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Bally J.,University of Colorado at Boulder | Ginsburg A.,ESO Headquarters | Arce H.,Yale University | Eisner J.,University of Arizona | And 3 more authors.
Astrophysical Journal | Year: 2017

Most massive stars form in dense clusters where gravitational interactions with other stars may be common. The two nearest forming massive stars, the BN object and Source I, located behind the Orion Nebula, were ejected with velocities of ∼29 and ∼13 km s-1 about 500 years ago by such interactions. This event generated an explosion in the gas. New ALMA observations show in unprecedented detail, a roughly spherically symmetric distribution of over a hundred 12CO J = 2-1 streamers with velocities extending from V LSR = -150 to +145 km s-1. The streamer radial velocities increase (or decrease) linearly with projected distance from the explosion center, forming a "Hubble Flow" confined to within 50″ of the explosion center. They point toward the high proper-motion, shock-excited H2 and [Fe ii] "fingertips" and lower-velocity CO in the H2 wakes comprising Orion's "fingers." In some directions, the H2 "fingers" extend more than a factor of two farther from the ejection center than the CO streamers. Such deviations from spherical symmetry may be caused by ejecta running into dense gas or the dynamics of the N-body interaction that ejected the stars and produced the explosion. This ∼1048 erg event may have been powered by the release of gravitational potential energy associated with the formation of a compact binary or a protostellar merger. Orion may be the prototype for a new class of stellar explosiozn responsible for luminous infrared transients in nearby galaxies. © 2017. The American Astronomical Society. All rights reserved.

Drew J.E.,University of Hertfordshire | Gonzalez-solares E.,University of Cambridge | Greimel R.,University of Graz | Irwin M.J.,University of Cambridge | And 31 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u, g, r, i and Hα at ~1 arcsec angular resolution. Its footprint spans the Galactic latitude range -5o < b < +5° at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes ±10° bring in much of the Galactic bulge. This European Southern Observatory public survey, begun on 2011 December 28, reaches down to ~20th magnitude (10σ) and will provide single-epoch digital optical photometry for ~300 million stars. The observing strategy and data pipelining are described, and an appraisal of the segmented narrow-band Hα filter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u - g), (g - r), (r - i) and (r - Hα) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u - g, g - r) and (r - Hα, r - i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VLT Survey Telescope (VST)/OmegaCam combination used by this survey is a perfect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Koepferl C.M.,Ludwig Maximilians University of Munich | Ercolano B.,Ludwig Maximilians University of Munich | Ercolano B.,Exzellenzcluster Universe | Dale J.,Ludwig Maximilians University of Munich | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

The time-scale over which and the modality by which young stellar objects (YSOs) disperse their circumstellar discs dramatically influence the eventual formation and evolution of planetary systems. By means of extensive radiative transfer modelling, we have developed a new set of diagnostic diagrams in the infrared colour-colour plane (K - [24] versus K - [8]), to aid with the classification of the evolutionary stage of YSOs from photometric observations. Our diagrams allow the differentiation of sources with unevolved (primordial) discs from those evolving according to different clearing scenarios (e.g. homologous depletion versus inside-out dispersal), as well as from sources that have already lost their disc. Classification of over 1500 sources in 15 nearby star-forming regions reveals that approximately 39 per cent of the sources lie in the primordial disc region, whereas between 31 and 32 per cent disperse from the inside-out and up to 22 per cent of the sources have already lost their disc. Less than 2 per cent of the objects in our sample lie in the homogeneous draining regime. Time-scales for the transition phase are estimated to be typically a few 105 yr independent of stellar mass. Therefore, regardless of spectral type, we conclude that currently available infrared photometric surveys point to fast (of the order of 10 per cent of the global disc lifetime) inside-out clearing as the preferred mode of disc dispersal. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Jordan C.H.,James Cook University | Jordan C.H.,CSIRO | Walsh A.J.,James Cook University | Lowe V.,CSIRO | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We introduce the Millimetre Astronomer's Legacy Team - 45 GHz (MALT-45) Galactic plane survey and describe pilot survey results with the Australia Telescope Compact Array (ATCA). The pilot survey was conducted to test the instrumentation and observational technique of MALT-45, before commencing the full survey. We mapped two half-square degree regions within the southern Galactic plane around the G333 giant molecular cloud, using fast mosaic mapping. Using the new Compact Array Broad-band Backend on the ATCA, we were able to observe two 2048MHzspectral windows, centred on frequencies 43.2 and 48.2 GHz. Although only a coarse spectral resolution of around 7 km s-1 was available to us, we detect widespread, extended emission in the CS (1-0) ground state transition.We also detect eight Class I CH3OH masers at 44 GHz and three SiO masers in vibrationally excited (1-0) transitions. We also detect the H53α radio recombination line, non-vibrationally excited SiO (1-0) and emission in the CH3OH 11-00 A+ line ©2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Foster J.B.,Boston University | Jackson J.M.,Boston University | Barnes P.J.,University of Florida | Barris E.,Boston University | And 13 more authors.
Astrophysical Journal, Supplement Series | Year: 2011

We describe a pilot survey conducted with the Mopra 22m radio telescope in preparation for the Millimeter Astronomy Legacy Team Survey at 90GHz (MALT90). We identified 182 candidate dense molecular clumps using six different selection criteria and mapped each source simultaneously in 16 different lines near 90GHz. We present a summary of the data and describe how the results of the pilot survey shaped the design of the larger MALT90 survey. We motivate our selection of target sources for the main survey based on the pilot detection rates and demonstrate the value of mapping in multiple lines simultaneously at high spectral resolution. © 2011. The American Astronomical Society. All rights reserved.

Bally J.,University of Colorado at Boulder | Ginsburg A.,ESO Headquarters | Kasliwal M.M.,California Institute of Technology
EAS Publications Series | Year: 2016

AO imaging of the near IR [Fe ii] and H2 lines and ALMA CO J = 2-1 data confirms the explosive nature of the BN/KL outflow in Orion. N-body interactions in compact groups may be responsible for the production of powerful, explosive protostellar outflows and luminous infrared flares. The Orion event may have been triggered by a protostellar merger. First results of a search for Orion-like events in 200 nearby galaxies with the SPitzer InfraRed Intensive Transients Survey (SPIRITS) are briefly discussed. © 2016 EAS, EDP Sciences.

Eisner J.A.,University of Arizona | Bally J.M.,University of Colorado at Boulder | Ginsburg A.,ESO Headquarters | Sheehan P.D.,University of Arizona
Astrophysical Journal | Year: 2016

We present ALMA observations of the Orion Nebula that cover the OMC1 outflow region. Our focus in this paper is on compact emission from protoplanetary disks. We mosaicked a field containing ∼600 near-IR-identified young stars, around which we can search for sub-millimeter emission tracing dusty disks. Approximately 100 sources are known proplyds identified with the Hubble Space Telescope. We detect continuum emission at 1 mm wavelengths toward ∼20% of the proplyd sample, and ∼8% of the larger sample of near-IR objects. The noise in our maps allows 4σ detection of objects brighter than ∼1.5 mJy, corresponding to protoplanetary disk masses larger than 1.5 M J (using standard assumptions about dust opacities and gas-to-dust ratios). None of these disks are detected in contemporaneous CO(2-1) or C18O(2-1) observations, suggesting that the gas-to-dust ratios may be substantially smaller than the canonical value of 100. Furthermore, since dust grains may already be sequestered in large bodies in Orion Nebula cluster (ONC) disks, the inferred masses of disk solids may be underestimated. Our results suggest that the distribution of disk masses in this region is compatible with the detection rate of massive planets around M dwarfs, which are the dominant stellar constituent in the ONC. © 2016. The American Astronomical Society. All rights reserved.

Voronkov M.A.,CSIRO | Voronkov M.A.,Astro Space Center | Walsh A.J.,James Cook University | Caswell J.L.,CSIRO | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We report the first detection of a methanol maser in the 101-92 A- transition at 23.4 GHz, discovered during the H2O southern Galactic Plane Survey (HOPS) with the 22-m Mopra Radio Telescope. In the region covered by HOPS, the 23.4-GHz maser was found at only one location, G357.97-0.16, which was also a prominent source of maser emission in the J2-J1 E series near 25GHz. The Australia Telescope Compact Array (ATCA) was used to follow up these detections at high angular resolution and prove the maser nature of the observed emission. The analysis shows that the new methanol maser at 23.4GHz is a class I maser, which has properties similar to the 9.9- and 25-GHz masers (i.e. traces strong shocks with higher than average temperature and density). All class I masers were found to originate at the same spatial location (within the measurement uncertainty of 0.5arcsec) in the vicinity of the dominant infrared source, but at a clearly distinct position from nearby OH, H2O and class II methanol masers at 6.7GHz. All maser species are distributed approximately on a line, but it is not clear at present whether this has any physical significance. We also detected a weak (1.3mJy) continuum source at 25GHz near the OH maser (at the most northern site, associated with a class II methanol maser and an H2O maser renowned for its extremely wide spread of velocity components). The continuum source has not been reported at lower frequencies and is therefore a candidate hypercompact Hii region. We also used the ATCA to find the strongest and only the fifth known 9.9-GHz maser towards G357.97-0.16 and another 23.4-GHz maser towards G343.12-0.06 not seen in HOPS. © 2011 CSIRO Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Bally J.,University of Colorado at Boulder | Ginsburg A.,ESO Headquarters | Silvia D.,Michigan State University | Youngblood A.,University of Colorado at Boulder
Astronomy and Astrophysics | Year: 2015

Aims. Adaptive optics (AO) 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 AO system GeMS and near-IR imager GSAOI are presented. The images reach resolutions of 0.08 to 0.10′′, close to the 0.07′′ diffraction limit of the 8-m telescope at 2.12 μm. 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 ~103 times their own diameter through a lower density medium at Mach 103. 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-1. 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 107 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 yr 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. © 2015 ESO.

Lanzuisi G.,Max Planck Institute for Extraterrestrial Physics | Lanzuisi G.,Harvard - Smithsonian Center for Astrophysics | Lanzuisi G.,TU Munich | Civano F.,Harvard - Smithsonian Center for Astrophysics | And 15 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present the X-ray spectral analysis of the 390 brightest extragalactic sources in the Chandra-Cosmic Evolution Survey catalogue, showing at least 70 net counts in the 0.5-7 keV band. This sample has a 100 per cent completeness in optical-infrared identification, with ~75 per cent of the sample having a spectroscopic redshift and ~25 per cent a photometric redshift. Our analysis allows us to accurately determine the intrinsic absorption, the broad-band continuum shape (Γ) and intrinsic L2-10 distributions, with an accuracy better than 30 per cent on the spectral parameters for 95 per cent of the sample. The sample is equally divided in type 1 (49.7 per cent) and type 2 active galactic nuclei (48.7 per cent) plus few passive galaxies at low z. We found a significant difference in the distribution of Γ of type 1 and type 2, with small intrinsic dispersion, a weak correlation of Γ with L2-10 and a large population (15 per cent of the sample) of high luminosity, highly obscured (QSO2) sources. The distribution of the X-ray/Optical flux ratio (Log(FX/Fi)) for type 1 is narrow (0 < X/O < 1), while type 2 are spread up to X/O = 2. The X/O correlates well with the amount of X-ray obscuration. Finally, a small sample of Compton-thick candidates and peculiar sources is presented. In the appendix, we discuss the comparison between Chandra and XMM-Newton spectra for 280 sources in common. We found a small systematic difference, with XMM-Newton spectra that tend to have softer power laws and lower obscuration. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

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