High-resolution spectroscopy of the star RR Lyrae at high cadence

Abstract

This research presents a spectroscopic and photometric analysis of atmospheric dynamics in the variable star RR Lyrae. Pulsating RR Lyrae type stars play an important role in astrophysics as standard candles and as witnesses of galactic evolution. Though they have been studied for over a century, we still do not completely understand several aspects of their pulsations. The prototype and brightest star of the class, RR Lyrae itself, is probably one of the best-studied stars of its class. Recently, it has been observed by NASAs planet-hunting Kepler mission with a one-minute cadence, resulting in the most precise dataset of an RR Lyrae star in existence. We obtained simultaneous spectroscopy to the Kepler data with a similar cadence (one-minute integrations) using the highresolution spectrograph attached to the 2.7-m telescope at McDonald observatory. The combination of the spectroscopic and photometric data allows for an unprecedentedly detailed study of the stars atmospheric dynamics, casting light upon some poorly understood aspects of its pulsation. We investigated how the changes in the star’s light curve correlate to properties of its spectrum such as changes in the radial velocity curve derived from different (hydrogen and metal) lines, line broadening and amplitudes. This works towards the constraint of atmospheric parameters such as the macroturbulent velocity of the stellar atmosphere.