Comets provide a unique opportunity to study the formation of the Solar System since they are among the best-preserved specimens of the material of the proto-solar nebula out of which the Solar System formed. Understanding how comets become active and generate comae is critical to developing more accurate models of nucleus composition and structure. One complication in modeling observations is that some comets exhibit different kinds of activity, depending on how far they are from the Sun. The activity of comets within 3 Astronomical Units (AU) of the Sun, for example, is well understood to be dominated by the sublimation of water ice from the nucleus. On the other hand, the activity of many comets that are active beyond 4 AU appear to be driven by CO outgassing and sometimes expel dramatic outbursts of gas and dust. A second complication is that some molecules are often released into comae by distributed sources, which can give misleading results about the relative molecular abundances and kinds of activity in comets. Another issue of concern is the amount of processing that comets experience after their formation due to different volatilities of molecules in the nucleus and the effect of anisotropic outgassing on derived production rates. The principal goal of this project, lead by Dr. Maria Womack at St Cloud State University, is to derive and analyze CO production rates in near and distant comets from mm-wavelength spectra. A large dataset of millimeter-wavelength mapping data of molecular emission in comets Hale-Bopp and Hyakutake and spectra for eight other comets is in hand and reduced, and new observations are proposed for other sufficiently bright comets. These data will be used with recently improved kinematic and excitation models in order to constrain outgassing mechanisms and excitation conditions of molecules in comae near the Sun. Lineshapes and spatial brightness profiles from the data will be used to analyze anisotropic emission and to quantify the amount of distributed sources in comae for CO, H2CO, HCN and other species. Spectral lineshapes and production rates of CO and other volatiles in comets beyond 4 AU will be modeled in order to investigate the quiescent and outbursting stages of distant cometary activity, and to measure properties of molecules sublimating from icy grains in the coma. St Cloud State University (SCSU) undergraduate students known as "Cometwatchers" will participate in this project as employed research assistants and in upper-level astrophysics courses. Funds will be used to pay students and to improve the student-run SCSU observatory in order to provide them with a collaborative learning environment in scientific research. This award is made under the Research in Undergraduate Institutions program at NSF. ***
