Søren Frimann – Niels Bohr Institute - University of Copenhagen

Niels Bohr Institute > Research > PhD theses > 2016 > Søren Frimann


Søren FrimannSøren Frimann

A thesis submitted February 2015 for the degree of Doctor of Philosophy and defended March 21, 2016.

The PhD School of Science
Faculty of Science,
Centre for Star and Planet Formation,
Niels Bohr Institute, University of Copenhagen

  Jes Kristian Jørgensen


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Recent advances in both observations and numerical simulations of star-forming regions have opened up the possibility of coupling these two fields together. This thesis presents detailed radiative transfer models created from large-scale simulations of star-forming molecular clouds. The radiative transfer models are used to calculate synthetic observables, which are compared directly to a number of observational studies.

The research deals with the earliest stages of star formation – the protostellar phase – where the protostars are still embedded within massive dusty envelopes with size-scales of roughly 0.1 pc. We use spectral energy distributions of the protostars in the simulation to calculate evolutionary tracers, and find their distributions to match the observations well, save for some optical depth issues that can be traced back to the resolution of the simulation. We also study the distribution of protostellar luminosities in the simulation, and find that both median and spread matches the observed distribution well. Both of these tests are important benchmarks of the simulation since they show that the overall evolution of the protostars in the simulation matches the observational results. We also study the occurrence of circumstellar disks in the same simulation and find that they are ubiquitous at all stages of the protostellar evolution, as well as evidence of variable accretion.

A special emphasis is put on the study of protostellar accretion, which may have important physical consequences for the evolution of protostellar systems. The sublimation of CO-ice from dust grains in the surrounding envelope can be used to trace accretion variability in protostars, because the increased heating during an accretion burst will cause the CO-ice to sublimate into the gas-phase where the excess can be measured by telescopes. We recreate such observations from a numerical simulation, and find that it is indeed possible to trace accretion variability in such a manner, thereby confirming the approach taken by an observational study. The synthetic observations fail to reproduce the full spread of values seen in the real observations, which can be traced back to a lack of accretion variability in the simulation. This particular simulation does not include disk physics, and we attribute this lack of accretion variability to that effect.

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