IRC+10216's Innermost Envelope -- The eSMA's View

Abstract

We used the Extended Submillimeter Array (eSMA) in its most extended configuration to investigate the innermost (within a radius of 290 R* from the star) circumstellar envelope (CSE) of IRC+10216. We imaged the CSE using HCN and other molecular lines with a beam size of 0."22 x 0."46, deeply into the very inner edge (15 R*) of the envelope where the expansion velocity is only 3 km/s. The excitation mechanism of hot HCN and KCl maser lines is discussed. HCN maser components are spatially resolved for the first time on an astronomical object. We identified two discrete regions in the envelope: a region with a radius of . 15 R*, where molecular species have just formed and the gas has begun to be accelerated (region I) and a shell region (region II) with a radius of 23 R* and a thickness of 15 R*, whose expansion velocity has reached up to 13 km/s, nearly the terminal velocity of 15 km/s. The Si${}^{34}$S line detected in region I shows a large expansion velocity of 16 km/s due to strong wing components, indicating that the emission may arise from a shock region in the innermost envelope. In region II, the P.A. of the most copious mass loss direction was found to be 120 +/- 10 degrees, which may correspond to the equatorial direction of the star. Region II contains a torus-like feature. These two regions may have emerged due to significant differences in the size distributions of the dust particles in the two regions.

26 pages, 8 figures, accepted for publication in The Astrophysical Journal. Please find the pdf at http://www.submm.caltech.edu/~hs/astroph/0904.0280.pdf and the ps file at http://www.submm.caltech.edu/~hs/astroph/0904.0280.ps

References in corpus (3)

• Submillimeter narrow emission lines from the inner envelope of IRC+10216
• Continuum emission around AGB stars at 1.2 mm
• The eSMA: description and first results

Cited by in corpus (9)

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• The abundance of HCN in circumstellar envelopes of AGB stars of different chemical types
• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
• The Small-Scale Physical Structure and Fragmentation Difference of Two Embedded Intermediate Mass Protostars in Orion
• The abundance of 28Si32S, 29Si32S, 28Si34S, and 30Si32S in the inner layers of the envelope of IRC+10216
• Mapping the Linearly Polarized Spectral Line Emission around the Evolved Star IRC+10216
• Monitor variability of millimeter lines in IRC +10216
• H12CN and H13CN excitation analysis in the circumstellar outflow of R Scl
• Vibrationally excited HCN transitions in circumstellar envelopes of carbon-rich AGB stars