Gamma Lyrae
 Location of γ Lyrae |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Lyra |
| Right ascension | 18h 58m 56.62241s[1] |
| Declination | +32° 41′ 22.4003″[1] |
| Apparent magnitude (V) | 3.261[2] |
| Characteristics | |
| Spectral type | B9 III[3] |
| U−B color index | –0.125[2] |
| B−V color index | –0.047[2] |
| Astrometry | |
| Radial velocity (Rv) | –21.1[4] km/s |
| Proper motion (μ) | RA: –3.09[1] mas/yr Dec.: +1.11[1] mas/yr |
| Parallax (π) | 5.26 ± 0.27[1] mas |
| Distance | 620 ± 30 ly (190 ± 10 pc) |
| Details | |
| Radius | 15[5] R☉ |
| Surface gravity (log g) | 3.5[6] cgs |
| Temperature | 10,080[6] K |
| Metallicity [Fe/H] | +0.11[6] dex |
| Rotational velocity (v sin i) | 71–72[7] km/s |
| Other designations | |
Gamma Lyrae (γ Lyr, γ Lyrae) is the second brightest star in the northern constellation of Lyra. It has the traditional names Sulafat (Sulaphat), from the Arabic السلحفاة al-sulḥafāt "turtle", and Jugum,[9] from the Latin iugum "yoke". The connection with turtles is that fine harps were traditionally made of tortoiseshell. The apparent visual magnitude of Sulafat is 3.3,[2] which is readily visible to the naked eye. Parallax measurements yield an estimated distance of 620 light-years (190 parsecs) from the Earth.
This is a giant star with a stellar classification of B9 III,[3] indicating it has exhausted the supply of hydrogen at its core and evolved away from the main sequence. The effective temperature of the outer envelope of this star is 10,080 K,[6] giving it the blue-white hue typical of a B-type star.[10] The interferometry-measured angular diameter of this star is 0.74 ± 0.10 mas,[11] which, at its estimated distance, equates to a physical radius of roughly 15 times the radius of the Sun.[5]
In 1909, Canadian astronomer Samuel A. Mitchell identified this star as a spectroscopic binary, although he was unable to split the absorption lines of the components. He found that a period of 25.6 days matched his measurements.[12] It was reported as a spectroscopic binary as recently as 2001,[13] but is now believed to be a single star[14][15] with a high rate of rotation for stars of this type.[13]
In China, 漸台 (Jiāntāi), meaning Clepsydra Terrace, refers to an asterism consisting of this star, δ2 Lyrae, β Lyrae and ι Lyrae.[16] Consequently, γ Lyrae itself is known as 漸台三 (Jiāntāisān, English: the Third Star of Clepsydra Terrace.)
References
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- ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
