Phi Virginis

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 Hipparcos mission, it is located roughly 118 light-years (36 parsecs) distant from the Sun.^[1]

φ Virginis
(incl. Elgafar)

Location of φ Virginis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Virgo
Right ascension	14h 28m 12.13894s[1]
Declination	−02° 13′ 40.6579″[1]
Apparent magnitude (V)	+4.81[2]
Characteristics
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: −139.53[1] mas/yr Dec.: −4.04[1] mas/yr
Parallax (π)	27.58±1.01 mas[1]
Distance	118 ± 4 ly (36 ± 1 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 0^m.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]