The following document lists the file abstract/EDWEK_IVC.abs
from catalogue VI/111.
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We propose to use the ISO satellite to study the process of grain destruction by grain-grain collsions in a set of 12 low velocity clouds, previously observed with the IRAS. Grain destruction by grain-grain collisions is the dominant grain destruction mechanism in low velocity clouds (v < 100 km/sec), in which sputtering is significantly surpressed because of the low gas temperatures, and grains are accelerated to high velocities by the betatron acceleration mechanism. Collisions between the grains will vaporize, and fragment larger grains, and eject macromolecules from the grain surfaces by cratering collisions. Very small particles are stochastically heated, undergo temperature fluctuations, and radiate an excess of near infrared emission (lamda<30 um) over that expected for grains in thermal equilibrium. This near infrared excess is a measure of the abundance of small grains, and therefore a powerful diagnostic for the amount of grain processing in low-velocity shocks. With the ISO observations we expect to confirm a trend,already /bla suggested by the IRAS data, which show a correlation of the F(60)/F(100) flux ratio on on cloud velocity, and a marginal dependence of the F(12)/F(100) ratio on velocity as well. We also plan to map out in detail three intermediate velocity clouds in order to study spatial variations of the IR spectrum within these clouds. The proposed observations will be done in a set of filters designed to observe PAHs, very small silicate grains, and larger dust particles, and search for trends in the abundances of the various dust component with cloud velocity. Detailed confirmation of the IRAS trends with the ISO will constitute the first observational evidence for grains by grain-grain collisions, and will provide new insight into this important grain destruction mechanism in low velocity shocks.