Corona Australis Molecular Cloud
| Nebula | |
|---|---|
Image of Corona Australis Molecular Cloud | |
| Observation data: J2000.0 epoch | |
| Right ascension | 19h 01m 51s |
| Declination | –36° 58.9′ |
| Distance | 425 ly (130 pc) |
| Apparent dimensions (V) | 16.0° × 6.5° |
| Constellation | Corona Australis |
| Physical characteristics | |
| Radius | 8 ly |
| Designations | CrA Dark Cloud, CrA MCLD, CrA region |
The Corona Australis molecular cloud, located at a distance of 130 parsecs (~430 ly), is a dark nebula of gas and dust and is one of the nearest star formation regions from Earth. Sometimes referred to as the CrA Dark Cloud or the CrA Cloud, it hosts several reflection nebulae − NGC 6729, NGC 6726/6727, and IC 4812 being the most notable. The globular cluster known as NGC 6723, which appears close by, is actually 29,000ly away, and so not part of the region. The cloud is located in the constellation Corona Australis, close to the border with Sagittarius, between Gamma Coronae Australis and Epsilon Coronae Australis and stretches roughly 8ly across.
The cloud is located at about 18% below the galactic plane and covers an angular area of 16.0° × 6.5° on the celestial sphere. Temperatures of the cloud ranges from 13–22 K, and there is a total of about 7,000 times the mass of the Sun in material. Over half of the mass of the complex is concentrated around a small area, and this is the most active star-forming region. There are embedded infrared sources within the complex. A total of 425 infrared sources have been detected near the L1688 cloud. These are presumed to be young stellar objects, including 16 classified as protostars, 123 T Tauri stars with dense circumstellar disks, and 77 weaker T Tauri stars with thinner disks. The last two categories of stars have estimated ages ranging from 100,000 to a million years.
Known to exhibit significant extinction, as high as 45 magnitudes at visual wavelengths (AV∼45 mag), astronomers have identified 55 distinct optical members within the CrA Cloud as of 2008. At the core is the Coronet protostar cluster, a loose collection of about 30 young stars with a wide range of masses at various stages of evolution. Surrounding the cluster are a few late stage B stars, numerous Herbig–Haro objects, and several YSOs. At the opposite end of the mass spectrum, are two confirmed brown dwarfs along with seven more candidates. There are also many embedded infrared sources within the complex. The molecular cloud has been most widely surveyed in the infrared, X-rays, radio waves and in the millimeter continuum.