General Description of Research Projects (in 1997)

Surveying Variable Stars - Ed Schmidt

The observation of faint variable stars has been the main research emphasis at Behlen Observatory since the equipment was modernized and automated ten years ago. The ability to measure the brightnesses and colors of a large number of stars allows us to search out those of particular interest to astrophysicists and to make concentrated observations of selected variables. Several stars which drastically change the way they vary over times of years to decades have been discovered. So far, this has defied explanation. A number of stars which were thought to vary due to internal instability were found to be binary star systems in which the two stars are so close together that they actually touch. Some of these have been studied in detail to learn their fundamental properties. Although many stars are known which vary in brightness over periods of hours, observations from Behlen Observatory have identified a small number of such stars which show peculiar patterns of variation. It seems likely that these represent a new and rare type of star and further research is being conducted to learn their properties and how they relate to other stars.

Variables in Globular Clusters- Todd Young (Wayne State College)

Variable stars are stars whose brightness changes over time. Some stars have an erratic variability, while some vary with a very regular periodicity. Two common examples of the latter are the Cepheid and RR Lyrae variable stars. For both these types of variable stars there exists an extremely useful relationship between their intrinsic brightness and the period of their variability -- the longer the period, the brighter the star. My research consists of finding these variable stars in globular clusters. Globular clusters are clusters of up to 1,000,000 stars that are bound together by gravity. By finding these variable stars and measuring their periods, a distance to the variable stars and the cluster itself can be determined using the method described above. The shape of the brightness curve for a variable star also provides information concerning its history and how exactly it is pulsating; and when these variable stars are found in a globular cluster, they also provide information about the history and evolution of the cluster.

Multiperiodic RR Lyrae Stars - Kevin Lee

This project also focuses on the pulsating variable stars known as RR Lyrae stars. Most of these stars pulsate with only one period on the order of 0.3 to 0.8 days. These stars repeat their light curves with remarkable regularity. However, some RR Lyraes show a much longer secondary periodicity. These are known as Blazhko Effect stars and they have considerable scatter to their light curves (see FM Per for example). The cause of the Blazhko Effect is still unknown. We are working on developing a database of the characteristics of Blazhko Effect stars and regular monoperiodic RR Lyrae stars. It is hoped that a correlation between the presence of the Blazhko Effect and another parameter can be found that might shed light on its cause.

Quasars - Stephanie Snedden and Martin Gaskell

Quasars and active galaxies are the focus of extragalactic research at UNL. We are interested in the "Broad Line Region" (BLR), close by the central source that powers active galaxies and quasars, (believed to be a supermassive black hole). We use spectra from the Hubble Space Telescope and ground based telescopes to deduce the physical properties of the gas that makes up the BLR. The Space Telescope spectra are taken in the ultraviolet region of the electromagnetic spectrum while the spectra from the ground are from the visible region. Each tells about different energies within the BLR gas, which in turn yields information about how physical conditions in the gas can change. Our observatory has been used to monitor brightness changes in nearby quasars.

Eclipsing Binaries - Kam-Ching Leung and Kevin Lee

Eclipsing binary systems are pairs of stars that vary in brightness because one star actually eclipses (cuts in front of) the other star. These stars have been of great importance in astronomy since they allow the calculation of the masses and radii of the stars. The major focus of this work so far has been the star KV GEM. This star was originally classified in the General Catalogue of Variable Stars as an RR Lyrae (RRc) star. However, our V and R photometric data clearly show KV Gem to be an eclipsing binary. The Delta V light curve of KV Gem is shown here along with the V-R color data. The very low correlation coefficient (0.41) between V (the brightness) and V-R (the color) is indicative of an eclipsing binary. One would expect a much stronger correlation for an RRc (a pulsating) star.

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