Eta Tucanae
Star in the constellation Tucana
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Eta Tucanae, Latinized from η Tucanae, is a probable binary star[7] system in the southern constellation of Tucana, a few degrees to the north of Epsilon Tucanae. It is visible to the naked eye as a dim, white-hued point of light with an apparent visual magnitude of +5.00.[3] parallax measurements provide a distance estimate of about 154 light years from the Sun, and it is drifting further away with a mean radial velocity of +32.5 km/s.[6] It is a member of the 30 million year old Tucana-Horologium association of co-moving stars.[7][3]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Tucana[1] |
| Right ascension | 23h 57m 35.07852s[2] |
| Declination | −64° 17′ 53.6229″[2] |
| Apparent magnitude (V) | +5.00[3] |
| Characteristics | |
| Evolutionary stage | main sequence[4] |
| Spectral type | A1V[3] |
| U−B color index | +0.08[5] |
| B−V color index | +0.06[5] |
| Astrometry | |
| Radial velocity (Rv) | +32.50[6] km/s |
| Proper motion (μ) | RA: +78.850[2] mas/yr Dec.: −62.049[2] mas/yr |
| Parallax (π) | 21.2425±0.3639 mas[2] |
| Distance | 154 ± 3 ly (47.1 ± 0.8 pc) |
| Absolute magnitude (MV) | 1.62[1] |
| Details | |
| Mass | 1.94[7] M☉ |
| Radius | 1.8[8] R☉ |
| Luminosity | 23[4] L☉ |
| Surface gravity (log g) | 4.31[9] cgs |
| Temperature | 9,057[4] K |
| Rotational velocity (v sin i) | 190[7] km/s |
| Other designations | |
| η Tuc, CPD−64°4391, FK5 2026, GC 33223, HD 224392, HIP 118121, HR 9062, SAO 255609, GSC 09130-01766[10] | |
| Database references | |
| SIMBAD | data |
The radial velocity for Eta Tucanae displays strong oscillations, suggesting this is a spectroscopic binary system. A companion was directly detected in 2014, but this result has some unexplained anomalies.[7] The primary component is an A-type main-sequence star with a stellar classification of A1V.[3] It is spinning rapidly with a projected rotational velocity of 190 km/s,[7] giving it an equatorial bulge that is 15% larger than the polar radius.[11] The star has 1.9[7] times the mass of the Sun and 1.8[8] times the Sun's radius. It is radiating 23[4] times the luminosity of the Sun from its photosphere at an effective temperature of 9,057 K.[4]