Corona Australis Molecular Cloud
Molecular Cloud in Constellation Corona Australis
From Wikipedia, the free encyclopedia
The Corona Australis molecular cloud, located at a distance of 130 parsecs (~430 ly),[2][3] is a dark nebula of gas and dust and is one of the nearest star formation regions from Earth.[4] 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.[5] The globular cluster known as NGC 6723, which appears close by, is actually 29,000ly away, and so not part of the region.[6] 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.
| Nebula | |
|---|---|
Image of Corona Australis Molecular Cloud | |
| Observation data: J2000.0 epoch | |
| Right ascension | 19h 01m 51s[1] |
| Declination | –36° 58.9′[1] |
| 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 cloud is located at about 18% below the galactic plane and covers an angular area of 16.0° × 6.5° on the celestial sphere.[4] 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[update].[4] 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.[7] 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.[8] 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.
Observations
In the north of the constellation is the Corona Australis Molecular Cloud, a dark molecular cloud with many embedded reflection nebulae, including NGC 6729, NGC 6726–7, and IC 4812. A star-forming region of around 7000 M☉,[9] it contains Herbig–Haro objects, T Tauri stars with dense circumstellar disks, (protostars) and some very young stars.[10] Located about 430 light years (130 parsecs) away, it is one of the closest star-forming regions to our solar system.[11] The related NGC 6726 and 6727, along with unrelated NGC 6729, were first recorded by Johann Friedrich Julius Schmidt in 1865.[12]
