Mario Trieloff — Page 2

arXiv2011

Thermal conductivity measurements of porous dust aggregates: I. Technique, model and first results

We present a non-invasive technique for measuring the thermal conductivity of fragile and sensitive materials. In the context of planet formation research, the investigation of the thermal conductivity of porous dust aggregates provide important knowledge about the influence of heating processes, like internal heating by radioactive decay of short-lived nuclei, e.g. 26Al, on the evolution and growth of planetesimals. The determination of the thermal conductivity was performed by a combination of laboratory experiments and numerical simulations. An IR camera measured the temperature distribution of the sample surface heated by a well-characterized laser beam. The thermal conductivity as free parameter in the model calculations, exactly emulating the experiment, was varied until the experimental and numerical temperature distributions showed best agreement. Thus, we determined for three types of porous dust samples, consisting of spherical, micrometer-sized SiO2 particles, with volume filling factors in the range of 15% to 54%, the thermal conductivity to be 0.002 to 0.02 W/(m*K), respectively. From our results, we can conclude that the thermal conductivity mainly depends on the volume filling factor. Further investigations, which are planned for different materials and varied contact area sizes (produced by sintering), will prove the appropriate dependencies in more detail.

astro-ph.EP↗

arXiv2007

Evolution of interstellar dust and stardust in the solar neighbourhood

The abundance evolution of interstellar dust species originating from stellar sources and from condensation in molecular clouds in the local interstellar medium of the Milky Way is studied and the input of dust material to the Solar System is determined. A one-zone chemical evolution model of the Milky Way for the elemental composition of the disk combined with an evolution model for its interstellar dust component similar to that of Dwek (1998) is developed. The dust model considers dust-mass return from AGB stars as calculated from synthetic AGB models combined with models for dust condensation in stellar outflows. Supernova dust formation is included in a simple parameterized form which is gauged by observed abundances of presolar dust grains with supernova origin. For dust growth in the ISM a simple method is developed for coupling this with disk and dust evolution models. The time evolution of the abundance of the following dust species is followed in the model: silicate, carbon, silicon carbide, and iron dust from AGB stars and from SNe as well as silicate, carbon, and iron dust grown in molecular clouds. It is shown that the interstellar dust population is dominated by dust accreted in molecular clouds; most of the dust material entering the Solar System at its formation does not show isotopic abundance anomalies of the refractory elements, i.e., inconspicuous isotopic abundances do not point to a Solar System origin of dust grains. The observed abundance ratios of presolar dust grains formed in SN ejecta and in AGB star outflows requires that for the ejecta from SNe the fraction of refractory elements condensed into dust is 0.15 for carbon dust and is quite small ($\sim10^{-4}$) for other dust species.

astro-ph↗