LAMOST Views $\delta$ Scuti Pulsating Stars

TL;DR

This study catalogs and analyzes 766 $ ext{δ}$ Scuti stars observed by LAMOST, identifying a subgroup of unusual cool variables and exploring their physical properties, which may revise classification and enhance understanding of stellar pulsation.

Contribution

The paper presents the first large spectroscopic catalog of $ ext{δ}$ Scuti stars from LAMOST, discovering a new subgroup of cool, unusual variables and analyzing their properties and implications.

Findings

131 unusual cool variable stars identified

Approximately 25% of known $ ext{δ}$ Scuti stars may be misclassified

Discovery of binary or multiple system candidates among $ ext{δ}$ Scuti stars

Abstract

About 766 $\delta$ Scuti stars were observed by LAMOST by June 16, 2017. Stellar atmospheric parameters of 525 variables were determined, while spectral types were obtained for all samples. In the paper, those spectroscopic data are catalogued. We detect a group of 131 unusual and cool variable stars (UCVs) that are distinguished from the normal $\delta$ Scuti stars (NDSTs). On the H-R diagram and the $\log g-T$ diagram, the UCVs are far beyond the red edge of pulsational instability trip. Their effective temperatures are lower than 6700\,K with periods in the range from 0.09 to 0.22\,days. NDSTs have metallicity close to that of the Sun as expected, while UCVs are slightly metal poor than NDSTs. The two peaks on the distributions of the period and stellar atmospheric parameters are all caused by the existence of UCVs. When those UCVs are excluded, it is discovered that the effective temperature, the gravitational acceleration and the metallicity all are correlated with the pulsating period for NDSTs and their physical properties and evolutionary states are discussed. The detecting of those UCVs indicates that about 25\% of the known $\delta$ Scuti stars may be misclassified. However, if some of them are confirmed to be pulsating stars, they will be a new-type pulsator and their investigations will shed light on theoretical instability domains and on the theories of interacting between the pulsation and the convection of solar-type stars. Meanwhile, 88 $\delta$ Scuti stars are detected to be the candidates of binary or multiple systems.