arXiv subjects

Lihuan Yu

Publications and source records attributed to Lihuan Yu.

3 recordsLinked to original sources

arXiv2026

A homogeneous analysis of archival and new low-resolution spectra of YZ Cancri

YZ Cancri is an SU UMa-type dwarf nova with sparse and heterogeneous optical spectroscopy. We present a homogeneous analysis of archival outburst-related spectra and seven new low-resolution quiescent spectra. We consistently characterize the Balmer, He I, Fe II, O I, and occasional He II and Bowen features, and assess which state-dependent differences are robustly supported. We applied a common continuum-normalization and line-measurement procedure, measuring equivalent widths, integrated line intensities, and selected profile parameters, and comparing line morphologies and intensity ratios between quiescent and outburst-related states. Because the spectra have modest and nonuniform resolving power and are not orbital-phase resolved, profile widths and centroid shifts are used only as relative diagnostics. Outburst-related spectra are dominated by broad Balmer absorption or composite profiles, whereas quiescent spectra show strong single-peaked Balmer and He I emission, recurrent Fe II λ5169, and weak O I λ7772 emission. He II λ4686 is detected in only two quiescent exposures, and the Bowen blend in one. The quiescent Balmer decrement is relatively flat, while the He I ratios show substantial exposure-to-exposure scatter. The measured Fe II ratios show no clear systematic departure from optically thin reference values, although blending limits their interpretation. These spectra establish an empirical state-dependent description of YZ Cnc and provide a reference dataset for future phase-resolved, higher-resolution spectroscopy.

astro-ph.SR↗

arXiv2026

A Catalog of 45,206 Hα Emission-line Stars from LAMOST MRS DR7

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 $\mathrm{Hα}$ 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 $\mathrm{Hα}$ emission-line morphologies through a simplified scheme. The catalog comprises 56\,649 spectra with relatively prominent $\mathrm{Hα}$ emission lines from 45\,206 unique stars, with each emission-line component accompanied by approximate estimates of its wavelength, amplitude, and width. All $\mathrm{Hα}$ 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.

astro-ph.SR↗

arXiv2024

Derivative Spectroscopy and its Application at Detecting the Weak Emission/Absorption Lines

The development of spectroscopic survey telescopes like Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), Apache Point Observatory Galactic Evolution Experiment and Sloan Digital Sky Survey has opened up unprecedented opportunities for stellar classification. Specific types of stars, such as early-type emission-line stars and those with stellar winds, can be distinguished by the profiles of their spectral lines. In this paper, we introduce a method based on derivative spectroscopy (DS) designed to detect signals within complex backgrounds and provide a preliminary estimation of curve profiles. This method exhibits a unique advantage in identifying weak signals and unusual spectral line profiles when compared to other popular line detection methods. We validated our approach using synthesis spectra, demonstrating that DS can detect emission signals three times fainter than Gaussian fitting. Furthermore, we applied our method to 579,680 co-added spectra from LAMOST Medium-Resolution Spectroscopic Survey, identifying 16,629 spectra with emission peaks around the Hα line from 10,963 stars. These spectra were classified into three distinct morphological groups, resulting in nine subclasses as follows. (1) Emission peak above the pseudo-continuum line (single peak, double peaks, emission peak situated within an absorption line, P Cygni profile, Inverse P Cygni profile); (2) Emission peak below the pseudo-continuum line (sharp emission peak, double absorption peaks, emission peak shifted to one side of the absorption line); (3) Emission peak between the pseudo-continuum line.

astro-ph.SR↗