Research
I worked with Per Aannestad to study the evolution of grain size
distributions that are processed by nonthermal and chemical sputtering processes
in the expanding envelopes of cool stars. The gas and dust are treated as
two separate fluids with a term in the dynamical equations to couple the two
fluids together. The dust, spherical amorphous carbon grains, can reach a
velocity relative to the gas such that the collisions between the gas and dust
can cause carbon atoms to be removed from the surface by nonthermal
sputtering. The nonthermal sputtering yield is dominated by grain
collisions with Helium. We found that the effects of nonthermal
sputtering can be important in processing dust grains around high luminosity
stars. These results are summarized in a paper that has been published as
MNRAS 318, 67 (2000). A pdf version of the
paper is available by clicking here. This work was presented at the winter 1999 AAS meeting in
Chemical sputtering is the erosion of a grain surface due to
chemical reactions with the gas was also included. This type of
sputtering is important around low temperature, low luminosity stars. The
conditions in the area around the star allow the grains to remain in the region
where the density of atomic hydrogen is high and where the grain temperature is
near 600 K. Sputtering by other atomic species, such as oxygen and
nitrogen, is ignored in this work due to their low abundance relative to atomic
hydrogen. A preliminary version of this work was presented at the winter
2000 AAS meeting in
The model above was applied to calculating the amount of carbon dust injected back into the interstellar medium (ISM). The model falls short of the expected amount of dust largely due to the model’s inability to handle stars with very thick, dusty envelopes. These are the stars that would inject the most material into galactic ISM, which would explain the shortfall.
I presented my dissertation summary at the winter 2001 AAS meeting in
This work was partially funded by the Arizona NASA Space Grant Consortium.