Master Thesis defense by Victoria Quist

Title: Spatially resolved molecular emission as a tracer of the physics and chemistry of young stars

Star formation is a complicated physical and chemical process. With the Atacama Large Millimeter/submillimeter Array (ALMA), it is possible to study chemistry on solar system scales. In addition, line rich spectra of a young stellar object help understand the chemistry during star formation because it is possible to look at complex organic molecules.

In this thesis, we analysed the binary system IRAS16293-2422 (IRAS16293), using the data from the ALMA Protostellar Interferometric Line Survey (PILS) and detailed dust and line radiative transfer simulations. Looking at different complex organic molecules, the structure of the molecule is studied. We investigated how the upper energy and the optical depth change the structure of the molecules. We also looked at the temperature profile for an optical thick envelope and how it matches the empirical temperature profile from the observed data from PILS. Furthermore, we tried to recreate the observed data with the radiative transfer simulations and looked further into the temperature profile for an envelope. Finally, a constrain on the luminosity of IRAS16293A and IRAS16293B is found from the empirical temperature profile.

For the analysis of the structure of IRAS16293B and the optical depth, it looks like they are related. However, more investigation needs to be done to make sure that there is a relationship. Furthermore, it also needs to be tested for other protostars. We found a correlation between the upper energy for a transition and the extent of the molecular emission. From this, we can say that the higher the upper energy is, the smaller is the extent of the emission from the line. This correlation represents the temperature profile for an optical thick envelope for the highest of the energies, the empirical temperature profile. We recreate the empirical temperature profile we saw in the observed data from PILS from the radiative transfer simulations. The empirical fits match well the outcome of the dust radiative transfer simulations with an inner optically thick and outer optically thin envelope. Finally, from an analysis of the change in luminosity compared with the temperature profile and the empirical temperature profile, it was possible to constrain the luminosities of the two sources in IRAS16293 to 13 L_sun and 8 L_sun. The difference in the luminosity can be due to the difference in the age, accretion rate, mass or size of the two protostars.

This MSc thesis defense will take place virtually via zoom and can be joined via the following zoom link: