Coexisting conical bipolar and equatorial outflows from a high-mass protostar

Abstract

The BN/KL region in the Orion molecular cloud is an archetype for the study of the formation of stars much more massive than the Sun. This region contains luminous young stars and protostars but, like most star-forming regions, is difficult to study in detail because of the obscuring effects of dust and gas. Our basic expectations are shaped to some extent by the present theoretical picture of star formation, the cornerstone of which is that protostars accrete gas from rotating equatorial disks and shed angular momentum by ejecting gas in bipolar outflows. The main source of the outflow in the BN/KL region may be an object known as radio source I, which is commonly believed to be surrounded by a rotating disk of molecular material. Here we report high-resolution observations of silicon monoxide (SiO) and water maser emission from the gas surrounding source I. We show that within 60 AU of the source (about the size of the Solar System), the region is dominated by a conical bipolar outflow, rather than the expected disk. A slower outflow, close to the equatorial plane of the protostellar system, extends to radii of 1,000 AU.

Wide‐Angle Wind‐driven Bipolar Outflows: High‐Resolution Models with Application to Source I of the Becklin‐Neugebauer/Kleinmann‐Low OMC‐I Region

“…Greenhill et al (2003) note a bridge of maser emission connecting the southern and western arms of the bicone, with a clear velocity gradient that is consistent with the edge of a rotating disk. Orienting the outflow northeast to southwest makes the ejection perpendicular to the disk, as seen in many low-mass young stellar objects, and suggests that the H 2 O masers seen on larger scales are also oriented with, and thus probably produced by, the same outflow as the SiO masers (Greenhill et al 1998).…”

“…The presence of a velocity gradient is ambigious in the observations. For example, in the data of Greenhill et al (1998), the redshifted lobes show a velocity gradient with values ranging from 25 km s −1 at the base of the X to 15 km s −1 at its farthest extent. The blueshifted lobes do not show such a clear gradient however they do show a similar range of velocities.…”

“…SiO masers are distributed along an X-shaped locus of clumps extending 20 to 70 AU from the continuum radio source (Snyder & Buhl 1974;Wright & Plambeck 1983;Lane 1982;Plambeck, Wright, & Carlstrom 1990). Subsequent observations by Menten & Reid (1995); Greenhill et al (1998) ;Doeleman, Lonsdale, & Pelkey (1999) have established that the maser sources appear to part of an outflow from source I. The maser proper motions lie in the range of 10 to 23 km s −1 , oriented primarily along the limbs of the X, with systematically red-shifted and blue-shifted lobes about a southeast-northwest symmetry axis.…”

“…A number of models have been proposed to explain the pattern of maser proper motion and line of sight velocity (Plambeck, Wright, & Carlstrom (1990);Greenhill et al (1998)). Recently Greenhill et al (2003Greenhill et al ( , 2005) have presented a model based on high resolution radio observations where the outflow is northeast-southwest so that the masers are situated along a biconical outflow with a wide opening angle.…”

Combined IRAM andHerschel/HIFI study of cyano(di)acetylene in Orion KL: tentative detection of DC3N

“…Menten & Reid (1995) detected the radio continuum emission of the IR source n and the very embedded radio source I (located a few arcseconds to the south of the young and massive star IRc2), which could be a binary system with a total mass of ∼20 M , according to measurements of the proper motions of this source and the object BN (Goddi et al 2011). Source I has been proposed as a possible driver of the two outflows observed in Orion KL: a high-velocity (30−100 km s −1 ), wide-angle (∼1 rad) outflow A&A 559, A51 (2013) that extends northwest-southeast over 0.3 pc, and a low-velocity (∼18 km s −1 ) elongated northeast-southwest outflow (Genzel & Stutzki 1989;Greenhill et al 1998;Zapata et al 2009). …”