5 Lacertae

5 Lacertae (5 Lac) is a spectroscopic binary in the constellation Lacerta. Its apparent magnitude is 4.36.

5 Lacertae
Location of 5 Lacertae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Lacerta
Right ascension  22h 29m 31.823s[1]
Declination +47° 42′ 24.79″[1]
Apparent magnitude (V) 4.36[2]
Characteristics
Spectral type K9Ia + B2V[3]
U−B color index +1.11[2]
B−V color index +1.68[2]
Variable type LC[4]
Astrometry
Radial velocity (Rv)−3.4±0.2[5] km/s
Proper motion (μ) RA: −0.37±0.13[1] mas/yr
Dec.: −3.33±0.12[1] mas/yr
Parallax (π)1.98 ± 0.18[1] mas
Distance1,600 ± 100 ly
(510 ± 50 pc)
Orbit[5]
Period (P)41.95±0.20 yr
Eccentricity (e)0.49±0.01
Periastron epoch (T)2427578.3±260 JD
Argument of periastron (ω)
(secondary)		323±5.0°
Semi-amplitude (K1)
(primary)		12.2±1.2 km/s
Semi-amplitude (K2)
(secondary)		112.0±8.2 km/s
Details
5 Lacertae A
Mass5.11±0.18[6] M☉
Radius319.2+26.6
−32.0[6] R☉
Luminosity17473±3344[6] L☉
Temperature3713±56[6] K
Rotational velocity (v sin i)50[7] km/s
Age110±10[6] Myr
5 Lacertae B
Temperature7,580[8] K
Rotational velocity (v sin i)89[2] km/s
Other designations
V412 Lac, BD+46° 3719, FK5 3799, HD 213310/1, HIP 111022, HR 8572, SAO 52055[3]
Database references
SIMBADdata
5 Lacertae in optical light

5 Lacertae is a slow irregular variable star with a small amplitude. Photometry from the Hipparcos satellite showed brightness changes between Hipparcos magnitudes 4.39 and 4.56 with no clear periodicity.[4] It was given the variable star designation V412 Lacertae in 1999 in a special name-list dedicated to variables detected from Hipparcos.[9]

The spectrum of 5 Lacertae clearly indicates both a hot component and a cooler component, recognised even in early spectra. Published spectral types for the brighter cool component vary from K4 to M0, with a luminosity class of giant or supergiant. The hotter star is generally classed as a relatively unevolved late B or early A star, but an automated classification program gave it a spectral class of B2V.[10]

Radial velocity variations in the absorption lines from the two separate stars have been measured to determine the orbit. This has an unusually long period of almost 42 years. The two stars have an eccentric orbit with a projected axis of about 15 au.[5]

References
  1. van Leeuwen, F. (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.Vizier catalog entry
  2. Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  3. "5 Lacertae". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-26.
  4. 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....102025S.
  5. Hendry, E. M. (1978). "Observations of a second maximum for the very long period spectroscopic binary 5 Lac". Publications of the Astronomical Society of the Pacific. 90: 184–187. Bibcode:1978PASP...90..184H. doi:10.1086/130304.
  6. Baines, Ellyn K.; et al. (2018). "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer". The Astronomical Journal. 155 (1). 30. arXiv:1712.08109. Bibcode:2018AJ....155...30B. doi:10.3847/1538-3881/aa9d8b.
  7. Van Belle, Gerard T (2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review. 20 (1): 51. arXiv:1204.2572. Bibcode:2012A&ARv..20...51V. doi:10.1007/s00159-012-0051-2.
  8. Hohle, M.M; Neuhäuser, R; Schutz, B.F (2010). "Masses and luminosities of O- and B-type stars and red supergiants". Astronomische Nachrichten. 331 (4): 349. arXiv:1003.2335. Bibcode:2010AN....331..349H. doi:10.1002/asna.200911355.
  9. Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Frolov, M. S.; Antipin, S. V.; Kireeva, N. N.; Pastukhova, E. N. (1999). "The 74th Special Name-list of Variable Stars". Information Bulletin on Variable Stars. 4659 (4659): 1. Bibcode:1999IBVS.4659....1K.
  10. Skiff, B. A. (2014). "VizieR On-line Data Catalog: Catalogue of Stellar Spectral Classifications". VizieR On-line Data Catalog. Bibcode:2014yCat....1.2023S.
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