Thirty Years of Cometary Spectroscopy from McDonald Observatory

We report on the results of a spectroscopic survey of 130 comets that was conducted at McDonald observatory from 1980 through 2008. Some of the comets were observed on only one night, while others were observed repeatedly. For 20 of these comets, no molecules were detected. For the remaining 110 comets, some emission from CN, OH, NH, C$_{3}$, C$_{2}$, CH, and NH$_{2}$ molecules were observed on at least one occasion. We converted the observed molecular column densities to production rates using a Haser (1957) model. We defined a restricted data set of comets that had at least 3 nights of observations. The restricted data set consists of 59 comets. We used ratios of production rates to study the trends in the data. We find two classes of comets: typical and carbon-chain depleted comets. Using a very strict definition of depleted comets, requiring C$_{2}$ \underline{and} C$_{3}$ to both be depleted, we find 9% of our restricted data set comets to be depleted. Using a more relaxed definition that requires only C$_{2}$ to be below a threshold (similar to other researchers), we find 25% of the comets are depleted. Two-thirds of the depleted comets are Jupiter Family comets, while one-third are Long Period comets. 37% of the Jupiter Family comets are depleted, while 18.5% of the Long Period comets are depleted. We compare our results with other studies and find good agreement.Comment: Accepted for Icarus; 15 figures, 9 tables (some multi-page and in landscape mode

On the Influence of Conduction Electrons on the Ferroelectric Curie Temperature

The frequency dependence of the transverse optical mode in the long-wavelength limit on the density of conduction electrons is calculated. This dependence is a consequence of the dielectric properties of the free electron gas which gives a change of the effective ion-ion interaction. By putting the limiting frequency equal to zero one finds an equation for the ferroelectric Curie temperature

The Return of \u3ci\u3eHexagenia\u3c/i\u3e (Ephemeroptera: Ephemeridae) to the Lower Fox River, Wisconsin

Burrowing mayflies (Hexagenia bilineata) were collected in 1991 in the vicinity of the DePere dam on the Fox River, Brown County, Wisconsin. Because Hexagenia mayflies are indicators of good water quality, their emergence from the Fox River is evidence of improvement in conditions at the sediment-water interface