Abstract
Context: Chemically peculiar A type (Ap) stars are a subgroup of the CP2 stars which exhibit anomalous overabundances of numerous elements, e.g. Fe, Cr, Sr and rare earth elements. The pulsating subgroup of the 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, that accounts for modulations of the temperature-pressure structure caused by vertical abundance gradients, for the roAp star 10 Aquilae (HD 176232). 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 minimization routine together with the magnetic spectrum synthesis code synthmag. 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 log tau_5000=-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.
Highlights
10 Aql (HR 7167, HD 176232, HIP 93179) is one of the brightest rapidly oscillating Ap stars
Model atmospheres were computed with the LLmodels code, which accounts for the individual abundances and stratification of chemical elements
The most distinguished characteristic of rapidly oscillating Ap (roAp) pulsations is the dependence of the radial velocity (RV) amplitude and phase on the particular chemical element/ion
Summary
10 Aql (HR 7167, HD 176232, HIP 93179) is one of the brightest rapidly oscillating Ap (roAp) stars. To get a self-consistent model atmosphere of an Ap star, one needs to take into account anomalous abundances of most elements of the Mendelejev table and the stratified distribution of those elements, which contribute significantly to the continuum and line opacities. Such modelling was performed for a few roAp stars: α Cir (Kochukhov et al 2009), HD 24712 (Shulyak et al 2009), and HD 101065 − Przybylski’ star (Shulyak et al 2010). Such modelling was performed for a few roAp stars: α Cir (Kochukhov et al 2009), HD 24712 (Shulyak et al 2009), and HD 101065 − Przybylski’ star (Shulyak et al 2010). Saio et al (2010) showed that the use of the self-consistent model atmopshere of HD 24712 allowed better modelling of pulsations and derivation of the theoretical
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