Tau4 Eridani
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Eridanus |
| τ4 Eridani A | |
| Right ascension | 03h 19m 31.0006s |
| Declination | −21° 45′ 28.315″ |
| Apparent magnitude (V) | 3.57−3.72 |
| τ4 Eridani B | |
| Right ascension | 03h 19m 30.6092s |
| Declination | −21° 45′ 26.348″ |
| Apparent magnitude (V) | 9.5 |
| Characteristics | |
| τ4 Eridani A | |
| Evolutionary stage | asymptotic giant branch |
| Spectral type | M3/4 III |
| U−B color index | +1.79 |
| B−V color index | +1.61 |
| Variable type | Lb |
| Astrometry | |
| τ4 Eridani A | |
| Radial velocity (Rv) | +41.7±0.7 km/s |
| Proper motion (μ) | RA: +52.774 mas/yr Dec.: +32.718 mas/yr |
| Parallax (π) | 10.6153±0.3213 mas |
| Distance | 307 ± 9 ly (94 ± 3 pc) |
| Absolute magnitude (MV) | −0.79 |
| τ4 Eridani B | |
| Proper motion (μ) | RA: +52.919 mas/yr Dec.: +34.104 mas/yr |
| Parallax (π) | 10.6682±0.1066 mas |
| Distance | 306 ± 3 ly (93.7 ± 0.9 pc) |
| Position (relative to A) | |
| Component | B |
| Angular distance | 5.7″ |
| Position angle | 291° |
| Projected separation | 5,800 AU |
| Details | |
| τ4 Eridani A | |
| Mass | 1.73±0.3 M☉ |
| Radius | 103 R☉ |
| Luminosity | 1,537 L☉ |
| Surface gravity (log g) | 0.91 cgs |
| Temperature | 3,652 K |
| τ4 Eridani B | |
| Mass | 0.9 M☉ |
| Other designations | |
| τ4 Eridani, τ4 Eri, 16 Eridani, BD−22°584, HD 20720, HIP 15474, HR 1003, SAO 168460 | |
| Database references | |
| τ4 Eridani A | |
| SIMBAD | data |
| τ4 Eridani B | |
| SIMBAD | data |
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 that varies from 3.57 to 3.72. The distance to this star can be estimated using the parallax method, which yields a value of roughly 300 light years.
The primary components ia an evolved red giant star currently on the asymptotic giant branch with a stellar classification of M3/4 III. It is a slow irregular variable star of type Lb, undergoing changes in magnitude over the range 3.57−3.72 with a periodicity of 23.8 d. This star has 1.73 times the mass of the Sun and 103 times the radius of the Sun. It shines with 1,537 times the luminosity of the Sun from its photosphere at an effective temperature of 3,650 K.
The secondary is a magnitude 9.5 star at an angular separation of 5.7″ along a position angle of 291°, as of 2013. This angular separation implies a projected separation of 5,800 astronomical units.