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