This book presents pioneering work on a critical observational test of the planet formation theory based on the theoretical study of the water snowline, beyond which water takes the form of ice, in the protoplanetary disks – the place where planets are formed. Since the water snowline is thought to divide the regions of rocky and gas-giant planet formation, the location of the snowline is essential for the planet formation process.
The book proposes a novel method to locate the snowlines using high-dispersion spectroscopic observations of water vapor lines, which is based on in sophisticated chemical modeling and line radiative transfer calculations. The author obtained the water vapor distribution in the disks using the chemical reaction network, which includes photoreactions and gas–grain interactions. The simulated transition lines of water vapor in the disks demonstrate that relatively weak transition lines with moderate excitation energies are the best tracers of water snowline.
Furthermore, the author observed submillimeter lines of water vapor in a disk using ALMA (Atacama Large Millimeter/submillimeter Array) to obtain the upper limit of the line fluxes with the highest sensitivity to date. These unprecedented findings are important in locating the snowlines in the disks, and the method goes a long way toward achieving a comprehensive understanding of the planet formation processes as well as of the origin of water on rocky planets, including our Earth, based on future observations using ALMA and SPICA (Space Infrared Telescope for Cosmology and Astrophysics).
Author(s): Shota Notsu
Series: Springer Theses
Publisher: Springer Singapore
Year: 2020
Language: English
Pages: 150
City: Singapore
Supervisors’ Foreword
Parts of this thesis have been published in the following journal articles.
Acknowledgements
Contents
1 Introduction
1.1 The Overview of the Protoplanetary Disks
1.2 The Definition of the H2O Snowline in the Protoplanetary Disks
1.3 The Positions of the H2O Snowline and the Roles of Water Molecules
1.4 Previous Direct Imaging Observations of Protoplanetary Disks
1.5 Previous Spectroscopic Observations of Strong Water Lines
1.6 Purposes and Structure of This Thesis
References
2 Modeling Studies I. The Case of the T Tauri Star
2.1 Methods
2.1.1 The Disk Physical Model
2.1.2 Overview of Disk Chemical Structure
2.1.3 Gas-Phase Reactions
2.1.4 Gas-Grain Interactions
2.1.5 Water Emission Line Profiles
2.2 Results
2.2.1 The Distributions of H2O Gas and Ice
2.2.2 The Overview of Ortho-H216O Lines from the T Tauri Disk
2.2.3 The Case of a Candidate Ortho-H216O Emission Line
2.2.4 The Case of a Ortho-H216O Emission Line that Probes the Hot Surface Layer
2.2.5 The Case of a Ortho-H216O Emission Line that Probes the Cold Water Resovoir
2.3 Discussions
2.3.1 Influence of Model Assumptions
2.3.2 Critical Density and the Assumption of LTE
2.3.3 Requirement for the Observations
2.4 Conclusion
References
3 Modeling Studies II. The Case of the Herbig Ae Star
3.1 Methods
3.2 Results
3.2.1 The H2O Gas and Ice Distributions
3.2.2 The Overview of Ortho-H216O Lines from a Herbig Ae Disk
3.2.3 The Case of Candidate Ortho-H216O Emission Lines
3.2.4 The Case of the Less Suited Ortho-H216O Emission Lines
3.2.5 The Candidate Ortho-H216O Line Fluxes
3.2.6 The Radial Distributions of Normalized Cumulative Line Fluxes
3.3 Discussions
3.3.1 Influence of Model Assumptions on the Line Properties
3.3.2 Critical Density and the Assumption of LTE
3.3.3 Previous Water Line Observations in Herbig Ae Disks
3.3.4 Requirement for the Observations of Candidate Ortho-H216O Lines
3.4 Conclusion
References
4 Modeling Studies III. Sub-millimeter H216O and H218O Lines
4.1 Methods
4.1.1 The Disk Physical Structures and Molecular Abundances
4.1.2 Water Emission Line Profiles from Protoplanetary Disks
4.2 Results
4.2.1 The Profiles of Sub-millimeter Water Emission Lines
4.2.2 The Local Intensity and Optical Depth Distributions
4.2.3 The Normalized Radial Cumulative Line Fluxes
4.2.4 The Properties of All Other Sub-millimeter Water Emission Lines
4.3 Discussions
4.3.1 Influence of Dust Emission on Water Line Properties
4.3.2 Influence of Different H2O Snowline Positions and Line Velocity Resolutions
4.3.3 Requirement for the Future Observations
4.4 Conclusion
References
5 ALMA Observation of the Protoplanetary Disk Around HD 163296
5.1 Observation
5.1.1 Setup of Our Observation and Data Reduction
5.1.2 Targets
5.2 Water Lines
5.2.1 Upper Limit of the Water Line Fluxes
5.2.2 Matched Filtering Analysis
5.3 Dust Continuum Image and Radial Profiles
5.4 The First Detection of 13C17O in a Protoplanetary Disk
5.5 Conclusion
References
6 Summary and Future Works
6.1 Modeling Studies I, II
6.2 Modeling Studies III
6.3 ALMA Observations
6.4 Future Works
References
Appendix Curriculum Vitae
