Abstract

Planetary nebulae (PNe) reveal the near-final stages of the evolution of intermediate-mass (1-8 solar mass) stars, immediately after such stars shed their envelopes through copious asymptotic giant branch (AGB) mass loss. PNe reveal products of intermediate-mass stellar nucleosynthesis just before they enrich the interstellar medium, and their central stars provide subjects for studying the origins of white dwarfs and interacting binary systems involving compact objects. The processes that shape planetary nebulae and determine their chemistries can be unveiled through multiwavelength observational studies of molecule-rich PNe ranging from young and rapidly evolving nebulae, such as NGC 7027, NGC 6302, and NGC 6537, to more "mature" bi-lobed nebulae, such as NGC 2899 and NGC 2818. In this dissertation, I present analysis of Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) panchromatic images of NGC 7027 revealing the spatial distributions of emission lines covering low-ionization species such as singly-ionized Fe, N, and Si, through H recombination lines, to more highly ionized O and Ne. I use these HST/WFC3 imaging results to describe the recent, rapid evolution of NGC 7027 in terms of a series of shaping events. I then present results from a program of Atacama Large Millimeter Array (ALMA) Band 6 and Band 3 molecular line mapping of a sample of nearby, bipolar/pinched-waist, molecule-rich PNe (NGC 6302, NGC 6537, Hubble 5, NGC 2440, NGC 6445, NGC 2899, and NGC 2818). The resulting velocity-resolved, high-resolution radio interferometric images of these bipolar PNe afford unparalleled opportunities to study their structures, kinematics, and molecular content. Isotopologues of CO as well as various molecular line tracers of high-energy irradiation including HCN, HNC, HCO$^+$, SO, and CS -- many of these detected in these PNe for the first time -- are mapped to reveal key details concerning the compositions and the velocity fields of the equatorial tori and (in some cases) polar regions of the sample PNe. All of our ALMA sample objects show evidence of having descending from progenitor AGB stars of $\geq4$ M$\odot$, with post-AGB ages ranging from $1000-19000$ years. Our survey reveals the morphological evolution of the molecular tori of bipolar PNe over this timescale, and expands on previously studied trends in HCN/HNC ratio and HCO$^+$ emission. Molecular diagnostic diagrams are utilized to further analyze $^{12}$C/$^{13}$C and CN hyperfine ratios to probe progenitor mass ranges and emission-line optical depths. Collectively, these ALMA survey results provide insight into the rapid structural evolution as well as the zones of UV- and X-ray-irradiated molecular gas that characterize dusty, molecule-rich, bipolar PNe.

Publication Date

1-2025

Document Type

Dissertation

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (Ph.D.)

College

College of Science

Advisor

Anthony Vodacek

Advisor/Committee Member

Joshua Faber

Advisor/Committee Member

Letizia Stanghellini

Campus

RIT – Main Campus

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