Phi Virginis
Binary star system in the constellation Virgo
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Phi Virginis (φ Virginis, abbreviated Phi Vir, φ Vir) is a binary star[7] in the zodiac constellation of Virgo. It can be seen with the naked eye, having an apparent visual magnitude of +4.81.[2] Based upon parallax measurements obtained during the Gaia mission, it is located roughly 121 light-years (37 parsecs) distant from the Sun.[1]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Virgo |
| Right ascension | 14h 28m 12.13890s[1] |
| Declination | −02° 13′ 40.6490″[1] |
| Apparent magnitude (V) | +4.81[2] |
| Characteristics | |
| Evolutionary stage | subgiant[1] |
| Spectral type | G2 IV[2] |
| B−V color index | +0.683[3] |
| Astrometry | |
| Radial velocity (Rv) | −9.88±0.15[3] km/s |
| Proper motion (μ) | RA: −138.727[1] mas/yr Dec.: −3.338[1] mas/yr |
| Parallax (π) | 26.8792±0.1264 mas[1] |
| Distance | 121.3 ± 0.6 ly (37.2 ± 0.2 pc) |
| Absolute magnitude (MV) | 1.68[4] |
| Details[3] | |
| Mass | 1.80[5] M☉ |
| Radius | 4 R☉ |
| Luminosity | 12.6 L☉ |
| Surface gravity (log g) | 3.4 cgs |
| Temperature | 5,534 K |
| Metallicity [Fe/H] | −0.06 dex |
| Rotational velocity (v sin i) | 15.5 km/s |
| Age | 1.5[5] Gyr |
| Other designations | |
| Elgafar, φ Vir, 105 Virginis, BD−01°2957, FK5 533, GJ 550.2, GJ 9481, HD 126868, HIP 70755, HR 5409, SAO 139951[6] | |
| Database references | |
| SIMBAD | data |
The two components are designated Phi Virginis A (officially named Elgafar /ˈɛlɡəfɑːr/, the traditional name for the system)[8] and B.
Nomenclature
φ Virginis (Latinised to Phi Virginis) is the binary's Bayer designation. The designations of the two components as Phi Virginis A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[9]
Ideler described an Arabic lunar mansion "El-ġafr" (Arabic الغفر al-ghafr) for the stars Phi, Iota and Kappa Virginis.[10] In 2016, the IAU organized a Working Group on Star Names (WGSN)[11] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[12] It approved the name Elgafar for the component Phi Virginis A on 1 June 2018 and it is now so included in the List of IAU-approved Star Names.[8]
In Chinese, 亢宿 (Kàng Xiù), meaning Neck, refers to an asterism consisting of Phi Virginis, Kappa Virginis, Iota Virginis, and Lambda Virginis.[13] Consequently, Phi Virginis itself is known as 亢宿三 (Wěi Xiù sān), "the Third Star of Neck".[14]
Properties
The primary component, Phi Virginis A, has a stellar classification of G2 IV,[2] indicating that it is a G-type subgiant which is evolving away from the main sequence. It is slightly variable with an amplitude of 0m.06.[15] The star has about 1.8 times the mass of the Sun,[5] 4 times the Sun's radius, and shines with 12.6 times the luminosity of the Sun.[3] It is around 1.5[5] billion years old and is spinning with a projected rotational velocity of 15.5 km/s. The effective temperature of the star's outer atmosphere is 5,534 K.[3]
The secondary, Phi Virginis B, is a magnitude 9.10 companion at an angular separation of 5.160 arcseconds.[7] A second visual companion lies at an angular separation of 91.40 arcseconds along a position angle of 202°, as of 2000.[16]
The system is a source of X-ray emission with a luminosity of 2.158×1020 erg/s.[17]