Tau8 Eridani

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

Tau⁸ Eridani, Latinized from τ⁸ Eridani, is a binary star system in the constellation Eridanus. It is visible to the naked eye with a combined apparent visual magnitude of 4.65.^[5] The distance to this system can be estimated via the parallax method, yielding a value of around 380 light years.^[2]

τ⁸ Eridani

A light curve for Tau8 Eridani, plotted from TESS data[1]
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	03h 53m 42.70302s[2]
Declination	−24° 36′ 44.0309″[2]
Apparent magnitude (V)	4.63 - 4.65[3]
Characteristics
Spectral type	B6 V[4]
U−B color index	−0.48[5]
B−V color index	−0.13[5]
Variable type	SPB[3]
Astrometry
Radial velocity (Rv)	+23[6] km/s
Proper motion (μ)	RA: +31.28[2] mas/yr Dec.: −7.49[2] mas/yr
Parallax (π)	8.65±0.30 mas[2]
Distance	380 ± 10 ly (116 ± 4 pc)
Absolute magnitude (MV)	−0.67[7]
Orbit[8]
Period (P)	454.0±0.1 d
Eccentricity (e)	0.21±0.01
Periastron epoch (T)	2450497±3 JD[9]
Argument of periastron (ω) (secondary)	106±3°
Semi-amplitude (K1) (primary)	22.3±0.3 km/s
Details
τ8 Eri A
Mass	5.0±0.1[10] M☉
Luminosity	256[11] L☉
Surface gravity (log g)	4.00[12] cgs
Temperature	11,858[11] K
Rotational velocity (v sin i)	30[4] km/s
Age	32.8±9.9[10] Myr
Other designations
τ8 Eridani, τ8 Eri, 33 Eridani, CD−24°1945, HD 24587, HIP 18216, HR 1213, SAO 168925[13]
Database references
SIMBAD	data

This is a single-lined^[14] spectroscopic binary star system with an orbital period of about 454 days and an eccentricity of 0.21.^[8] The primary component is a B-type main sequence star with a stellar classification of B6 V.^[4] Gautier Mathys et al. announced that the star is variable, in 1986.^[15] It is a slowly pulsating B-type star that undergoes radial-velocity variation with a frequency of 1.1569 times per day.^[14] The star has about five^[10] times the mass of the Sun and shines with 256 times the Sun's luminosity.^[11] The outer atmosphere has an effective temperature of 11,858^[11] K and may possess a longitudinal magnetic field with a strength of −140±71 G.^[16]