Astronomy and Astrophysics – Astronomy
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...204.9904s&link_type=abstract
American Astronomical Society Meeting 204, #99.04; Bulletin of the American Astronomical Society, Vol. 36, p.986
Astronomy and Astrophysics
Astronomy
Scientific paper
Grain growth mechanisms that are important with respect to evolution of a molecular clouds are coagulation and mantle formation. Coagulation occurs by low impact grain collisions and mantle formation occurs by adsorption of gas phase atoms and molecules onto the grain surface. Previous studies have linked increase in RV (ratio of total to selective extinction) to changes in the size distribution of the grains due to coagulation. Thus, one can parameterize coagulation by evaluating RV for field stars and mantle formation can be constrained by observing IR absorption features in the spectra of these objects. For our study we focus on the Taurus Molecular Cloud complex. We used 2MASS database to survey this region and select highly reddened field stars. We then obtained visual photometric data and constructed extinction curves along the line of sight to these objects. Next we obtained spectroscopic data in the 3.1 μ m H2O ice band to investigate mantle growth as a function of the optical depth in TMC. These data were used to investigate which growth mechanism is dominant in TMC. We also used UV extinction data, which has been shown to be very diagnostic of the dust properties, to understand the grain properties along these lines of sight to three field stars in TMC.
Although we tried to select highly reddened stars for this work, our sample was limited by the problem of obtaining good visual photometric data for stars with extinctions much higher than the threshold for ice detection. We have only three stars, with visual extinction larger than 6.0, that have good extinction data. Our results confirms the model that the TMC is made up of two components, a diffuse screen in which dense clumps are embedded. We also find that both mantle formation and coagulation occur in the clumps of TMC but mantle formation seems to be the dominant process responsible for changing the optical properties of dust. Our data does show that there is a correlation between coagulation and mantle formation, but due to the limited dataset the details of this correlation are not clear at this time.
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