2024/08/27 by G. Valle, M. Dell’Omodarme, Valle, G. +5
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2408.14900
openalex publication_date 2024/08/27 · openalex created_date 2024/09/21 · openalex updated_date 2026/07/28
By adopting the recently empirically derived dependence of α-elements on [α/\rm Fe] instead of the conventionally applied uniform one, we tested the agreement between stellar model predictions and observations for red giant branch (RGB) stars in the APO-K2 catalogue. We particularly focused on the biases in effective temperature scales and on the robustness of age estimations. We computed a grid of stellar models relying on the empirical scaling of α-elements, investigating the offset in effective temperature ΔT between these models and observations, using univariate analyses for both metallicity [Fe/H] and [α/\rm Fe]. To account for potential confounding factors, we then employed a multivariate generalised additive model to study the dependence of ΔT on [Fe/H], [α/\rm Fe], log g, and stellar mass. The initial analysis revealed a negligible trend of ΔT with [Fe/H], in contrast with previous works in the literature. A slight ΔT difference of 25 K was detected between stars with high and low α-enhancement. Our multivariate analysis reveals a dependence of ΔT on both [Fe/H] and [α/\rm Fe], and highlights a significant dependence on stellar mass. This suggests a discrepancy in how effective temperature scales with stellar mass in the models compared to observations. Despite differences in assumed chemical composition, our analysis, through a fortunate cancellation effect, yields ages that are largely consistent with recent studies of the same sample. Notably, our analysis identifies a 6% fraction of stars younger than 4 Ga within the high-α population. However, our analysis of the [C/N] ratio supports the possible origin of the these stars as a result of mergers or mass transfer events.