Tau9 Eridani
Binary star in the constellation Eridanus
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Tau9 Eridani (τ9 Eri) is a binary star in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 4.63.[2] The distance to this system can be estimated using the parallax method, which yields a value of roughly 327 light years.[2]
  | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Eridanus |
| Right ascension | 03h 59m 55.48381s[1] |
| Declination | −24° 00′ 58.3798″[1] |
| Apparent magnitude (V) | 4.63[2] |
| Characteristics | |
| Evolutionary stage | main sequence[3] |
| Spectral type | B9.5V Si[4] |
| U−B color index | −0.40[2] |
| B−V color index | −0.13[2] |
| Variable type | α2 CVn[5] |
| Astrometry | |
| Radial velocity (Rv) | 25.5±0.5[6] km/s |
| Proper motion (μ) | RA: +12.12[1] mas/yr Dec.: +16.48[1] mas/yr |
| Parallax (π) | 9.96±0.22 mas[1] |
| Distance | 327 ± 7 ly (100 ± 2 pc) |
| Absolute magnitude (MV) | −0.44[5] |
| Orbit[7] | |
| Period (P) | 5.95382 days |
| Eccentricity (e) | 0.129 |
| Periastron epoch (T) | 246991.65 JD |
| Argument of periastron (ω) (secondary) | 183.2° |
| Semi-amplitude (K1) (primary) | 40.0 km/s |
| Semi-amplitude (K2) (secondary) | 89.9 km/s |
| Details | |
| τ9 Eri A | |
| Mass | 3.6[7] M☉ |
| Radius | 3.06[7] R☉ |
| Luminosity | 209[7] L☉ |
| Surface gravity (log g) | 4.11±0.11[8] cgs |
| Temperature | 12,580[7] K |
| Rotational velocity (v sin i) | 26.8[7] km/s |
| Age | 140[7] Myr |
| τ9 Eri B | |
| Mass | 1.6[7] M☉ |
| Radius | 1.5[7] R☉ |
| Luminosity | 6.3[7] L☉ |
| Temperature | 7530[7] K |
| Rotational velocity (v sin i) | 15[7] km/s |
| Other designations | |
| τ9 Eridani, τ9 Eri, 36 Eridani, CD−24°2022, FK5 2287, HD 25267, HIP 18673, HR 1240, SAO 169017[9] | |
| Database references | |
| SIMBAD | data |
This is a double-lined spectroscopic binary system with an orbital period of 5.95382 days and an eccentricity of 0.12.[7] The primary component, τ9 Eri A, is a magnetic chemically peculiar star[11] with a stellar classification of B9.5V Si,[4] indicating that it is a B-type main sequence star that shows abundance anomalies in its silicon absorption lines.[4] It is an Alpha² Canum Venaticorum variable[5] with a rotational periodicity of 5.954 days.[12] The averaged strength of the stellar effective magnetic field is 240.6±91.0 G.[4]
The primary component Tau9 Eridani A has an estimated 326%[11] the mass of the Sun and 3.1 times the Sun's radius.[8] It shines with 166[13] times the solar luminosity from an outer atmosphere at an effective temperature of 10,866 K.[13] The star is spinning with a projected rotational velocity of 30 km/s.[14] The secondary star, designated Tau9 Eridani B, is a late A-type or early F-type star with a mass of 1.6 solar masses and an effective temperature of 7530 K.[7]