The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides precise carbon and nitrogen abundances for over 100,000 red giant stars across the Milky Way Galaxy (MW). Recently, it has been shown that the carbon-to-nitrogen ratio (often expressed as [C/N]) can be indicative of the mass of a red giant star, from which an age can be inferred. In this work, we reaffirm that [C/N] can be used as a mass indicator for APOGEE red giants from Data Release 14 (DR14) and present [C/N] vs. [Fe/H] abundance tracks for red giants star across the MW (3 < R < 15 kpc). We derive empirical age tracks in the [C/N]-[Fe/H] plane using ages derived from seismic masses in the APOKASC catalog to interpret these abundance tracks as tracks in age. Similar to what has been found in other studies, we find a range of ages across all metallicities for stars in the plane of the Galaxy along with an age gradient for stars above the plane (|Z| > 1.0 kpc). We trace the youngest stars in the APOGEE sample and find a metallicity gradient in [Fe/H] of -0.074 dex/kpc across the Galaxy from 6 kpc to 12 kpc. This is in agreement with the gradient found over a similar radial range using young stars of the CoRoGEE sample (Anders et al. 2017). Additionally, we find that the more metal-rich stars located in the plane of the outer Galaxy (R > 7 kpc) tend to exhibit enhanced [C/N] relative to the more metal-poor stars, indicating that the metal-rich stars are actually older. We explore possible formation scenarios of these stars and find that radial migration is a plausible explanation for their current location in the Galaxy.
American Astronomical Society Meeting Abstracts #231
- Pub Date:
- January 2018