HD 170521

HD 170521, also known as HR 6937 or rarely 12 G. Coronae Australis, is a solitary star^[15] located in the southern constellation Corona Australis. It is faintly visible to the naked eye as an orange-hued point of light with an apparent magnitude of 5.69.^[2] The object is located relatively far at a distance of approximately 1,500 light years based on Gaia DR3 parallax measurements,^[1] and it is receding with a heliocentric radial velocity of 7.2 km/s.^[5] At its current distance, HD 170521's brightness is heavily diminished by 0.46 magnitudes due to extinction from interstellar dust^[16] and it has an absolute magnitude of −1.90.^[6]

HD 170521

Location of HD 170521 (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Corona Australis
Right ascension	18h 31m 56.22382s[1]
Declination	−43° 30′ 26.5714″[1]
Apparent magnitude (V)	5.69±0.01[2]
Characteristics
Spectral type	K2 III[3]
B−V color index	+1.34[4]
Astrometry
Radial velocity (Rv)	7.2±0.4[5] km/s
Proper motion (μ)	RA: −1.328 mas/yr[1] Dec.: −8.795 mas/yr[1]
Parallax (π)	2.1538 ± 0.1596 mas[1]
Distance	1,500 ± 100 ly (460 ± 30 pc)
Absolute magnitude (MV)	−1.90[6]
Details
Mass	1.55[7] M☉
Radius	78.6±4.1[8] R☉
Luminosity	934[9] L☉
Surface gravity (log g)	0.96[10] cgs
Temperature	4,474±122[11] K
Metallicity [Fe/H]	−0.49[7] dex
Rotational velocity (v sin i)	6.5±1[12] km/s
Other designations
12 G. Coronae Australis[13], CD−43°12600, CPD−34°8647, GC 25272, HD 170521, HIP 90842, HR 6937, SAO 229094[14]
Database references
SIMBAD	data

HD 170521 has a stellar classification of K2 III,^[3] indicating that it is an evolved red giant. It has 1.55 times the mass of the Sun^[7] but it has expanded to 78.6 times the Sun's radius.^[8] The object radiates 934 times the luminosity of the Sun^[9] from its enlarged photosphere at an effective temperature of 4,474 K.^[11] HD 170521 is metal deficient with an iron abundance only 32.4% that of the Sun (Fe/H) = −0.49^[7] and it spins modestly with a projected rotational velocity of 6.5 km/s.^[12]

References

1. 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. 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. Houk, Nancy (1978). Michigan catalogue of two-dimensional spectral types for the HD stars: Declinations −53° to −40°. Vol. 2. Bibcode:1978mcts.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. 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. 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. 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.
8. Kervella, P.; Thévenin, F.; Di Folco, E.; Ségransan, D. (October 2004). "The angular sizes of dwarf stars and subgiants". 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.
9. McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (21 November 2012). "Fundamental parameters and infrared excesses of Hipparcos stars: Parameters and IR excesses from Hipparcos". Monthly Notices of the Royal Astronomical Society. 427 (1): 343–357. arXiv:1208.2037. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x. eISSN 1365-2966. ISSN 0035-8711. S2CID 118665352.
10. McDonald, I.; Zijlstra, A. A.; Watson, R. A. (15 June 2017). "Fundamental parameters and infrared excesses of Tycho–Gaia stars". Monthly Notices of the Royal Astronomical Society. 471 (1): 770–791. arXiv:1706.02208. Bibcode:2017MNRAS.471..770M. doi:10.1093/mnras/stx1433. eISSN 1365-2966. ISSN 0035-8711. S2CID 73594365.
11. 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.
12. 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.
13. 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.
14. "HD 170521". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 19, 2023.
15. 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.
16. Gontcharov, George A.; Mosenkov, Aleksandr V. (28 September 2017). "Verifying reddening and extinction for Gaia DR1 TGAS main sequence stars". Monthly Notices of the Royal Astronomical Society. 472 (4): 3805–3820. arXiv:1709.01160. Bibcode:2017MNRAS.472.3805G. doi:10.1093/mnras/stx2219. eISSN 1365-2966. ISSN 0035-8711. S2CID 118879856.