HR 7031

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

HD 172991, also known as HR 7031 or rarely 20 G. Coronae Australis, is a binary star located in the southern constellation Corona Australis. It has a combined apparent magnitude of 5.44, 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 but is receding with a heliocentric radial velocity of −17.4 km/s. 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.

HD 172991 has a stellar classification of K1/2 III, 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. Although the two components can be resolved in the spectrum, they cannot be observed in telescopes, making observation difficult.

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

References

  1. 1 2 3 4 5 6 7 8 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. 1 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. S2CID 17128864.
  3. 1 2 3 4 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. 1 2 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. 1 2 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. 1 2 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. 1 2 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. 1 2 3 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. 1 2 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. 1 2 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.