Allgemeines Physikalisches Kolloquium - SS 2014
| Ort: | 48149 Münster, Wilhelm-Klemm-Straße 10, IG 1, HS 2 |
| Zeit: | Donnerstag, 22.05.2014, 16 Uhr c.t. |
| Kolloquiums-Kaffe: ab 15:45 Uhr vor dem Hörsaal |
H2 formation on cosmic dust grains (from the laboratory to observations) |
| Prof. Dr. Jean-Louis Lemaire, Observatoire de Paris, Université Cergy-Pontoise, France |
The formation of molecular hydrogen on dust grains in the interstellar medium (ISM) remains an unresolved question (suggested almost 50 years ago) despite soon 20 years of serious experimental and theoretical efforts as well as a wealth of observational results. Even if now there is no doubt about the catalytic role of dust grains in the formation process, a variety of multi-disciplinary experimental approaches have been used to examine the large number of parameters involved.
The first step to simulate this process in the laboratory is to create an analog of the dust grain. Some of the most important parameters of a dust surface are its stoichiometric composition and morphology. Carbonaceous or siliceous grains can be fabricated. Several techniques are used to create and characterize dust surfaces that mimic dust in space.
The second step covers the formation mechanisms of molecules on a dust surface. We are mainly interested in learning about the fate of the energy released (about 4.5 eV per H2) in the formation process, due to its paramount role in star formation. Important parameters include the temperatures of both the grain and the atomic gas impinging on the surface as well as the number and nature of available adsorption sites on the surface.
The third step is to establish an astronomical connection to the experimental results. In this case, near-infrared observations of H2 emission in different astronomical environments are used (in our case, we focus on the dusty rings of planetary nebulae) to verify our experimental hypothesis. The main problem here is that others excitation mechanisms often occur in parallel to the formation of H2. Clarifying the source of the infrared emission will then clarify the conditions allowing H2 formation to be observed.
An outlook on all these aspects will be presented. New perspectives will also be discussed.
| Einladender: Prof. Dr. Helmut Zacharias |
| Im Auftrag der Hochschullehrer des Fachbereichs Physik |
| Prof. Dr. N.A. Stolwijk |