  | |
| Observation data EpochJ2000 EquinoxJ2000 | |
|---|---|
| Constellation | Taurus |
| Right ascension | 03h 49m 09.74306s[1] |
| Declination | +24° 03′ 12.3017″[1] |
| Apparent magnitude (V) | 3.63[2] (3.84 / 5.46)[3] |
| Characteristics | |
| Spectral type | B8III[4] |
| U−Bcolor index | −0.36[5] |
| B−Vcolor index | −0.08[5] |
| Variable type | SPB[6] |
| Astrometry | |
| Radial velocity (Rv) | 8.5±2[7] km/s |
| Proper motion (μ) | RA: +19.079mas/yr[1] Dec.: −46.193mas/yr[1] |
| Parallax (π) | 8.1184±0.4791 mas[1] |
| Distance | 444.2 ± 4.6 ly (136.2±1.4[8] pc) |
| Absolute magnitude (MV) | −1.82[9] |
| Orbit[8] | |
| Primary | Aa1 |
| Companion | Aa2 |
| Period (P) | 290.9919±0.0028 d |
| Semi-major axis (a) | 1.768±0.018 au |
| Eccentricity (e) | 0.23565±0.00011 |
| Inclination (i) | 107.863±0.032° |
| Longitude of the node (Ω) | 334.202±0.025° |
| Periastronepoch (T) | BJD2450585.988±0.096 |
| Argument of periastron (ω) (secondary) | 335.697±0.082° |
| Semi-amplitude (K1) (primary) | 27.09±0.40 km/s |
| Semi-amplitude (K2) (secondary) | 37.63±0.53 km/s |
| Details[8] | |
| Aa1 | |
| Mass | 5.04±0.17 M☉ |
| Radius | 7.81±0.18 (equatorial) 6.48±0.50 (polar) R☉ |
| Luminosity | 1,260 L☉ |
| Surface gravity (log g) | 3.38±0.07 cgs |
| Temperature | 12,525±200 K |
| Rotational velocity (v sin i) | 217±9 km/s |
| Aa2 | |
| Mass | 3.64±0.12 M☉ |
| Radius | 3.2±0.3[10] R☉ |
| Luminosity | 250 L☉ |
| Surface gravity (log g) | 4.20±0.15 cgs |
| Temperature | 12,835±450 K |
| Rotational velocity (v sin i) | 47±7 km/s |
| Ab | |
| Mass | 2.09[11] M☉ |
| Other designations | |
| Atlas,27 Tau,BD+23°557,FK5 142,HD 23850,HIP 17847,HR 1178,SAO 76228 | |
| Database references | |
| SIMBAD | data |
Atlas/ˈætləs/,[12] designation27 Tauri, is atriple star system in theconstellation ofTaurus. It is a member of thePleiades, anopen star cluster (M45). It is 444light-years (136parsecs) away,[8] and is 3.92 degrees north of theecliptic.
27 Tauri is the star'sFlamsteed designation. It has the proper name Atlas;Atlas was aTitan and the father of thePleiades sisters inGreek mythology.
In 2016 theInternational Astronomical Union organized aWorking Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN approved the nameAtlas for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[14]
Atlas is a triple star system, with the inner pair orbiting in under a year and the outer star orbiting in 260 years. The outer star, component Ab (sometimes component B, such as in CCDM and SIMBAD[15]), has been resolved at a distance of0.784″ from the unresolvedspectroscopic binary. It is too close to have been assigned a spectral class, but has anapparent magnitude of 6.8, three magnitudes fainter than the combined magnitude of the closer pair. Its mass is estimated to be twice that of the Sun. In the WDS catalog, there are 8 other stars, ranging from B-I, which have been classed as companions of Atlas.[11]
The inner pair have a well-defined orbit with a period of 291 days, asemi-major axis of13 mas, and an eccentricity of 0.24. At an inclination of 108° to theplane of the sky, it does not showeclipses.[16] Although the two stars cannot be resolved, the primary, component Aa1, is calculated to be 1.6 magnitudes brighter than the secondary, component Aa2.[11] The primary star is rapidlyrotating and is significantlyoblate; the ratio of the polar to equatorial radius is 0.83. It rotates at an inclination of either64°±20° or116°±20°, the latter consistent with its rotation being aligned with the orbit.[8]
Low amplitude variability of the brightness of Atlas was tentatively detected in observations bySTEREO and clearly detected byKepler/K2. The light curve varies with several periods, the most prominent being 2.427, 0.7457 and 1.214 days.[10]
