Physics
Scientific paper
Jul 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009hst..prop12205u&link_type=abstract
HST Proposal ID #12205. Cycle 18
Physics
Scientific paper
We will undertake differential proper-motion measurements of the circumstellar dust shell of an asymptotic giant branch star, IRC +10 216, to understand kinematics and the dust-gas coupling in the shell. We will take the second-epoch long-exposure images of the so-called concentric arcs in F606W and short-exposure images of the central asymmetric lobes in F814W using WFC3 and compare them with the first-epoch archived WFPC2 images. These circular concentric arcs are enigmatic because their apparent time intervals {on the order of 100 yr} do not seem to be consistent with any obvious physical processes associated with the central star {pulsation of the star on the order of 1 yr and thermal pulses of 10,000 to 100,000 yr}. With proximity to the target { 135 pc} and a relatively long interval between two-epoch observations {12-13 yr}, we expect that these shells show translational shifts of at most 7-8 pixels measurable with the cross-correlational analysis of distinct local shell structure. With such measurements of the translational shift of the shell structures, we can measure the expansion velocities of these concentric arcs and the central lobes directly. We will then compare the HST imaging results which probe the dust component of the shell with the previous CO mapping results which probe the gas component of the shell. Because the shell's 3-D kinematics is known from the CO data the concentric arcs can be deprojected to trace their true space motion, allowing us to disentangle the mysterious discordance of the arcs' apparent time intervals with respect to the time scales of relevant physical processes. By comparing the CO and HST results, we wil attempt to verify if the dust-gas coupling is indeed at work in AGB winds. This will be the first attempt to address observationally this one of the fundamental assumptions of dust-driven mass-loss.;
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