Tau5 Eridani

For other star systems with this Bayer designation, see Tau Eridani.

Tau⁵ Eridani, Latinized from τ⁵ Eridani, is a binary star system in the constellation Eridanus. It is visible to the naked eye with a combined apparent visual magnitude of 4.26.^[2] The distance to this system, as estimated using the parallax technique, is around 293 light years.^[1]

τ⁵ Eridani

Location of τ5 Eridani (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	03h 33m 47.27613s[1]
Declination	−21° 37′ 58.3830″[1]
Apparent magnitude (V)	4.26[2]
Characteristics
Spectral type	B0 V + B9 V[3]
U−B color index	0.35[2]
B−V color index	−0.09[2]
Astrometry
Proper motion (μ)	RA: +44.94[1] mas/yr Dec.: −28.16[1] mas/yr
Parallax (π)	11.12±0.21 mas[1]
Distance	293 ± 6 ly (90 ± 2 pc)
Absolute magnitude (MV)	−0.51[4]
Orbit[5]
Period (P)	6.2236 d
Eccentricity (e)	0.2
Periastron epoch (T)	2424446.548 JD
Argument of periastron (ω) (secondary)	313°
Semi-amplitude (K1) (primary)	107 km/s
Semi-amplitude (K2) (secondary)	103 km/s
Details
τ5 Eri A
Mass	3.30+0.24 −0.20[6] M☉
Radius	3.2[3] R☉
Luminosity	188[7] L☉
Surface gravity (log g)	4.00±0.15[6] cgs
Temperature	12,514±425[8] K
Rotational velocity (v sin i)	55±8[3] km/s
Age	157+23 −45[6] Myr
τ5 Eri B
Radius	2.6[3] R☉
Rotational velocity (v sin i)	50±8[3] km/s
Other designations
τ5 Eridani, τ5 Eri, 19 Eridani, BD−22°628, HD 22203, HIP 16611, HR 1088, SAO 168634[9]
Database references
SIMBAD	data

Tau⁵ Eridani is a double-lined spectroscopic binary system.^[10] The two stars orbit each other closely with a period of 6.2 days and an eccentricity of 0.2.^[5] On average, the two stars are separated by around 0.183 AU.^[3]

The primary component is a B-type main sequence star with a stellar classification of B0 V.^[3] It is around 157 million years old and is spinning with a projected rotational velocity of 55 km/s.^[3] The star has around 3.3^[6] times the mass of the Sun and 3.2^[3] times the Sun's radius. It radiates 188^[7] times the solar luminosity from an outer atmosphere at an effective temperature of 12,514 K.^[8]

The secondary component has a stellar classification of B9 V.^[3] It is slightly smaller, with an estimated size equal to 2.6 times the radius of the Sun.^[3]

Although τ⁵ Eridani has no bright visual companion stars, the galaxy IC 1953 is less than 10' away. It is one of the brighter members of a loose group of galaxies called the Eridanus Group scattered around the components of τ Eridani.