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STARs that 'R' Young : When do stars form in clustered environments?

Periodic Reporting for period 1 - STARRY (STARs that 'R' Young : When do stars form in clustered environments?)

Okres sprawozdawczy: 2016-02-01 do 2018-01-31

"The study of the formation of stars provides an excellent illustration of how progress in science results from the interplay of observation on the one hand, and theory on the other. More than 100 years ago, Sir James Jeans considered the formation of the Solar System and proposed that it began as a huge gaseous cloud containing only atoms and molecules. He showed that if such a cloud exceeded a certain mass, the mutual gravitational attraction between these particles would be sufficient to cause the cloud to shrink to ever smaller sizes and higher densities. As the contracting gas can heat up, the net result of this ""gravitational contraction"" is an enormously hot, dense, object where the conditions are extreme enough for nuclear fusion to begin. A star is born.

The question that naturally arises is whether there are such clouds where stars can form. Although not realised at the time, the observational story started a bit earlier, when Sir William Herschel found well-defined dark patches on the sky, from which no star light emanated. His first reaction appears to have been one of shock, ""My God, a hole in the sky!"", but we now know that in these places there are so many dust particles that they can block the light from the background stars just as fog blocks our view on a misty day. These dark clouds turn out to be very cold and massive enough to provide the material to build one or more stars. These cool, dark clouds are even capable of contracting into a star. The cradles of stars were found.

An additional finding is that many stars are not alone, but are often found in groups of dozens to even hundreds of stars and such groups are called clusters. The next question that arises is whether the stars are born in this manner or grouped together later in life? It would appear that they may be born at the same time – in the context of the star formation through a cloud collapse, it makes sense that a very large cloud can give rise to more than one star. This is indeed what is found in model simulations; large clouds can result in many stars.

This project takes this notion one step further and investigates whether no stars form in clusters, or whether all stars form in clusters. It is based on research in the nineties which provided evidence for an effect that young massive stars were mostly found in clusters, while lower mass young stars were not. With the advent of the GAIA space telescope we aim to address this issue by studying an order of magnitude more objects, search for the presence of clusters around them, and then verify the earlier claim by looking at the presence of clusters as a function of mass of the star. Thanks to the GAIA telescope, we will not only discover more such young objects to study, but also be able parameterise the clusters in terms of their age and size.
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The STARRY (STARs that ‘R’ Young) ITN consists of two linked projects that are carried out by one Early Stage Researcher each. The basis of the first project is to find and characterize young star in the GAIA catalogue. The unprecedented large number of objects that will be observed by GAIA (1 billion) and for which important parameters will be measured, allows for a fresh and unbiased look at young stars, and will result in many more so-called “Herbig Ae/Be stars” a class of object that straddles both low and high mass stars. The second project will then look for the presence for clusters around these objects and characterize these. Ultimately, we will obtain the final word about under which conditions low mass and high stars stars are formed, and whether this occurs in clusters. We are now halfway the project, prior to the next datarelease of GAIA with data for all billion objects.

Both Early Stage Researcher have received extensive training, not only in research and research methodologies, but also in transferable skills such as computing, enterpreneurial skills as well as bespoke language teaching. They have presented their works at various international conferences and have actively participated in public outreach, by giving talks and participating in various outreach events.

As far as the research is concerned, methodologies have been implemented, coded and tested on the earlier GAIA release data to full satisfaction. For the first project, the properties of Herbig Ae/Be stars have been documented and tests indicate that more than 80% of those known can be automatically selected from GAIA data, while 98.8% of stars are automatically rejected. Similarly, for project 2, the methodologies have been tested, coded and implemented, and using the early GAIA data, (previously known) clusters in a semi-automatic manner are recovered, while their parameters are reproduced at high accuracy. The project is looking forward to the release of GAIA DR2, which promises an exciting time ahead.
Given the large amount of data involved (GAIA alone will contain in excess of 1 billion stars), both projects require a (semi-) automated approach. Therefore both projects include a significant software development element and the new software tools to mine and analyse astronomical data are, next to the new samples of young stars (project 1) and clusters (project 2), the main exploitable results of the STARRY ITN. The scientific analysis of the new young stars and clusters will bring important new insights on the role and importance of clusters in star formation, and will immediately result in 2 PhD theses of the ESR’s respectively, whereas the new insights will lead to further research into the issues outside the Action. The software tools can be used to select many different samples of star from not only GAIA, but many other archives. Hence they can address various other problems related to star formation and stellar evolution. As the software will be distributed freely, other interested researchers can make use of the products of this ITN.