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تسجيل مستخدم جديدMid-infrared interferometry on spectral lines: III. Ammonia and Silane around IRC+10216 and VY CMa
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Using the U.C. Berkeley Infrared Spatial Interferometer with an RF filterbank, the first interferometric observations of mid-infrared molecular absorption features of ammonia (NH_3) and silane (SiH_4) with very high spectral resolution (R ~ 100000) were made. Under the assumptions of spherical symmetry and uniform outflow, these new data permitted the molecular stratification around carbon star IRC+10216 and red supergiant VY CMa to be investigated. For IRC+10216, both ammonia and silane were found to form in the dusty outflow significantly beyond both the dust formation and gas acceleration zones. Specifically, ammonia was found to form before silane in a region of decaying gas turbulence (>~ 20 R_star), while the silane is produced in a region of relatively smooth gas flow much further from the star (>~ 80 R_star). The depletion of gas-phase SiS onto grains soon after dust formation may fuel silane-producing reactions on the grain surfaces. For VY CMa, a combination of interferometric and spectral observations suggest that NH_3 is forming near the termination of the gas acceleration phase in a region of high gas turbulence (~ 40 R_star).
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The U. C. Berkeley Infrared Spatial Interferometer has measured the mid-infrared visibilities of the carbon star IRC+10216 and the red supergiant VY CMa. The dust shells around these sources have been previously shown to be time-variable, and these n
ew data are used to probe the evolution of the dust shells on a decade time-scale, complementing contemporaneous studies at other wavelengths. Self-consistent, spherically-symmetric models at maximum and minimum light both show the inner radius of the IRC+10216 dust shell to be much larger (150 mas) than that expected from the dust condensation temperature, implying that dust production has slowed or stopped in recent years. Apparently, dust does not form every pulsational cycle (638 days), and these mid-infrared results are consistent with recent near-IR imaging which indicates little or no new dust production in the last three years (Tuthill et al 2000). Spherically symmetric models failed to fit recent VY CMa data, implying that emission from the inner dust shell is highly asymmetric and/or time-variable.
The U. C. Berkeley Infrared Spatial Interferometer has been outfitted with a filterbank system to allow interferometric observations of mid-infrared spectral lines with very high spectral resolution (R ~ 10^5). This paper describes the design, implem
entation, and performance of the matched 32-channel filterbank modules, and new spectral line observations of Mars and IRC+10216 are used to demonstrate their scientific capability. In addition, observing strategies are discussed for accurate calibration of fringe visibilities in spectral lines, despite strong atmospheric fluctuations encountered in the infrared.
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