BQ Octantis

BQ Octantis (BQ Oct) is a variable star in the constellation Octans. It is an S-type star with an apparent magnitude of 6.82. It lies less than a quarter degree from the South Celestial Pole (SCP), making it the closest star to the SCP brighter than magnitude 10. While it is much nearer than Sigma Octantis (the star commonly used as the south pole star), it is too dim to the naked eye to use as a visual reference under typical skies.

BQ Octantis
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Octans
Right ascension  14h 35m 29.5920s[1]
Declination −89° 46′ 18.170″[1]
Apparent magnitude (V) 6.8 (var)[2]
Characteristics
Evolutionary stage S5,1[3]
Variable type Lb?[2]
Astrometry
Radial velocity (Rv)−3.5[4] km/s
Proper motion (μ) RA: −8.78[1] mas/yr
Dec.: −8.84[1] mas/yr
Parallax (π)1.6953 ± 0.0904[1] mas
Distance1,900 ± 100 ly
(590 ± 30 pc)
Details
Radius160[1] R☉
Luminosity3,767[5] L☉
Temperature3,520[5] K
Other designations
CD−89°10, FK5 3985, HD 110994, HIP 71348, SAO 258660[6]
Database references
SIMBADdata

BQ Octantis is a red giant on the asymptotic giant branch. Its spectrum has been classified as M3III or M4III.[7] The spectrum shows abnormal abundances of s-process elements and particularly ZrO, so it is classified as an S star. These stars have dredged up fusion products from the interior, especially carbon. They have reached approximately equal levels of carbon and oxygen in their atmospheres, which causes dramatic changes to the atmospheric chemistry which are visible in the spectrum. As an S star, its spectrum is classified as S5,1, with S5 approximately equivalent to the temperature of an M5 giant and the 1 indicating that the ZrO bands are relatively weak.[3]

BQ Octantis is a variable star. An amplitude of 0.05 magnitudes about an apparent magnitude of 6.82 has been derived from Hipparcos satellite photometry. The same photometry found a possible period of 0.82 d but this was very uncertain and no variability type could be determined.[8] It is listed in the General Catalogue of Variable Stars as a possible slow irregular variable.[2] It was classified as a variable star in 1977,[9] on the basis of a 1960 study.[10]

References
  1. 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.
  2. 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.
  3. Stephenson, C. B. (1984). "A general catalogue of S stars". Publications of the Warner & Swasey Observatory. Bibcode:1984PW&SO...3....1S.
  4. Evans, D. S. (1967). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and Their Applications. 30: 57. Bibcode:1967IAUS...30...57E.
  5. Bergeat, J.; Knapik, A.; Rutily, B. (2002). "Carbon-rich giants in the HR diagram and their luminosity function". Astronomy and Astrophysics. 390 (3): 967–986. Bibcode:2002A&A...390..967B. doi:10.1051/0004-6361:20020525.
  6. "V* BQ Oct". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 9 January 2015.
  7. Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009- )". VizieR On-line Data Catalog. Bibcode:2014yCat....1.2023S.
  8. 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.
  9. Kukarkin, B. V.; Kholopov, P. N.; Fedorovich, V. P.; Kireyeva, N. N.; Kukarkina, N. P.; Medvedeva, G. I.; Perova, N. B. (1977). "62nd Name-List of Variable Stars". Information Bulletin on Variable Stars. 1248: 1. Bibcode:1977IBVS.1248....1K.
  10. Stoy, R. H. (1960). "Photoelectric Three Colour Magnitudes for Southern Stars". Monthly Notes of the Astronomical Society of South Africa. 19: 69. Bibcode:1960MNSSA..19...69S.
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