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Abstract

We present deep near- and mid-infrared images of six high-mass young stellar objects (YSOs) in order to help understand the physical mechanisms of their formation. We have searched for shocked H2 emission around such massive protostars. All but one of these regions exhibit series of molecular hydrogen emission knots, either in perfect alignment or in more complex configurations. In the case of the Class I object Mol 7, the protostars driving a couple of highly bipolar collimated outflows appear to be members of a binary or multiple system. A similar scenario appears to apply to Mol 143. The protostar Mol 12 drives a large little-collimated bipolar outflow with a number of H2 emission nebulosities. In two other methanol cores studied here, we also found shocked molecular hydrogen knots driven by highly embedded YSOs, some of them in clusters. From their near-IR to millimetre-wavelength spectral energy distributions, we derived stellar masses and temperatures, extinctions, luminosities, disc masses, and accretion rates. We provide photometric evidence that the dense dust core housing Mol 12, a Class I YSO, has eclipsed the light of an early-type main-sequence star. The latter is probably a physical companion to the protostar, as indicated by both having nearly identical coordinates and parallaxes as measured by Gaia (DR2) in the case of the star and by VLBI techniques in the case of the water maser associated with the YSO. This eclipse lasted about 15 years (1985–2000) and amounted to ΔAV ≃ 22. Since the year 2002, no further significant variations have been recorded.

Infrared imaging of high-mass young stellar objects: evidence of multiple shocks and of a new protostar/star eclipsing system

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