Tod F. Ramseyer

The McDonald Observatory faint comet survey: gas production in 17 comets

Abstract We present spectral data from 152 observations of 17 comets obtained with an Intensified Dissector Scanner spectrograph at McDonald Observatory. We present the details of the observations and reduction of these data to production rates. These production rates are then analyzed to show that comets seem to be reasonably homogeneous as a group. The ratios of production rates remain constant with activity level and with heliocentric distance, with the exception of Q(NH2)/Q(CN), which shows a heliocentric distance dependence.

The Crab pulsar in the visible and ultraviolet with 20 microsecond effective time resolution

Observations of PSR 0531+21 with the High Speed Photometer on the HST in the visible in October 1991 and in the UV in January 1992 are presented. The time resolution of the instrument was 10.74 microsec; the effective time resolution of the light curves folded modulo the pulsar period was 21.5 microsec. The main pulse arrival time is the same in the UV as in the visible and radio to within the accuracy of the establishment of the spacecraft clock, +/- 1.05 ms. The peak of the main pulse is resolved in time. Corrected for reddening, the intensity spectral index of the Crab pulsar from 1680 to 7400 A is 0.11 +/- 0.13. The pulsed flux has an intensity less than 0.9 percent of the peak flux just before the onset of the main pulse. The variations in intensity of individual main and secondary pulses are uncorrelated, even within the same rotational period.

Near-infrared spectra of cataclysmic variables

We present results from the first systematic survey of the near-infrared (1-2.5 μm) spectra of cataclysmic variables. Emission lines of H I and He I are present in most objects. He II emission is observed in V Sge. Lines from high-ionization species may be present in TT Ari and SS Cyg. Absorption features typical of late-type stars are detected in some systems. Spectra of SS Cyg over several years show possible variability of the absorption line strengths. On some occasions the absorption lines in SS Cyg may be stronger than those expected from a K5 V star

Discovery of a second narrow absorption feature in the near-infrared spectrum of Io

Abstract Extension of our high resolution survey of the near-infrared reflectance spectrum of Io to shorter wavelengths has revealed a second relatively sharp absorption feature that, in strength, width, and constancy, appears similar to the one discovered in 1990. The new feature is centered at vacuum wavelength 1.9820 ± 0.0005 μm (5045 ± 1 cm−1) and has an equivalent width of about 0.5 cm−1 (5% deep in our spectra). This new feature is not present in the laboratory spectra of dilute CO2 in a matrix, and therefore CO clusters, which have been proposed as an identification for the carrier of the original narrow absorption feature at 2.125 μm, do not appear to be responsible for the second feature. The spectrum of cold H2S ice crystals shows considerable structure near this wavelength. The difference in width between this feature and that of the much broader Ionian H2S ice features at longer wavelengths may be the result of different phases of ice, at different temperatures, that are emphasized in the different spectral regions. Alternatively, the trapping of H2S in an SO2 matrix may account for the small discrepancy in observed wavelength. Possible tests for the H2S identification of the carrier are discussed.

Photometry of Gliese 372

Photometry of Gliese 372 was obtained during the 1996–1997 and 1997–1998 observing seasons. Our 3 σ limit on the presence of night-to-night variations, such as those due to eclipses or starspots, is ±0.024 mag. Over a single night, our limit on the presence of flares, eclipses, or other photometric variations is typically ±0.02. If the system is eclipsing, there was a 40% chance that we would have detected the eclipse based on the quoted uncertainties of the ephemeris. The observed lack of flares or photometric variations due to starspots suggests a low level of stellar activity.