Astronomy:Kappa Andromedae

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Short description: Star in the constellation of Andromeda
Kappa Andromedae
Andromeda constellation map.svg
Red circle.svg
Location of κ Andromedae (circled)
Observation data
Equinox J2000.0]] (ICRS)
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
Mass2.768+0.1
−0.109[6] M☉
Radius2.29±0.06[7] R☉
Luminosity78.5[7] L☉
Surface gravity (log g)4.10±0.03[8] cgs
Temperature11,361±66[8] K
Rotational velocity (v sin i)176[9] km/s
Age47+27
−40[6] Myr
Other designations
κ And, 19 Andromedae, BD+43°4522, FK5 1619, HD 222439, HIP 116805, HR 8976, SAO 53264, PPM 64525[10]
Database references
SIMBADdata

Kappa Andromedae, Latinized from κ Andromedae, is the Bayer designation for a bright star in the northern constellation of Andromeda. It is visible to the naked eye with an apparent visual magnitude of 4.1.[2] 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 the Sun.[1] It is drifting closer with a radial velocity of −15 km/s,[4] and there is a high likelihood (86%) that it is a member of the Beta Pictoris moving group.[11] The star has one known companion exoplanet, Kappa Andromedae b.[12]

Properties

The stellar classification of Kappa Andromedae is B9 IVn, indicating that it is a subgiant star in the process of evolving away from the main sequence. The star has an estimated 2.8[6] times the mass of the Sun and is radiating 78.5[7] times the Sun's luminosity. It is spinning rapidly, with a projected rotational velocity of 162 km/s. Its true rotational velocity is 283.8 km/s, which is about 85% of its critical rotation rate (the rate at which it would break up).[6] With such a rapid rotation rate, the star is deformed into an oblate spheroid, such that while the polar radius is 1.959 R☉, the equatorial radius is significantly larger, at 2.303 R☉.[6] The outer envelope of the star is radiating energy into space with an effective temperature of 10,342 K at the equator and 12,050 K at its poles, producing a blue-white hue.[6]

The age of Kappa Andromedae has been the subject of debate. The discovery paper for Kappa Andromedae b[12] argued that the primary's kinematics are consistent with membership in the Columba Association, which would imply a system age of 20-50 million years, while a subsequent work derived an older age of 220±100 million years based on the star's position on the Hertzsprung-Russell diagram position [7] assuming that the star is not a fast rotator viewed pole-on. Direct measurements of the star later showed that Kappa Andromedae A is in fact a rapid rotator viewed nearly pole-on[6] and yield a best-estimated age of 47+27−40 million years.

Planetary system

κ Andromedae (upper centre)

In November 2012, members of the Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS) survey reported the discovery of a faint, directly-imaged companion Kappa Andromedae b.[12] Follow-up photometry and spectroscopy of kappa And b with the Subaru Telescope, Keck Observatory, and Large Binocular Telescope constrained its mass to be about 13 Jupiter masses, temperature to be between 1700 K and 2150 K, and orbit to be highly eccentric with a semimajor axis likely greater than about 75 AU. The companion's spectrum shows evidence for water and carbon monoxide molecules and suggests the object has a low surface gravity.[13][14][15]

The Kappa Andromedae planetary system[16][13]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(years) 		Eccentricity Inclination Radius
b 13+12−2 MJ 57–133AU 242–900y 0.69–0.85 114.9–140° —

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).[17]

See also

  • List of extrasolar planets directly imaged

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V 
  2. ↑ 2.0 2.1 2.2 2.3 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, doi:10.1086/110819, Bibcode: 1969AJ.....74..375C 
  4. ↑ 4.0 4.1 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, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Jones, Jeremy et al. (2016). "The Age of the Directly Imaged Planet Host Star κ Andromedae Determined from Interferometric Observations". The Astrophysical Journal Letters 822 (1): 7. doi:10.3847/2041-8205/822/1/L3. Bibcode: 2016ApJ...822L...3J. 
  7. ↑ 7.0 7.1 7.2 7.3 Hinkley, Sasha; Pueyo, Laurent; Faherty, Jacqueline K.; Oppenheimer, Ben R.; Mamajek, Eric E.; Kraus, Adam L.; Rice, Emily L.; Ireland, Michael J. et al. (September 2013). "The Kappa Andromedae System: New Constraints on the Companion Mass, System Age & Further Multiplicity". The Astrophysical Journal 763 (2): L32. doi:10.1088/2041-8205/763/2/L32. Bibcode: 2013ApJ...763L..32C. 
  8. ↑ 8.0 8.1 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, doi:10.1086/427855, Bibcode: 2005AJ....129.1642F 
  9. ↑ 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, doi:10.1051/0004-6361:20065224, Bibcode: 2007A&A...463..671R 
  10. ↑ "kap And". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=kap+And. 
  11. ↑ Lee, Jinhee; Song, Inseok (July 2019). "Development of models for nearbaby young stellar moving groups: creation, revision, and finalization of the models". Monthly Notices of the Royal Astronomical Society 486 (3): 3434–3450. doi:10.1093/mnras/stz1044. Bibcode: 2019MNRAS.486.3434L. 
  12. ↑ 12.0 12.1 12.2 Carson (November 2012). "Direct Imaging Discovery of a 'Super-Jupiter' Around the late B-Type Star κ And". The Astrophysical Journal 763 (2): L32. doi:10.1088/2041-8205/763/2/L32. Bibcode: 2013ApJ...763L..32C. 
  13. ↑ 13.0 13.1 Currie, Thayne (2018), "SCExAO/CHARIS Near-infrared Direct Imaging, Spectroscopy, and Forward-Modeling of κ And b: A Likely Young, Low-gravity Superjovian Companion", The Astrophysical Journal 156 (6): 291, doi:10.3847/1538-3881/aae9ea, Bibcode: 2018AJ....156..291C }
  14. ↑ Stone, Jordan M. et al. (December 2020), "High Contrast Thermal Infrared Spectroscopy with ALES: The 3-4μm Spectrum of κ Andromedae b", The Astronomical Journal 160 (6): 262, doi:10.3847/1538-3881/abbef3, Bibcode: 2020AJ....160..262S 
  15. ↑ Wilcomb, K et al. (2020), "Moderate-resolution K-band Spectroscopy of Substellar Companion κ Andromedae b", The Astrophysical Journal 160 (5): 207, doi:10.3847/1538-3881/abb9b1, Bibcode: 2020AJ....160..207W }
  16. ↑ Uyama, Taichi (2020), "Atmospheric Characterization and Further Orbital Modeling of κ Andromeda b", The Astrophysical Journal 159 (2): 40, doi:10.3847/1538-3881/ab5afa, Bibcode: 2020AJ....159...40U }
  17. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日

External links



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