The identification of new Herbig Ae/Be stars from LAMOST DR7

Abstract

Herbig Ae/Be stars (HAeBes) are critical tracers of intermediate- and high-mass star formation, yet their census remains incomplete compared to low-mass young stellar objects like T-Tauri stars. To expand the known population, we systematically searched for HAeBes in LAMOST DR7 low-resolution spectra. Following Sun et al., we applied Uniform Manifold Approximation and Projection (UMAP) for dimensionality reduction and Support Vector Machine (SVM) classification, identifying $\sim$240,000 spectra with potential H$α$ emission. After removing contaminants (non-stellar objects, extragalactic sources, CVs, and Algol systems) and restricting to B/A-type stars, we obtained 1,835 candidates through 2MASS/WISE visual inspection. Spectral energy distribution analysis confirmed 143 sources with infrared excess ($J$-band or longer wavelengths), including 92 known HAeBes. From the remaining 51 candidates, we classified 26 with strong infrared excess as new HAeBes. Color-index analysis of confirmed HAeBes and classical Ae/Be stars (CAeBes) revealed that the $(K-W1)_0$ vs. $(W2-W3)_0$ diagram effectively separates these populations: CAeBes predominantly occupy $(K-W1)_0 \leq 0.5$ and $(W2-W3)_0 \leq 1.1$, while other regions trace transition disks ($(K-W1)_0 < 0.5$ and $(W2-W3)_0 > 1.1$), globally depleted disks ($(K-W1)_0 > 0.5$ and $(W2-W3)_0 < 1.1$), and Class I/Flat/II HAeBes ($(K-W1)_0 > 0.5$ and $(W2-W3)_0 > 1.1$). More importantly, the HAeBes exhibit a clear evolutionary gradient on this diagram, with those in the Class III, Class II, Flat-SED, and Class I evolutionary stages being effectively distinguished by concentric ellipses that are roughly centered at (0,0) with semi-major axes of $a$=1.5, $a$=3.0, and $a$=4.0, and a semi-major to semi-minor axis ratio of 1.6:1.

Figures (11)

• Figure 1: Six morphological classifications of H$\alpha$ emission line profiles: (a) Single-peak emission profile (b) Single-peak emission superimposed on an absorption feature (c) Double-peak emission profile (d) Double-peak emission superimposed on an absorption feature (e) Low signal-to-noise ratio (SNR) profile where the emission line remains detectable (f) P Cygni profile (characterized by both emission and blueshifted absorption components)
• Figure 2: Two SED fitting examples of the new identified Herbig Ae/Be star (the left panel) and candidate (right panel). The blue, cyan, purple and green dots are the available (unsaturated) photometric data of Pan-STARRS, APASS, Tycho-2 and the $J-$ band of 2MASS which are engaged in the SED fitting process, while gray solid dots denote the saturated bands or the infrared bands that are excluded from the SED fitting. The blue line denotes the best fitted photospheric level of the model spectrum. Infrared bands exhibiting significant excess emission are marked with yellow ($>3\sigma$) and orange ($>5\sigma$) diamonds.
• Figure 3: The $M_{\rm RP}$ vs. $BP-RP$ color-magnitude diagram of the newly identified HAeBes (red asterisks) and the candidates (solid Wistia rectangles). The HAeBes of the literature are denoted as blue solid dots. Also plotted are the 1 Myr and 10 Myr isochrone of the PARSEC model for solar metallicity Bre2012.
• Figure 4: The age (left panel) and mass (right panel) distribution of the newly identified HAeBes and the candidates.
• Figure 5: The $(K-W1)_0$ vs. $(H-K)_0$ color-color diagram of the previous known HAeBes (solid blue dots), newly identified HAeBes (red asterisks) and candidates (solid Wistia rectangles). The colors of the symbols represent the evolutionary stages of the protoplanetary disks, ranging from light to dark, which correspond to Class III, Class II, Flat-SED, and Class I. The previously identified CAeBes and PMS stars with transitional disks Cieza2012 are represented by gray diamonds (where color darkness indicates density) and magenta crosses, respectively. As a comparison, the regions of CAeBes and HAeBes that proposed by Zha2022 are denoted as cyan and black dashed lines, respectively. The cyan solid line indicates the intrinsic color indices of main-sequence B-type and A-type stars derived from the BT-settl stellar atmospheric model Pec2013, while the black arrow shows the extinction vector of $A_{V}$=5.0.