A Catalog of 45,206 H{\alpha} Emission-line Stars from LAMOST MRS DR7

TL;DR

This paper presents a novel derivative spectroscopy method to detect and classify Hα emission-line stars in LAMOST MRS DR7, resulting in a large catalog of over 45,000 stars, many of which are newly identified.

Contribution

The authors develop a new derivative spectroscopy technique for automated detection and morphological classification of emission-line stars in large spectral datasets.

Findings

Catalog of 45,206 emission-line stars compiled

83% have single emission peaks, 5.6% double, 11.5% P Cygni profiles

39,497 new emission-line sources discovered

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 (DS), 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 $\mathrm{H\alpha}$ spectral line profiles from the LAMOST-MRS Data Release 7 (DR7), 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 $\mathrm{H\alpha}$ emission-line morphologies through a simplified scheme. The catalog comprises 56\,649 spectra with relatively prominent $\mathrm{H\alpha}$ emission lines from 45\,206 unique stars, with each emission-line component accompanied by approximate estimates of its wavelength, amplitude, and width. All $\mathrm{H\alpha}$ 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.