R Coronae Australis
R Coronae Australis (R CrA) is a variable binary system in the constellation Corona Australis. It has varied between magnitudes 10 and 14.36. 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.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Corona Australis |
| Right ascension | 19h 01m 53.6503s |
| Declination | −36° 57′ 07.87″ |
| Apparent magnitude (V) | +11.91 |
| Characteristics | |
| Spectral type | B5IIIpe |
| Variable type | INSA |
| Astrometry | |
| Radial velocity (Rv) | −36.0±4.9 km/s |
| Proper motion (μ) | RA: 1.582 mas/yr Dec.: −30.835 mas/yr |
| Parallax (π) | 10.5361 ± 0.6971 mas |
| Distance | 152.9+8.1 −7.3 pc |
| Absolute magnitude (MV) | −0.30 |
| Orbit | |
| Period (P) | 45±2 yr |
| Semi-major axis (a) | 0.1968±0.0045" (27-28 AU) |
| Eccentricity (e) | 0.4 |
| Inclination (i) | 70° |
| Details | |
| A | |
| Mass | 3.5 M☉ |
| Radius | 6.2 R☉ |
| Luminosity | 132 L☉ |
| Temperature | 9,550 K |
| Age | 1+1 −0.5 Myr |
| B | |
| Mass | 0.3 - 0.55 M☉ |
| Surface gravity (log g) | 3.45±0.06 cgs |
| Temperature | 3,650 - 3,870 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
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. 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). 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.
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. The companion was later directly observed to be a red dwarf with a mass between 0.3 M☉ and 0.55 M☉. It has also been proposed that the primary component is itself a close binary.