Epsilon1 Arae

For other star systems with this Bayer designation, see Epsilon Arae.

Epsilon¹ Arae is a star in the southern constellation Ara, the Altar. Its name is a Bayer designation that is Latinized from ε¹ Arae, and abbreviated Epsilon¹ Ara or ε¹ Ara. This star is visible to the naked eye with an apparent visual magnitude of +4.1^[2] Based upon an annual parallax shift of 8.85 mas,^[1] this star is approximately 368 light-years (113 parsecs) distant from the Earth. It is drifting further away with a radial velocity of +24 km/s.^[5]

Epsilon¹ Arae

The location of ε1 Arae (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ara
Right ascension	16h 59m 35.048s[1]
Declination	−53° 09′ 37.58″[1]
Apparent magnitude (V)	+4.068[2]
Characteristics
Spectral type	K3 III[3]
U−B color index	+1.71[4]
B−V color index	+1.45[4]
Astrometry
Radial velocity (Rv)	+23.85±0.03[5] km/s
Proper motion (μ)	RA: +1.015 mas/yr[1] Dec.: +21.455 mas/yr[1]
Parallax (π)	8.8520±0.1517 mas[1]
Distance	368 ± 6 ly (113 ± 2 pc)
Absolute magnitude (MV)	−0.79±0.16[6]
Details[5]
Mass	1.63±0.21 M☉
Radius	29.52±2.45 R☉
Luminosity	347+90 −71 L☉
Surface gravity (log g)	1.85±0.07 cgs
Temperature	4,302±45 K
Metallicity [Fe/H]	−0.19±0.06 dex
Rotational velocity (v sin i)	4.20±0.45 km/s
Age	1.82±0.60 Gyr
Other designations
CPD−52°10372, FK5 632, GC 22869, HD 152980, HIP 83153, HR 6295, SAO 244331, PPM 345574[7]
Database references
SIMBAD	data

ε¹ Arae is an evolved giant star^[8] with a stellar classification of K3 III.^[3] It is around 63% more massive than the Sun. At an age of about 1.8 billion years, the outer envelope of the star has expanded to almost 30 times the Sun's radius. It is radiating 347 times the luminosity of the Sun from its photosphere at an effective temperature of 4,302 K,^[5] giving it the orange-hued glow of a K-type star.^[9]

ε¹ Arae was known as 龜一(spelled as "Guī yī", meaning: "the 1st (star) of Guī") in traditional Chinese astronomy.^[10][11] Allen erroneously called it Tso Kang (左更).^[12] He probably confused the constellation "Ara" with "Ari", as Tso Kang is actually in Aries.^[10][11]