An Infrared Jet from a High-Mass Young Star

Abstract

Jets are a direct consequence of accretion in the inner regions of circumstellar disks. They trace the structure of the accretion disk and, indirectly, the star formation mechanism. Here we report on the discovery of a near-infrared jet from a young B1 star, one of the most luminous young stars known to exhibit such a structure. The jet is seen in L' images of IRAS 18556+0136 in the G35.2-0.74N region; a significant fraction of the emission is due to Brα line emission. At shorter wavelengths, the jet is obscured: the colors of the bipolar nebula are consistent with 25 mag visual extinctions to the near lobe and 40 mag to the far lobe. A previously detected radio continuum source and an elongated clump of OH maser spots coincide with a break in the jet. This is interpreted as the location of the circumstellar disk surrounding the embedded young star. A lower limit of ~170 mag is derived for the extinction to the exciting source. This provides an estimate of 0.15 M☉ for the mass of the circumstellar disk within ~1500 AU of the central source. Emission knots on either side of a second, weaker radio continuum source offset ~3'' from the jet source suggests the presence of a second outflow source in the region. The lack of known jets in high-mass protostars, in contrast to their prevalence among low-mass systems, points to a difference in the star formation process, e.g., mergers. The jet from this B1 star suggests that the mechanisms that form low-mass stars can operate up to at least 10 M☉ stars.