WX Coronae Australis

WX Coronae Australis (WX CrA) is an R Coronae Borealis (R CrB) star in the constellation Corona Australis, one of the brightest examples of this extremely rare class of variable star.[7] Despite the rarity, Corona Australis hosts another R CrB star, V Coronae Australis.

WX Coronae Australis

A visual band light curve of WX Coronae Australis, from AAVSO data[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Corona Australis
Right ascension 18h 08m 50.467s[2]
Declination −37° 19′ 43.21″[2]
Apparent magnitude (V) 10.25 - <16.5[3]
Characteristics
Spectral type C(R5)[3]
Variable type R CrB[3]
Astrometry
Proper motion (μ) RA: 1.421[2] mas/yr
Dec.: −7.108[2] mas/yr
Parallax (π)0.1641 ± 0.0281 mas[2]
Distanceapprox. 20,000 ly
(approx. 6,000 pc)
Details
Mass1.00[4] M☉
Luminosity7,400[4] L☉
Temperature5,300[5] K
Other designations
WX CrA, CD−37°12227, HD 324924[6]
Database references
SIMBADdata

WX Coronae Australis is a luminous star with a large excess of carbon and very little hydrogen. It has the spectrum of a carbon star, of type R5 indicating that it shows strong carbon molecular bands but not as red overall as the majority of carbon stars. Its brightness is variable, with 78.9-day pulsations producing changes of about 0.1 magnitudes, as well as occasional deep fades by six or more magnitudes. This classifies it as an R Coronae Borealis variable.[3][8] These stars are likely to have formed from the merger of two white dwarfs into a hydrogen-deficient carbon-rich hot supergiant that then cooled. The deep fades are caused by obscuration by carbon-rich dust condensing around the star.[7][5]

WX Coronae Australis was first reported to be variable in 1928 after it was detected on two different photographic plates at magnitudes 12.2 and 16.0. It was catalogued as HV (Harvard Variable) 4119. The type of variability was not known at the time,[9] but in 1936 its spectrum was measured as R5 and it was tentatively classified as an R CrB star.[10] By 1996 it had been observed to fade 13 times at an average interval of 2,000 days.[11]

References
  1. "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
  2. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. "R CrB". International Variable Star Index. Retrieved 2021-03-24.
  4. Willingale, Graham A. P. (1989). A theoretical study of the R. Coronae Borealis group of variable stars (Thesis). University of St Andrews. hdl:10023/4656.
  5. Clayton, Geoffrey C.; Geballe, T. R.; Herwig, Falk; Fryer, Christopher; Asplund, Martin (2007). "Very Large Excesses of 18O in Hydrogen-deficient Carbon and R Coronae Borealis Stars: Evidence for White Dwarf Mergers". The Astrophysical Journal. 662 (2): 1220–1230. arXiv:astro-ph/0703453. Bibcode:2007ApJ...662.1220C. doi:10.1086/518307. S2CID 12061197.
  6. SIMBAD, WX Coronae Australis (accessed 13 July 2014)
  7. Tisserand, P.; Clayton, G. C.; Bessell, M. S.; Welch, D. L.; Kamath, D.; Wood, P. R.; Wils, P.; Wyrzykowski, Ł.; Mróz, P.; Udalski, A. (2020). "A plethora of new R Coronae Borealis stars discovered from a dedicated spectroscopic follow-up survey". Astronomy & Astrophysics. 635: A14. arXiv:1809.01743. Bibcode:2020A&A...635A..14T. doi:10.1051/0004-6361/201834410. S2CID 119547939.
  8. Lawson, W. A.; Cottrell, P. L. (1997). "The radial velocity variations of cool hydrogen-deficient carbon stars". Monthly Notices of the Royal Astronomical Society. 285 (2): 266. Bibcode:1997MNRAS.285..266L. doi:10.1093/mnras/285.2.266.
  9. Woods, Ida E.; Shapley, Martha B. (1928). "Observations and Orbit of a New Eclipsing Binary, H.V. 4159". Harvard College Observatory Bulletin. 854: 6. Bibcode:1928BHarO.854....6W.
  10. Swope, Henrietta H. (1936). "Two Eclipsing Variables of Unusually Period, and a Variable with an R5 Spectrum". Harvard College Observatory Bulletin. 902: 6. Bibcode:1936BHarO.902....6S.
  11. Jurcsik, J. (1996). "On the Frequency of the Decline Events of R CRB Type Variables". Acta Astronomica. 46: 325. Bibcode:1996AcA....46..325J.
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