HR 8768

HR 8768, also known as LN Andromedae, is a formerly suspected variable star[3] in the constellation Andromeda. Located approximately 490 parsecs (1,600 ly) away from Earth, it shines with an apparent visual magnitude 6.41, thus it can be seen by the naked eye under very favourable conditions. Its spectral classification is B2V, meaning that it's a hot main sequence star, emitting light approximately with a blackbody spectrum at an effective temperature of 18,090 K.[10]

HR 8768
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  23h 02m 45.15s[1]
Declination +44° 03′ 31.50″[1]
Apparent magnitude (V) 6.37[2]
Characteristics
Spectral type B2V[3]
Apparent magnitude (U) 5.8[4]
Apparent magnitude (B) 6.377[5]
Apparent magnitude (J) 6.368[6]
Apparent magnitude (H) 6.482[6]
Apparent magnitude (K) 6.496[6]
Variable type suspected[3]
Astrometry
Radial velocity (Rv)−11.30±0.1[7] km/s
Proper motion (μ) RA: 0.35±0.41[1] mas/yr
Dec.: −5.82±0.44[1] mas/yr
Parallax (π)2.0618 ± 0.0580[8] mas
Distance1,580 ± 40 ly
(490 ± 10 pc)
Absolute magnitude (MV)-1.66[9]
Details
Mass6.5[10] M☉
Luminosity1,959[9] L☉
Surface gravity (log g)3.94±0.13[10] cgs
Temperature18090±730[10] K
Rotational velocity (v sin i)8±4[10] km/s
Age9.5±4.8[11] Myr
Other designations
2MASS J23024514+4403314, HR 8768, BD+43° 4378, HD 217811, SAO 52626, HIP 113802, WDS J23028+4404AB
Database references
SIMBADdata

Companion

In the Washington Double Star Catalog HR 8768 has a faint optical companion star with an apparent magnitude of 9.88,[12] 7.5″ from HR 8768. The separation has decreased from 4.0″ when it was discovered as a double in 1828.[13] The two stars share the same Hipparcos identifier HIP 113802, and have very similar parallaxes and proper motions.[14]

Variability

In 1979, the blue magnitude of HR 8768 was reported to vary by about 0.025 every 28 minutes. Such variability was not known for any class of variable, but the position in the Hertzsprung–Russell diagram at the main sequence (low luminosity) end of the same instability strip as the β Cephei stars would make high-overtone radial pulsations the likely cause.[9] Follow-up studies failed to find the same rapid variations, or any significant variations in brightness.[15] However, HR 8768 was added to the General Catalogue of Variable Stars as LN Andromedae.[3]

Analysis of Hipparcos photometry shows variability of about 0.0059 magnitudes with a main period of 3.25 d. The statistical threshold for these variations is at a level which is only met by 0.01% of stars.[2]

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. Koen, Chris; Eyer, Laurent (2002). "New periodic variables from the Hipparcos epoch photometry". Monthly Notices of the Royal Astronomical Society. 331 (1): 45. Bibcode:2002MNRAS.331...45K. doi:10.1046/j.1365-8711.2002.05150.x.
  3. N. N. Samus; O. V. Durlevich; et al. "LN And database entry". Combined General Catalog of Variable Stars (2017 ed.). CDS. Retrieved 2018-11-12.
  4. Reed, B. C. (May 2003). "Catalog of Galactic OB Stars". The Astronomical Journal. 125 (5): 2531–2533. Bibcode:2003AJ....125.2531R. doi:10.1086/374771.
  5. "HR 8768". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 15, 2018.
  6. Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; et al. (June 2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues (2246): II/246. Bibcode:2003yCat.2246....0C.
  7. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  8. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  9. Jakate, S. M. (1979). "A new class of early-type ultra-short-period variables". The Astronomical Journal. 84: 1042. Bibcode:1979AJ.....84.1042J. doi:10.1086/112510.
  10. Lyubimkov, N.; Lambert, D. L.; Poklad, D. B.; Rachkovskaya, T. M.; Rostopchin, S. I. (February 2013). "Carbon, nitrogen and oxygen abundances in atmospheres of the 5-11 M☉ B-type main-sequence stars". Monthly Notices of the Royal Astronomical Society. 428 (4): 3497–3508. arXiv:1212.0987. Bibcode:2013MNRAS.428.3497L. doi:10.1093/mnras/sts287.
  11. Tezlaff, L. S.; Neuhäuser, R.; Hohle, N. N. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x.
  12. "BD+43 4378B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 15, 2018.
  13. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  14. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  15. Shaw, J. S.; Fraquelli, D. A.; Martins, D. H.; Andrew, S. B. (1983). "HR 8768 - an Ultra Short Period Variable?". Information Bulletin on Variable Stars. 2288: 1. Bibcode:1983IBVS.2288....1S.
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