An infrared jet from a high-mass young star

Jets are a direct consequence of accretion in the inner regions of circumst ellar disks. They trace the structure of the accretion disk and, indirectly , the star formation mechanism. Here we report on the discovery of a near-i nfrared jet from a young B1 star, one of the most luminous young stars know n to exhibit such a structure. The jet is seen in L' images of IRAS 18556+0 136 in the G35.2-0.74N region; a significant fraction of the emission is du e to Br alpha line emission. At shorter wavelengths, the jet is obscured: t he colors of the bipolar nebula are consistent with 25 mag visual extinctio ns 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 similar to 170 m ag is derived for the extinction to the exciting source. This provides an e stimate of 0.15 M. for the mass, of the circumstellar disk within similar t o 1500 AU of the central source. Emission knots on either side of a second, weaker radio continuum source offset similar to3" from the jet source sugg ests the presence of a second outflow source in the region. The lack of kno wn 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., m ergers. The jet from this B1 star suggests that the mechanisms that form lo w-mass stars can operate up to at least 10 M. stars.