Upsilon2 Eridani

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

Upsilon² Eridani (υ² Eridani, abbreviated Upsilon² Eri, υ² Eri), officially named Theemin /ˈθiːmən/,^[8][9] is a star in the constellation of Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.8.^[2] Based upon parallax measurements obtained during the Gaia mission,^[1] it is approximately 211 light-years distant.

υ² Eridani

Location of υ2 Eridani (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	04h 35m 33.03796s[1]
Declination	−30° 33′ 44.4313″[1]
Apparent magnitude (V)	3.804[2]
Characteristics
Evolutionary stage	Red clump[3]
Spectral type	G8+ III[4]
U−B color index	+0.740[2]
B−V color index	+0.968[2]
Astrometry
Radial velocity (Rv)	−4.0±0.9[5] km/s
Proper motion (μ)	RA: −49.422 mas/yr[1] Dec.: −12.543 mas/yr[1]
Parallax (π)	15.4501±0.1081 mas[1]
Distance	211 ± 1 ly (64.7 ± 0.5 pc)
Absolute magnitude (MV)	−0.139±0.033[6]
Details[6]
Mass	3.15±0.13 M☉
Radius	14.09±0.34 R☉
Luminosity	114±4 L☉
Surface gravity (log g)	2.570±0.084 cgs
Temperature	5,023±42 K
Metallicity [Fe/H]	0.018±0.037 dex
Other designations
Theemin, υ2 Eridani, Upsilon2 Eridani, 52 Eridani, CD−30°1901, CPD−30°631, FK5 170, GC 5614, HD 29291, HIP 21393, HR 1464, PPM 280424, SAO 195148[7]
Database references
SIMBAD	data

It is an evolved red clump^[3] giant star with a stellar classification of G8+ III.^[4] The star has 3.15 times the Sun's mass and 14.09 times the Sun's radius. It radiates 114 times the solar luminosity from its outer atmosphere at an effective temperature of 5,023 K.^[6]

Nomenclature

υ² Eridani (Latinised to Upsilon² Eridani) is the star's Bayer designation.

It bore the traditional name Theemin (also written as Theemim and Beemin).^[10] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[11] to catalogue and standardize proper names for stars. The WGSN approved the name Theemin for this star on February 1, 2017, and it is now included in the List of IAU-approved Star Names.^[9]

In the Almagest, Ptolemy called it hē kampē, "the bend in the river;" Arab writers corrupted this to bhmn, later becoming beemin, beemun in the West. Subsequently, its etymology was incorrectly derived from Hebrew תאומים (te'omim), meaning "twins," producing Theemin.^[12][13]

In Chinese, 天園 (Tiān Yuán), meaning Celestial Orchard, refers to an asterism consisting of Upsilon² Eridani, Chi Eridani, Phi Eridani, Kappa Eridani, HD 16754, HD 23319, Theta Eridani, HD 24072, HD 24160, Upsilon⁴ Eridani, Upsilon³ Eridani and Upsilon¹ Eridani.^[14] Consequently, the Chinese name for Upsilon² Eridani itself is 天園十二 (Tiān Yuán shíèr, English: the Twelfth Star of Celestial Orchard).^[15]