2 Lacertae

2 Lacertae is a binary star in the constellation of Lacerta. With an apparent magnitude of about 4.5,[2] it is faintly visible to the naked eye. Its parallax, measured by the Hipparcos spacecraft, is 5.88 milliarcseconds,[1] corresponding to a distance of about 550 light years (170 parsecs). It is projected against the Lacertae OB1 stellar association to the northeast of the main concentration of stars, but it is likely to be a foreground object.[7]

2 Lacertae
Location of 2 Lacertae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Lacerta
Right ascension  22h 21m 01.54727s[1]
Declination +46° 32′ 11.6461″[1]
Apparent magnitude (V) 4.540[2]
Characteristics
Spectral type B6V[3] + B6V[4]
U−B color index −0.49[4]
B−V color index −0.14[4]
Variable type Ellipsoidal (suspected)[5]
Astrometry
Radial velocity (Rv)−9.5 ± 2[6] km/s
Proper motion (μ) RA: 22.35[1] mas/yr
Dec.: 1.45[1] mas/yr
Parallax (π)5.88 ± 0.14[1] mas
Distance550 ± 10 ly
(170 ± 4 pc)
Absolute magnitude (MV)−1.19[7]
Orbit[4]
Period (P)2.616430 ± 0.000003 yr
Eccentricity (e)0.040 ± 0.018
Periastron epoch (T)2427770 ± 0.18
Argument of periastron (ω)
(secondary)		97.4 ± 25.3°
Semi-amplitude (K1)
(primary)		79.5 ± 1.8 km/s
Semi-amplitude (K2)
(secondary)		100.0 ± 1.8 km/s
Details
Mass5.01[8] M☉
Luminosity1,084[8] L☉
Surface gravity (log g)3.0[4] cgs
Temperature13,996[8] K
Rotational velocity (v sin i)54[8] km/s
Other designations
BD+45° 3894, HD 212120, HIP 110351, HR 8523, SAO 51904
Database references
SIMBADdata
Photograph of Lacerta

2 Lacertae is a double-lined spectroscopic binary. Its components are too close to be resolved, however periodic Doppler shifts in its spectrum reveal that there are two stars orbiting each other. Both stars are B-type main-sequence stars, orbiting each other every 2.616 days and with an eccentricity of about 0.04. The primary is estimated to be about one magnitude brighter than the secondary. The primary component is close to moving off the main sequence, and has nearly exhausted its core hydrogen (possibly also its companion).[4] It is estimated to have completed over 90% of its time on the main sequence.[8]

References
  1. van Leeuwen, F.; et al. (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. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  3. Lesh, Janet Rountree (1968). "The Kinematics of the Gould Belt: An Expanding Group?". Astrophysical Journal Supplement. 17: 371. Bibcode:1968ApJS...17..371L. doi:10.1086/190179.
  4. Hilditch, R. W. (1974). "The binary systems 14 Cephei and 2 Lacertae". Monthly Notices of the Royal Astronomical Society. 169 (2): 323–329. Bibcode:1974MNRAS.169..323H. doi:10.1093/mnras/169.2.323.
  5. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....1.2025S.
  6. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington. Bibcode:1953GCRV..C......0W.
  7. Kaltcheva, Nadia (2009). "Lacerta OB1 Revisited". Publications of the Astronomical Society of the Pacific. 121 (884): 1045. Bibcode:2009PASP..121.1045K. doi:10.1086/606037.
  8. 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.

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