Epsilon Coronae Australis

Epsilon Coronae Australis (ε CrA), is a star system located in the constellation Corona Australis. Varying in brightness between apparent magnitudes of 4.74 to 5 over 14 hours, it is the brightest W Ursae Majoris variable (low mass contact binary) in the night sky.

Epsilon Coronae Australis

A light curve for Epsilon Coronae Australis plotted from TESS data[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Corona Australis
Right ascension	18h 58m 43.37714s[2]
Declination	−37° 06′ 26.4865″[2]
Apparent magnitude (V)	+4.75[3]
Characteristics
Spectral type	F4V Fe-0.8[4]
U−B color index	+0.01[3]
B−V color index	+0.39[3]
Variable type	W UMa[5]
Astrometry
Radial velocity (Rv)	57.90 ± 1.2[6] km/s
Proper motion (μ)	RA: −132.40[2] mas/yr Dec.: −110.62[2] mas/yr
Parallax (π)	33.13±0.33 mas[2]
Distance	98.4 ± 1.0 ly (30.2 ± 0.3 pc)
Absolute magnitude (MV)	2.21[7]
Orbit[8]
Period (P)	0.59143357 ± 0.00000016 d
Semi-major axis (a)	3.795 ± 0.052 R☉
Eccentricity (e)	0
Inclination (i)	73.05 ± 0.16°
Longitude of the node (Ω)	2.0113 ± 0.0033°
Periastron epoch (T)	JD 2442296.95907 ± 0.0070
Details
ε CrA A
Mass	1.9[8] M☉
Radius	2.167[8][note 1] R☉
Temperature	6481 ± 20[8] K
Rotational velocity (v sin i)	148.5[9] km/s
ε CrA B
Mass	0.24[8] M☉
Radius	0.869[8][note 1] R☉
Temperature	5939 ± 19[8] K
Other designations
ε CrA, CD−37°13001, CPD−37°8433, HD 175813, HIP 93174, HR 7152, SAO 210781[5]
Database references
SIMBAD	data

Naming

Nicolas Louis de Lacaille gave Epsilon Coronae Australis its Bayer designation. It is also known as HR 7152, and HD 175813.

Properties

Epsilon Coronae Australis is an F4V dwarf star with an effective temperature of 6000 Kelvin. It ranges between apparent magnitudes of 4.74 to 5 over 14 hours,^[10] an absolute magnitude of +2.45, and a mass of 1.1 solar masses. Epsilon Coronae Australis is a W Ursae Majoris variable, indicating that it has a contact companion within the Roche limit of the primary. The star is located at a distance of 30 pc (97 light years) from the Sun.^[7] Yildiz and colleagues estimated the age of the system at 2.83 ± 0.28 billion years based on study of the properties of the system and estimated rate of mass transfer. They found the current masses of the primary and secondary to be 1.72 ± 0.04 and 0.22 ± 0.02 solar masses respectively, from their original masses of 1.06 ± 0.03 and 2.18 ± 0.06 solar masses.^[11]

Notes

1. Radii were given as a ratio of the radius to the semi-major axis; the semi-major axis is 3.795 R_☉.