Hydrogen and Helium Shock Phenomena during Rising Light in RR Lyrae Fundamental Mode Pulsators

TL;DR

This study investigates hydrogen and helium spectral line behaviors during light rise in RR Lyrae stars, revealing universal patterns in metal-poor stars and variability in metal-rich ones, with implications for stellar ionization processes.

Contribution

It provides the first detailed measurements of H and He spectral lines during pulsation phases in RR Lyrae stars, highlighting differences based on metallicity and pulsation characteristics.

Findings

Universal line progression in metal-poor RRab stars

Weak He I emission in some metal-rich RRab stars

Detection of He II emission in several RRab stars, including Blazhko variables

Abstract

We present measurements of H and He emission and absorption lines produced in RRab fundamental mode pulsators during primary light rise. The lines define universal progressions of rise and decay in metal-poor RRab stars. Such a progression cannot be constructed for He in metal-rich RRab (those with [Fe/H]> -0.8) because weak He I emission is detected in only two of the six metal-rich RRab in our survey. Great variety exists in the phase variations of the blue- and red-shifted absorption components of the 5876 A line during pre- and post-emission phases. Detection of measurable He II 4686 A emission in eight RRab, three of them Blazhko variables, provides an additional constraint on ionization of Helium.