Gamma Virginis
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 Porrima in Virgo. |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Virgo |
| Right ascension | 12h 41m 39.64344s[1] |
| Declination | –01° 26′ 57.7421″[1] |
| Apparent magnitude (V) | 2.74 (3.650/3.560[2]) |
| Characteristics | |
| Spectral type | F0 V/F0 V[2] |
| U−B color index | -0.05 |
| B−V color index | 0.36 |
| Variable type | unknown |
| Astrometry | |
| Radial velocity (Rv) | -19.5[3] km/s |
| Proper motion (μ) | RA: –614.76[1] mas/yr Dec.: 61.34[1] mas/yr |
| Parallax (π) | 85.58 ± 0.60[1] mas |
| Distance | 38.1 ± 0.3 ly (11.68 ± 0.08 pc) |
| Absolute magnitude (MV) | 2.38 (3.12/3.14) |
| Orbit[4] | |
| Companion | Gamma Virginis B |
| Period (P) | 168.93 ± 0.30 yr |
| Semi-major axis (a) | 3.662 ± 0.013" |
| Eccentricity (e) | 0.8825 ± 0.0010 |
| Inclination (i) | 148.82 ± 0.43° |
| Longitude of the node (Ω) | 213.79 ± 0.72° |
| Periastron epoch (T) | 2005.438 ± 0.067 |
| Details | |
| Mass | 1.56[3] M☉ |
| Surface gravity (log g) | 4.26[3] cgs |
| Temperature | 6,757[5] K |
| Metallicity [Fe/H] | –0.07[2] dex |
| Age | 1.14[6] Gyr |
| Other designations | |
| γ Vir A: HD 110379, HR 4825, LFT 937, LTT 4843 | |
| γ Vir B: HD 110380, HR 4826, LFT 937, LTT 4844 | |
Gamma Virginis (γ Vir, γ Virginis) is a binary star system in the constellation Virgo.
Name
This star system has the traditional name Porrima, the alternative name of Antevorta, one of the Camenae or ancient Roman goddesses of prophecy.[7]
In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Laouiyet al Aoua, which was translated into Latin as Angulus Latratoris, meaning the angle of the barker.[8] This star, along with β Vir (Zavijava), η Vir (Zaniah), δ Vir (Auva) and ε Vir (Vindemiatrix), were Al ʽAwwāʼ, the Barker.[7]
In Chinese, 太微左垣 (Tài Wēi Zuǒ Yuán), meaning Left Wall of Supreme Palace Enclosure, refers to an asterism consisting of γ Virginis, η Virginis, δ Virginis, ε Virginis and α Comae Berenices.[9] Consequently, γ Virginis itself is known as 太微左垣二 (Tài Wēi Zuǒ Yuán èr, English: the Second Star of Left Wall of Supreme Palace Enclosure.),[10] representing 東上相 (Dōngshǎngxiāng), meaning The First Eastern Minister.[11] 東上相 (Dōngshǎngxiāng), westernized into Shang Seang by R.H. Allen and the meaning is "the High Minister of State".[7]
Properties
Gamma Virginis is a binary star, consisting of two stars of approximately equal apparent magnitudes 3.65 and 3.56, and of spectral type F0V.[2] With an orbital period of 168.93 years,[4] it was an easy object for amateur astronomers until the beginning of the 1990s, but in 2011 the smaller apparent distance between the stars requires a larger telescope to resolve the individual components. The last time they were at periapsis was in 1836. The distance will again be wide enough in 2020 to view with a small telescope. The star system has a combined apparent magnitude of 2.9. The system is 39 light years away from the Sun.
As Gamma Virginis is close to the ecliptic, it can be occulted by the Moon and (extremely rarely) by planets. In June 2011, Saturn came within a quarter of a degree from Porrima.
Based upon X-ray emissions—an indicator of the strength of the stellar magnetic field—this system has an estimated age of 1.14 billion years.[6]
Changes of distance and position angle
This table shows the apparent distance between the two stars and their relative position angle: first three columns show data predicted from an orbit calculated in 1937, the next two columns show in 2006,[12] the next three columns show observations reported by the Hanwell Community Observatory.[13]
| Predicted from 1937 Strand orbit | Predicted from 2006 Docobo orbit | Observations 2003 to 2005 | |||||
|---|---|---|---|---|---|---|---|
| Year | distance | position angle | distance | position angle | Date | distance | position angle |
| 1995 | 2.5″ | 280 | 2.25″ | 277.6 | |||
| 2000 | 1.8″ | 267 | 1.50″ | 260.9 | |||
| 2002 | 1.5″ | 259 | 1.13″ | 247.5 | |||
| 2003 | 0.92″ | 236.6 | 2003 Dec. | 0.6″ | 219° | ||
| 2004 | 1.2″ | 246 | 0.68″ | 218.4 | 2004 Dec. | 0.4″ | 177° |
| 2005 | 0.44″ | 179.8 | 2005 April | 0.27-0.29″ | 161±0.6° | ||
| 2006 | 0.8″ | 221 | 0.41″ | 103.5 | |||
| 2008 | 0.4″ | 126 | 0.93″ | 41.0 | |||
| 2010 | 0.9″ | 44 | 1.39″ | 23.6 | |||
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Lua error in package.lua at line 80: module 'strict' not found. Note: see VizieR catalogue I/311.
- ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 3.0 3.1 3.2 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 4.0 4.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 6.0 6.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 7.0 7.1 7.2 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ (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) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ↑ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ↑ INTERNATIONAL ASTRONOMICAL UNION COMMISSION 26 (DOUBLE STARS)
- ↑ Christopher Taylor, Hanwell Community Observatory
