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Protoplanetary Disk Demographics with ALMA.

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Title:Protoplanetary Disk Demographics with ALMA.
Authors:Ansdell, Megan C.
Contributors:Astronomy (department)
Date Issued:Aug 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:The recent successes of exoplanet surveys have resulted in thousands of planetary
systems being discovered and characterized. Yet exactly how these planets formed remains
unclear, as similar demographic surveys of the preceding protoplanetary disks were, until
recently, hindered by the limited sensitivity and resolution of (sub-)mm telescopes. The
revolutionary Atacama Large Millimeter/sub-millimeter Array (ALMA) has overcome these
observational barriers, freeing observers from the need to focus on only the brightest disks,
which likely do not represent the typical pathways to planet formation. This work leverages
the power of ALMA to conduct the rst large-scale, high-sensitivity surveys of (sub-)mm
continuum and line emission for complete samples of protoplanetary disks at distinct stages
of disk evolution. These observations are capable of placing statistical constraints on
the evolution of fundamental disk properties, thereby providing new insights into how
protoplanetary disks evolve into the observed exoplanet population. We focus on obtaining
bulk disk masses in both dust and gas, as these fundamental properties are thought to
strongly in
uence subsequent planetary architectures, yet remain poorly understood on a
population level. We utilize a well-established method of translating (sub-)mm continuum

ux into dust mass, and apply a recently developed technique for e ciently inferring gas
mass from CO isotopologue line emission. Our ALMA surveys reveal a clear decline in
disk dust mass with age, along with a potentially swifter decline in gas mass, both of which
indicate that giant planet formation is either rare or rapid|the former being more consistent
with exoplanet trends. We also nd that in OB clusters external photoevaporation driven
by the highest-mass stars enhances both dust and gas depletion much more severely than
previously thought. Our surveys illustrate the power of disk population studies in furthering
our understanding of \typical" disk evolution and ultimately the most common pathways
to planet formation.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Astronomy

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