Mira Variables Based on Emission Lines in LAMOST DR9

Abstract

We present a sample of 335 Mira variables, extracted from DR9 of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey. These variables are characterized by the Balmer emissions (H δ , H γ , H β , and H α ) and the metal emissions (Fe i λ λ 4202, 4308, 4376, and Mg i λ 4571) observed in M giant spectra. We distinguished oxygen-rich stars from carbon-rich stars through the identification of carbon molecular bands present in the optical spectra. For the oxygen-rich stars we examined multiple attributes, such as the link between line strength and bolometric luminosity, and the connection between atmospheric parameters and their periods. We observed that Fe i λ λ 4202, 4308 showed a significantly gradual progression, which can be postulated to trace the fluorescent emission resulting from pulsation shocks. Regarding the correlation between T _eff and the period, T _eff remains relatively constant over varying periods, with no clear trend, while both log g and [Fe/H] show a decreasing trend within a period range of 450 days, and this decreasing of the log g trend is consistent with the results in the literature. To shed more light on the variations of Balmer lines, we showcase time-series spectra for two objects, demonstrating that the Balmer lines reach their peak intensity during the brightest phase of the stellar cycle.

Keywords

• Mira variable stars
• Asymptotic giant branch stars