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

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 Å line during pre-and post-emission phases. Detection of measurable He ii 4686 Å emission in eight RRab, three of them Blazhko variables, provides an additional constraint on ionization of Helium.