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Contact Eclipsing Binary Observations

Located in dark skies near Santa Margarita Lake, just east of San Luis Obispo on the Central California Coast (midway between Los Angeles and San Francisco), the Orion Observatory conducts astronomical observations all night long (primarily automatically), every clear night, of contact eclipsing binary stars. These stars, which revolve around each other in just six to eight hours, take turns eclipsing each other and, as a result, have a constantly varying light intensity, brightest when the two stars are side-by-side as seen from Earth, and dimmest when one star is in front of the other, thus blocking its light. A thermoelectrically-cooled CCD (charge coupled device) camera is used to record the binary’s light intensity (and that of surrounding, non-varying stars) every minute throughout the entire night, thus obtaining a record (light curve) of brightness versus time. Light curves of these contact binaries (known as W Ursa Majoris binaries) vary from one night or season to the next due to the migration of large groups of dark starspots of streams of matter flowing between the stars. A special GPS clock monitors time to a thousandth of a second.  The exact timing of the eclipses can also change (by a few seconds) over a few year’s time due to influence of large planets in orbit around the contact binary. The nightly eclipsing binary light curves are analyzed to determine various stellar and binary parameters, as well as changes in eclipse timing.

CCD Photometry Developments

Photometric measurements of variable stars are usually made differentially by comparing the brightness of the variable star of interest with a nearby non-variable star. This differential comparison allows various extraneous changes that affect both stars, such as changes in the thickness of the atmosphere (air mass), sky brightness (due to moonlight), etc., to be canceled out. The precision of photometric measurements can be improved, if more than one comparison star is utilized—an ensemble of non-variable comparison stars. While such ensemble photometry provides a modest improvement on truly clear nights, the most significant improvement occur on poorer-quality nights, such as nights with thin cirrus clouds. The purpose of this project is to determine, in practice, the degree of improvement that can be obtained on various quality nights. This project is being pursued in cooperation with the Dark Ridge Observatory.

Pulsating Cepheid Observations

Cepheid stars shine more brightly (absolute brightness) than almost any other stars. Cepheids pulsate, huffing and puffing over a period of days or even months. Their pulsation period, which is quite regular, is related to their absolute brightness, and this relationship makes Cepheids highly useful indicators of distances to other galaxies. The use of Cepheids as distance indicators is based on our physical understanding of these stars, and observations of Cepheids in our own galaxy provide the basis for this understanding. The Orion Observatory has, for the past several years, been observing the brightest Cepheids in our galaxy observable from Earth’s northern hemisphere. A set of photometric observations made every clear night for each Cepheid by a robotic telescope located at the Fairborn Observatory in Arizona. Analysis of the light curves for these stars will highlight changes in the pulsation periods as well as changes in the shapes of the light curves, adding key data that should aid our physical understanding of these vital distance indicators.

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