Eta2 Coronae Australis

Eta² Coronae Australis (Eta² CrA), Latinized from η² Coronae Australis, is a solitary star^[14] located in the southern constellation of Corona Australis. It is visible to the naked eye as a dim, blue-white hued star with an apparent visual magnitude of 5.59.^[2] Gaia DR3 parallax measurements imply a distance of 770 light years from the Solar System,^[1] but it is drifting closer with a radial velocity of −23 km/s.^[6] At its current distance Eta² CrA's brightness is diminished by 0.27 magnitudes due to stellar extinction from interstellar dust^[15] and it has an absolute magnitude of −0.24.^[7]

For other stars with this Bayer designation, see η Coronae Australis.

η² Coronae Australis

Location of Eta2 CrA (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Corona Australis
Right ascension	18h 49m 34.99649s[1]
Declination	−43° 26′ 02.7522″[1]
Apparent magnitude (V)	5.59±0.01[2]
Characteristics
Evolutionary stage	main sequence star[3]
Spectral type	B9 IV[4]
B−V color index	−0.08[5]
Astrometry
Radial velocity (Rv)	−23.0±4.3[6] km/s
Proper motion (μ)	RA: −2.963 mas/yr[1] Dec.: −25.374 mas/yr[1]
Parallax (π)	4.25 ± 0.1158 mas[1]
Distance	770 ± 20 ly (235 ± 6 pc)
Absolute magnitude (MV)	−0.24[7]
Details
Mass	3.23±0.08[3] M☉
Radius	5.82±0.31[8] R☉
Luminosity	171+20 −18[3] L☉
Surface gravity (log g)	3.47[9] cgs
Temperature	10,940±255[3] K
Metallicity [Fe/H]	+0.06[9] dex
Rotational velocity (v sin i)	30[10] km/s
Age	213[11] Myr
Other designations
Eta2 CrA, 26 G. Coronae Australis[12], CD−43°12854, CPD−43°8779, GC 25766, HD 173861, HIP 92382, HR 7068, SAO 229307[13]
Database references
SIMBAD	data

This object has a stellar classification of B9 IV,^[4] indicating that is a slightly evolved a B-type subgiant star. However, Zorec & Royer (2012) model it to be a dwarf star that has completed 80.4% of its main sequence lifetime.^[3] It is estimated to be 213 million years old^[11] and it has a mass that is 3.23 times that of the Sun.^[3] The star is radiating 171 times the luminosity of the Sun^[3] from its photosphere 5.82 times the radius of the Sun^[8] at an effective temperature of 10,940 K.^[3] Eta² CrA has a near-solar metallicity at [Fe/H] = +0.06^[9] and spins modestly with a projected rotational velocity of 30 km/s.^[10] Some earlier catalogues listed the object as a chemically peculiar star but that status is now considered to be doubtful.^[16]

Sources

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. Zorec, J.; Royer, F. (January 2012). "Rotational velocities of A-type stars IV: Evolution of rotational velocities". Astronomy & Astrophysics. 537: A120. arXiv:1201.2052. Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691. eISSN 1432-0746. ISSN 0004-6361. S2CID 55586789.
4. Houk, Nancy (1978). Michigan catalogue of two-dimensional spectral types for the HD stars: Declinations −53° to −40°. Vol. 2. Bibcode:1978mcts.book.....H.
5. Corben, P. M.; Stoy, R. H. (1968). "Photoelectric Magnitudes and Colours for Bright Southern Stars". Monthly Notes of the Astronomical Society of Southern Africa. 27: 11. Bibcode:1968MNSSA..27...11C.
6. 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.
7. 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.
8. 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. 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. Levato, Hugo; Grosso, Mónica (June 2004). "New Projected Rotational Velocities of All Southern B-type Stars of the Bright Star Catalogue". Symposium - International Astronomical Union. 215: 51–52. Bibcode:2004IAUS..215...51L. doi:10.1017/S0074180900195191. ISSN 0074-1809.
11. Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694–706, arXiv:1606.09028, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035, S2CID 119108982.
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. "Eta02 CrA". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved March 8, 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. 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.
16. Renson, P.; Manfroid, J. (19 March 2009). "Catalogue of Ap, HgMn and Am stars". Astronomy & Astrophysics. 498 (3): 961–966. Bibcode:2009A&A...498..961R. doi:10.1051/0004-6361/200810788. eISSN 1432-0746. ISSN 0004-6361. S2CID 55849045.