HD 193721

HD 193721 (HR 7785) is an astrometric binary[14] in the southern circumpolar constellation Octans. It has an apparent magnitude of 5.77,[2] allowing it to be faintly seen with the naked eye. Parallax measurements place the system 760 light years[1] away from the Solar System and it is currently receding with a heliocentric radial velocity 8.6 km/s.[5]

HD 193721
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Octans
Right ascension 20h 33m 17.6366s[1]
Declination −80° 57′ 53.5944″[1]
Apparent magnitude (V) 5.77±0.01[2]
Characteristics
Spectral type G6/8 II[3]
U−B color index +0.85[4]
B−V color index +1.14[4]
Astrometry
Radial velocity (Rv)8.6±0.7[5] km/s
Proper motion (μ) RA: +9.794 mas/yr[1]
Dec.: −16.081 mas/yr[1]
Parallax (π)4.2823 ± 0.165 mas[1]
Distance760 ± 30 ly
(234 ± 9 pc)
Absolute magnitude (MV)−0.24[6]
Details
Mass3.49[7] M☉
Radius24.38[8] R☉
Luminosity300±5[9] L☉
Surface gravity (log g)2.14±0.02[1] cgs
Temperature4953±122[8] K
Metallicity [Fe/H]−0.15[10] dex
Rotational velocity (v sin i)2.7±1.1[11] km/s
Other designations
47 G. Octantis[12], CPD−81°901, FK5 3994, GC 28453, HD 193721, HIP 101427, HR 7785, SAO 258861, WDS J20333-8058A[13]
Database references
SIMBADdata

HD 193721 has a stellar classification of G6/8 II[3] — intermediate between a G6 and 8 bright giant. At present it has 3.49 times the mass of the Sun,[7] but has expanded to 24.4 times its girth.[8] It shines with a luminosity of 300 L☉[9] from its enlarged photosphere at an effective temperature of 4,953 K,[8] giving a yellow hue. HD 193721 is metal deficent with an iron abundance 71% that of the Sun[10] and spins leisurely with a projected rotational velocity of 2.7 km/s.[11]

The system has an companion designated CPD −81°900. The object has a spectral classification of F8[15] and is located 25.5″ along a position angle of 0° (as of 1998).[16] CPD −81°900 is a foreground object, having a higher parallax[17] and different proper motion.[16]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (March 2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H. ISSN 0004-6361.
  3. Houk, N.; Cowley, A. P. (1975). University of Michigan Catalogue of two-dimensional spectral types for the HD stars. Volume I. Declinations -90_ to -53_ƒ0. Bibcode:1975mcts.book.....H.
  4. Johnson, H. L.; Mitchell, R. I.; Iriarte, B.; Wisniewski, W. Z. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99–110. Bibcode:1966CoLPL...4...99J.
  5. 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. ISSN 1063-7737. S2CID 119231169.
  6. Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. ISSN 1063-7737. S2CID 119257644.
  7. Kervella, Pierre; Arenou, Frédéric; Thévenin, Frédéric (2022). "Stellar and substellar companions from Gaia EDR3". Astronomy & Astrophysics. 657: A7. arXiv:2109.10912. Bibcode:2022A&A...657A...7K. doi:10.1051/0004-6361/202142146. eISSN 1432-0746. ISSN 0004-6361.
  8. Stassun, Keivan G.; et al. (9 September 2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. ISSN 0004-6256.
  9. 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.
  10. Anders, F.; et al. (August 2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy & Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. ISSN 0004-6361.
  11. De Medeiros, J. R.; Alves, S.; Udry, S.; Andersen, J.; Nordström, B.; Mayor, M. (January 2014). "A catalog of rotational and radial velocities for evolved stars: V. Southern stars⋆⋆⋆". Astronomy & Astrophysics. 561: A126. arXiv:1312.3474. Bibcode:2014A&A...561A.126D. doi:10.1051/0004-6361/201220762. ISSN 0004-6361.
  12. Gould, Benjamin Apthorp (1878). "Uranometria Argentina : brillantez y posicion de las estrellas fijas, hasta la septima magnitud, comprendidas dentro de cien grados del polo austral : con atlas". Resultados del Observatorio Nacional Argentino. 1. Bibcode:1879RNAO....1.....G.
  13. "HR 7785". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved July 1, 2022.
  14. Frankowski, A.; Jancart, S.; Jorissen, A. (19 December 2006). "Proper-motion binaries in the Hipparcos catalogue". Astronomy & Astrophysics. 464 (1): 377–392. arXiv:astro-ph/0612449. Bibcode:2007A&A...464..377F. doi:10.1051/0004-6361:20065526. eISSN 1432-0746. ISSN 0004-6361.
  15. Stoy, R. H. (1968). "Cape photographic catalague for 1950.0, zones −80° to −90°". Annals of the Cape Observatory. 22. Bibcode:1968AnCap..22.....S.
  16. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (December 2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920. ISSN 0004-6256.
  17. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
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