Atmospheres of RR Lyrae Stars: Hypersonic Shock waves, Helium line detection and Magnetic fields. A few spectra for George Preston on the occasion of his birthday

Abstract

During intensive/comparative studies with Preston's spectroscopic works (1961, 1962, 1964 & 1965) on RR Lyrae atmospheric phenomena, I unexpectedly found the existence of hypersonic shock waves (Chadid 1996 & 2008), that are strongly connected with the turbulence amplification mechanism (Chadid 1996b) and the Blazhko modulation (1997). Here I will show how the hypersonic shocks are at the origin of helium line formation and connected with the helium emission and line doubling detected by Preston (2009, 2011). I will present new neutral and single ionized helium line data in the hypersonic Blazhko star S Arae. The He II appears as a weak emission and its origin is strongly connected with the hypersonic shock in S Arae. The shock is extremely strong and can reach a Mach number >30. The HeI lines first appear in emission, over ~2% of the pulsation period, followed by the HeI absorption doubling phenomenon occurring simultaneously with the neutral metallic absorption line phenomenon over ~8% of the pulsation period. Despite several claimed detections of magnetic fields in RR Lyrae, Preston (1967) found none after two years of observations. This is consistent with my recent spectro-polarimetric measurements (2004), over four years, concluding that RR Lyr is a bona fide nonmagnetic star, leading to the falsification of all the models of the Blazhko effect requiring strong photospheric magnetic fields. I report on a new series of high precision circular polarization spectroscopic observations of Blazhko star RV UMa. The longitudinal field measurements of RV UMa show a mean longitudinal magnetic field of B_l = -13+/-35 G, and no significant detection over the entire pulsation cycle. These spectroscopic results reveal a serious challenge for explaining the complex behavior in the pulsation of hypersonic atmospheres of RR Lyrae stars.