2026AJ....171...93L

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 for dimensionality reduction and Support Vector Machine classification, identifying ∼240,000 spectra with potential Hα emission. After removing contaminants (nonstellar objects, extragalactic sources, cataclysmic variables, and Algol systems) and restricting to B/A-type stars, we obtained 1835 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 versus (W2 - W3)₀ diagram effectively separates these populations: CAeBes predominantly occupy (K - W1)₀ ≤ 0.5 and (W2 - W3)₀ ≤ 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 semimajor axes of a = 1.5, a = 3.0, and a = 4.0, and a semimajor to semiminor axis ratio of 1.6:1.