Classical Be Stars and Classical Be Star Binaries from LAMOST DR12

TL;DR

This study delivers a large census of Classical Be (CBe) stars and CBe binaries using LAMOST DR12, identifying 504 CBe stars (including 141 new) and 14 RV-variable CBe binaries, of which two are Gaia DR3 astrometric binaries and ALS 8814 is a previously reported Be+BH candidate. A further 60 CBe stars with high RUWE and 34 potential cluster members are identified, with 37 runaway stars exhibiting peculiar velocities between $40$ and $101\ \mathrm{km\,s^{-1}}$. The authors combine multi-epoch spectroscopy, IR contaminant screening, and Gaia-based astrometric and kinematic diagnostics to characterize the Be population and its binarity, supporting binary interaction as a key Be-star formation channel while highlighting the presence of wide or unseen companions. The results demonstrate the value of integrating spectroscopic RV monitoring with Gaia astrometry and cluster/kinematics analyses to identify and study CBe binaries, runaways, and cluster members in a single, large catalog. This dataset provides a foundation for future dynamical and evolutionary investigations of CBe systems and their binary companions.

Abstract

Classical Be (CBe) stars are rapidly rotating B-type stars with Balmer emission lines that originated from the decretion disks surrounding them in their spectra. Accounting for $\sim$20% of all B-type stars, most CBe stars are thought to form through mass and angular momentum transfer from their companions. It follows that in most close CBe star binaries, the companions are expected to be post-main-sequence stars rather than main-sequence (MS) stars. Hitherto, $\sim$100 CBe star binaries have been identified, the majority of which are Be/X-ray binaries. As expected, none of the others have indeed been confirmed as CBe+MS binary stars. To further study and verify the origin of CBe stars, identifying additional CBe star binaries is indispensable. In this study, we report 504 CBe stars identified using data from Data Release 12 of the Large sky Area Multi-Object fiber Spectroscopic Telescope. Among these, 141 are newly identified and 14 exhibiting radial velocity variations are identified as CBe star binaries. Besides, 60 CBe stars with high normalized unit weight error (RUWE) but not confirmed by dynamics are proposed as potential CBe star binaries. We also find that 34 CBe stars are potential cluster members. By calculating peculiar velocities, 37 runaway stars are identified with peculiar velocities ranging from $\sim$40 km s$^{-1}$ to $\sim$101 km s$^{-1}$.

Figures (6)

• Figure 1: The distribution of CBe stars in our sample on the HRD. Most sources in our sample are marked by red dots, while two outliers, J033630.81+480913.2 and J063809.24+034454.6, are marked by an orange dot and an aquamarine dot, respectively.
• Figure 2: a, Distribution of total number of observations of the 504 CBe stars in LAMOST. b, Distribution of number of observations of the 504 CBe stars in low-resolution survey of LAMOST. c, Distribution of number of observations of the 504 CBe stars in medium-resolution survey of LAMOST.
• Figure 3: The two spectra with maximum RV separation for each 13 newly identified CBe star binaries. Spectra are plotted by light solid lines, while model lines are plotted by dark dashed lines. To strengthen the visual contrast, we plot the logarithm of all the fluxes and the spectrum with obsid of 1063814069 (belongs to J035933.84+555751.1) is amplified by a factor of 7.
• Figure 4: The contrast of RVs measured by He II 4686 line and He I 6678 line of LAMOST 035933.84+555751.1. We convert wavelengths into RV space and the RV zero points for He II 4686 line and He I 6678 line are 4686.98 $\mathrm{\AA}$ and 6680 $\mathrm{\AA}$, respectively. In both panels, we use solid blue lines and red dashed lines to represent spectra and best-fit model lines, respectively. The vertical red lines show the measured RVs and the light red shaded areas reflect the 1 $\sigma$ uncertainties.
• Figure 5: The contrast of spectral type sequence for O stars and LAMOST 035933.84+555751.1. The background figure is taken from 2026enap....2...43M. The resolutions of spectra in background figure are $\sim$2,500. The LAMOST/LRS spectrum (resolution: $\sim$1,800) of LAMOST 035933.84+555751.1 is plotted by red line and the key metal spectral lines to identify spectral type are highlighted by two blue squares.