Extending The Sma Spectral-line Survey Of Irc+10216 In The 400 Ghz Band

Astronomy and Astrophysics – Astrophysics

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Interstellar dust grains are thought to evolve in the colder regions of space from the gas and solids there, material believed to come from Asymptotic Giant Branch (AGB) stars. IRC+10216 is a well studied such star with high mass loss. Close to the Sun ( 150 pc), it is an ideal place to study the physical and chemical processes in AGB circumstellar envelopes. Using the Submillimeter Array (SMA), we recently carried out the first interferometric spectral line-survey of IRC+10216 in the 345 GHz band, with an angular resolution of 3"x2". This survey has led to the discovery of many narrow lines of molecular emission, implying expansion velocities of 4 km/s (in contrast with the typical value of the expansion velocity of 14.5 km/s known from previous surveys). Maps of these lines show that they are produced in the inner envelope, within 60 AU of the star, where the stellar wind is still being accelerated. Following this line survey in the 294-355 GHz frequency range, we are now extending the frequency coverage to 396-420 GHz. We will add higher frequency transitions for several molecules that were detected in our 345 GHz line survey, allowing us to better characterize the physical conditions in the inner circumstellar envelope. We will be able to derive abundances of several molecular species, for comparison with chemical models. Continuum fluxes at higher frequencies will help constrain the SED due to dust emission. These observations partially fill the gap between our previous survey (379-355 GHz) and the recently published survey at even higher frequencies (490-1900 GHz) with the Herschel HIFI. The SMA is a joint collaboration between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics.

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