Master's Thesis Defense by Martine Lützen
Title: Complex organic chemistry toward young stars: Methanol in Isolated Cores
Abstract: The origin of life remains one of the most fundamental questions in many scientific fields. The regions around young stars show abundant complex organic molecules, COMs, and it is interesting to investigate what role, if any, these play in the chemistry on emerging planets and thus whether they may in fact constitute precursors for the building blocks of life. Methanol (CH3OH) is one of many COMs unambiguously detected throughout the interstellar medium and is of particular interest due to its simplicity and high abundance. Furthermore, methanol is thought to be the starting point for synthesizing more complex molecules. This thesis centers on the spectral modelling of methanol across three protostellar cores: B335, L483, and BHR71-IRS1 - the latter being a part of the large ALMA survey, COMPASS. Initially, data reduction of the BHR71-IRS1 observations was performed. This led to a refined continuum selection from the standard ALMA pipeline identification as well as a deeper cleaning across the data. Subsequently, four distinct spectral models, manual and automated 0D and 1D models, were produced and applied throughout the spectra. The automated models were created using the sophisticated 3D continuum and line radiative transfer code RADMC-3D. By systematically applying these methods across the data, the advantages and limitations of each method were assessed. The manual models incorporated calculations of the integrated emission intensity, optical depths, and considerations of the beam filling. The latter proved crucial for reproducing the optically thick emission, which is notoriously challenging to constrain. Based on the findings of the analyses, a set of recommendations were provided for effectively modelling methanol and other molecular species, considering both emission characteristics and user-specific requirements. The results showed that, in general, the 0D models, whether manual or RADMC-3D, were sufficient in reproducing the emission lines. Of the two, RADMC-3D showed remarkable consistency in column densities for the optically thin emission across sources and molecules.
Supervisor: Jes Jørgensen
Censor: Liv Hornekær, Aarhus Universitet