Speaker
Description
The surface [C/N] ratios of evolved giants are strongly affected by the first dredge-up (FDU) of nuclear processed material from stellar cores and have therefore been used as a mass diagnostic. Past studies have assumed scaled solar mixtures of carbon and nitrogen. We use subgiants identified in APOGEE DR17 to map out the birth trends of these elements. We find [C/N] has strong trends with [Fe/H] and an offset between the alpha-rich and alpha-poor populations. With APOKASC3 data, we find functions that describe the post-FDU [C/N] of red giants relative to their mass and metallicity. These functions can be used to obtain masses for stars up to 1.5-1.7 solar masses, but [C/N] as a diagnostic loses predicting power at higher masses. We show that the observed pattern arises from the combination of birth trends and the dredge-up. Additionally, by examining red clump stars, we extend our functions into higher mass ranges, reaching 2 solar masses before the fit loses predictive power. By comparing the red clump and red giant stars, we are also able provide tests for the extra mixing effects that occur on the upper giant branch. This data will place powerful constraints on theoretical stellar models and stellar population studies.
