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YSO Bulletin
- Special Corona Issue! -

While the world is reeling from the Coronavirus outbreak I thought it might be good to look at a Corona that is a thing of beauty rather than one of fear. So I give you one of the most active star formation regions in the sky - Corona Australis, the Southern Crown.
This is an area that has been the subject of many surveys since its variables were first studied seriously back in the 1930's by some members of the AAVSO, among others. After the constellation's first variable (R CrA) was discovered others quickly followed and today a great many young stars are known in just this small area of the sky. The picture below gives a resume of the most notable objects, and clicking on it will take you to a truly astounding image taken by Aussie imager Alex Woronow
Many of the nebulae here are reflection nebulae, scattering the radiation from the dynamic processes going on within them. The main nebula is NGC 6729 which is illuminated by one of the most important variables here, TY CrA. Although most of the young stars in the area are low-mass objects (T Tauri stars) TY is a higher-mass star known as a Herbig AeBe star (Haebe) and it is also an eclipsing binary. This means we are able to determine its mass directly rather than through hypothesising. It also possesses a massive accretion disc.
But it is not just bright 'illuminated' clouds that we find; the dark cloud near R CrA called Bernes 157 (actually discovered in the 19th century by the Scottish astronomer Dunlop from Paramatta, Australia) has, it is thought, the power to obscure 45 magnitudes! Note also the numerous HH objects which are active outflows from stars in the process of formation.

A Little bit of Astrophysics...

Situated not too far away is a huge structure called the UCL (Upper Cen-Lupus) superbubble, an expanding area of star formation. It is theorised that the CrA region could have been located near the UCL's centre some 14 million years ago since it is moving away in the required direction, no doubt helping to trigger star formation as it encounters other areas of potential star forming. Since the CrA area lacks many high-mass, luminous stars it is not thought to be part of the Gould Belt (about which I am working on a paper!) so it could well be indeed a 'cast-off' from the UCL, maybe as the result of some drastic event in the distant past.
There bambinos! Now wasn't that better than self-isolation or social distancing?

Note: I shall be participationg in the AAVSO section leaders' meeting on April 1st (and no, that's not an April Fool joke). I know it's imminent but if anyone has any points they would like raising, just drop me a line.