Detecting shock waves in non-fundamental mode RR Lyrae using large sample of spectra in SDSS and LAMOST

TL;DR

This study develops a pattern recognition pipeline to detect shock wave signatures in RR Lyrae stars using large spectral datasets, revealing hydrogen emission lines and their properties in non-fundamental mode RR Lyrae variables.

Contribution

It introduces the first detection of hydrogen emission lines in non-fundamental mode RR Lyrae stars and links shock wave signatures to stellar phenomena like the Blazhko effect.

Findings

First detection of hydrogen emission in RRc and multi-mode RR Lyrae stars.

Anti-correlation between emission intensity and radial velocity.

Potential connection between shock waves and the Blazhko effect.

Abstract

Steps toward the nature inside RR Lyrae variables can not only improve our understanding of variable stars but also innovate the precision when we use them as tracers to map the structure of the universe. In this work, we develop a hand-crafted one-dimensional pattern recognition pipeline to fetch out the "first apparitions", the most prominent observational characteristic of shock. We report the first detection of hydrogen emission lines in the first-overtone and multi-mode RR Lyrae variables. We find that there is an anti-correlation between the intensity and the radial velocity of the emission signal, which is possibly caused by opacity changing in the helium ionization zone. Moreover, we find one RRd star with hydrogen emission that possibly shows Blazhko-type modulations. According to our discoveries, with an enormous volume of upcoming data releases of variable stars and spectra, it may become possible to build up the bridge between shock waves and big problems like the Blazhko effect in non-fundamental mode RR Lyrae stars.