Catalog of carbon enhanced stars and CEMP candidates

The Galactic Archaeology with HERMES (GALAH) survey is a large scale, magnitude limited, southern stellar spectroscopic survey providing spectra, stellar parameters and chemical abundances for stars located in different components of the Galaxy. Random selection, based only on object's brightness and its celestial coordinates, implies that a representative set of peculiar stellar types are observed.

Here we focus on carbon enhanced stars which can be identified by peculiar features present in their GALAH spectra. First, the presence of Swan bands, which are known indicators of carbon enhancement, have been studied by a supervised algorithm. Next we used this core sample to identify further candidates using their spectral similarity, as estimated by an unsupervised dimensionality reduction method.

In the dataset we identified 918 stars whose spectra were classified to contain carbon enhancement in one or more observations of the same object of which 11 stars were already reported before in the literature. Using reliable stellar physical parameters we separated them into two distinct groups of dwarf and giant population. The later includes 28 metal poor candidates (CEMP) among them. Using repeated spectroscopic observations we try to determine fraction of binary systems among identified objects and investigate possibility of carbon enhanced dwarf binary (dC) star based on variability of the measured radial velocities.

We conclude that data collected by the GALAH may be used to identify representative sets of peculiar stars, including carbon enhanced and CEMP stars.