* Astronomy

Title: ALMA Observations of the Orion Proplyds
Author: Rita K. Mann, James Di Francesco, Doug Johnstone, Sean M. Andrews, Jonathan P. Williams, John Bally, Luca Ricci, A. Meredith Hughes, Brenda C. Matthews

We present ALMA observations of protoplanetary disks ("proplyds") in the Orion Nebula Cluster. We imaged 5 individual fields at 856um containing 22 HST-identified proplyds and detected 21 of them. Eight of those disks were detected for the first time at submillimeter wavelengths, including the most prominent, well-known proplyd in the entire Orion Nebula, 114-426. Thermal dust emission in excess of any free-free component was measured in all but one of the detected disks, and ranged between 1-163 mJy, with resulting disk masses of 0.3-79 Mjup. An additional 26 stars with no prior evidence of associated disks in HST observations were also imaged within the 5 fields, but only 2 were detected. The disk mass upper limits for the undetected targets, which include OB stars, theta1Ori C and theta1Ori F, range from 0.1-0.6 Mjup. Combining these ALMA data with previous SMA observations, we find a lack of massive (>3 Mjup) disks in the extreme-UV dominated region of Orion, within 0.03 pc of O-star theta1Ori C. At larger separations from theta1Ori C, in the far-UV dominated region, there is a wide range of disk masses, similar to what is found in low-mass star forming regions. Taken together, these results suggest that a rapid dissipation of disk masses likely inhibits potential planet formation in the extreme-UV dominated regions of OB associations, but leaves disks in the far-UV dominated regions relatively unaffected.

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Title: Dynamical Evidence for a Magnetocentrifugal Wind from a 20 Msun Binary Young Stellar Object
Authors: L. J. Greenhill, C. Goddi, C. J. Chandler, L. D. Matthews, E. M. L. Humphreys

In Orion BN/KL, proper motions of 7 mm vibrationally-excited SiO masers trace rotation of a nearly edge-on disk and a bipolar wide-angle outflow 10-100 AU from radio Source I, a binary young stellar object (YSO) of ~20 solar masses. Here we map ground-state 7 mm SiO emission with the Very Large Array and track proper motions over 9 years. The innermost and strongest emission lies in two extended arcs bracketing Source I. The proper motions trace a northeast-southwest bipolar outflow 100-1000 AU from Source I with a median 3D motion of ~18 km/s. An overlying distribution of 1.3 cm H2O masers betrays similar flow characteristics. Gas dynamics and emission morphology traced by the masers suggest the presence of a magnetocentrifugal disk-wind. Reinforcing evidence lies in the colinearity of the flow, apparent rotation across the flow parallel to the disk rotation, and recollimation that narrows the flow opening angle ~120 AU downstream. The arcs of ground-state SiO emission may mark the transition point to a shocked super-Alfvenic outflow.

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Title: Acetone in Orion BN/KL - High-resolution maps of a special oxygen-bearing molecule
Authors: T.-C. Peng, D. Despois, N. Brouillet, A. Baudry, C. Favre, A. Remijan, A. Wootten, T. L. Wilson, F. Combes, G. Wlodarczak

As one of the prime targets of interstellar chemistry study, Orion BN/KL clearly shows different molecular distributions between large nitrogen- (e.g., C2H5CN) and oxygen-bearing (e.g., HCOOCH3) molecules. However, acetone (CH3)2CO, a special complex O-bearing molecule, has been shown to have a very different distribution from other typical O-bearing molecules in the BN/KL region. We searched for acetone within our IRAM Plateau de Bure Interferometer 3 mm and 1.3 mm data sets. Twenty-two acetone lines were searched within these data sets. The angular resolution ranged from 1.8 x 0.8 to 6.0 x 2.3 arcsec^2, and the spectral resolution ranged from 0.4 to 1.9 km s-1. Nine of the acetone lines appear free of contamination. Three main acetone peaks (Ace-1, 2, and 3) are identified in Orion BN/KL. The new acetone source Ace-3 and the extended emission in the north of the hot core region have been found for the first time. An excitation temperature of about 150 K is determined toward Ace-1 and Ace-2, and the acetone column density is estimated to be 2-4 x 10^16 cm-2 with a relative abundance of 1-6 x 10^-8 toward these two peaks. Acetone is a few times less abundant toward the hot core and Ace-3 compared with Ace-1 and Ace-2.
We find that the overall distribution of acetone in BN/KL is similar to that of N-bearing molecules, e.g., NH3 and C2H5CN, and very different from those of large O-bearing molecules, e.g., HCOOCH3 and (CH3)2O. Our findings show the acetone distribution is more extended than in previous studies and does not originate only in those areas where both N-bearing and O-bearing species are present. Moreover, because the N-bearing molecules may be associated with shocked gas in Orion BN/KL, this suggests that the formation and/or destruction of acetone may involve ammonia or large N-bearing molecules in a shocked-gas environment.

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WISE Feels the Heat from Orion's Sword

The tangle of clouds and stars that lie in Orion's sword is showcased in a new, expansive view from NASA's Wide-field Infrared Survey Explorer, or WISE. Orion, the famous hunter, is visible in evening skies throughout the world from about December through April. The constellation appears tranquil and still to the naked eye, but lying in its sword, at what appears to be a slightly fuzzy star, is a turbulent cauldron of stellar birth.
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