GY Andromedae

GY Andromedae (GY And) is an α2 Canum Venaticorum type variable star in the northern constellation Andromeda. Its brightness fluctuates in visual magnitude between 6.27m and 6.41m, making it a challenge to view with the naked eye even in good seeing conditions. The magnetic activity on this star shows an unusually long period of variability, cycling about once every 23 years.[9] Based upon parallax measurements, this star is located at a distance of about 520 light-years (160 parsecs) from the Earth.[1]

GY Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  01h 38m 31.82463s[1]
Declination +45° 23′ 58.9324″[1]
Apparent magnitude (V) 6.36[2]
Characteristics
Spectral type B9 pe[3]
U−B color index -0.10[2]
B−V color index +0.04[2]
Variable type α2 CVn
Astrometry
Radial velocity (Rv)+3.0[4] km/s
Proper motion (μ) RA: -15.64[1] mas/yr
Dec.: -0.77[1] mas/yr
Parallax (π)6.23 ± 0.72[1] mas
Distanceapprox. 520 ly
(approx. 160 pc)
Absolute magnitude (MV)+0.68[5]
Details
Mass2.47 ± 0.15[5] M☉
Radius2.6 ± 0.4[5] R☉
Luminosity52[5] L☉
Surface gravity (log g)4.01 ± 0.14[5] cgs
Temperature10,723[6] K
Metallicity [Fe/H]0.86[6] dex
Rotational velocity (v sin i)31[7] km/s
Orbit[8]
CompanionGY And B
Period (P)272.99 days
Semi-major axis (a)> 0.25 AU
Eccentricity (e)0.47
Argument of periastron (ω)
(secondary)		17.7°
Other designations
BD +44°341, HD 9996, HIP 7651, HR 465, SAO 37393.[3]
Database references
SIMBADdata

This is classified as an Ap/Bp star, with a peculiar spectrum[9] showing lines of chromium and europium that change in intensity over a period matching the variability cycle, although opposite in phase.[10] Its most striking characteristic is the presence of the unstable element promethium in its emission spectrum. All isotopes of this element are radioactive with half lives of 17.7 years or less. The promethium in the outer envelope may be generated by the spontaneous fission of higher mass transuranic elements.[11]

System

Based on radial velocity measurements taken at the Dominion Astrophysical Observatory between 1927 and 1935 Canadian astronomer William Edmund Harper strongly suspected that this star is a spectroscopic binary.[12] In 1958, American astronomer Horace W. Babcock confirmed the binary nature of the star.[13] It has an orbital period of 273 days with a large eccentricity of 0.47. The two components are separated by an estimated distance of at least 3.74 × 107 km, or 0.25 Astronomical Units.[8]

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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. Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series. 34: 1–49. Bibcode:1978A&AS...34....1N.
  3. "V* GY And -- Variable Star of alpha2 CVn type", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-01
  4. Wilson, R. E. (1953), General Catalogue of Stellar Radial Velocities, Carnegie Institute of Washington, D.C., Bibcode:1953GCRV..C......0W
  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. Aller, M. F. (July 1972), "A model atmosphere analysis of the Ap star HR 465", Astronomy and Astrophysics, 19: 248–260, Bibcode:1972A&A....19..248A
  7. Royer, F.; et al. (October 2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943
  8. Scholz, G. (1978), "Spectroscopic investigations of the magnetic AP star HD 9996", Astronomische Nachrichten, 299 (2): 81–85, Bibcode:1978AN....299...81S, doi:10.1002/asna.19782990204
  9. Leroy, J. L. (November 1995), "Linear polarimetry of AP stars. V. A general catalogue of measurements", Astronomy and Astrophysics Supplement, 114: 79, Bibcode:1995A&AS..114...79L
  10. Preston, George W.; Wolff, Sidney C. (June 1970), "The Very Slow Spectrum, Magnetic, and Photometric Variations of HD 9996", Astrophysical Journal, 160: 1071, Bibcode:1970ApJ...160.1071P, doi:10.1086/150494
  11. Mitalas, R.; Marlborough, J. M. (April 1973), "Some tests and consequences of the identification of promethium in HR 465", Astrophysical Journal, 181: 475–480, Bibcode:1973ApJ...181..475M, doi:10.1086/152063
  12. Harper, W. E. (1937). "The radial velocities of 917 stars". Publications of the Dominion Astrophysical Observatory Victoria B.C. 7: 1–97. Bibcode:1937PDAO....7....1H.
  13. Babcock, Horace W. (1958). "A Catalog of Magnetic Stars". Astrophysical Journal Supplement. 3: 141–210. Bibcode:1958ApJS....3..141B. doi:10.1086/190035.
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