Mission Gaia of the European Space Agency has published its 2nd public data release on April 25 2018. It includes measurement of position in space and of complete 3-dimensional space vector for 7 million stars. This article which is a result of years of work on data from the on-board spectrograph makes a fundamental contribution by measurement of radial velocities, i.e. a factor of 10-fold increase to what has been available so far. These measurements can be supplemented by another 400-thousand stars from the Galah survey which have their radial velocities measured at a much higher level of accuracy (Zwitter et al. 2018) and which have measurements of abundances of 24 chemical elements in their atmospheres (Buder et al. 2018) -- in both cases we contributed as coauthors. This result is a core achievement within the point 1 mentioned in the chapter B.3 above.
COBISS.SI-ID: 907905
If you want to classify spectra of 400,000 stars where each spectrum is represented by information on fluxes in 16,000 spectral bins the automation of the whole process is essential. In the featured research article we used the mathematical technique tSNE which was adapted and sped up, so that the process could be run on out computer clusters. The results are excellent and the technique is rapidly becoming a standard for classification of massive spectroscopic sky surveys. The technique can be used beyon classification and applied for the analysis of structure in the multi-dimensional space of abundances of individual chemical elements. We have shown that is yields very useful results for star clusters, including the very young ones which are still actively interacting with the interstellar medium (Kos et al. 2018, arXiv:1811.11762).
COBISS.SI-ID: 761217
Our Sun is a star with medium levels of activity which is similar to processes observed in other active stars but with an added value that our star reveals these processes in exquisite detail. Paper presents a physical analysis of observations with a coronograph on-board the PROBA-3 space mission. Its results are of direct relevance to analysis of yound and chromospherically active objects which are discussed under the next item.
COBISS.SI-ID: 841089
This paper present discovery and analysis of over 38000 young stars with chromospheric activity which have been observed by the RAVE survey. Together with a more recent analysis of 3147 stars from the Galah survey (Zerjal et al. 2019), which have been found to have an overabundance of Lithium and are therefore very young, it represents the largest sample of young stars which have been recently interacting with the interstellar medium.
COBISS.SI-ID: 761473
Swan bands - characteristic molecular absorption features of the C2 molecule - are a spectroscopic signature of carbon-enhanced stars. They can also be used to identify carbon-enhanced metal-poor (CEMP) stars. We used 627 708 spectra from the Galah survey to search for carbon-enhanced stars with a supervised and unsupervised classification algorithm, relying on the imprint of the Swan bands. We identified 918 carbon-enhanced stars, including 12 already described in the literature. An unbiased selection function of the GALAH survey allows us to perform a population study of carbon-enhanced stars. Most of them are giants, out of which we find 28 CEMP candidates. A large fraction of our carbon-enhanced stars with repeated observations show variation in radial velocity, hinting that there is a large fraction of variables among them. 32 of the detected stars also show strong Lithium enhancement in their spectra.
COBISS.SI-ID: 906113