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The stellar parameters of RR Lyrae stars vary considerably over a pulsationcycle, and their determination is crucial for stellar modelling. We present adetailed spectroscopic analysis of the pulsating star RR Lyr, the prototype ofits class, over a complete pulsation cycle, based on high-resolution spectracollected at the 2.7-m telescope of McDonald Observatory. We used simultaneousphotometry to determine the accurate pulsation phase of each spectrum anddetermined the effective temperature, the shape of the depth-dependentmicroturbulent velocity, and the abundance of several elements, for each phase.The surface gravity was fixed to 2.4. Element abundances resulting from ouranalysis are stable over the pulsation cycle. However, a variation inionisation equilibrium is observed around minimum radius. We attribute thismostly to a dynamical acceleration contributing to the surface gravity.Variable turbulent convection on time scales longer than the pulsation cyclehas been proposed as a cause for the Blazhko effect. We test this hypothesis tosome extent by using the derived variable depth-dependent microturbulentvelocity profiles to estimate their effect on the stellar magnitude. Theseeffects turn out to be wavelength-dependent and much smaller than the observedlight variations over the Blazhko cycle: if variations in the turbulent motionsare entirely responsible for the Blazhko effect, they must surpass the scalescovered by the microturbulent velocity. This work demonstrates the possibilityof a self-consistent spectroscopic analysis over an entire pulsation cycleusing static atmosphere models, provided one takes into account certainfeatures of a rapidly pulsating atmosphere.

An In-Depth Spectroscopic Analysis of RR Lyr Variations over the Pulsation Cycle