HD 124639

HD 124639 is a Be star in the southern constellation of Apus. It has an apparent visual magnitude of 6.42,[2] which makes it a challenge to view with the naked eye even under the best viewing conditions. Based upon an annual parallax shift of 3.41 mas as seen from Earth, it is 956 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction of 0.17 due to interstellar dust.[9] The star is moving further away with a heliocentric radial velocity of +27 km/s.[5]

HD 124639
Observation data
Epoch J2000      Equinox J2000
Constellation Apus
Right ascension  14h 24m 22.06544s[1]
Declination −82° 50′ 53.6732″[1]
Apparent magnitude (V) 6.42[2]
Characteristics
Spectral type B8 Ve[3] or B9 IVe[4]
U−B color index −0.33[2]
B−V color index +0.02[2]
Astrometry
Radial velocity (Rv)+26.70±1.78[5] km/s
Proper motion (μ) RA: −15.391[1] mas/yr
Dec.: −9.045[1] mas/yr
Parallax (π)3.4127 ± 0.0336[1] mas
Distance956 ± 9 ly
(293 ± 3 pc)
Absolute magnitude (MV)−0.92[6]
Details
Mass4.4±0.3[3] M☉
Luminosity676+35
−33[7] L☉
Surface gravity (log g)3.50±0.10[3] cgs
Temperature12,700±380[7] K
Rotational velocity (v sin i)237±18[7] km/s
Age126[3] Myr
Other designations
CD−82° 255, HD 124639, HIP 70418, HR 5327, SAO 258697[8]
Database references
SIMBADdata

This is a B-type main-sequence star with a stellar classification of B8 Ve.[3] The 'e' suffix indicates the presence of emission lines in the spectrum from ejected circumstellar material that is being heated by the host star. At the age of 126[3] million years, it has completed 96% of its lifespan on the main sequence.[7] Levenhagen and Leister (2006) class it as a B9 IVe star,[4] which would suggest it has already evolved into a subgiant star.

HD 124639 is spinning rapidly with a projected rotational velocity of 237 km/s; the centrifugal force along the equator is equal to 56% of its surface gravity. The pole of the star is inclined by 70°±17° to the line-of-sight from the Earth.[7] It has 4.4[3] times the mass of the Sun and is radiating 676 times the Sun's luminosity from its photosphere at an effective temperature of 12,700 K.[7]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051.
  2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
  3. Levenhagen, R. S.; Leister, N. V. (February 2004), "Physical Parameters of Southern B- and Be-Type Stars", The Astronomical Journal, 127 (2): 1176–1180, Bibcode:2004AJ....127.1176L, doi:10.1086/381063.
  4. Levenhagen, R. S.; Leister, N. V. (2006), "Spectroscopic Analysis of Southern B and Be Stars", Monthly Notices of the Royal Astronomical Society, 371: 252–62, arXiv:astro-ph/0606149, Bibcode:2006MNRAS.371..252L, doi:10.1111/j.1365-2966.2006.10655.x.
  5. Kharchenko, N. V.; et al. (2007), "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ˜55000 stars and mean radial velocities of 516 Galactic open clusters and associations", Astronomische Nachrichten, 328 (9): 889–896, arXiv:0705.0878, Bibcode:2007AN....328..889K, doi:10.1002/asna.200710776.
  6. 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.
  7. Zorec, J.; et al. (November 2016), "Critical study of the distribution of rotational velocities of Be stars. I. Deconvolution methods, effects due to gravity darkening, macroturbulence, and binarity", Astronomy & Astrophysics, 595: 26, Bibcode:2016A&A...595A.132Z, doi:10.1051/0004-6361/201628760.
  8. "HD 124639". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 19, 2018.
  9. Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694–706, arXiv:1606.09028, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035.
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