Theta Octantis

θ Octantis, Latinized as Theta Octantis, is a single[9] star in the southern circumpolar constellation of Octans, near the constellation border with Hydrus. It is visible t othe naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.78.[2] The star is located approximately 217 light years from the Sun based on parallax,[1] and is drifting further away with a radial velocity of +22.5 km/s.[5]

Theta Octantis
Location of θ Octantis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Octans
Right ascension  00h 01m 35.70158s[1]
Declination −77° 03′ 56.6092″[1]
Apparent magnitude (V) 4.78[2]
Characteristics
Spectral type K3III[3]
U−B color index +1.41[4]
B−V color index +1.27[4]
Astrometry
Radial velocity (Rv)+22.48±0.17[5] km/s
Proper motion (μ) RA: −57.30[1] mas/yr
Dec.: −177.06[1] mas/yr
Parallax (π)15.02 ± 0.18[1] mas
Distance217 ± 3 ly
(66.6 ± 0.8 pc)
Absolute magnitude (MV)0.66[2]
Details
Mass1.20[6] M☉
Radius15.84+0.42
−1.02[5] R☉
Luminosity79.2±1.5[5] L☉
Surface gravity (log g)2.16[6] cgs
Temperature4,325+147
−55[5] K
Rotational velocity (v sin i)< 1.0[7] km/s
Other designations
θ Oct, CPD−77° 1596, FK5 904, GC 33321, HD 224889, HIP 122, HR 9084, SAO 258207[8]
Database references
SIMBADdata

This is an aging giant star with a stellar classification of K3III,[3] having exhausted the supply of hydrogen at its core then cooled and expanded. It has been catalogued as a red clump giant,[10] which would indicate it is on the horizontal branch and is undergoing core helium fusion. At present it has 16[5] times the radius of the Sun. This star has 1.20[6] times the mass of the Sun and is radiating 79[5] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,325 K.[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.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. Vizier catalog entry
  3. Houk, Nancy; Cowley, A. P. (1979). "Michigan catalogue of two-dimensional spectral types for the HD stars". 1. Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan. Bibcode:1978mcts.book.....H. Cite journal requires |journal= (help)
  4. Mallama, A. (2014). "Sloan Magnitudes for the Brightest Stars". The Journal of the American Association of Variable Star Observers. 42: 443. Bibcode:2014JAVSO..42..443M. Vizier catalog entry
  5. 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.
  6. Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry
  7. De Medeiros, J. R.; Alves, S.; Udry, S.; Andersen, J.; Nordström, B.; Mayor, M. (2014). "A catalog of rotational and radial velocities for evolved stars". Astronomy & Astrophysics. 561: A126. arXiv:1312.3474. Bibcode:2014A&A...561A.126D. doi:10.1051/0004-6361/201220762. Vizier catalog entry
  8. "tet Oct". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-08-30.
  9. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  10. Gontcharov, G. A. (2009). "Red giant clump in the Tycho-2 catalogue". Astronomy Letters. 34 (11): 785. arXiv:1607.00619. Bibcode:2008AstL...34..785G. doi:10.1134/S1063773708110078. Vizier catalog entry
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