Herschel Studies of Circumstellar Volatile Isotopes: Supporting Observations from the Ground and SOFIA
Abstract
The long standing question of ''What are the origin, evolution, and fate of our Universe and/or Galaxy?" has puzzled humankind for centuries. One approach to answering this question is to gain further understanding of stellar evolution, since stars are fundamental in galaxy development and evolution. A compilation of stellar composition can reveal the age, dynamics, and possibly the evolution of a galaxy. Stars are the factories of heavy elements, including carbon, nitrogen, and oxygen, that are fundamental in chemical complexity associated with planetary systems. Primitive materials have revealed a component of “atypical” isotopic signatures of these fundamental elements denoting a possible stellar origin. Understanding the processes by which these elements derive are essential for astrophysics on cosmochemical, galactic, stellar, and planetary scales. We propose to perform a comprehensive program of radioastronomical and infrared observations in circumstellar envelopes to definitively measure C, N, and O isotope ratios and test current models of photo-selective isotope fractionation vs. nucleosynthetically determined values. These data augment current programs underway with the Herschel Space Observatory. The broad implications for this study include fundamental values necessary for furthering our current understanding of stellar nucleosynthesis, circumstellar chemistry, Galactic chemical evolution, and the origin of presolar grains found in primitive materials. We will focus on isotopologues of species formed in thermochemical equilibrium and trace the natal, nucleosynthetic isotope ratio. We will survey a sample of evolved stars with varying degrees of nuclear processing, evolutionary states, and envelope chemistry (e.g. oxygen-rich vs. carbon-rich). The isotope ratios of 12C/13C, 14N/15N, 16O/17O, and 16O/18O will be obtained and compared to previous studies conducted on species now considered to be affected by chemical effects in the circumstellar shell as well as results we will obtain from Herschel. These observations will provide constraints on the true internal processes that are occurring in evolved stars as well as photo-selective chemistry affecting molecular abundances in the envelopes. The observational program proposed here will provide a self-consistent study of the natal isotopic composition of circumstellar envelopes and test recent theories of circumstellar chemistry. This fundamental information on the isotopic composition of material ejected from evolved stars will help improve current models of Galactic chemical evolution and help constrain star formation rates and stellar ages. Isotopically enriched matter found in some primitive materials have been associated with dust derived from these objects, though there is a lack of data currently available to fully constrain the origins. This work will allow a detailed comparison of laboratory analyses of extraterrestrial materials with a comprehensive astronomical dataset, and strongly constrain theoretical astrochemistry models of circumstellar chemistry. Realization of the project goals will greatly enhance the scientific return from the Herschel Space Observatory and SOFIA, and provide powerful context and motivation for astronomical observations to be made by future missions such as JWST.
- Publication:
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NASA APRA Proposal
- Pub Date:
- 2011
- Bibcode:
- 2011apra.prop..107M