Mira Variable Stars From LAMOST DR4 Data: Emission Features, Temperature Types, and Candidate Selection

TL;DR

This study analyzes LAMOST DR4 spectra of Mira variables, revealing emission features and temperature relationships, and identifies 191 new Mira candidates, enhancing understanding of their optical properties.

Contribution

It introduces a spectral analysis method linking emission features to temperature and identifies new Mira candidates from LAMOST data.

Findings

Flux ratio F_Hδ/F_Hγ increases as stars cool from M0 to M10.

Relationship between Balmer emission line strength and luminosity phase.

Identification of 191 new Mira candidates using spectral criteria.

Abstract

Based on an extensive spectral study of a photometrically confirmed sample of Mira variables, we find a relationship between relative Balmer emission-line strength and spectral temperature of O-rich Mira stars. The $F_{\rm H\delta}/F_{\rm H\gamma}$ flux ratio increases from less than unity to five as stars cool down from M0 to M10, which is likely driven by increasing TiO absorption above the deepest shock-emitting regions. We also discuss the relationship between the equivalent widths of the Balmer emission lines and the photometric luminosity phase of our Mira sample stars. Using our 291 Mira spectra as templates for reference, 191 Mira candidates are newly identified from the LAMOST DR4 catalog. We summarize the criteria adopted to select Mira candidates based on emission-line indices and molecular absorption bands. This enlarged spectral sample of Mira variables has the potential to contribute significantly to our knowledge of the optical properties of Mira stars and will facilitate further studies of these late-type, long-period variables.