V Coronae Australis

V Coronae Australis (V CrA) is a R Coronae Borealis variable (RCB) star in the constellation Corona Australis. These are extremely hydrogen-deficient supergiants thought to have arisen as the result of the merger of two white dwarfs; fewer than 100 have been discovered as of 2012.^[9] V Coronae Australis dimmed in brightness from 1994 to 1998.^[10]

V Coronae Australis

A visual band light curve for V Coronae Australis, from AAVSO data[1]
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Corona Australis
Right ascension	18h 47m 32.30962s[2]
Declination	−38° 09′ 32.3079″[2]
Apparent magnitude (V)	9.4 - 17.9[3]
Characteristics
Evolutionary stage	R CrB[3]
Spectral type	R0[4]
Astrometry
Proper motion (μ)	RA: −1.104[2] mas/yr Dec.: −7.531[2] mas/yr
Parallax (π)	−0.3793±0.1513 mas[2]
Distance	5,500[5] pc
Details
Mass	0.6[6] M☉
Luminosity	6,550[5] L☉
Surface gravity (log g)	0.5[7] cgs
Temperature	6,250[6] K
Other designations
V CrA, CD−38°13089, HD 173539, HIP 92207[8]
Database references
SIMBAD	data

In 1896 it was announced that Evelyn Leland and Williamina Fleming had discovered that the star is a variable star.^[11] The visual apparent magnitude of V CrA has been observed to vary between magnitudes 9.4 and 17.9. A maximum magnitude of 8.3 has been estimated from photographic plates.^[12] It has around 60% the mass of the Sun and an effective (surface) temperature of around 6250 K.^[6]

The spectral class of R0 is typical of a carbon star, but the RCB stars are considered to a separate class of hydrogen-deficient stars, not normal asymptotic giant branch giants.^[13]