A Catalog of 45,206 H <i>α</i> Emission-line Stars from LAMOST MRS DR7

Abstract Stars that exhibit prominent emission lines in their spectra are referred to as emission-line stars, encompassing a wide range of stellar types and indicative of intriguing physical properties. The Large Sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) has released millions of spectra from its Medium-Resolution Survey (MRS). A small fraction of these spectra exhibit emission lines, yet they remain undiscovered and unanalyzed due to being buried in the vast dataset. We have developed a method based on derivative spectroscopy, which provides a novel approach for detecting and identifying emission-line stars by extracting signals from complex backgrounds and estimating spectral line profiles. Applying this method to the H α spectral line profiles from the LAMOST-MRS Data Release 7, we compiled a catalog of emission-line stars using the second- and third-derivative spectra for automated peak detection. This approach also facilitates the classification of H α emission-line morphologies through a simplified scheme. The catalog comprises 56,649 spectra with relatively prominent H α emission lines from 45,206 unique stars, with each emission-line component accompanied by approximate estimates of its wavelength, amplitude, and width. All H α spectral lines were classified into three morphological classes under a unified classification scheme: single emission peak (83.0%), double emission peaks (5.6%), and P Cygni-type profiles (11.5%), which encompass both P Cygni and inverse P Cygni features. Through cross-referencing with SIMBAD, 39,497 stars represent new emission-line sources discovered in our research.