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NGC 6334I - MM1
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Title: An extraordinary outburst in the massive protostellar system NGC6334I-MM1: quadrupling of the millimeter continuum
Author: T. R. Hunter, C. L. Brogan, G. MacLeod, C. J. Cyganowski, C. J. Chandler, J. O. Chibueze, R. Friesen, R. Indebetouw, C. Thesner, K.H. Young

Based on sub-arcsecond ALMA and SMA 1.3 mm continuum images of the massive protocluster NGC6334I obtained in 2015 and 2008, we find that the dust emission from MM1 has increased by a factor of 4.00.3 during the intervening years, and undergone a significant change in morphology. The continuum emission from the other cluster members (MM2, MM4 and the UCHII region MM3=NGC6334F) has remained constant. Long term single-dish maser monitoring at HartRAO finds that multiple maser species toward NGC6334I flared beginning in early 2015, a few months before our ALMA observation, and some persist in that state. New ALMA images obtained in July-August 2016 at 1.1 and 0.87 mm confirm the changes with respect to SMA 0.87 mm images from 2008, and indicate that the (sub)millimeter flaring has continued for at least a year. The excess continuum emission, centered on the hypercompact HII region MM1B, is extended and elongated (1.6" x 1.0" approx 2100 x 1300~au) with multiple peaks, suggestive of general heating of the surrounding subcomponents of MM1, some of which may trace clumps in a fragmented disk rather than separate protostars. In either case, these remarkable increases in maser and dust emission provide direct observational evidence of a sudden accretion event in the growth of a massive protostar yielding a sustained luminosity surge by a factor of 7020, analogous to the largest events in simulations by Meyer et al. (2017). This target provides an excellent opportunity to assess the impact of such a rare event on a protocluster over many years.

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Posts: 131433
Date:
NGC 6334 I
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Title: The Massive Protostellar Cluster NGC6334I at 220 AU Resolution: Discovery of Further Multiplicity, Diversity and a Hot Multi-Core
Author: C. L. Brogan, T. R. Hunter, C. J. Cyganowski, C. J. Chandler, R. Friesen, R. Indebetouw

We present VLA and ALMA imaging of the deeply-embedded protostellar cluster NGC6334I from 5 cm to 1.3 mm at angular resolutions as fine as 0.17 (220 AU). The dominant hot core MM1 is resolved into seven components at 1.3 mm, clustered within a radius of 1000 AU. Four of the components have brightness temperatures >200 K, radii ~300 AU, minimum luminosities ~10000 Lsun, and must be centrally heated. We term this new phenomenon a "hot multi-core". Two of these objects also exhibit compact free-free emission at longer wavelengths, consistent with a hypercompact HII region (MM1B) and a jet (MM1D). The spatial kinematics of the water maser emission centered on MM1D are consistent with it being the origin of the high-velocity bipolar molecular outflow seen in CO. The close proximity of MM1B and MM1D (440~AU) suggests a proto-binary or a transient bound system. Several components of MM1 exhibit steep millimetre SEDs indicative of either unusual dust spectral properties or time variability. In addition to resolving MM1 and the other hot core (MM2) into multiple components, we detect five new millimetre and two new centimetre sources. Water masers are detected for the first time toward MM4A, confirming its membership in the protocluster. With a 1.3 mm brightness temperature of 97 K coupled with a lack of thermal molecular line emission, MM4A appears to be a highly optically-thick 240 Lsun dust core, possibly tracing a transient stage of massive protostellar evolution. The nature of the strongest water maser source CM2 remains unclear due to its combination of non-thermal radio continuum and lack of dust emission.

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Posts: 131433
Date:
Cat's Paw Nebula
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NGC 6334 (also Cat's Paw Nebula, Gum 64, Sharpless 8, RCW 127 and ESO 392-EN9) is a magnitude +7.8 emission nebula located 5500 970 light-years away in the constellation Scorpius.

The nebula was discovered by British astronomer John Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflecting telescope at the Cape of Good Hope on the 7th June 1837.

Right Ascension 17h 19m 58s, Declination -35 57' 47"

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Posts: 131433
Date:
RE: NGC 6334
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Title: The ionisation toward the high-mass star-forming region NGC 6334 I
Authors: J. L. Morales Ortiz, C. Ceccarelli, D. C. Lis, L. Olmi, R. Plume, P. Schilke

Context. Ionisation plays a central role in the gas-phase chemistry of molecular clouds. Since ions are coupled with the magnetic fields, which can in turn counteract the gravitational collapse, it is of paramount importance to measure their abundance in star-forming regions.
Aims. We use spectral line observations of the high-mass star-forming region NGC 6334 I to derive the abundance of two of the most abundant molecular ions, HCO+ and N2H+, and consequently, the cosmic ray ionisation rate. In addition, the line profiles provide information about the kinematics of this region.
Methods. We present high-resolution spectral line observations conducted with the HIFI instrument on board the Herschel Space Observatory of the rotational transitions with Jup > 5 of the molecular species C17O, C18O, HCO+, H13CO+, and N2H+.
Results. The line profiles display a redshifted asymmetry consistent with a region of expanding gas. We identify two emission components in the spectra, each with a different excitation, associated with the envelope of NGC 6334 I. The physical parameters obtained for the envelope are in agreement with previous models of the radial structure of NGC 6334 I based on submillimetre continuum observations. Based on our new Herschel/HIFI observations, combined with the predictions from a chemical model, we derive a cosmic ray ionisation rate that is an order of magnitude higher than the canonical value of 10^(-17) s-1.
Conclusions. We detect an expansion of the envelope surrounding the hot core of NGC 6334 I, which is mainly driven by thermal pressure from the hot ionised gas in the region. The ionisation rate is dominated by cosmic rays originating from outside the source, although X-ray emission from the NGC 6334 I core could contribute to the ionisation in the inner part of the envelope.

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Title: The Abundance, Ortho/Para Ratio, and Deuteration of Water in the High-Mass Star Forming Region NGC 6334 I
Authors: M. Emprechtinger, D. C. Lis, R. Rolffs, P. Schilke, R. R. Monje, C. Comito, C. Ceccarelli, D. A. Neufeld, F. F. S. van der Tak

We present Herschel/HIFI observations of 30 transitions of water isotopologues toward the high-mass star forming region NGC 6334 I. The line profiles of H_2^{16}O, H_2^{17}O, H_2^{18}O, and HDO show a complex pattern of emission and absorption components associated with the embedded hot cores, a lower-density envelope, two outflow components, and several foreground clouds, some associated with the NGC 6334 complex, others seen in projection against the strong continuum background of the source. Our analysis reveals an H2O ortho/para ratio of 3 0.5 in the foreground clouds, as well as the outflow. The water abundance varies from ~10^{-8} in the foreground clouds and the outer envelope to ~10^{-6} in the hot core. The hot core abundance is two orders of magnitude below the chemical model predictions for dense, warm gas, but within the range of values found in other Herschel/HIFI studies of hot cores and hot corinos. This may be related to the relatively low gas and dust temperature (~100 K), or time dependent effects, resulting in a significant fraction of water molecules still locked up in dust grain mantles. The HDO/H_2O ratio in NGC 6334 I, ~2 10^{-4}, is also relatively low, but within the range found in other high-mass star forming regions.

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Posts: 131433
Date:
NGC 6334 I
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Title: The distribution of water in the high-mass star-forming region NGC 6334I
Authors: M. Emprechtinger, D. C. Lis, T. Bell, T. G. Phillips, P. Schilke, C. Comito, R. Rolffs, F. van der Tak, C. Ceccarelli, H. Aarts, A. Bacmann, A. Baudry, M. Benedettini, E.A. Bergin, G. Blake, A. Boogert, S. Bottinelli, S. Cabrit, P. Caselli, A. Castets, E. Caux, J. Cernicharo, C. Codella, A. Coutens, N. Crimier, K. Demyk, C. Dominik, P. Encrenaz, E. Falgarone, A. Fuente, M. Gerin, P. Goldsmith, F. Helmich, P. Hennebelle, T. Henning, E. Herbst, P. Hily-Blant, T. Jacq, C. Kahane, M. Kama, A. Klotz, J. Kooi, W. Langer, B. Lefloch, A. Loose, S. Lord, A. Lorenzani, S. Maret, G. Melnick, D. Neufeld, B. Nisini, V. Ossenkopf, S. Pacheco, L. Pagani, B. Parise, J. Pearson, C. Risacher, M. Salez, P. Saraceno, K. Schuster, J. Stutzki, X. Tielens, M. van der Wiel, C. Vastel, S. Viti, V. Wakelam, A. Walters,
F. Wyrowski, H. Yorke,
et al. (2 additional authors not shown)

We present observations of twelve rotational transitions of H2O-16, H2O-18, and H2O-17 toward the massive star-forming region NGC 6334 I, carried out with Herschel/HIFI as part of the guaranteed time key program Chemical HErschel Surveys of Star forming regions (CHESS). We analyse these observations to obtain insights into physical processes in this region.
We identify three main gas components (hot core, cold foreground, and outflow) in NGC 6334 I and derive the physical conditions in these components.
The hot core, identified by the emission in highly excited lines, shows a high excitation temperature of 200 K, whereas water in the foreground component is predominantly in the ortho- and para- ground states. The abundance of water varies between 4 10^-5 (outflow) and 10^-8 (cold foreground gas). This variation is most likely due to the freeze-out of water molecules onto dust grains. The H2O-18/H2O-17 abundance ratio is 3.2, which is consistent with the O-18/O-17 ratio determined from CO isotopologues. The ortho/para ratio in water appears to be relatively low 1.6(1) in the cold, quiescent gas, but close to the equilibrium value of three in the warmer outflow material (2.5(0.8)).

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Posts: 131433
Date:
RE: NGC 6334
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VISTA Captures Celestial Cat's Hidden Secrets

The Cat's Paw Nebula, NGC 6334, is a huge stellar nursery, the birthplace of hundreds of massive stars. In a magnificent new ESO image taken with the Visible and Infrared Survey Telescope for Astronomy (VISTA) at the Paranal Observatory in Chile, the glowing gas and dust clouds obscuring the view are penetrated by infrared light and some of the Cat's hidden young stars are revealed.
Towards the heart of the Milky Way, 5500 light-years from Earth in the constellation of Scorpius (the Scorpion), the Cat's Paw Nebula stretches across 50 light-years. In visible light, gas and dust are illuminated by hot young stars, creating strange reddish shapes that give the object its nickname.

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On the Trail of a Cosmic Cat

eso1003a.jpg

ESO has just released a stunning new image of the vast cloud known as the Cat's Paw Nebula or NGC 6334. This complex region of gas and dust, where numerous massive stars are born, lies near the heart of the Milky Way galaxy, and is heavily obscured by intervening dust clouds.

Few objects in the sky have been as well named as the Cat's Paw Nebula, a glowing gas cloud resembling the gigantic pawprint of a celestial cat out on an errand across the Universe. British astronomer John Herschel first recorded NGC 6334 in 1837 during his stay in South Africa. Despite using one of the largest telescopes in the world at the time, Herschel seems to have only noted the brightest part of the cloud, seen here towards the lower left.

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Title: Wide-Field Infrared Imaging Polarimetry of the NGC 6334 Region: A Nest of Infrared Reflection Nebulae
Authors: J. Hashimoto, M. Tamura, R. Kandori, N. Kusakabe, Y. Nakajima, M. Kurita, T. Nagata, T. Nagayama, J. Hough, A. Chrysostomou

We report the detection of eighteen infrared reflection nebulae (IRNe) in the J, H, & Ks linear polarimetric observations of the NGC 6334 massive star-formation complex, of which 16 IRNe are new discoveries. Our images cover ~180 square arcminutes, one of the widest near-infrared polarization data in star-formation regions so far. These IRNe are most likely associated with embedded young OB stars at different evolutionary phases, showing a variety of sizes, morphologies, and polarization properties, which can be divided into four categories. We argue the different nebula characteristics to be a possible evolutionary sequence of circumstellar structures around young massive stars.

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