KK Andromedae

KK Andromedae, also known as HD 9531, is a variable star in the northern constellation of Andromeda. It has an apparent visual magnitude of 5.90,[2] which places it near the lower limit of visibility to the naked eye even under good viewing conditions. An Alpha2 Canum Venaticorum variable, it varies in brightness by 0.012 magnitude every 0.66 days.[10] Based upon an annual parallax shift of 7.5 mas[1] as seen from Earth, it is located around 437 light years from the Sun. At that distance, the brightness of the star is diminished by an extinction of 0.26 magnitude due to interstellar dust.[8]

KK Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  01h 34m 16.62220s[1]
Declination +37° 14′ 13.8765″[1]
Apparent magnitude (V) 5.90[2]
Characteristics
Spectral type B9 IV[3]
U−B color index −0.3
B−V color index −0.067±0.001[2]
Variable type α2 CVn
Astrometry
Radial velocity (Rv)−1.4±1.8[4] km/s
Proper motion (μ) RA: +5.719[1] mas/yr
Dec.: −21.238[1] mas/yr
Parallax (π)7.4585 ± 0.1156[1] mas
Distance437 ± 7 ly
(134 ± 2 pc)
Absolute magnitude (MV)+0.35[5]
Details
Mass3.07±0.06[6] M☉
Radius2.7±0.4[5] R☉
Luminosity91[5] L☉
Surface gravity (log g)3.914±0.020[7] cgs
Temperature11,729±50[7] K
Rotation0.67 days[5]
Rotational velocity (v sin i)163±10[7] km/s
Age225[8] Myr
Other designations
KK And, BD+36° 277, HD 9531, HIP 7321, HR 446, SAO 54788[9]
Database references
SIMBADdata

Cowley et al. (1969) assigned this star a stellar classification of B9 IV,[3] which would indicate it is a B-type star in the subgiant stage that has exhausted the hydrogen supply at its core and is expanding. It is a catalogued as an Ap star that displays an abnormal silicon abundance,[11] but has been reported to actually be a helium-weak chemically peculiar star.[12] The star has just over three times the mass of the Sun[6] and about 2.7[5] times the Sun's radius. It is an estimated 225[8] million years old and is spinning rapidly with a projected rotational velocity of 163 km/s[7] and a rotation period of 16 hours.[5] KK And is radiating 91[5] times the Sun's luminosity from its photosphere at an effective temperature of 11,729 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. 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.
  3. Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
  4. Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  5. North, P. (June 1998), "Do SI stars undergo any rotational braking?", Astronomy and Astrophysics, 334: 181–187, arXiv:astro-ph/9802286, Bibcode:1998A&A...334..181N
  6. 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, A120.
  7. Huang, Wenjin; et al. (2010), "A Stellar Rotation Census of B Stars: From Zams to Tams", The Astrophysical Journal, 722 (1): 605–619, arXiv:1008.1761, Bibcode:2010ApJ...722..605H, doi:10.1088/0004-637X/722/1/605.
  8. 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.
  9. "KK And". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 18, 2018.
  10. Watson, Christopher (4 January 2010). "KK Andromedae". AAVSO Website. American Association of Variable Star Observers. Retrieved 1 November 2014.
  11. Renson, P.; Manfroid, J. (2009), "Catalogue of Ap, HgMn and Am stars", Astronomy and Astrophysics, 498 (3): 961, Bibcode:2009A&A...498..961R, doi:10.1051/0004-6361/200810788.
  12. Hric, Ladislav (July 1990), "The new helium-weak star HR 446", Astrophysics and Space Science, 169 (1–2): 177–181, Bibcode:1990Ap&SS.169..177H, doi:10.1007/BF00640707.

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