Exchange report by Mélisse Bonfand

SFB 956 sub-project: B3 
Supervisors: Prof. Dr. Karl Menten and Dr. Arnaud Belloche, Max-Planck Institute for radio astronomy, Bonn (Germany) 
Hosting institution: University of Virginia, Chemistry department, Charlottesville (USA) 
Supervisor at the hosting institution: Dr. Rob Garrod, Assistant professor of chemistry at the University of Virginia, Charlottesville (USA) 
Duration of stay abroad: 01/09/17 - 29/11/17

Scientific background and doctoral project:

I am studying the complex organic chemistry in star forming regions, focusing on the Sagittarius B2 (Sgr B2) molecular cloud, one of the most prominent star forming regions in our galaxy. In order to characterize the hot cores embedded in Sgr B2(N), one of Sgr B2’s main centers of activity, I am analyzing a complete spectral line survey obtained at 3 mm with the Atacama Large Millimeter/sub-millitemer Array (ALMA). This analysis revealed the presence of at least five hot cores in Sgr B2(N) with spectra full of spectral lines, allowing the identification of a large amount of chemical species, from simple diatomic molecules up to more complex molecules such as iso-propyl cyanide (i-C3H7CN). The study of the chemical processes involved in the formation of such complex organic molecules (COMs) is particularly interesting, especially because the chemical composition of the gas phase in hot cores such as those embedded in Sgr B2(N) is remarkably similar to the composition of Solar system comets. These molecules are thought to be produced in the early stage of the star formation process, but the pathways leading to their formation are still not completely understood. The degree of chemical complexity that can be reached in star forming regions is also an open issue and it is still unclear how this complex chemical material can survive through the protoplanetary phase and beyond.

Exchange experiences:

The SFB 956 student exchange program gave me the opportunity to visit the University of Virginia (UVa) in Charlottesville (USA) to work with Dr. Rob Garrod, assistant professor of chemistry. He is an expert in theoretical astrochemistry and has developed chemical models to explain the formation of COMs in star forming regions, considering these molecules are formed on the surface or within the ice mantle of dust grains. I used Rob’s chemical kinetics code, called MAGICKAL (Model for Astrophysical Gas and Ice Chemical Kinetics And Layering, Garrod 2013), to simulate the evolution of the chemistry in Sgr B2(N)’s hot cores, from the cold collapsing phase to the warm up of the envelope of the newly formed protostar. For each hot core, we used the physical properties derived from the observations to build their density and temperature profiles. Following the physical evolution of the hot cores, the code allowed me to gain insight into the different steps, from the formation of COMs on the grain surfaces to their sublimation into the gas phase, to explain their detection. At the end, the main outcome of the code contains the predictions of interstellar abundances of species that we compared directly to the observations to test the model.

At the UVa I worked in close collaboration with the members of Rod Garrod’s group. They helped me to get familiar with the code and to deal with most of the problems encountered. I gave a talk at the UVa about the complex organic chemistry in star forming regions and I also regularly attended meetings and talks at the National Radio Astronomy Observatory (NRAO) also in Charlottesville.


Life in Charlottesville:

Charlottesville is a charming city. People are nice and welcoming. The city itself is small, but it is home to a large campus where students may find a great variety of facilities (education, sport, entertainment). Charlottesville harbors many trees and green areas where one can encounter wild life on the way to work. One can also easily go for a hike in one of the beautiful natural parks close by the city.

Conclusions and acknowledgments:

I would like to thank the SFB 956 for giving me the opportunity to visit the UVa in Charlottesville. With this experience I learned a lot and met people from different fields with whom I had very interesting conversations. It was a great opportunity to present my research project and get comments and feedbacks from experts in different fields. I gained experience in chemical modelling, which was new for me and very different from my doctoral project, focused so far on the analysis of observational data. Finally, I would like to express my gratitude to Dr. Rob Garrod for inviting me to work in his group and to all his group members for providing me such a nice atmosphere for work. Especially Gwendoline Stéphan post-doc in Rob’s group and Eric Willis, grad student, with whom I worked in close collaboration for my project.