Phi Eridani

φ Eridani (Latinised as Phi Eridani) is a star in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.55.^[2] The distance to this star, as determined using the parallax method, is around 154 light-years.^[1]

φ Eridani

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	02h 16m 30.58563s[1]
Declination	−51° 30′ 43.7955″[1]
Apparent magnitude (V)	3.55[2]
Characteristics
Spectral type	B8IV-V[3]
U−B color index	−0.38[2]
B−V color index	−0.12[2]
Astrometry
Radial velocity (Rv)	10.40[4] km/s
Proper motion (μ)	RA: +91.03[1] mas/yr Dec.: −22.23[1] mas/yr
Parallax (π)	21.22±0.12 mas[1]
Distance	153.7 ± 0.9 ly (47.1 ± 0.3 pc)
Absolute magnitude (MV)	0.183±0.027[5]
Details
Mass	3.55[6] M☉
Radius	2.422[7] R☉
Luminosity	135[7] L☉
Surface gravity (log g)	4.21±0.14[6] cgs
Temperature	12,650[7] K
Rotation	0.343705[8] d
Rotational velocity (v sin i)	250[9] km/s
Age	44[6] Myr
Other designations
φ Eri, CPD−52°285, FK5 82, HD 14228, HIP 10602, HR 674, SAO 232696[10]
Database references
SIMBAD	data

This is a B-type star with a stellar classification of B8IV-V,^[3] suggesting it shows traits of a main-sequence star and a subgiant. It is spinning rapidly with a projected rotational velocity of 250 km/s. This rotation is giving the star an oblate shape with an equator that is 17% larger than the polar radius.^[9] It has 3.55 times the mass of the Sun and radiates 135 times the solar luminosity from its outer atmosphere at an effective temperature of about 12,650 K.^[6][7]

Phi Eridani may form a wide binary star system with a 9th-magnitude star at lies an angular separation of 86″. This companion is a G-type main-sequence star with a stellar classification of G2V.^[11] It may also have a physical association with the naked-eye star Eta Horologii.^[12] It is a member of the Tucana-Horologium association, a 45(±4)-Myr-old group of stars that share a common motion through space.^[5]