A catalogue of 323 cataclysmic variables from LAMOST DR6

Abstract

In this work, we present a catalogue of cataclysmic variables (CVs) identified from the Sixth Data Release (DR6) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). To single out the CV spectra, we introduce a novel machine-learning algorithm called UMAP to screen out a total of 169,509 Hα-emission spectra, and obtain a classification accuracy of the algorithm of over 99.6% from the cross-validation set. We then apply the template matching program PyHammer v2.0 to the LAMOST spectra to obtain the optimal spectral type with metallicity, which help us identify the chromospherically active stars and potential binary stars from the 169,509 spectra. After visually inspecting all the spectra, we identify 323 CV candidates from the LAMOST database, among them 52 objects are new. We further discuss the new CV candidates in subtypes based on their spectral features, including five DN subtype during outbursts, five NL subtype and four magnetic CVs (three AM Her type and one IP type). We also find two CVs that have been previously identified by photometry, and confirm their previous classification by the LAMOST spectra.

Searching for Cataclysmic Variable Stars in Unidentified X-Ray Sources

“…We search for a possible X-ray counterpart of the selected GAIA sources in (i) the ROSAT all-sky survey bright source catalog (Voges et al 1999), (ii) the second Swift-XRT point-source catalog (Evans et al 2020) and (iii) XMM-Newton DR-10 source catalog (Webb et al 2020). We select the GAIA sources that are located within 10" from the center of the X-ray source, and then we remove the sources that have been already identified as a CV or other types of objects by checking the catalogs of CVs (Ritter & Kolb 2003;Coppejans et al 2016;Jackim et al 2020;Sun et al 2021;Szkody et al 2021), and the SIMBAD astronomical database 1 .…”

“…Numerous efforts to identify new CVs and candidates have been made in previous works, and the number of known CVs is rapidly increasing with recent photometric and spectroscopic all-sky surveys (Ritter & Kolb 1998;Coppejans et al 2016;Sun et al 2021;Szkody et al 2021). The methods of confirming CVs are mainly divided into three types, namely, the observation of dwarfnova outbursts, identification of orbital/WD spin variations in photometric light curves, and confirmation of CV-like spectral properties.…”