Atlas (star)

Atlas
Image of the Pleiades star cluster
Atlas in the Pleiades cluster (circled)
Observation data
Epoch J2000      Equinox J2000
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−B color index −0.36[5]
B−V color index −0.08[5]
Variable type SPB[6]
Astrometry
Radial velocity (Rv)8.5±2[7] km/s
Proper motion (μ) RA: +19.079 mas/yr[1]
Dec.: −46.193 mas/yr[1]
Parallax (π)8.1184±0.4791 mas[1]
Distance444.2 ± 4.6 ly
(136.2±1.4[8] pc)
Absolute magnitude (MV)−1.82[9]
Orbit[8]
PrimaryAa1
CompanionAa2
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°
Periastron epoch (T)BJD 2450585.988±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
Mass5.04±0.17 M☉
Radius7.81±0.18 (equatorial)
6.48±0.50 (polar) R☉
Luminosity1,260 L☉
Surface gravity (log g)3.38±0.07 cgs
Temperature12,525±200 K
Rotational velocity (v sin i)217±9 km/s
Aa2
Mass3.64±0.12 M☉
Radius3.2±0.3[10] R☉
Luminosity250 L☉
Surface gravity (log g)4.20±0.15 cgs
Temperature12,835±450 K
Rotational velocity (v sin i)47±7 km/s
Ab
Mass2.09[11] M☉
Other designations
Atlas, 27 Tau, BD+23°557, FK5 142, HD 23850, HIP 17847, HR 1178, SAO 76228
Database references
SIMBADdata

Atlas /ˈætləs/,[12] designation 27 Tauri, is a triple star system in the constellation of Taurus. It is a member of the Pleiades, an open star cluster (M45). It is 444 light-years (136 parsecs) away,[8] and is 3.92 degrees north of the ecliptic.

Nomenclature

27 Tauri is the star's Flamsteed designation. It has the proper name Atlas; Atlas was a Titan and the father of the Pleiades sisters in Greek mythology.

In 2016 the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN approved the name Atlas for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[14]

Properties

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 of 0.784″ from the unresolved spectroscopic binary. It is too close to have been assigned a spectral class, but has an apparent 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]

A light curve for Atlas, adapted from White et al. (2017)[10]

The inner pair have a well-defined orbit with a period of 291 days, a semi-major axis of 13 mas, and an eccentricity of 0.24. At an inclination of 108° to the plane of the sky, it does not show eclipses.[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 rapidly rotating and is significantly oblate; the ratio of the polar to equatorial radius is 0.83. It rotates at an inclination of either 64°±20° or 116°±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 by STEREO and clearly detected by Kepler/K2. The light curve varies with several periods, the most prominent being 2.427, 0.7457 and 1.214 days.[10]

References

  1. ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. ^ "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 1 August 2017. Retrieved 21 June 2017.
  4. ^ David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. S2CID 33401607.
  5. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  6. ^ "NSV 1345". The International Variable Star Index. AAVSO. Retrieved 8 October 2022.
  7. ^ Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington. Bibcode:1953GCRV..C......0W.
  8. ^ a b c d e Torres, G.; Tkachenko, A.; et al. (July 2025). "Orbital and Physical Properties of the Pleiades Binary 27 Tau (Atlas)". The Astrophysical Journal. arXiv:2507.15933.
  9. ^ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  10. ^ a b c White, T. R.; et al. (November 2017). "Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades". Monthly Notices of the Royal Astronomical Society. 471 (3): 2882–2901. arXiv:1708.07462. Bibcode:2017MNRAS.471.2882W. doi:10.1093/mnras/stx1050.
  11. ^ a b c Tokovinin, Andrei (2018-03-01). "The Updated Multiple Star Catalog". The Astrophysical Journal Supplement Series. 235 (1): 6. arXiv:1712.04750. Bibcode:2018ApJS..235....6T. doi:10.3847/1538-4365/aaa1a5. ISSN 0067-0049. S2CID 119047709.
  12. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  13. ^ "IAU Working Group on Star Names (WGSN)". International Astronomical Union. Retrieved 22 May 2016.
  14. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  15. ^ "27 Tau B". simbad.cds.unistra.fr. Retrieved 2023-10-01.
  16. ^ Zwahlen, N.; North, P.; Debernardi, Y.; Eyer, L.; Galland, F.; Groenewegen, M. A. T.; Hummel, C. A. (2004). "A purely geometric distance to the binary star Atlas, a member of the Pleiades". Astronomy & Astrophysics. 425 (3): L45. arXiv:astro-ph/0408430. Bibcode:2004A&A...425L..45Z. doi:10.1051/0004-6361:200400062. S2CID 37047575.
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