Silicates Do Nucleate in Oxygen-rich Circumstellar Outflows: New Vapor Pressure Data for SiO

Details Silicates Do Nucleate in Oxygen-rich Circumstellar Outflows: New Vapor Pressure Data for SiO Silicates Do Nucleate in Oxygen-rich Circumstellar Outflows: New Vapor Pressure Data for SiO

Oct 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...649.1178n&link_type=abstract

The Astrophysical Journal, Volume 649, Issue 2, pp. 1178-1183.

Astronomy and Astrophysics

Astronomy

11

Astrochemistry, Methods: Laboratory, Stars: Mass Loss

Scientific paper

We have measured the vapor pressure of solid SiO as a function of temperature over the range from 1325 up to 1785 K in vacuo using a modified Thermo-Cahn thermogravimetric system. Although an extrapolation of the current vapor pressure data to 2200 K is close to that predicted from the work of Schick under reducing conditions, the vapor pressures measured at successively lower temperatures diverge significantly from such predictions and are several orders of magnitude lower than predicted at 1200 K. This new vapor pressure data has been inserted into a simple model for the gas expanding from a late-stage star. Using the new vapor pressure curve makes a significant difference in the temperature and stellar radius at which SiO gas becomes supersaturated, although SiO still becomes supersaturated at temperatures that are too low to be consistent with observations. We have therefore also explored the effects of vibrational disequilibrium (as explored by Nuth & Donn) of SiO in the expanding shell on the conditions under which nucleation occurs. These calculations are much more interesting in that supersaturation now occurs at much higher kinetic temperatures. We note, however, that both vibrational disequilibrium and the new vapor pressure curve are required to induce SiO supersaturation in stellar outflows at temperatures above 1000 K.

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