Wikipedia

HD 172991

HD 172991, also known as HR 7031 or rarely 20 G. Coronae Australis, is a binary star[14] located in the southern constellation Corona Australis. It has a combined apparent magnitude of 5.44,[2] making it faintly visible to the naked eye. The system is located relatively far at a distance of 1,220 light years based on Gaia DR3 parallax measurements[1] but is receding with a heliocentric radial velocity of −17.4 km/s.[5] At its current distance HD 172991's brightness is diminished by magnitudes due to interstellar dust and it has an absolute magnitude of −2.56.[6]

HD 172991/172992
Location of HD 172991 (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Corona Australis
Right ascension 18h 44m 57.15228s[1]
Declination −39° 41′ 10.2781″[1]
Apparent magnitude (V) 5.44±0.01[2]
Characteristics
A
Spectral type K1/2III[3]
B−V color index +0.87[4]
B
Spectral type B9/A1V[3]
Astrometry
Radial velocity (Rv)−17.4±0.8[5] km/s
Proper motion (μ) RA: +9.815 mas/yr[1]
Dec.: −6.261 mas/yr[1]
Parallax (π)2.6806 ± 0.1453 mas[1]
Distance1,220 ± 70 ly
(370 ± 20 pc)
Absolute magnitude (MV)−2.56[6]
Details
A
Mass4.98±0.05[7] M☉
Radius53.9±3.0[8] R☉
Luminosity1,750+188
−154[1] L☉
Surface gravity (log g)1.03[9] cgs
Temperature4,990±123[10] K
Metallicity [Fe/H]−0.41[9] dex
Rotational velocity (v sin i)3.9±2[11] km/s
Other designations
20 G. Coronae Australis[12], CD−39°12864, CPD−39°8163, GC 25628, HD 172991, 172992, HIP 91989, HR 7031, SAO 210518[13]
Database references
SIMBADdata

HD 172991 has a stellar classification of K1/2 III,[3] indicating that it is an evolved red giant. The companion, HD 172992, is a B-type star with a stellar classification of B9/A1 V.[3] Although the two components can be resolved in the spectrum, they cannot be observed in telescopes, making observation difficult.[15]

HD 172991 has 4.98 times the mass of the Sun[7] but it has expanded to 53.9 times the Sun's radius.[8] It radiates 1,750 times the luminosity of the Sun[1] from its enlarged photosphere at an effective temperature of 4,990 K,[10] giving it a yellowish-orange hue. It is metal deficient with an iron abundance 39% of the Sun's ([Fe/H] = −0.41)[9] and spins modestly with a projected rotational velocity of 3.9 km/s.[11]

References

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  1. ^ a b c d e f g Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b 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. S2CID 17128864.
  3. ^ a b c d Houk, N. (1982). Michigan Catalogue of Two-dimensional Spectral Types for the HD stars. Volume_3. Declinations -40_ƒ0 to -26_ƒ0. Bibcode:1982mcts.book.....H.
  4. ^ Corben, P. M.; Stoy, R. H. (1968). "Photoelectric Magnitudes and Colours for Bright Southern Stars". Monthly Notes of the Astronomical Society of South Africa. 27: 11. Bibcode:1968MNSSA..27...11C. ISSN 0024-8266.
  5. ^ a b 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. eISSN 1562-6873. ISSN 1063-7737. S2CID 119231169.
  6. ^ a b 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. eISSN 1562-6873. ISSN 1063-7737. S2CID 119257644.
  7. ^ a b Hohle, M.M.; Neuhäuser, R.; Schutz, B.F. (April 2010). "Masses and luminosities of O- and B-type stars and red supergiants". Astronomische Nachrichten. 331 (4): 349–360. arXiv:1003.2335. Bibcode:2010AN....331..349H. doi:10.1002/asna.200911355. eISSN 1521-3994. ISSN 0004-6337. S2CID 111387483.
  8. ^ a b Kervella, P.; Thévenin, F.; Di Folco, E.; Ségransan, D. (October 2004). "The angular sizes of dwarf stars and subgiants. Surface brightness relations calibrated by interferometry". Astronomy & Astrophysics. 426 (1): 297–307. arXiv:astro-ph/0404180. Bibcode:2004A&A...426..297K. doi:10.1051/0004-6361:20035930. eISSN 1432-0746. ISSN 0004-6361. S2CID 6077801.
  9. ^ a b c 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. eISSN 1432-0746. ISSN 0004-6361. S2CID 131780028.
  10. ^ a b 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. eISSN 1538-3881. hdl:1721.1/124721. S2CID 166227927.
  11. ^ a b 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. eISSN 1432-0746. ISSN 0004-6361. S2CID 54046583.
  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. ^ "HD 172991". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved March 16, 2023.
  14. ^ Eggleton, P. P.; Tokovinin, A. A. (11 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. eISSN 1365-2966. ISSN 0035-8711. S2CID 14878976.
  15. ^ Bonneau, D.; Blazit, A.; Foy, R.; Labeyrie, A. (November 1980). "Speckle interferometric measurements of binary stars". Astronomy and Astrophysics Supplement Series. 42: 185–188. Bibcode:1980A&AS...42..185B. ISSN 0365-0138.
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