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

TL;DR

This paper investigates hypersonic shock waves, helium line formation, and magnetic field measurements in RR Lyrae stars, revealing strong shocks and nonmagnetic atmospheres that challenge existing pulsation models.

Contribution

It provides new spectroscopic evidence of hypersonic shocks and helium line phenomena, and confirms the absence of significant magnetic fields in RR Lyrae stars.

Findings

Hypersonic shocks with Mach number >30 are present in RR Lyrae atmospheres.

Helium lines appear in emission and absorption doubling during pulsation.

No significant magnetic fields detected in RR Lyrae stars, challenging magnetic models of the Blazhko effect.

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.