Binary star in the constellation Corona Australis
HD 172991/172992Location of HD 172991 (circled)
Observation dataEpoch 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−Vcolor 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: +9.815mas /yr [ 1] Dec.: −6.261mas /yr [ 1] Parallax (π)2.6806± 0.1453 mas [ 1] Distance 1,220 ± 70 ly pc ) Absolute magnitude (MV )−2.56[ 6] Details A Mass 4.98± 0.05[ 7] M ☉ Radius 53.9± 3.0[ 8] R ☉ Luminosity 1,750+188 −154 [ 1] L ☉ Surface gravity (log g )1.03[ 9] cgs Temperature 4,990± 123[ 10] K Metallicity [Fe/H] −0.41[ 9] dex Rotational velocity (v sin i )3.9± 2[ 11] Other designations 20 G. Coronae Australis [ 12] CD −39°12864CPD −39°8163GC 25628HD 172991, 172992HIP 91989HR 7031SAO 210518[ 13] Database references SIMBAD data
HD 172991 , also known asHR 7031 or rarely20 G. Coronae Australis , is abinary star [ 14] constellation Corona Australis . It has a combinedapparent magnitude of 5.44,[ 2] naked eye . The system is located relatively far at a distance of 1,220light years based onGaia DR3 parallax measurements[ 1] radial velocity ofkm/s [ 5] magnitudes due tointerstellar dust and it has anabsolute magnitude of −2.56.[ 6]
HD 172991 has astellar classification of K1/2 III,[ 3] evolved red giant . The companion, HD 172992, is aB-type star with astellar classification of B9/A1 V.[ 3] spectrum , they cannot be observed intelescopes , making observation difficult.[ 15]
HD 172991 has 4.98 times themass of the Sun [ 7] Sun's radius .[ 8] luminosity of the Sun [ 1] photosphere at aneffective temperature ofK [ 10] iron abundance 39% of theSun 's ([Fe/H] = −0.41)[ 9] projected rotational velocity ofkm/s [ 11]
^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 atVizieR .^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 . ^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 . ^ 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 . ^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 . ^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 . ^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 . ^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 . ^a b c Anders, F.; et al. (August 2019)."Photo-astrometric distances, extinctions, and astrophysical parameters forGaia DR2 stars brighter thanG = 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 . ^a b Stassun, Keivan G.; et al. (9 September 2019)."The RevisedTESS 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 . ^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 . ^ 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 . ^ "HD 172991" .SIMBAD Centre de données astronomiques de Strasbourg . RetrievedMarch 16, 2023 .^ 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 . ^ 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 .
