Hydrogen lines in LAMOST low resolution spectra of RR Lyrae stars

TL;DR

This study analyzes LAMOST low-resolution spectra of RR Lyrae stars, identifying hypersonic shock features during their expansion phase, and highlights the potential for large-scale future surveys to deepen understanding of stellar pulsations.

Contribution

It reports the detection of hypersonic shock features in RR Lyrae stars using LAMOST spectra and demonstrates the potential of large surveys to study stellar pulsation mechanisms.

Findings

Detected hypersonic shock features in three RR Lyrae stars.

Fitted Hα line shapes to identify hypersonic atmospheric motions.

Highlighted the potential of future large surveys for stellar pulsation research.

Abstract

The LAMOST spectroscopic survey for Galactic structure and evolution has been in operation since October 2012, following a one-year pilot survey. The pilot survey produced a data release containing over 600,000 stellar spectra. By cross-checking with a large time series photometric database of RR Lyrae stars in high Galactic latitude regions, we found a total number of 157 stars that have been observed with LAMOST. In this sample, we successfully captured three RR Lyrae stars in the fast expansion phase, all of them showing significant hypersonic shock wave features in the spectra. By fitting the H{\alpha} line shape, we determine that the emission features seen within the broader H{\alpha} absorption line suggest hypersonic relative motions in the atmospheres of these three objects. With a further LAMOST survey of millions of stars, we will capture a large sample of RR Lyrae stars in their hypersonic expansion phase, and therefore provide a large database for the study of the internal structure and pulsation mechanism of RR Lyrae stars.