Alex G. Smith

The longer optical time scales of a large sample of quasars

Of a carefully studied sample of 60 quasars, 75% displayed evidence of long-term changes in the base levels of their optical fluxes. Internally consistent light curves were analyzed by three different methods in an effort to assign time scales to these changes. The familiar rapid, large-amplitude flares were specifically excluded from the study. The majority of the observed time scales range from 3 to 15 yr, but when they are translated into the rest frames of the objects, there is a strong concentration between 2 and 6 yr.

TIMESCALES OF LONG-TERM OPTICAL BASE-LEVEL FLUCTUATIONS IN THREE CLASSES OF AGN

The long-term optical light curves of many active galactic nuclei (AGN) disply smooth, cyclical changes in level on timescales of years. Earlier work by Smith et al. (1993) estimated the timescales of this previously undiscussed phenomenon for a sample of 60 classical radio-loud quasars. The present study extends the analysis to three additional groups of AGN: the BL Lacertids, the compact galaxies, and the radio-quiet quasars. The average timescale of the BL Lacertids is approximately equal to that of the classical quasars, lending credence to unified models of these objects. The long-term fluctuations of the compact galaxies and the radio-quiet quasars are slower. Our analysis tends to support the division of the BL Lacertids into two populations.

Correlated radio and optical variations in a sample of AGN

Radio light curves of 20 sources from the Metsahovi monitoring program are compared with optical light curves collected from the literature. The Discrete Correlation Function analysis is applied to the data sets. A new qualitative method to study correlations is introduced, where the radio light curves are replaced by model light curves consisting of exponential outbursts. The optical flux level is compared to the phase and flux level of the model flares. Seven sources show clear correlations using the DCF analysis with six more showing a possible correlation between optical and radio events with time lags from zero to several hundred days. For twelve sources at least one simultaneous optical and radio event is seen. For eleven sources, when comparing optical flux levels with the phase of the model radio outbursts, the optical flux levels were high at the peak of the model radio outbursts. For sixteen sources, when comparing the optical flux level with the radio model flare flux level, the optical flux level was high when radio flux level was high, as well.

Optical behavior of 20 violently variable extragalactic radio sources

A 7-yr photometric study of nearly 200 extragalactic radio sources has confirmed 20 of these objects as violent optical variables. Light curves and photometric data are given for these 20 sources, which are placed in one of four categories according to the type of variablitity displayed. (AIP)

SPECTRAL DISTRIBUTION OF THE DECAMETRIC RADIATION FROM JUPITER IN 1961

Abstract : Observations of the sporadic radiation from Jupiter were made in 1961 at observatories in Florida, in Australia, and in Chile, at various frequencies from 5 Mc/s to 85.5 Mc/s. A method was developed for computing the mean flux density for the apparition from measurements of peak flux density in consecutive 10-min intervals. Occurrence probability, peak flux density, and mean flux density for the apparition were determined as functions of frequency, and all three quantities were found to decrease monotonically with increase in frequency above 10 Mc/s. The decrease in mean flux density with increasing frequency indicated a spectral index in excess of 5.2 over much of the observed spectrum. Peak flux densities at 5 Mc/s and 10 Mc/s were about 10 to the minus 19th power W/sq m (c/s). No activity was detected at 85.5 Mc/s. The ratio of mean flux density to peak flux density for 1-min intervals during noise storms was found to be essentially independent of frequency, suggesting that there is no appreciable change of noise-burst shape with frequency. The mean power emitted at decameter wavelengths by Jupiter in 1961 was estimated to be about 5 X 10 to the 10th power watts, which is 1 or 2 orders of magnitude greater than that emitted at decimeter wavelengths. The average efficiency with which the solar-wind power incident on the Jovian magnetosphere is converted into decametric radiation power was estimated to be about 0.00001. (Author)

Search for correlated radio and optical events in long-term studies of extragalactic sources

For the first time, long-term records of radio and optical fluxes of a large sample of variable extragalactic sources have been assembled and compared, with linear cross-correlation analysis being used to reinforce the visual comparisons. Only in the case of the BL Lac object OJ 287 is the correlation between radio and optical records strong. In the majority of cases there is no evidence of significant correlation, although nine sources show limited or weak evidence of correlation. The results do not support naive extrapolation of the expanding source model. The general absence of strong correlation between the radio and optical regions has important implications for the energetics of events occurring in such sources. (AIP)

Jupiter's Decametric Emission Correlated with the Longitudes of the First Three Galilean Satellites.

An analysis of data obtained at a variety of frequencies since 1957 has confirmed Biggs observation that the satellite Io appears to control the emission of decametric radio energy by Jupiter. The correlation is stronger when intensity, rather than simple probability, is included in the analysis. There is also evidence of a similar influence by the satellites Europa and Ganymede.

Decametric radio pulses from Jupiter - Characteristics.

On occasion the decametric radio bursts from Jupiter contain pulses of millisecond duration. Study of data for 2 years shows that the distribution in Jovian longitude of these fast pulses is different from that of the more common pulses of longer duration. The two classes of pulses also appear to be differently affected by the position of the innermost Galilean satellite.

Extraterrestrial Noise as a Factor in Space Communications

Present-day refinements in communication systems make it appear that extraterrestrial noise sources may establish a fundamental limitation on long-range communications. The various cosmic and solar system radio sources are considered with respect to their intensities, spectral distributions, and temporal characteristics. The most severe forms of interference occur in the long-wavelength regions of the radio-frequency spectrum, so that the future of space communications probably lies in the perfecting of low-noise microwave systems.

Astronomical hypersensitization techniques applied to photomicrography: Kodak Technical Pan Film 2415

Kodak Technical Pan Film 2415 is a valuable recording medium because of its unusually fine grain and high resolution. Hypersensitization techniques developed by astronomers can increase its normally low speed several‐fold in the range of exposures commonly employed in microscopy. The speed gains are even larger for very long exposures such as those encountered in fluorescence work. Troublesome effects from reciprocity failure are virtually eliminated. When active development is added to hypersensitization, well‐exposed negatives can be obtained at ISO indexes as high as 1600. As in astronomy, the same general techniques can be applied to a wide variety of emulsions.