The Effects of Grain Size and Grain Growth on the Chemical Evolution of Cold Dense Clouds

Details The Effects of Grain Size and Grain Growth on the Chemical Evolution of Cold Dense Clouds The Effects of Grain Size and Grain Growth on the Chemical Evolution of Cold Dense Clouds

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p..75a&link_type=abstract

The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole

Astronomy and Astrophysics

Astronomy

Scientific paper

We investigate the formation of molecules during the chemical evolution of a cold dense interstellar cloud using a gas-grain numerical code in order to study the effects of grain size distributions and grain growth on molecular abundances. Most models with grain surface chemistry have used so-called classical grains with a canonical dust to gas mass ratio of 1:100, characterized by a radius of 0.1 μm and a number density 1.33 10-12 n_H, where n_H is the number density of hydrogen in all forms. In our calculation, we have used two different size distributions based on earlier models and compared our findings with classical grains. To incorporate different granular sizes, we divided the distribution of sizes utilized into five logarithmically equally-spaced ranges, integrated over each range to find its total granular number density, and assigned that number density to an average size in that range. We then followed the chemical evolution of the surface populations of the five average-sized grains along with the gas phase chemistry; i.e., the gas phase interaction with five representative grains. We found that the effective surface area (product of number density and grain cross section) is an important parameter. In particular, the fractional abundances of surface species on grains within a given distribution scale with the effective surface areas of the grain distribution components in the absence of grain growth. We found that the grain growth with time increases the rate of depletion of molecules, such as CO, produced in the gas phase, which results in lower gas-phase abundances and higher surface abundances. We compared our model results with observed abundances in TMC1 and L134N. Use of a size distribution for grains in gas-grain models does not improve the agreement of calculated and observed abundances, in the gas or on grains, as compared with models containing ''classical'' grains of a fixed radius of 0.1 μm in these two clouds. This result helps to verify the quality of the classical grain approximation for cold cloud models. Further, it provides an important basis for future considerations that may require size distributions.

Affiliated with

Also associated with

No associations

Rating

The Effects of Grain Size and Grain Growth on the Chemical Evolution of Cold Dense Clouds does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The Effects of Grain Size and Grain Growth on the Chemical Evolution of Cold Dense Clouds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Effects of Grain Size and Grain Growth on the Chemical Evolution of Cold Dense Clouds will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-929078