Radio Studies of Planetary Nebulae: Probing Radiation-driven Molecular Chemistry

点击翻译按钮获取中文摘要

Stars generate their energy through fusion of hydrogen to helium in their cores. When a star's hydrogen supply runs out, the star expands dramatically to become a "red giant". Red giants generate elements (like carbon and oxygen) that are essential for life as we know it. The outer layers of a red giant, which are only weakly bound to the star's core by gravity, are easily driven away from the star by its intense radiation. Intense ultraviolet radiation from the star's hot core then can turn the ejected red giant gas into a giant, glowing plasma cloud that astronomers call a "planetary nebula". Some planetary nebulae also contain a rich mixture of chemicals, in molecular form, that may resemble the atmosphere of the young Earth. Each planetary nebula thereby gives us a snapshot of the process by which stars enrich the Universe in the building blocks of life. The investigator will use radio telescope observations of planetary nebulae to determine the mixture of molecular gases that are released into interstellar space. The results will advance the field of astronomy by deepening human understanding of how the essential elements of life arrived on Earth and might arrive on planets orbiting other stars. To support education and diversity in the sciences, the investigator will also develop a summer short course for middle and high school students to explain, among other things, how astronomers determine the compositions of interstellar gases, and will generate exhibits about planetary nebulae for use in planetariums around the world.The extremes of physical conditions within molecule-rich planetary nebulae make these geometrically simple objects particularly fertile ground for research. Images of these regions aid in improving astronomers' understanding of radiation-driven chemistry in (UV) photon-dominated regions (PDRs) and X-ray-dominated regions (XDRs). The investigator plans a comprehensive campaign of observations and modeling of key tracers of irradiated molecular gas for a sample comprising the nearest and best-studied molecule-rich planetary nebulae (PNe). The investigator will fully exploit the broad frequency coverage and wide-field mapping capabilities of single-dish and interferometric (sub)mm-wave radio astronomy facilities, including the Atacama Large Millimeter Array (ALMA). The investigator will make use of "off-the-shelf" modeling codes to interpret the observational results in terms of molecular gas distributions, temperatures, densities, and compositions within the target PNe. The results will have broad applicability, given that the PDRs and XDRs in the PNe, that are the focus of this study, are representative of a diverse array of astrophysical environments, from star-forming cores within molecular clouds to molecular tori surrounding active galactic nuclei.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.