When stars reach the end of their life cycle, their outer atmospheres begin to detach, and eventually most of the original stellar mass is lost. This material flows away from the star and cools, creating a so-called �circumstellar envelope.� Astronomical observations have shown that these envelopes foster a very rich chemistry, with the detection thus far of over 75 different chemical species. The majority of these compounds have been discovered in the gas phase using the high spectral resolution offered by radio and millimeter telescopes. One of the most striking aspects of circumstellar chemistry is the presence of unusual metal and phosphorus-bearing molecules, many of which are free radicals. The most recent discoveries include rare metal cyanide species such as KCN and FeCN, as well as metal oxide and hydroxides. Molecules found that contain phosphorus include CCP, CP, PO, and HCP. Given the large number of unidentified spectral lines that are observed in circumstellar environments, there are likely to be more such molecules awaiting discovery. However, new identifications require laboratory spectroscopy measurements, which provide the necessary rotational transition frequencies for interstellar observations. Such work is challenging, because the metal and phosphorus-bearing molecules of interest are highly reactive and require exotic production methods in the laboratory. Also, high spectral precision is needed, necessitating the use of microwave and millimeter techniques. In this talk, an overview of the current knowledge and newest results pertaining to metal and phosphorus chemistry in circumstellar gas will be given. Related laboratory studies will be discussed, as well. Future directions for astronomical and spectroscopic work in this area will also be presented. Finally, the ultimate fate of circumstellar molecules as dying stars reach their final phase as planetary nebulae will be reviewed.

Exotic chemistry in circumstellar environments: Laboratory and astronomical studies

247th National Meeting (2014)

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