First Detection of Shock Waves in RRc Stars

Although shock waves have been well documented in fundamental-mode RRab stars, their existence in first-overtone pulsator stars, RRc stars, has remained uncertain. Building upon the spectroscopic frameworks established by M. Chadid et al., we present the first direct detection of multistructured shock phenomena in RRc stars. Using high-resolution phase-resolved spectroscopy, we identify unambiguous shock signatures, including H α emission, line-doubling, and large-scale variations in radial velocity and line broadening.Our analysis reveals a structured sequence of distinct shock fronts: the main outward shock, Sh He+H , the ballistic shock, Sh Ball , and a gravitational collapse shock, Sh Gravity . These phenomena produce measurable dynamical and spectroscopic effects at both photospheric and higher atmospheric layers. We find that RRc stars sustain hypersonic shock regimes despite the absence of He I or He II emission typically used in RRab classification schemes. This discrepancy is attributed to the compact and low-opacity nature of RRc atmospheres, which promotes rapid shock dissipation. These discoveries challenge conventional models of RRc atmospheres and update the classification scheme. We propose an extension to existing classification frameworks to accommodate the unique shock dynamics of RRc stars. These results challenge the long-standing assumption that first-overtone RR Lyrae pulsators lack strong shocks and demonstrate that RRc stars exhibit complex, multiphase atmospheric dynamics. Altogether, our findings reshape the current understanding of RRc atmospheric dynamics.