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تسجيل مستخدم جديدOdin detection of O2
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We present the detection of molecular oxygen with Odin toward the dense molecular core rho Oph A, which is part of a region of active star formation. The observed spectral line is the (N,J = 1,1-1,0) ground state transition of molecular oxygen at 119 GHz (2.5 mm wavelength). The center of the line is at the LSR velocity of a number of optically thin lines from other species in the region and the O2 line also has a very similar, narrow, line width. Within the 10 arcmin beam, the integrated line intensity is 28 mK km/s, which corresponds to 5 sigma of the rms noise. A standard LTE analysis results in an O2 abundance of 5E(-8), with an uncertainty of at least a factor of two. We show that standard methods, however, do not apply in this case, as the coupling of the Odin beam to the source structure needs to be accounted for. Preliminary model results indicate O2 abundances to be higher by one order of magnitude than suggested by the standard case. This model predicts the 487 GHz line of O2 to be easily detectable by the future Herschel-HIFI facility, but to be out of reach for observations on a shorter time scale with the Odin space observatory.
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The Odin satellite has been used to search for the 118.75-GHz line of molecular oxygen (O2)in the Galactic centre. Odin observations were performed towards the Sgr A* circumnuclear disk (CND), and the Sgr A +20 km/s and +50 km/s molecular clouds usin
g the position-switching mode. Supplementary ground-based observations were carried out in the 2-mm band using the ARO Kitt Peak 12-m telescope to examine suspected SiC features. A strong emission line was found at 118.27 GHz, attributable to the J=13-12 HC3N line. Upper limits are presented for the 118.75-GHz O2 (1,1-1,0) ground transition line and for the 118.11-GHz 3Pi2, J=3-2 ground state SiC line at the Galactic centre. Upper limits are also presented for the 487-GHz O2 line in the Sgr A +50 km/s cloud and for the 157-GHz, J=4-3, SiC line in the Sgr A +20 and +50 km/s clouds, as well as the CND. The CH3OH line complex at 157.2 - 157.3 GHz has been detected in the +20 and +50 km/s clouds but not towards Sgr A*/CND. A 3-sigma upper limit for the fractional abundance ratio of [O2]/[H2] is found to be X(O2) < 1.2 x 10exp(-7) towards the Sgr A molecular belt region.
Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O2, and water, H2O. Contrary to expectation, the space missions SWAS and Odin found only very small amounts of water v
apour and essentially no O2 in the dense star-forming interstellar medium. Only toward rho Oph A did Odin detect a weak line of O2 at 119 GHz in a beam size of 10 arcmin. A larger telescope aperture such as that of the Herschel Space Observatory is required to resolve the O2 emission and to pinpoint its origin. We use the Heterodyne Instrument for the Far Infrared aboard Herschel to obtain high resolution O2 spectra toward selected positions in rho Oph A. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models. The 487.2GHz line was clearly detected toward all three observed positions in rho Oph A. In addition, an oversampled map of the 773.8GHz transition revealed the detection of the line in only half of the observed area. Based on their ratios, the temperature of the O2 emitting gas appears to vary quite substantially, with warm gas (> 50 K) adjacent to a much colder region, where temperatures are below 30 K. The exploited models predict O2 column densities to be sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these model, the observationally determined O2 column densities seem not to depend strongly on the derived gas temperatures, but fall into the range N(O2) = (3 to >6)e15/cm^2. Beam averaged O2 abundances are about 5e-8 relative to H2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz of about 4 - 5 arcmin, encompassing the entire rho Oph A core.
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The Odin satellite has been used to detect emission and absorption in the 557-GHz H2O line in the Galactic Centre towards the Sgr A* Circumnuclear Disk (CND), and the Sgr A +20 km/s and +50 km/s molecular clouds. Strong broad H2O emission lines have
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