2025PASP..137d4204M

We present new L-band spectra for 28 Northern Galactic Be stars, obtained with the CID-InSb spectrograph at the 2.1 m telescope OAN/UNAM San Pedro Martir Observatory. For 19 of these stars we establish positions on the Lenorzer diagram, which is a diagnostic tool of circumstellar environments. It is constructed using flux ratios of the hydrogen infrared recombination lines (Br_α, Hu₁₄ and Pf_γ) and gives information about the density of the emitting gas. We compare the positions on Lenorzer diagram with H_α emissions recorded on the BeSS database. Our main results show that over two decades, γ Cas has maintained a stable circumstellar disk (CSD); 28 Cyg has undergone at least one complete cycle of growth and dissipation of its disk, this being the first report of that cycle in the infrared range; the star 28 Tau seems to have experienced the dissipation and subsequent growth of a new CSD; and, 12 Vul seems to have completely lost its disk. In our analysis, we find a significant relation between the positions of Be stars on the Lenorzer diagram and the variation in the H_α emission. The emissions of optically thick media are consistent with positive H_α variations, while those of optically thin with negative variation; this accounts for the effects that changes on internal regions of Be disk have on the external ones.