Adding Fuel to the Fire: Investigating Star and Planet Formation through Observations of Episodically Accreting Protostars and Gapped Protoplanetary Disks
Date
2022-09-23
Authors
Francis, Logan
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Abstract
The advent of the Atacama Large Millimeter/sub-millimeter Array (ALMA) has provided a revolutionary
depth and clarity to our view of forming stars and planets. With these improved capabilities,
observations can provide novel evidence to shed light on a variety of fundamental open questions
which I consider in this dissertation. The assembly of mass to form stars occurs mostly through the
accretion of material from a circumstellar disk, a process which is likely extremely time variable.
Our knowledge of variable accretion in the youngest protostars is poorly constrained, however, as
they are not visible at optical and shorter wavelengths. I have thus analyzed observations of
variable protostars monitored with sub-mm/mm interferometers, which can measure the thermal
response of the dust to accretion changes and probe the structure of the protostellar environment.
%add one more sentence saying something about toy models?
The quality of data required by these observational programs is only possible with the improved
relative flux calibration strategies I have developed, which provide
an unprecedented level of calibration accuracy. In later stages of a young stellar object's
evolution, planets are expected to form from the condensation of material in the disk. The
transition disk class of objects contain prominent gaps in their dust distribution, which may be the
signpost of forming planets or disk dispersal. Using the exquisite resolution possible with ALMA, I
have performed the first systematic study of inner disks within transition disk gaps, providing new
constraints
for theories of planet formation, planet-disk interaction, and dust evolution. The enigmatic
transition disk of the DM Tau T Tauri star is highly turbulent and accreting at an unusually high
rate, which is difficult to reconcile with past observations of transition disks that have shown
their gaps to be highly depleted of gas. Using ALMA observations of gas-tracing molecules and
thermochemical modelling, I have identified a particularly shallow gas gap in DM Tau and evaluated
planet-disk interaction and photoevaporative dispersal models as origins of the dust gap.
Description
Keywords
star formation, planet formation, submm/mm astronomy, radio interferometry, accretion, transition disks