IRAS Observations of Dust Heating and Energy Balance in the FHO Ophiuchi Dark Cloud

Abstract

The total luminosity of the Rho Ophiuchi molecular cloud is derived from IRAS data and is found to match the luminosity of known embedded sources very closely. High resolution 60 and 100 micron band IRAS images have been reduced to yield equilibrium color temperature maps and 60 micron band dust optical depth maps for the region. These data along with optically thin C18O column density data are used to evaluate dust grain sizes and compositions via competing grain models. Radiative modeling shows that a standard power law distribution of graphite and silicate grains is responsible for IRAS 60 and 100 micron band emissions. These grains are heated to about one tenth of the cloud's depth in the core region. Their optical depths closely follow molecular column density structure, but these grains are considerably colder than the molecular gas. We also find that a 10 nm minimum particle radius cutoff is appropriate for the 60 and 100 micron band emissions while very small grains or PAH molecules dominate the cloud's 12 and 25 micron band emissions.