R Coronae Australis

R Coronae Australis (R CrA) is a variable binary system in the constellation Corona Australis.[2][8] It has varied between magnitudes 10 and 14.36.[9] A small reflection/emission nebula NGC 6729 extends from the star towards SE. It is also the brightest feature of the Coronet Cluster, therefore sometimes called R CrA Cluster.

R Coronae Australis
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Corona Australis
Right ascension 19h 01m 53.6503s[1]
Declination −36° 57′ 07.87″[1]
Apparent magnitude (V) +11.91
Characteristics
Spectral type B5IIIpe[2]
Variable type INSA[3]
Astrometry
Radial velocity (Rv)−36.0±4.9[4] km/s
Proper motion (μ) RA: 1.582[5] mas/yr
Dec.: −30.835[5] mas/yr
Parallax (π)10.5361 ± 0.6971 mas[5]
Distance152.9+8.1
−7.3[6] pc
Absolute magnitude (MV)−0.30[7]
Orbit
Period (P)45±2[8] yr
Semi-major axis (a)0.1968±0.0045[8]"
(27-28 AU[6])
Eccentricity (e)0.4[6]
Inclination (i)70[6]°
Details
A
Mass3.5[7] M☉
Radius6.2[7] R☉
Luminosity132[7] L☉
Temperature9,550[7] K
Age1+1
−0.5[6] Myr
B
Mass0.3 - 0.55[6] M☉
Surface gravity (log g)3.45±0.06[6] cgs
Temperature3,650 - 3,870[6] K
Other designations
CD−37°13027, HIP 93449, Wray 15-1887
Database references
SIMBADdata
A colour photo of the R Coronae Australis region in the southern Milky Way.

This star is moving toward the Solar System with a radial velocity of 36 km s−1. It was previously believed that in roughly 222,000 years, this system could have approached within 1.77 light-years (0.54 parsecs) of the Sun. However, the estimate had a considerable margin of error in it.[10] With the release of Gaia DR2, the star was determined to be 4 times further from the Sun than initially believed, constraining the approach to only 111 ± 31 light-years (34.0 ± 9.5 parsecs).[5] Examination of other objects known to be in the same star-forming region gives a distance of 152.9+8.1
−7.3 pc, suggesting an error in the Gaia parallax for R CrB itself.[6]

A companion to the star was proposed in 2019 with a mass between 0.1 and 1 Solar masses, depending on the characteristics of the stellar environment, orbiting the primary in 43–47 years.[8] The companion was later directly observed to be a red dwarf with a mass between 0.3 M☉ and 0.55 M☉.[6] It has also been proposed that the primary component is itself a close binary.[7]

References
  1. van Leeuwen, F. (13 August 2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  2. "R Coronae Australis". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 29 June 2014.
  3. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  4. Gontcharov, G. A. (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. S2CID 119231169.
  5. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051.
  6. Mesa, D.; et al. (2019). "Exploring the R CrA environment with SPHERE. Discovery of a new stellar companion". Astronomy and Astrophysics. 624. arXiv:1902.02536. Bibcode:2019A&A...624A...4M. doi:10.1051/0004-6361/201834682. S2CID 155675656.
  7. Sissa, E.; Gratton, R.; Alcalà, J. M.; Desidera, S.; Messina, S.; Mesa, D.; d'Orazi, V.; Rigliaco, E. (2019). "The origin of R CrA variability. A complex triple system hosting a disk". Astronomy and Astrophysics. 630. arXiv:1908.07256. Bibcode:2019A&A...630A.132S. doi:10.1051/0004-6361/201936101. S2CID 201103714.
  8. Cugno, G.; Quanz, S. P.; Launhardt, R.; Musso Barcucci, A.; Brems, S. S.; Cheetham, A.; Godoy, N.; Kennedy, G. M.; Henning, T.; Müller, A.; Olofsson, J.; Pepe, F.; Quirrenbach, A.; Reffert, S.; Rickman, E. L.; Ségransan, D. (3 April 2019). "ISPY – NaCo Imaging Survey for Planets around Young stars". Astronomy & Astrophysics. 624: A29. arXiv:1902.04092. doi:10.1051/0004-6361/201935142. S2CID 102491664.
  9. BSJ (14 June 2010). "R Coronae Australis". AAVSO Website. American Association of Variable Star Observers. Retrieved 29 June 2014.
  10. Dybczyński, P. A. (April 2006), "Simulating observable comets. III. Real stellar perturbers of the Oort cloud and their output", Astronomy and Astrophysics, 449 (3): 1233–1242, Bibcode:2006A&A...449.1233D, doi:10.1051/0004-6361:20054284
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