HD 161840

HD 161840 is a single,^[8] blue-white hued star in the southern zodiac constellation of Scorpius. It is faintly visible to the naked eye with an apparent visual magnitude of 4.79.^[2] With an annual parallax shift of 6.5 mas^[1] it is located roughly 500 light years from the Sun. It is moving closer with a heliocentric radial velocity of −13 km/s.^[2]

HD 161840

Observation data Epoch J2000      Equinox J2000
Constellation	Scorpius
Right ascension	17h 48m 10.47559s[1]
Declination	−31° 42′ 11.5636″[1]
Apparent magnitude (V)	4.79[2]
Characteristics
Spectral type	B8 Ib/II[3]
B−V color index	−0.028±0.023[2]
Astrometry
Radial velocity (Rv)	−13.3±2.8[2] km/s
Proper motion (μ)	RA: +6.845[1] mas/yr Dec.: −8.161[1] mas/yr
Parallax (π)	6.5831 ± 0.3618 mas[1]
Distance	500 ± 30 ly (152 ± 8 pc)
Absolute magnitude (MV)	−1.37[2]
Details
Mass	3.93±0.08[4] M☉
Radius	3.2[5] R☉
Luminosity	565+59 −53[4] L☉
Surface gravity (log g)	3.38[6] cgs
Temperature	11066+77 −76[4] K
Rotational velocity (v sin i)	24[4] km/s
Other designations
CD−31° 14609, HD 161840, HIP 87220, HR 6628, SAO 209303[7]
Database references
SIMBAD	data

There has been some uncertainty as to the classification of this stage. Houk (1979) lists a stellar class of B8 Ib/II for HD 161840,^[3] which corresponds to a B-type bright giant/lesser supergiant mix. Multiple studies still use an older classification of B8 V,^[8][6][4] suggesting instead this is a B-type main-sequence star. Garrison and Gray (1994) assigned it a class of B8 III-IV,^[9] which would put it on the subgiant/giant star track. It has an estimated 3.93^[4] times the mass of the Sun and 3.2^[5] times the Sun's radius. The star is radiating 565^[4] times the Sun's luminosity from its photosphere at an effective temperature of 11,066 K.^[4]

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. 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.
3. Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1982mcts.book.....H.
4. Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
5. Pasinetti Fracassini, L. E.; et al. (2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy & Astrophysics, 367 (3rd ed.): 521–24, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
6. Hempel, M.; Holweger, H. (September 2003), "Abundance analysis of late B stars. Evidence for diffusion and against weak stellar winds", Astronomy and Astrophysics, 408: 1065–1076, Bibcode:2003A&A...408.1065H, doi:10.1051/0004-6361:20030889.
7. "HD 161840". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-08-04.
8. Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
9. Garrison, R. F.; Gray, R. O (1994), "The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation", The Astronomical Journal, 107: 1556, Bibcode:1994AJ....107.1556G, doi:10.1086/116967.