PhD Defense by Sigurd Sigersen Jensen

Title: The evolution of water during star formation: a study of the water deuteration around young protostars

Water is a key molecule in astrochemistry: it is essential for life as we know it, it is a major constituent of the solid-mass reservoir in planet-forming disks, and it serves as a prominent gas coolant in star-forming clouds. This thesis studies the evolution of water during the earliest stages of star formation, from the molecular cloud to the embedded protostellar phase. The aim is to determine when and how the D/H ratio of water is established, and how it evolves. The D/H ratio depends sensitively on the formation environment of water. Water formed in cold and dense regions will have higher D/H ratios than water formed in less dense or warmer regions. By establishing the evolution of the D/H ratio we can determine when the water is formed and how it is subsequently processed during the formation of stars and planets.

This research presents two major conclusions: 1) the D/H ratio of water is set prior to the protostellar collapse and inherited to the embedded protostellar phase and 2) the D/H ratio of water appears to correlate with the local cloud environment. The first conclusion shows that water is primarily formed in the molecular cloud and prestellar core phases, and not through local processes in the embedded phase. The second conclusion is closely related to the first: as the water D/H ratio is inherited, the conditions in the molecular cloud and prestellar core sets the D/H ratio. These conditions, e.g., the duration and temperature, are likely different between isolated cores with no external influences, and clustered cores, where radiation and shocks from nearby stars may influence the dynamics and temperature.

These results propose a chemical differentiation among protostellar sources which is driven by the surrounding environment through inheritance, which could have profound implications for the habitability in other planetary systems.

Participate via Zoom: https://ucph-ku.zoom.us/j/67386448533?pwd=WVVjV2ZYMks2enA0WVF1S0luTmFOUT09