Upsilon4 Eridani

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

Upsilon⁴ Eridani is a close binary star system in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.56.^[2] Based upon parallax measurements, the pair are located around 54.6 parsecs (178 ly) from the Sun.^[1]

Upsilon⁴ Eridani

Location of Upsilon4 in Eridanus (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	04h 17m 53.66241s[1]
Declination	−33° 47′ 54.0569″[1]
Apparent magnitude (V)	3.56[2]
Characteristics
Spectral type	B8V + B9.5V[3]
U−B color index	−0.36[2]
B−V color index	−0.12[2]
Astrometry
Radial velocity (Rv)	+17.6[4] km/s
Proper motion (μ)	RA: +62.52[1] mas/yr Dec.: −7.24[1] mas/yr
Parallax (π)	18.33±0.15 mas[1]
Distance	178 ± 1 ly (54.6 ± 0.4 pc)
Absolute magnitude (MV)	−0.20[5]
Orbit[6]
Period (P)	5.0103250±0.0000008 d
Semi-major axis (a)	1.902±0.006 mas
Eccentricity (e)	0
Inclination (i)	146.2±0.1°
Periastron epoch (T)	2454407.7214 ± 0.002 JD
Semi-amplitude (K1) (primary)	62.68±0.17[7] km/s
Semi-amplitude (K2) (secondary)	64.70±0.15[7] km/s
Details[6]
υ4 Eri A
Mass	3.17±0.07 M☉
Radius	2.32±0.18 R☉
Luminosity	100.6±4.3 L☉
Surface gravity (log g)	4.21±0.07 cgs
Temperature	12,930±440[8] K
Rotational velocity (v sin i)	19[8] km/s
Age	146[8] Myr
υ4 Eri B
Mass	3.07±0.07 M☉
Radius	2.32±0.18 R☉
Luminosity	87.4±3.3 L☉
Surface gravity (log g)	4.21±0.07 cgs
Temperature	12,250 K
Other designations
υ4 Eri, 41 Eridani, CD−34°1614, HD 27376, HIP 20042, HR 1347, SAO 194902[9]
Database references
SIMBAD	data

This is a double-lined spectroscopic binary star system,^[10] which means that the Doppler-shifted spectral lines of both components can be distinguished. The pair have a circular orbit with a period of five days. The system is composed of two B-type main-sequence stars: one has a stellar classification of B8V and the other B9.5V.^[3] Both stars show HgMn peculiarities in their spectrum,^[7] and their properties are nearly identical.^[6] The spin rate of the two stars is synchronized to their orbital period.^[6] It is possible that a nearby K-type star is also related.^[3]