The Orion Fingers: Near-IR Adaptive Optics Imaging of an Explosive Protostellar Outflow

Aims. Adaptive optics images are used to test the hypothesis that the explosive BN/KL outflow from the Orion OMC1 cloud core was powered by the dynamical decay of a non-hierarchical system of massive stars. Methods. Narrow-band H2, [Fe II], and broad-band Ks obtained with the Gemini South multi-conjugate adaptive optics (AO) system GeMS and near-infrared imager GSAOI are presented. The images reach resolutions of 0.08 to 0.10", close to the 0.07" diffraction limit of the 8-meter telescope at 2.12 microns. Comparison with previous AO-assisted observations of sub-fields and other ground-based observations enable measurements of proper motions and the investigation of morphological changes in H2 and [Fe II] features with unprecedented precision. The images are compared with numerical simulations of compact, high-density clumps moving ~1000 times their own diameter through a lower density medium at Mach 1000. Results. Several sub-arcsecond H2 features and many [Fe II] 'fingertips' on the projected outskirts of the flow show proper motions of ~300 km/s. High-velocity, sub-arcsecond H2 knots ('bullets') are seen as far as 140" from their suspected ejection site. If these knots propagated through the dense Orion A cloud, their survival sets a lower bound on their densities of order 10^7 cm^-3, consistent with an origin within a few au of a massive star and accelerated by a final multi-body dynamic encounter that ejected the BN object and radio source I from OMC1 about 500 years ago. Conclusions. Over 120 high-velocity bow-shocks propagating in nearly all directions from the OMC1 cloud core provide evidence for an explosive origin for the BN/KL outflow triggered by the dynamic decay of a non-hierarchical system of massive stars. Such events may be linked to the origin of runaway, massive stars.Comment: Accepted to A&A. 25 pages, 18 figures. Figure 1 (http://goo.gl/whAz3m) is particularly colorful. The FITS images will be made available from CDS. Resubmission fixed broken bibliograph

The Orion Protostellar Explosion and Runaway Stars Revisited : Stellar Masses, Disk Retention, and an Outflow from the Becklin-Neugebauer Object

© 2020 The American Astronomical Society. All rights reserved.The proper motions of the three stars ejected from Orion's OMC1 cloud core are combined with the requirement that their center of mass is gravitationally bound to OMC1 to show that radio source I (Src I) is likely to have a mass around 15 M o˙ consistent with recent measurements. Src I, the star with the smallest proper motion, is suspected to be either an astronomical-unit-scale binary or a protostellar merger remnant produced by a dynamic interaction ∼550 yr ago. Near-infrared 2.2 μm images spanning ∼21 yr confirm the ∼55 km s -1 motion of "source x" (Src x) away from the site of stellar ejection and point of origin of the explosive OMC1 protostellar outflow. The radial velocities and masses of the Becklin-Neugebauer (BN) object and Src I constrain the radial velocity of Src x to be. Several high proper-motion radio sources near BN, including Zapata 11 ([ZRK2004] 11) and a diffuse source near IRc 23, may trace a slow bipolar outflow from BN. The massive disk around Src I is likely the surviving portion of a disk that existed prior to the stellar ejection. Though highly perturbed, shocked, and reoriented by the N-body interaction, enough time has elapsed to allow the disk to relax with its spin axis roughly orthogonal to the proper motion.Peer reviewedFinal Published versio

A Keplerian disk around Orion Source I, a ~15 Msun YSO

We report ALMA long-baseline observations of Orion Source I (SrcI) with resolution 0.03-0.06" (12-24 AU) at 1.3 and 3.2 mm. We detect both continuum and spectral line emission from SrcI's disk. We also detect a central weakly resolved source that we interpret as a hot spot in the inner disk, which may indicate the presence of a binary system. The high angular resolution and sensitivity of these observations allow us to measure the outer envelope of the rotation curve of the H$_2$O $5_{5,0}-6_{4,3}$ line, which gives a mass $M_I\approx15\pm2$ Msun. We detected several other lines that more closely trace the disk, but were unable to identify their parent species. Using centroid-of-channel methods on these other lines, we infer a similar mass. These measurements solidify SrcI as a genuine high-mass protostar system and support the theory that SrcI and the Becklin Neugebauer Object were ejected from the dynamical decay of a multiple star system $\sim$500 years ago, an event that also launched the explosive molecular outflow in Orion.Comment: Accepted to ApJ. Data at https://zenodo.org/record/1213350, source repository at https://github.com/keflavich/Orion_ALMA_2016.1.00165.

Accretion and outflow structures within 1000 AU from high-mass protostars with ALMA longest baselines

Understanding the formation of massive stars is one of the unsolved problems in modern astronomy. The main difficulty is that the intense radiation from the high-luminosity stars and the thermal pressure from the resulting ionized gas (both insignificant for low-mass stars) may be able to reverse the accretion flow and prevent the star from accreting fresh material. Such feedback effects can naturally be mitigated if accretion proceeds through discs, which is the established mechanism to form sun-like stars. However, recent 3D MHD simulations have shown that accretion on 1000 au scales is through filaments rather than a large disc. This theoretical prediction has never been confirmed via observations owing to the poor linear resolution of previous studies (>1000 au). Here we present the first observational evidence that mass assembly in young high-mass stars forming in protoclusters is predominantly asymmetric and disordered. In particular, we observed the innermost regions around three deeply embedded high-mass protostars with very high spatial resolution (~100 au). We identified multiple massive (several solar masses), warm (50-150 Kelvin) filamentary streamers pointing onto the central sources, which we interpret as multi-directional accretion channels. These structures inhibit the formation of a large, steady disc. Nevertheless, the identification of fast collimated outflows in the three observed systems indicates that (non-steady) compact discs may be present (we measure upper limits on their radii of <80 for one object and <350 astronomical units for the remaining two objects). Our finding contrasts with the simplified classic paradigm of an ordered (and stable) disc/jet system and provides an experimental confirmation of a multi-directional and unsteady accretion model for massive star formation supported by recent 3D (magneto)hydrodynamic simulations.Comment: Submitted to Nature on Dec 19 2017, transferred to Nature Astronomy after review on February 8 2018, rejected after a recommendation for acceptance by one reviewer, and a more critical report by a second reviewer. To be submitted to ApJ. Comments from colleagues (even critical ones) are welcom

First detection of CS masers around a high-mass young stellar object, W51 e2e

We report the discovery of maser emission in the two lowest rotational transitions of CS toward the high-mass protostar W51 e2e with ALMA and the JVLA. The masers from CS J=1-0 and J=2-1 are neither spatially nor spectrally coincident (they are separated by ~150 AU and ~30 km/s), but both appear to come from the base of the blueshifted outflow from this source. These CS masers join a growing list of rarely-detected maser transitions that may trace a unique phase in the formation of high-mass protostars.Comment: Accepted to A