Rosseland and Planck Mean Opacities for Protoplanetary Discs

In this paper, we present mean gas and dust opacities relevant to the physical conditions typical of protoplanetary discs. As the principal absorber for temperatures below ~1,500 K, we consider spherical and aggregate dust particles of various sizes, chemical structure, and porosity, consisting of ice, organics, troilite, silicates, and iron. For higher temperatures, ions, atoms, molecules, and electrons are included as the main opacity sources. Rosseland and Planck mean opacities are calculated for temperatures between 5 K and 10,000 K and gas densities ranging from 10^{-18} g/ccm to 10^{-7} g/ccm. The dependence on the adopted model of dust grains is investigated. We compare our results with recent opacity tables and show how different opacity models affect the calculated hydrodynamical structure of accretion discs.Comment: 12 pages, 4 figures, to be published in A&A, 200

Production of dust by massive stars at high redshift

The large amounts of dust detected in sub-millimeter galaxies and quasars at high redshift pose a challenge to galaxy formation models and theories of cosmic dust formation. At z > 6 only stars of relatively high mass (> 3 Msun) are sufficiently short-lived to be potential stellar sources of dust. This review is devoted to identifying and quantifying the most important stellar channels of rapid dust formation. We ascertain the dust production efficiency of stars in the mass range 3-40 Msun using both observed and theoretical dust yields of evolved massive stars and supernovae (SNe) and provide analytical expressions for the dust production efficiencies in various scenarios. We also address the strong sensitivity of the total dust productivity to the initial mass function. From simple considerations, we find that, in the early Universe, high-mass (> 3 Msun) asymptotic giant branch stars can only be dominant dust producers if SNe generate <~ 3 x 10^-3 Msun of dust whereas SNe prevail if they are more efficient. We address the challenges in inferring dust masses and star-formation rates from observations of high-redshift galaxies. We conclude that significant SN dust production at high redshift is likely required to reproduce current dust mass estimates, possibly coupled with rapid dust grain growth in the interstellar medium.Comment: 72 pages, 9 figures, 5 tables; to be published in The Astronomy and Astrophysics Revie