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Binary star system in the constellation Boötes From Wikipedia, the free encyclopedia
Gamma Boötis, Latinised from γ Boötis, is a binary star[12] system in the northern constellation of Boötes the herdsman, forming the left shoulder of this asterism.[13] The primary component has the proper name Seginus /sɪˈdʒaɪnəs/[citation needed], the traditional name of the Gamma Bootis system.[14] It has a white hue and is visible to the naked eye with a typical apparent visual magnitude of +3.03.[2] Based on parallax measurements obtained during the Hipparcos mission, it is located at a distance of approximately 85 light-years from the Sun, but is drifting closer with a radial velocity of −32 km/s.[6]
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Boötes |
| Right ascension | 14h 32m 04.67180s[1] |
| Declination | +38° 18′ 29.7043″[1] |
| Apparent magnitude (V) | +3.03[2] +3.02 to +3.07[3] |
| Characteristics | |
| Spectral type | A7 IV+(n)[2] or A7 III[4] |
| U−B color index | +0.120[4] |
| B−V color index | +0.191[4] |
| Variable type | δ Sct[5] |
| Astrometry | |
| Radial velocity (Rv) | −32.40±1.0[6] km/s |
| Proper motion (μ) | RA: −115.71[1] mas/yr Dec.: +151.16[1] mas/yr |
| Parallax (π) | 37.58 ± 0.14 mas[1] |
| Distance | 86.8 ± 0.3 ly (26.61 ± 0.10 pc) |
| Absolute magnitude (MV) | +0.93[4] |
| Details | |
| Aa | |
| Mass | 2.10[7] M☉ |
| Radius | 4.65±0.04[8] R☉ |
| Luminosity | 33.4[9] L☉ |
| Surface gravity (log g) | 3.75±0.05[4] cgs |
| Temperature | 7,800[10] K |
| Metallicity [Fe/H] | −0.08[4] dex |
| Rotational velocity (v sin i) | 121[10] km/s |
| Age | 0.9[4] or 1.0[7] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The double nature of this system was discovered by American astronomer S. W. Burnham in 1878, and has the discovery code BU 616.[15] The system is resolved into a pair separated by 33.4 arcseconds with a magnitude difference of 9.27. The brighter primary is itself a close pair separated by 0.069″,[16] as discovered by B. L. Morgan and associates in 1975.[15] The primary or 'A' component of this double star system is designated WDS J14321+3818 ('B' is the star UCAC2 45176266[17]) in the Washington Double Star Catalog. Parallax measurements for component B give a distance of approximately 1,996 light-years.[18] Gamma Boötis' two components are themselves designated WDS J14321+3818Aa (Seginus)[14] and Ab.
The stellar classification of Gamma Boötis is A7IV+(n),[2] matching an A-type star with somewhat "nebulous" lines due to rapid rotation. It was found to be a short-period variable star in 1914 by German astronomers P. Guthnick and R. Prager. Non-radial pulsations were detected in 1992 by Edward J. Kennelly and colleagues.[10] It is a Delta Scuti-type variable star with a period of 6.96753 h that varies from magnitude +3.02 down to +3.07.[3] This dominant mode is 21.28 cycles per day with an amplitude of 0.05 in magnitude.[10] Additional pulsations occur at 18.09, 12.02, 11.70 and 5.06 cycles per day.[4]
These types of stars are usually on the main sequence or slightly evolved.[4] The primary is around one billion years old with 2.1[7] times the mass of the Sun and five[20] times the Sun's radius. Measurements of the projected rotational velocity range from 115 to 145 km/s,[4] suggesting a high rate of spin. On average, the star is radiating 33.4[9] times the luminosity of the Sun from its photosphere at an effective temperature of 7,800 K.[10]
The system displays a statistically significant infrared excess due to a circumstellar disk. A model fit to the data indicates this material has a mean temperature of 85 K and is orbiting at a distance of 99±10 AU.[9]
γ Boötis (Latinised to Gamma Boötis) is the binary's Bayer designation. WDS J14321+3818 is the wider system's designation in the Washington Double Star Catalog. The designations of the two constituents as WDS J14321+3818A and B, and those of A's components—WDS J14321+3818Aa and Ab—derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[21]
Gamma Boötis bore the traditional name Ceginus (later Seginus), from cheguius or theguius, apparently Latin mistranscriptions of an Arabic rendering of Greek Boötes.[22] Two possibilities have been suggested: from Arabic بوطس bwṭs, in one of the manuscripts of the Almagest, with undotted ب b mistaken for an undotted ث th, و w taken as w and spelled 'gu', and ط ṭ completely misread,[23] or from Arabic بؤوتس bwʾwts, with undotted ب b mistaken for an undotted ث th, ؤ w-hamza mistaken for غ ġ, و w read as u, and undotted ن n misread as an undotted ى y and transcribed i—that is, as th-g-u-i-s with unwritten vowels (and the Latin grammatical ending -us) filled in for theguius.[24]
In 2016, the IAU organized a Working Group on Star Names (WGSN)[25] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[26] It approved the name Seginus for WDS J14321+3818Aa on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[14]
Gamma Boötis was listed as Haris in Bečvář, apparently derived from the Arabic name of the constellation of Boötes, Al-Haris Al-Sama meaning "the guard of the north".[22]
In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Menkib al Aoua al Aisr (منكب العواء الأيسر – mankibu lʿawwaaʾi lʾaysar), which was translated into Latin as Humerus Sinister Latratoris, meaning 'the left shoulder of barker'.[27]
In Chinese astronomy, Gamma Boötis is called 招搖, Pinyin: Zhāoyáo, meaning Twinkling Indicator, because this star is marking itself and standing alone in Twinkling Indicator asterism, Root mansion (see: Chinese constellation).[28] 招搖 (Zhāoyáo), westernized into Chaou Yaou, but the name Chaou Yaou was designated for Beta Boötis (Nekkar) by R.H. Allen and the meaning is "to beckon, excite, or move."[13]
USS Seginus (AK-133) was a U.S. Navy Crater-class cargo ship named after the star.
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