A self-consistent chemically stratified atmosphere model for the roAp star 10 Aquilae

摘要

Context. Chemically peculiar A-type (Ap) stars are a subgroup of the CP2 stars that exhibit anomalous overabundances of numerous elements, e.g. Fe, Cr, Sr, and rare earth elements. The pulsating subgroup of Ap?stars, the roAp stars, present ideal laboratories to observe and model pulsational signatures, as well as the interplay of the pulsations with strong magnetic fields and vertical abundance gradients. Aims. Based on high-resolution spectroscopic observations and observed stellar energy distributions, we construct a self-consistent model atmosphere for the roAp star 10 Aquilae (HD?176232). It accounts for modulations of the temperature-pressure structure caused by vertical abundance gradients. We demonstrate that such an analysis can be used to determine precisely the fundamental atmospheric parameters required for pulsation modelling. Methods. Average abundances were derived for 56 species. For Mg, Si, Ca, Cr, Fe, Co, Sr, Pr, and Nd, vertical stratification profiles were empirically derived using the DDAFit minimisation routine together with the magnetic spectrum synthesis codeSynthmag. Model atmospheres were computed with the LLmodels code, which accounts for the individual abundances and stratification of chemical elements. Results. For the final model atmosphere, Teff?=?7550 K and log????(g)?=?3.8 were adopted. While Mg, Si, Co, and Cr exhibit steep abundance gradients, Ca, Fe, and Sr showed much wider abundance gradients between logτ5000?=??1.5 and 0.5. Elements Mg and Co were found to be the least stratified, while Ca and Sr showed strong depth variations in abundance of up to ?≈?6?dex.