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 Austin, Texas.  Click here to read the abstract.  This work was also presented at the Four Corners section meeting of the APS in the Fall of 1999.


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 Atlanta, Georgia.  Click here to read the abstract.


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 San Diego, California.  Click here for a pdf version of the abstract.  I successfully defended my dissertation in Spring 2002.  A second summary of the work appeared in PASP 115(no. 809), 889 (2003).  An electronic copy of my dissertation is available for download here.


This work was partially funded by the Arizona NASA Space Grant Consortium.