Kappa Andromedae

Kappa Andromedae (κ And, κ Andromedae) is the Bayer designation for a bright star in the constellation of Andromeda. Its apparent visual magnitude is 4.1. Based on the star's ranking on the Bortle Dark-Sky Scale, it is luminous enough to be visible from the suburbs and from urban outskirts, but not from brightly lit inner city regions. Parallax measurements made during the Hipparcos mission place it at a distance of approximately 168 light-years (52 parsecs) from Earth.

"19 Andromedae" redirects here. For the galaxy, see Andromeda XIX.
Kappa Andromedae
Location of κ Andromedae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  23h 40m 24.50763s[1]
Declination +44° 20′ 02.1566″[1]
Apparent magnitude (V) 4.139[2]
Characteristics
Spectral type B9 IVn[3]
U−B color index -0.221[2]
B−V color index -0.067[2]
Astrometry
Radial velocity (Rv)-15.0[4] km/s
Proper motion (μ) RA: +80.73[1] mas/yr
Dec.: -18.70[1] mas/yr
Parallax (π)19.37 ± 0.19[1] mas
Distance168 ± 2 ly
(51.6 ± 0.5 pc)
Absolute magnitude (MV)+0.59[5]
Details
Mass2.8+0.1
−0.2[6] M☉
Radius2.29 ± 0.06[6] R☉
Luminosity78.5[6] L☉
Surface gravity (log g)4.10 ± 0.03[7] cgs
Temperature11,361 ± 66[7] K
Rotational velocity (v sin i)176[8] km/s
Age220 ± 100[6] Myr
Other designations
19 Andromedae, BD+43°4522, FK5 1619, HD 222439, HIP 116805, HR 8976, SAO 53264
Database references
SIMBADdata

Kappa Andromedae has a stellar classification of B9 IVn, indicating that it is a subgiant star in the process of evolving away from the main sequence. It has 2.3 times the radius of the Sun and is spinning rapidly, with a projected rotational velocity of 176 km/s. The outer envelope of the star is radiating energy into space with an effective temperature of 11,361 K, producing a blue-white hue.

Chinese naming

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of κ Andromedae, α Lacertae, 4 Lacertae, π2 Cygni, π1 Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for κ Andromedae itself is 螣蛇二十一 (Téng Shé èrshíyī, English: the Twenty First Star of Flying Serpent).[9]

System
Kappa Andromedae b (upper left), discovered by the Subaru SEEDS survey.

In November 2012, a young, hot gas giant planet, about 13 times the mass of and slightly larger than Jupiter, was directly imaged in orbit around κ And at a projected separation of 55 ± 2 AU.[10]

Observations at multiple wavelengths indicate a temperature of about 1,700 K and the estimated age is approx. 30 million years.[10]

In September 2013, the mass of the companion was revised to be 50±13 Jupiter masses due to a much older estimated age for the star, 220±100 million years. This makes it a brown dwarf and it is given a spectral type of L1.[6] The companion is shining by its residual heat of formation, cooling as it ages. As a result, an older system age implies a larger mass (and initial supply of energy) to reach the same current brightness. This more recent study used data from the Project 1640 integral-field spectrograph to fit a temperature of about 2,040 K.[6]

A 2016 study calculated the age of Kappa Andromedae from its rotational velocity, luminosity and oblateness, and came up with an age of the system of 47+27
−40 million years and a mass of 22+8
−9 Jupiters for the companion.[11]

The Kappa Andromedae planetary system[12][6]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(years)		 Eccentricity Inclination Radius
b 50+16
−13 MJ		 40–236 144–2033 0.02–0.85 59–159° —

See also
  • List of extrasolar planets directly imaged

References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. Harmanec, P.; et al. (1980), "Photoelectric photometry at the Hvar Observatory. IV - A study of UBV variations of a group of bright northern Be stars", Bulletin of the Astronomical Institutes of Czechoslovakia, Bulletin, 31 (3): 144–159, Bibcode:1980BAICz..31..144H
  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. Palmer, D. R.; et al. (1968), "The radial velocities spectral types and projected rotational velocities of 633 bright northern A stars", Royal Observatory Bulletin, 135: 385, Bibcode:1968RGOB..135..385P
  5. 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.
  6. Sasha Hinkley; Laurent Pueyo; Jacqueline K. Faherty; Ben R. Oppenheimer; Eric E. Mamajek; Adam L. Kraus; Emily L. Rice; Michael J. Ireland; Trevor David; Lynne A. Hillenbrand; Gautam Vasisht; Eric Cady; Douglas Brenner; Aaron Veicht; Ricky Nilsson; Neil Zimmerman; Ian R. Parry; Charles Beichman; Richard Dekany; Jennifer E. Roberts; Lewis C. Roberts Jr.; Christoph Baranec; Justin R. Crepp; Rick Burruss; J. Kent Wallace; David King; Chengxing Zhai; Thomas Lockhart; Michael Shao; Remi Soummer; Anand Sivaramakrishnan; Louis A. Wilson (September 2013). "The Kappa Andromedae System: New Constraints on the Companion Mass, System Age & Further Multiplicity". The Astrophysical Journal. 779 (2): 153. arXiv:1309.3372. Bibcode:2013ApJ...779..153H. doi:10.1088/0004-637X/779/2/153.
  7. Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal, 129 (3): 1642–1662, arXiv:astro-ph/0412542, Bibcode:2005AJ....129.1642F, doi:10.1086/427855
  8. Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224
  9. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日
  10. Carson; et al. (November 2012). "Direct Imaging Discovery of a 'Super-Jupiter' Around the late B-Type Star κ And". The Astrophysical Journal. 763 (2): L32. arXiv:1211.3744. Bibcode:2013ApJ...763L..32C. doi:10.1088/2041-8205/763/2/L32.
  11. Jones, Jeremy; White, R. J.; Quinn, S.; Ireland, M.; Boyajian, T.; Schaefer, G.; Baines, E. K. (2016). "The Age of the Directly Imaged Planet Host Star κ Andromedae Determined from Interferometric Observations". The Astrophysical Journal Letters. 822 (1): 7. arXiv:1604.02176. Bibcode:2016ApJ...822L...3J. doi:10.3847/2041-8205/822/1/L3.
  12. Blunt, Sarah; et al. (2017). "Orbits for the Impatient: A Bayesian Rejection-sampling Method for Quickly Fitting the Orbits of Long-period Exoplanets". The Astronomical Journal. 153 (5). 229. arXiv:1703.10653. Bibcode:2017AJ....153..229B. doi:10.3847/1538-3881/aa6930.
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