Vol 21, No 9

Estimation of ages and masses via carbon and nitrogen abundances for 556 007 giants from LAMOST

Xu Zhang, Sven Buder, Ya-Qian Wu, Gang Zhao


Abstract Estimating ages for a large number of giants is of great importance for studying Galactic evolution. In this work, we determine stellar ages and masses for 556 007 giants from LAMOST Data Release 5 (DR5) with empirical relations estimated from chemical [C/N] abundance ratios. Our sample reveals the two wellknown sequences in the age−[α/M] relation. The high-α sequence is composed of stars older than 8 Gyr and low-α sequence is composed of stars with age ranging from 0 Gyr to 13.8 Gyr. Our sample also shows a flat age−[M/H] relation up until 12 Gyr. We compare these distributions with Galactic Chemical Evolution models for reference. When looking at the spatial distribution of stars in 2 Gyr age bins, we find that young stars are concentrated towards the Galactic plane and older stars extend to higher height above and below the disk. We find a smooth transition of median Galactic height for different age bins, which suggests a strong age-dependence on Galactic scale height.


Keywords stars: fundamental parameters — Galaxy: structure — Galaxy: evolution — Galaxy: abundances

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