Tau4 Eridani
Binary star system in the constellation Eridanus
From Wikipedia, the free encyclopedia
Tau4 Eridani (Ï4 Eridani, Ï4 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.[2] The distance to this star can be estimated using the parallax method, which yields a value of roughly 300 light years.[1]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Eridanus |
| Ï4 Eridani A | |
| Right ascension | 03h 19m 31.0006s [1] |
| Declination | â21° 45â² 28.315â³ [1] |
| Apparent magnitude (V) | 3.57â3.72[2] |
| Ï4 Eridani B | |
| Right ascension | 03h 19m 30.6092s[3] |
| Declination | â21° 45â² 26.348â³[3] |
| Apparent magnitude (V) | 9.5[4] |
| Characteristics | |
| Ï4 Eridani A | |
| Evolutionary stage | asymptotic giant branch[5] |
| Spectral type | M3/4 III[6] |
| UâB color index | +1.79[7] |
| BâV color index | +1.61[7] |
| Variable type | Lb[2] |
| Astrometry | |
| Ï4 Eridani A | |
| Radial velocity (Rv) | +41.7±0.7[8] km/s |
| Proper motion (μ) | RA: +52.774 mas/yr[1] Dec.: +32.718 mas/yr[1] |
| Parallax (Ï) | 10.6153±0.3213 mas[1] |
| Distance | 307 ± 9 ly (94 ± 3 pc) |
| Absolute magnitude (MV) | â0.79[9] |
| Ï4 Eridani B | |
| Proper motion (μ) | RA: +52.919 mas/yr[3] Dec.: +34.104 mas/yr[3] |
| Parallax (Ï) | 10.6682±0.1066 mas[3] |
| Distance | 306 ± 3 ly (93.7 ± 0.9 pc) |
| Position (relative to A) | |
| Component | B |
| Angular distance | 5.7[4]â³ |
| Position angle | 291[4]° |
| Projected separation | 5,800[10] AU |
| Details | |
| Ï4 Eridani A | |
| Mass | 1.73±0.3[11] Mâ |
| Radius | 103[12] Râ |
| Luminosity | 1,537[13] Lâ |
| Surface gravity (log g) | 0.91[14] cgs |
| Temperature | 3,652[12] K |
| Ï4 Eridani B | |
| Mass | 0.9[10] Mâ |
| Other designations | |
| Ï4 Eridani, Ï4 Eri, 16 Eridani, BDâ22°584, HD 20720, HIP 15474, HR 1003, SAO 168460[15] | |
| Database references | |
| Ï4 Eridani A | |
| SIMBAD | data |
| Ï4 Eridani B | |
| SIMBAD | data |
The primary components ia an evolved red giant star currently on the asymptotic giant branch[5] with a stellar classification of M3/4 III.[6] It is a slow irregular variable star of type Lb, undergoing changes in magnitude over the range 3.57â3.72[2] with a periodicity of 23.8 d.[16] This star has 1.73 times the mass of the Sun[11] and 103 times the radius of the Sun.[12] It shines with 1,537 times the luminosity of the Sun from its photosphere[13] at an effective temperature of 3,650 K.[12]
The secondary is a magnitude 9.5 star at an angular separation of 5.7Ⳡalong a position angle of 291°, as of 2013.[4] This angular separation implies a projected separation of 5,800 astronomical units.[10]