Age of FGK Dwarfs Observed with LAMOST and GALAH: Considering the Oxygen Enhancement

Varying oxygen abundance could impact modeling-inferred ages. This work aims to estimate the ages of dwarfs considering observed oxygen abundance. To characterize 67,503 LAMOST and 4006 GALAH FGK-type dwarf stars, we construct a grid of stellar models, which take into account oxygen abundance as an independent model input. Compared with ages determined with commonly used a-enhanced models, we find a difference of similar to 9% on average when the observed oxygen abundance is considered. The age differences between the two types of models are correlated to Fe/H] and O/a], and they are relatively significant on stars with Fe/H]. -0.6 dex. Generally, varying 0.2 dex in O/a] will alter the age estimates of metal-rich (-0.2 < Fe/H] < 0.2) stars by similar to 10% and relatively metal-poor (-1 < Fe/H] < -0.2) stars by similar to 15%. Of the low-O stars with Fe/H] < 0.1 dex and O/a] similar to-0.2 dex, many have fractional age differences of. 10% and even reach up to 27%. The fractional age difference of high-O stars with O/a] similar to 0.4 dex reaches up to -33% to -42% at Fe/H]. -0.6 dex. We also analyze the chemical properties of these stars. We find a decreasing trend of Fe/H] with ages from 7.5-9 Gyr to 5-6.5 Gyr for the stars from the LAMOST and GALAH. The O/Fe] of these stars increases with decreasing age from 7.5-9 Gyr to 3-4 Gyr, indicating that the younger population is more O rich.