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TOPIC: Sagittarius B2 (North)
Blobrana


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Posts: 131433
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Sagittarius B2 (M)
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Title: Herschel/HIFI Observations of Hydrogen Fluoride Toward Sagittarius B2(M)
Authors: R. R. Monje, M. Emprechtinger, T. G. Phillips, D.C. Lis, P. F. Goldsmith, E. A. Bergin, T. A. Bell, D. A. Neufeld, P. Sonnentrucker

Herschel/HIFI observations have revealed the presence of widespread absorption by hydrogen fluoride (HF) J = 1-0 rotational transition, toward a number of Galactic sources. We present observations of HF J = 1-0 toward the high-mass star-forming region Sagittarius B2(M). The spectrum obtained shows a complex pattern of absorption, with numerous features covering a wide range of local standard of rest velocities (-130 to 100 km^-1). An analysis of this absorption yields HF abundances relative to H2 of ~1.3 x 10^-8, in most velocity intervals. This result is in good agreement with estimates from chemical models, which predict that HF should be the main reservoir of gas-phase fluorine under a wide variety of interstellar conditions. Interestingly, we also find velocity intervals in which the HF spectrum shows strong absorption features that are not present, or are very weak, in spectra of other molecules, such as 13CO (1-0) and CS (2-1). HF absorption reveals components of diffuse clouds with small extinction that can be studied for the first time. Another interesting observation is that water is significantly more abundant than hydrogen fluoride over a wide range of velocities toward Sagittarius B2(M), in contrast to the remarkably constant H2O/HF abundance ratio with average value close to unity measured toward other Galactic sources.

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Blobrana


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RE: Sagittarius B2 (North)
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Title: K-shell Emission of Neutral Iron Line from Sgr B2 Excited by Subrelativistic Protons
Authors: Vladimir Dogiel, Dmitrii Chernyshov, Katsuji Koyama, Masayoshi Nobukawa, Kwong-Sang Cheng

We investigated the emission of K \alpha iron line from the massive molecular clouds in the Galactic center (GC). We assume that at present the total flux of this emission consists of time variable component generated by primary X-ray photons ejected by Sagittarius A* (Sgr A*) in the past and a relatively weak quasi-stationary component excited by impact of protons which were generated by star accretion onto the central black hole. The level of background emission was estimated from a rise of the 6.4 keV line intensity in the direction of several molecular clouds, that we interpreted as a stage when the X-ray front ejected by Sgr A* entered into these clouds. The 6.4 keV emission before this intensity jump we interpreted as emission generated by subrelativistic cosmic rays there. The cross-section of K \alpha vacancies produced by protons differs from that of electrons or X-rays. Therefore, we expect that this processes can be distinguished from the analysis of the equivalent width of the iron line and time variations of the width can be predicted. The line intensity from the clouds depends on their distance from Sgr A* and the coefficient of spacial diffusion near the Galactic center. We expect that in a few years the line intensity for the cloud G\,0.11-0.11 which is relatively close to Sgr A* will decreases to the level \lesssim 10% from its present value. For the cloud Sagittarius B2 (Sgr B2) the situation is more intricate. If the diffusion coefficient D\gtrsim 10^{27} cm^2 s^{-1} then the expected stationary flux should be about 10% of its level in 2000. In the opposite case the line intensity from Sgr B2 should drop down to zero because the protons do not reach the cloud.

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Blobrana


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Title: A Trigonometric Parallax of Sgr B2
Authors: M. J. Reid, K. M. Menten, X. W. Zheng, A. Brunthaler, Y. Xu

We have measured the positions of water masers in Sgr B2, a massive star forming region in the Galactic center, relative to an extragalactic radio source with the Very Long Baseline Array. The positions measured at 12 epochs over a time span of one year yield the trigonometric parallax of Sgr B2 and hence a distance to the Galactic center of Ro=7.9 (+0.8/-0.7) kpc. The proper motion of Sgr B2 relative to Sgr A* suggests that Sgr B2 is about 0.13 kpc nearer than the Galactic center, assuming a low-eccentricity Galactic orbit.

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Blobrana


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RE: Sagittarius B2 (North)
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Astronomers love their sky maps, and the latest map is fantastic. It reveals thousands of previously undiscovered knots of cold cosmic dust, each a potential star waiting to be born.
The new atlas of dust covers the inner regions of our Milky Way Galaxy, where stars, gas and dust are all packed tightly together, where chaos reigns, where massive stars are born.
It's so dusty in there that optical telescopes can't see anything.
But cosmic material emits and reflects various forms of radiation besides the visible. The new observations were made in submillimetre-wavelength light, which is between infrared light and radio waves on the electromagnetic spectrum.

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Title: Infall, Fragmentation and Outflow in Sgr B2
Authors: Sheng-Li Qin, Jun-Hui Zhao, James M. Moran, Daniel Marrone, N. Patel, Sheng-Yuan Liu, Yi-Jehng Kuan, Jun-Jie Wang

Observations of H2CO lines and continuum at 1.3 mm towards Sagittarius B2 (North) and Sgr B2(M) cores were carried out with the SMA. Researchers imaged H2CO line absorption against the continuum cores and the surrounding line emission clumps. The results show that the majority of the dense gas is falling into the major cores where massive stars have been formed. The filaments and clumps of the continuum and gas are detected outside of Sgr B2(N) and Sgr B2(M) cores. Both the spectra and moment analysis show the presence of outflows from Sgr B2(M) cores. The H2CO gas in the red-shifted outflow of Sgr B2(M) appears to be excited by a non-LTE process which might be related to the shocks in the outflow.

sagB2

Position (2000): RA: 17:47:20.40, Dec: -28:23:7.00

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The Sgr B2 molecular cloud is locate approximately 120--130 pc from the Galactic centre and is the location of high luminosity star-formation as well as a rich source of molecular species. This large core, 5--10 pc in diameter, is also a site of H_2O and OH masers.

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