(Proposal ID) S15A-148

(PI) Ita, Yoshifusa

(Proposal Title)
 Dust Kinematics in the Winds of Evolved Massive Stars

(Abstract)
We propose to measure outflow velocities of dust grains v_{dust} in the fast 
(of the order of 10^3 km/s) stellar winds of evolved massive stars, by 
adopting the spectropolarimetric technique as has been used to investigate 
dusty outflows from a starburst galaxy, M82. Dust grains flowing in stellar 
winds scatter line emission emanating from the central star in a particular 
scattering angle with respect to the observer. Hence, such line emission is 
singly scattered, and thus, linearly polarized. On the contrary, both 
intrinsic line emission from the local gas component and diffuse line emission 
permeating through the ambient circumstellar matter after many scattering are 
unpolarized. Therefore, the polarized line emission reveals the dust grain 
velocities, because these polarized lines are Doppler-shifted according to the 
outflow speed of the local dust grains. In the ALMA era, the circumstellar 
velocity structure of the molecular gas component v_{gas} will be probed 
extensively. Our study will pave the way, for the first time, for providing 
the matching velocity information for the dust component as observational 
constraints to be compared against theoretical considerations of dust-gas 
coupling.