Venue: GO Jones UG1
The evolution of dust and gas is studied from the diffuse to denser regions in the interstellar medium and in protostellar envelopes and disks. With a new two-component dust model we are able to explain the observations of dust in the interstellar medium. From diffuse to dense regions changes in the dust spectral energy distribution (SED) arise which are assumed to occur due to changes in dust particle properties. With coagulating big grains and very small grains into aggregates we are able to explain the observed changes in the SED: the decrease in temperature, the increase in emissivity and the decrease in the spectral index. Recent observations with Herschel in the far-infrared allow us to study the inside of photodissociation regions (PDRs) which are at the interface of HII regions and molecular clouds and which show strong dust and gas line emission at the long wavelengths. We analyse the CO line and dust emission in order to determine the physical properties of different PDRs. We find strong spatial correlations between dust and CO and both independent tracers give the same physical properties, so that we conclude that both tracers come from the same region. Comparing the results of the different PDRs, we find a strong correlation of the CO (and dust) temperatures with the incident radiation field. We are also able to analyse CO line emission in condensations correlated with protostellar disks and envelopes and analysing Herschel data we obtain the physical properties in these star forming regions.