The Enigmatic, Highly Variable, High-Mass Young Stellar Object Mol 12: A New Extreme Herbig Be (Proto)star

We report new medium-resolution spectroscopy covering the wavelength range from 0.6 to 2.4 μm, as well as multi-epoch, multi-wavelength photometry, of the Class I high-mass embedded young stellar object Mol 12 (IRAS 05373+2349). It is embedded (AV≃12) in the centre of a dense core at a distance of 1.59 kpc from the Sun and has a total luminosity of 1.74×103L⊙. The spectra show a large number of permitted atomic emission lines, mostly for Fe, H, C, N, and Ca, that originate in the inner zones of a very active protoplanetary disc and no photospheric absorption lines. Conspicuously, the He I line at 1.0830 μm displays a complex P-Cygni profile. Also, the first overtone CO emission band-heads at 2.3 μm are seen in emission. From the strengths of the principal emission lines, we determined the accretion rate and luminosity to be M˙∼10−5M⊙ y−1 and Lacc∼103L⊙, respectively. Decade-long light curves show a series of irregular brightness dips of more than four magnitudes in r, becoming shallower as the wavelength increases and disappearing at λ>3μm. The colour–magnitude diagrams suggest the occurrence of a series of eclipses caused by the passage of small dust cloudlets in front of the star, producing more than 10 magnitudes of extra extinction.