Upsilon1 Eridani

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

Upsilon¹ Eridani (υ¹ Eri) is a single star in the constellation Eridanus. It has an apparent visual magnitude is 4.51,^[2] which is bright enough to be faintly visible to the naked eye on a clear, dark night. The distance to this star, as determined using the parallax method,^[1] is around 127 light years.

υ¹ Eridani

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	04h 33m 30.55236s[1]
Declination	−29° 45′ 59.3725″[1]
Apparent magnitude (V)	4.51[2]
Characteristics
Evolutionary stage	red clump[3]
Spectral type	K0 III-IV[4]
U−B color index	+0.70[2]
B−V color index	+0.98[2]
Astrometry
Radial velocity (Rv)	+20.89±0.69[5] km/s
Proper motion (μ)	RA: −114.78[1] mas/yr Dec.: −271.79[1] mas/yr
Parallax (π)	25.67±0.24 mas[1]
Distance	127 ± 1 ly (39.0 ± 0.4 pc)
Absolute magnitude (MV)	1.60[5]
Details
Mass	1.54[5] M☉
Radius	7.3[6] R☉
Luminosity	24[5] L☉
Surface gravity (log g)	3.09[5] cgs
Temperature	4,941[5] K
Metallicity [Fe/H]	−0.16±0.08[5] dex
Rotational velocity (v sin i)	2.15[7] km/s
Other designations
υ1 Eridani, υ1 Eri, 50 Eridani, CD−30°1883, HD 29085, HIP 21248, HR 1453, SAO 169570[8]
Database references
SIMBAD	data

This is an evolved red clump^[3] giant star with a stellar classification of K0III-IV.^[4] The measured angular diameter, after correction for limb darkening, is 1.74±0.02 mas.^[9] At an estimated distance of this star, this yields a physical size of about 7.3 times the radius of the Sun.^[6] It has 154%^[5] of the Sun's mass and radiates 24 times the solar luminosity from its outer atmosphere at an effective temperature of 4,941 K.^[5]