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

Abstract

We report new medium-resolution spectroscopy covering the wavelength range from 0.6 to 2.4 $\mathsf{\mu }$m, 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 ($A_V\simeq 12$) in the centre of a dense core at a distance of 1.59 kpc from the Sun and has a total luminosity of $1.74\times {10}^3{L}_{\odot }$. 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 $\mathsf{\mu }$m displays a complex P-Cygni profile. Also, the first overtone CO emission band-heads at 2.3 $\mathsf{\mu }$m are seen in emission. From the strengths of the principal emission lines, we determined the accretion rate and luminosity to be $\dot{M}\sim {10}^{-5}{M}_{\odot }$ y⁻¹ and $L_{\mathrm{acc}}\sim {10}^3{L}_{\odot }$, 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 $\lambda >3\mathsf{\mu }$m. 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.