Lambda Andromedae

λ Andromedae

Location of λ Andromedae (upper right).
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension 23h 37m 33.84261s[1]
Declination +46° 27′ 29.3380″[1]
Apparent magnitude (V) 3.819[2]
Characteristics
Spectral type G8 III-IV[3]
U−B color index +0.688[2]
B−V color index +0.996[2]
Variable type RS CVn type[4]
Astrometry
Radial velocity (Rv)+6.8[5] km/s
Proper motion (μ) RA: +159.31[1] mas/yr
Dec.: -422.38[1] mas/yr
Parallax (π)37.87 ± 0.21[1] mas
Distance86.1 ± 0.5 ly
(26.4 ± 0.1 pc)
Absolute magnitude (MV)1.91[6]
Details
Mass1.0 ± 0.2[3] M☉
Radius7.0 ± 0.7[3] R☉
Luminosity23.4[3] L☉
Surface gravity (log g)2.75 ± 0.25[3] cgs
Temperature4,800 ± 100[3] K
Metallicity [Fe/H]–0.56[7] dex
Rotation54 d[3]
Rotational velocity (v sin i)7.3[8] km/s
Other designations
BD+45° 4283, FK5 890, GJ 9832, HD 222107, HIP 116584, HR 8961, LTT 16964, NLTT 57442, SAO 53204.[4]

Lambda Andromedae (λ And, λ Andromedae) is the Bayer designation for a binary star in the northern constellation of Andromeda. At an estimated distance of approximately 86.1 light-years (26.4 parsecs) from Earth,[1] it has an apparent visual magnitude of +3.8.[2] This is bright enough to be seen with the naked eye.

Lambda Andromedae is a single-lined spectroscopic binary with an orbital period of 20.5212 days.[9] The spectrum of the primary matches a stellar classification of G8 III-IV, suggesting that it is an evolved star that lies part way between the subgiant and giant stages. The mass of this star is similar to the Sun, but it has expanded to around seven times the Sun's radius. It is radiating over 23[3] times the luminosity of the Sun from its outer envelope at an effective temperature of 4,800 K,[3] giving it the characteristic yellow hue of a G-type star.

This is an RS Canum Venaticorum variable and its brightness varies by 0.225 magnitudes, reaching a maximum of 3.70, with a period of 54.2 days.[9] Such variability is theorized to occur because of tidal friction, which results in chromospheric activity. However, the orbit of this system is nearly circular, so the cause of this system's variability remains uncertain.[9] The X-ray luminosity of this star, as measured by the ROSAT satellite, is 2.95 × 1030 erg s−1.[3]

Naming

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of λ 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, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, λ Andromedae itself is known as 螣蛇十九 (Téng Shé shíjiǔ, English: the Nineteenth Star of Flying Serpent)[10]

References

  1. 1 2 3 4 5 6 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. 1 2 3 4 Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society, 172: 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667.
  3. 1 2 3 4 5 6 7 8 9 10 Drake, Jeremy J.; et al. (November 2011), "Close to the dredge: precise X-Ray C and N abundances in λ Andromeda and its precocious red giant branch mixing problem", The Astronomical Journal, 142 (5): 144, arXiv:1109.3663Freely accessible, Bibcode:2011AJ....142..144D, doi:10.1088/0004-6256/142/5/144.
  4. 1 2 "lam And -- Variable of RS CVn type", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-06-21.
  5. ↑ Wilson, Ralph Elmer (1953), General catalogue of stellar radial velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
  6. ↑ Elgarøy, Øystein; Engvold, Oddbjørn; Lund, Niels (March 1999), "The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity", Astronomy and Astrophysics, 343: 222–228, Bibcode:1999A&A...343..222E.
  7. ↑ Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics, 352: 495–507, Bibcode:1999A&A...352..495M.
  8. ↑ Massarotti, Alessandro; et al. (January 2008), "Rotational and radial velocities for a sample of 761 HIPPARCOS giants and the role of binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  9. 1 2 3 Frasca, A.; et al. (February 2008), "Spots, plages, and flares on λ Andromedae and II Pegasi", Astronomy and Astrophysics, 479 (2): 557–565, arXiv:0711.3322Freely accessible, Bibcode:2008A&A...479..557F, doi:10.1051/0004-6361:20077915.
  10. ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日
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