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Séminaire du Jeudi 28 septembre 2017

IRC+10216 in 3-D : morphology of a TP-AGB star envelope

Michel Guelin & Michael Bremer (IRAM)
Thursday September 28th - 11am
IPAG Seminar Room - IPAG

During their late pulsating phase, AGB stars expel most of their mass in the form of massive dusty envelopes, an event that largely controls the composition of interstellar matter. The envelopes, however, are distant and opaque to visible and NIR radiation : their structure remains poorly known and the mass-loss process poorly understood. Millimeter-wave interferometry, which combines the advantages of longer wavelength, high angular resolution and very high spectral resolution is the optimal investigative tool for this purpose. Mm waves pass through dust with almost no attenuation. Their spectrum is rich in molecular lines and hosts the fundamental lines of the ubiquitous CO molecule, allowing a tomographic reconstruction of the envelope structure. CW Leo, the C-rich TP-AGB star closest to the Sun, and its expanding envelope IRC+10216 are the best objects for such an investigation. Two years ago, we reported the first detailed study of the CO(2-1) line emission in that envelope, made with the IRAM 30-m telescope. It revealed a series of dense gas shells unresolved by the telescope beam (HPBW 11′′). We now report much higher angular resolution observations made with the SMA, PdB and ALMA interferometers (with synthesized beamwidths of 3′′, 1” and 0.3′′, respectively). Outside the small (r < 0.3′′) dust formation zone, the gas appears to expand radially at a constant velocity, 14.5 km/s, with small turbulent motions. Based on that property, we have reconstructed the 3-D structure of the outer envelope and the mass loss history during the last 10^4 yr. The mechanisms controlling mass loss and the effect of the envelope structure on chemistry will be discussed.


Sous la tutelle de:

tutelles

Sous la tutelle de:

CNRS Université Grenoble Alpes