Tau⁴ Eridani (τ⁴ Eridani, τ⁴ Eri) is a binary star system in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.65.[2] The distance to this star can be estimated using the parallax method, which yields a value of roughly 300 light years.[1]

τ⁴ Eridani

Location of τ4 Eridani (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	03h 19m 31.00224s[1]
Declination	−21° 45′ 28.3049″[1]
Apparent magnitude (V)	3.65[2]
Characteristics
Evolutionary stage	asymptotic giant branch[3]
Spectral type	M3/4 III[4]
U−B color index	+1.79[2]
B−V color index	+1.61[2]
Variable type	Lb[5]
Astrometry
Radial velocity (Rv)	+41.7±0.7[6] km/s
Proper motion (μ)	RA: +51.89[1] mas/yr Dec.: +32.92[1] mas/yr
Parallax (π)	10.6153 ± 0.3213 mas[7]
Distance	307 ± 9 ly (94 ± 3 pc)
Absolute magnitude (MV)	−0.79[8]
Details
Mass	1.8±0.3[9] M☉
Radius	106[10] R☉
Luminosity	1,537[11] L☉
Temperature	3,712[9] K
Other designations
τ4 Eridani, τ4 Eri, 16 Eridani, BD-22° 584, HD 20720, HIP 15474, HR 1003, SAO 168460.[12]
Database references
SIMBAD	data

This is an evolved red giant star currently on the asymptotic giant branch[3] with a stellar classification of M3/4 III.[4] It is a slow irregular variable star of type Lb, undergoing changes in magnitude over the range 3.57−3.72[5] with a periodicity of 23.8 d.[13] The measured angular diameter of Tau⁴ Eridani is 10.58±1.00 mas.[14] At its estimated distance, this yields a physical size of about 106 times the radius of the Sun.[10] It shines with 1,537[11] times the luminosity of the Sun from an outer atmosphere at an effective temperature of 3,712 K.[9]

This is most likely a binary star system.[15] The companion is a magnitude 9.5 star at an angular separation of 5.7″ along a position angle of 291°, as of 2013.[16]

References