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Post Info TOPIC: Messier 17


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RE: Messier 17
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A Cosmic Rose With Many Names

This new image of the rose-coloured star forming region Messier 17 was captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESOs La Silla Observatory in Chile. It is one of the sharpest images showing the entire nebula and not only reveals its full size but also retains fine detail throughout the cosmic landscape of gas clouds, dust and newborn stars.
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Title: The Submillimetre Polarisation Spectrum of M17
Authors: Lingzhen Zeng, Charles L. Bennett, Nicholas L. Chapman, David T. Chuss, Izaskun Jimenez-Serra, Giles Novak, John E. Vaillancourt

We present 450 Ám polarimetric observations of the M17 molecular cloud obtained with the SHARP polarimeter at the Caltech Submillimetre Observatory. Across the observed region, the magnetic field orientation is consistent with previous submillimetre and far-infrared polarisation measurements. Our observations are centred on a region of the molecular cloud that has been compressed by stellar winds from a cluster of OB stars. We have compared these new data with previous 350 Ám polarimetry and find an anti-correlation between the 450 to 350 Ám polarisation magnitude ratio and the ratio of 21 cm to 450 Ám intensity. The polarisation ratio is lower near the east end of the studied region where the cloud is exposed to stellar winds and radiation. At the west end of the region, the polarisation ratio is higher. We interpret the varying polarisation spectrum as evidence supporting the radiative alignment torque (RAT) model for grain alignment, implying higher alignment efficiency in the region that is exposed to a higher anisotropic radiation field.

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The Smoky Pink Core of the Omega Nebula

eso1201a.jpg

A new image of the Omega Nebula, captured by ESO's Very Large Telescope (VLT), is one of the sharpest of this object ever taken from the ground. It shows the dusty, rose-coloured central parts of this famous stellar nursery and reveals extraordinary detail in the cosmic landscape of gas clouds, dust and newborn stars.
The colourful gas and dark dust in the Omega Nebula serve as the raw materials for creating the next generation of stars. In this particular section of the nebula, the newest stars on the scene - dazzlingly bright and shining blue-white - light up the whole ensemble. The nebula's smoky-looking ribbons of dust stand in silhouette against the glowing gas. The dominant reddish colours of this portion of the cloud-like expanse, arise from hydrogen gas, glowing under the influence of the intense ultraviolet rays from the hot young stars.

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Omega Nebula
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Brand new telescope captures Omega Nebula in all its glory

A spectacular stellar nursery shines through the gas and dust clouds of the Omega Nebula 5,500 light years from Earth in the heart of the Milky Way.
The image is the first to be released from the VLT Survey Telescope (VST) that sits on the summit of Paranal Hill in the Atacama desert in northern Chile.
Dotted with hot young stars, the region is part of the constellation of Sagittarius, the Archer, and is known by other names including the Swan Nebula and Messier 17.

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The Omega Nebula, a stellar nursery where infant stars illuminate and sculpt a vast pastel fantasy of dust and gas, is revealed in all its glory by a new ESO image.
The Omega Nebula, sometimes called the Swan Nebula, is a dazzling stellar nursery located about 5500 light-years away towards the constellation of Sagittarius (the Archer). An active star-forming region of gas and dust about 15 light-years across, the nebula has recently spawned a cluster of massive, hot stars. The intense light and strong winds from these hulking infants have carved remarkable filigree structures in the gas and dust.
When seen through a small telescope the nebula has a shape that reminds some observers of the final letter of the Greek alphabet, omega, while others see a swan with its distinctive long, curved neck. Yet other nicknames for this evocative cosmic landmark include the Horseshoe and the Lobster Nebula.

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Omega Nebula
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Title: 3D numerical model of the Omega Nebula (M17): simulated thermal X-ray emission
Authors: J. Reyes-Iturbide, P. F. Velazquez, M. Rosado, A. Rodriguez-Gonzalez, R. F. Gonzalez, A. Esquivel

We present 3D hydrodynamical simulations of the superbubble M17, also known as the Omega nebula, carried out with the adaptive grid code yguazu'-a, which includes radiative cooling. The superbubble is modelled considering the winds of 11 individual stars from the open cluster inside the nebula (NGC 6618), for which there are estimates of the mass loss rates and terminal velocities based on their spectral types. These stars are located inside a dense interstellar medium, and they are bounded by two dense molecular clouds.
We carried out three numerical models of this scenario, considering different line of sight positions of the stars (the position in the plane of the sky is known, thus fixed). Synthetic thermal X-ray emission maps are calculated from the numerical models and compared with ROSAT observations of this astrophysical object. Our models reproduce successfully both the observed X-ray morphology and the total X-ray luminosity, without taking into account thermal conduction effects.

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Swan nebula
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A new image from NASA's Spitzer Space Telescope shows a turbulent star-forming region, where rivers of gas and stellar winds are eroding thickets of dusty material.
The picture provides some of the best examples yet of the ripples of gas, or bow shocks, that can form around stars in choppy cosmic waters.

"The stars are like rocks in a rushing river. Powerful winds from the most massive stars at the center of the cloud produce a large flow of expanding gas. This gas then piles up with dust in front of winds from other massive stars that are pushing back against the flow" - Matt Povich of the University of Wisconsin, Madison.

Povich is lead author of a paper describing the new findings in the Dec. 10 issue of the Astrophysical Journal.

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The Swan Nebula
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Well-positioned for northern and southern observers, the Swan Nebula lies 5,000 light years away among the rich star clouds of Sagittarius about 10 degrees north of the "teapot".á The Swan is one of the three finest emission nebulae visible to small telescopes.

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M17
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A team of European astronomers offer new evidence that high-mass stars could form in a similar way to low-mass stars, that is, from accretion of gas and dust through a disk surrounding the forming star. Their article, published in Astronomy & Astrophysics, reports the discovery of a jet of molecular hydrogen arising from a forming high-mass star located in the Omega nebula (M17). This detection confirms the hypothesis based on their earlier discovery that this forming high-mass star is surrounded by a large accretion disk.
While astronomers now understand the overall process of low-mass star formation very well, the formation process of massive stars is still very much under debate. Recent astronomical observations suggest that high-mass starsá could form through accretion processes, just like low-mass stars do. For instance, in 2004, European astronomers discovered a large accretion disk that probably surrounds a forming high-mass star, in the star-forming region M17, also known as the Omega nebula and located at a distance of about 7000 light years.
Looking again at M17 with the new spectrograph SINFONIá at the ESO-VLT, the same European groupá report discovering a jet of molecular hydrogen (H2) that apparently arises from the forming high-mass star. The picture below illustrates this discovery, which is being published in Astronomy & Astrophysics.
The ejection of material through a jet or an outflow is always linked to accretion of gas and dust, either onto the circumstellar disk or onto the central protostar. The detection of the H2 jet thus provides evidence that ongoing accretion processes occur in the M17 disk. The team also estimates the mass outflow and mass accretion rates, which suggest that a star of high mass is forming within the M17 disk. This is an additional clue that high-mass stars form in a similar way to lower mass stars.

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