NSF Award
2307305
Mass loss from circumstellar envelopes in the late stages of stellar evolution is a major avenue by which the interstellar medium (ISM) becomes enriched in gas, dust, and heavy elements. This research project will investigate the gas phase molecular content of stellar ejecta, from asymptotic giant branch (AGB) stars to protoplanetary nebule (PPNe) and planetary nebulae (PNe). The investigators will extend their ongoing program of radio astronomical observations and laboratory measurements to characterize the molecular inventory and physical properties of these objects. Results from the project will allow astronomers to understand the nature of stellar ejecta and their influence on the diffuse ISM. The project will train graduate and undergraduate students in advanced techniques of radio astronomy and laboratory astrophysics.<br/><br/>This research program seeks to elucidate how molecular material evolves from the AGB phase, through the intermediate PPNe phase, to the advanced PNe phase. To accomplish this, the investigators will undertake: (1) a better assessment of the carbon budget and isotope ratios through an extensive analysis of a highly sensitive broadband millimeter-wave survey of the carbon-rich envelope of the AGB star IRC+10216; (2) laboratory measurements of the rotational spectra of new metal-bearing carbides in the radio band to aid their identification in circumstellar envelopes; (3) an analysis of high spatial resolution images of the oxygen-rich envelope of VY Canis Majoris in a variety of molecules to understand the influence of the C/O ratio; and (4) evaluation of the molecular and isotopic composition of a diverse sample of carbon-rich and oxygen-rich PPNe and PNe by radio astronomical observations. A better understanding of the nature of the stellar ejecta, particularly PNe, would also advance our understanding of how they enrich the diffuse ISM.<br/><br/>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.
