUs, within the orbit of Neptune. HD 120987 E is located 66 arcsec from the primary. It has an apparent visual magnitude of 8.51, and was first discovered by William Herschel. It is a visual binary to HD 120987 A, and was the first component of the quintuple system discovered. HD 120987 AE orbits the AB pair at a distance of 57 AUs, or about twice the distance of Neptune from the Sun. == References == *http://www.alcyone.de/cgi-bin/search.pl?object=HR5222 *http://server3.wikisky.org/starview?object_type=1&object_id=3204 *http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+120987&submit=SIMBAD+search *http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%402228202&Name=CD-35%20%209089&submit=submit *http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%402228204&Name=CD-35%20%209090C&submit=submit *http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%402228205&Name=CD-35%20%209090D&submit=submit 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 120987」の詳細全文を読む スポンサード リンク
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