Eta Serpentis
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Serpens |
| Right ascension | 18h 21m 18.60056s[1] |
| Declination | –02° 53′ 55.7766″[1] |
| Apparent magnitude (V) | 3.260[2] |
| Characteristics | |
| Spectral type | K0 III-IV[3] |
| U−B color index | +0.643[2] |
| B−V color index | +0.940[2] |
| Astrometry | |
| Radial velocity (Rv) | +8.4[4] km/s |
| Proper motion (μ) | RA: –547.75[1] mas/yr Dec.: –701.42[1] mas/yr |
| Parallax (π) | 53.93 ± 0.18[1] mas |
| Distance | 60.5 ± 0.2 ly (18.54 ± 0.06 pc) |
| Absolute magnitude (MV) | +1.87[5] |
| Details | |
| Mass | 2.0[6] M☉ |
| Radius | 5.897 ± 0.028[7] R☉ |
| Luminosity | 19 ± 1[8] L☉ |
| Surface gravity (log g) | 3.21[3] cgs |
| Temperature | 4,890[3] K |
| Metallicity [Fe/H] | –0.42[3] dex |
| Rotational velocity (v sin i) | 2.6[9] km/s |
| Other designations | |
Eta Serpentis (η Ser, η Serpentis) is a star in the constellation Serpens. In particular, it lies in Serpens Cauda, the snake's tail. The star has an apparent visual magnitude of 3.260,[2] making it visible to the naked eye. Parallax measurements give a distance estimate of 60.5 light-years (18.5 parsecs) from the Earth.[1]
This star is larger than the Sun, with twice the mass and almost six times the radius.[6][7] The spectrum matches a stellar classification of K0 III-IV,[3] with the luminosity class of III-IV corresponding to an evolved star that lies between the subgiant and giant stages. The expanded outer envelope star is radiating about 19 times the luminosity of the Sun at an effective temperature of 4,890 K.[3] At this temperature, it has an orange hue typical of a K-type star.[11] Eta Serpentis displays solar-like oscillations with a period of 0.09 days.[12]
Eta Serpentis was previously classified as a carbon star, which would have made it the brightest carbon star in the sky, although this classification was since found to be erroneous.[13]
Name
In Chinese astronomy, the star is known as 天市左垣 (Tiān Shì Zuǒ Yuán), meaning 'Left Wall of Heavenly Market Enclosure'; the name refers to an asterism that represents eleven old states in China. The leftmost borderline of the enclosure consists of η Serpentis, δ Herculis, λ Herculis, μ Herculis, ο Herculis, 112 Herculis, η Ophiuchi, ζ Aquilae, θ1 Serpentis, ν Ophiuchi and ξ Serpentis.[14] Consequently, η Serpentis itself is known as 天市左垣八 (Tiān Shì Zuǒ Yuán bā, the Eighth Star of Left Wall of Heavenly Market Enclosure, representing the region of Donghai (東海, lit. meaning 'eastern sea'),[15][16] possibly a reference to the East China Sea.[citation needed]
References
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- ↑ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 23 日
- ↑ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
