Study of pre main sequence stars identified from lamost survey

Abstract

Understanding pre-main sequence (PMS) stars is crucial for explaining the fundamental processes governing the earliest stages of stellar evolution. Stars are born into protostars through the gravitational collapse of gas and dust-enriched clouds. The gradual dissipation of material in the protostar newlinegives rise to a circumstellar disk, extending into the PMS phase. Young stars in this early phase acquire mass through circumstellar accretion and reach the main sequence stage. The historical context of PMS star classifcations identifed based on the presence of emission lines, including T Tauri newlinestars and Herbig Ae/Be (HAeBe) stars are now extended to IntermediateMass T Tauri Stars (IMTTS) as well. This work is setting the stage for the study of these classifcations of PMS stars situated in the Galactic anticenter region, utilizing data from the Large Sky Area Multi-Object Fiber newlineSpectroscopic Telescope (LAMOST) surveys. Recognizing the literature gap in the collective analysis of PMS stars, the need for a comprehensive examination of mass accretion mechanisms and their dependence on mass is emphasized. The introductory section lays the groundwork by highlighting the signifcance of the PMS phase in stellar evolution, which also point towards the observable characteristics like emission lines in the spectrum and IR excess in the spectral energy distribution. The thesis initiates the work by investigating the complexity of identifying PMS sources collectively by studying different classifcations and comparing them as a consolidated PMS sample. Using LAMOST data, initially, we identifed 379 PMS samples that are classifed into 119 HAeBe and 260 CTTS. Our initial condition included the selection of LAMOST spectra based on the presence of Hand#945; emission line and signal-to-noise ratio greater than 10 in r-band. In the case of HAeBe stars, the selection criteria encompassed O-, B-, A-, and up to F5 spectral type stars exhibiting infrared excess.