TY - BOOK

T1 - Evolution of Deeply Embedded Protostars

T2 - Simulations Meet Observations

AU - Frimann, Søren

PY - 2016

Y1 - 2016

N2 - Recent advances in both observations and numerical simulations ofstar-forming regions have opened up the possibility of coupling thesetwo fields together. This thesis presents detailed radiative transfermodels created from large-scale simulations of star-forming molecularclouds. The radiative transfer models are used to calculate syntheticobservables, which are compared directly to a number of observationalstudies. The numerical simulations form several hundredprotostars, meaning that, for the first time, such a comparison can bedone in a truly statistical manner. The goal of this comparison is bothto benchmark the simulations by testing if observational results canbe reproduced, and to use the simulations to aid in the interpretationof the observations.The research deals with the earliest stages of star formation – theprotostellar phase – where the protostars are still embedded withinmassive dusty envelopes with size-scales of roughly 0.1 pc1. We usespectral energy distributions of the protostars in the simulation tocalculate evolutionary tracers, and find their distributions to matchthe observations well, save for some optical depth issues that can betraced back to the resolution of the simulation. We also study thedistribution of protostellar luminosities in the simulation, and findthat both median and spread matches the observed distribution well.Both of these tests are important benchmarks of the simulation sincethey show that the overall evolution of the protostars in the simulationmatches the observational results. We also study the occurrenceof circumstellar disks in the same simulation and find that they areubiquitous at all stages of the protostellar evolution.A special emphasis is put on the study of protostellar accretion,which may have important physical consequences for the evolutionof protostellar systems. The sublimation of CO-ice from dust grainsin the surrounding envelope can be used to trace accretion variabilityin protostars, because the increased heating during an accretionburst will cause the CO-ice to sublimate into the gas-phase where theexcess can be measured by telescopes. We recreate such observationsfrom a numerical simulation, and find that it is indeed possible totrace accretion variability in such a manner, thereby confirming theapproach taken by an observational study. The synthetic observationsfail to reproduce the full spread of values seen in the real observations,which can be traced back to a lack of accretion variability in thesimulation. This particular simulation does not include disk physics,and we attribute this lack of accretion variability to that effect.We also carry out an observational follow-up study, attempting tolink evidence of accretion bursts together with evidence of circumstellardisks. The study targets 20 embedded protostars in the Perseusmolecular cloud, and reveals plenty of evidence for variable accretionthrough observations of C18O (an optically thin isotopologue of CO).The study also reveals that low-luminosity protostars are more likelyto have enhanced C18O emission, which is interpreted to mean thatthe low-luminosity protostars are between accretion bursts, while thehigh-luminosity objects are those that are currently undergoing accretionbursts.

AB - Recent advances in both observations and numerical simulations ofstar-forming regions have opened up the possibility of coupling thesetwo fields together. This thesis presents detailed radiative transfermodels created from large-scale simulations of star-forming molecularclouds. The radiative transfer models are used to calculate syntheticobservables, which are compared directly to a number of observationalstudies. The numerical simulations form several hundredprotostars, meaning that, for the first time, such a comparison can bedone in a truly statistical manner. The goal of this comparison is bothto benchmark the simulations by testing if observational results canbe reproduced, and to use the simulations to aid in the interpretationof the observations.The research deals with the earliest stages of star formation – theprotostellar phase – where the protostars are still embedded withinmassive dusty envelopes with size-scales of roughly 0.1 pc1. We usespectral energy distributions of the protostars in the simulation tocalculate evolutionary tracers, and find their distributions to matchthe observations well, save for some optical depth issues that can betraced back to the resolution of the simulation. We also study thedistribution of protostellar luminosities in the simulation, and findthat both median and spread matches the observed distribution well.Both of these tests are important benchmarks of the simulation sincethey show that the overall evolution of the protostars in the simulationmatches the observational results. We also study the occurrenceof circumstellar disks in the same simulation and find that they areubiquitous at all stages of the protostellar evolution.A special emphasis is put on the study of protostellar accretion,which may have important physical consequences for the evolutionof protostellar systems. The sublimation of CO-ice from dust grainsin the surrounding envelope can be used to trace accretion variabilityin protostars, because the increased heating during an accretionburst will cause the CO-ice to sublimate into the gas-phase where theexcess can be measured by telescopes. We recreate such observationsfrom a numerical simulation, and find that it is indeed possible totrace accretion variability in such a manner, thereby confirming theapproach taken by an observational study. The synthetic observationsfail to reproduce the full spread of values seen in the real observations,which can be traced back to a lack of accretion variability in thesimulation. This particular simulation does not include disk physics,and we attribute this lack of accretion variability to that effect.We also carry out an observational follow-up study, attempting tolink evidence of accretion bursts together with evidence of circumstellardisks. The study targets 20 embedded protostars in the Perseusmolecular cloud, and reveals plenty of evidence for variable accretionthrough observations of C18O (an optically thin isotopologue of CO).The study also reveals that low-luminosity protostars are more likelyto have enhanced C18O emission, which is interpreted to mean thatthe low-luminosity protostars are between accretion bursts, while thehigh-luminosity objects are those that are currently undergoing accretionbursts.

UR - https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122252884405763

M3 - Ph.D. thesis

BT - Evolution of Deeply Embedded Protostars

PB - The Niels Bohr Institute, Faculty of Science, University of Copenhagen

ER -