Bowling Green State University
Subject Listing - Physics/Astronomy
Advisor: Dr. Andrew Layden
Saturday, Oral Session 7, Presentation 1, Robinson Hall 228
RR LYRAE VARIABLE STAR COLORS: A TOOL FOR MEASURING INTERSTELLAR REDDENING
RR Lyrae variable stars (RRL) are a common stellar candle for measuring large interstellar distances. Interstellar gas and dust between the target RRL and Earth absorb blue light, reddening the color and diminishing the intensity of starlight. Within about 10-20 degrees of the Galactic Plane, the amount of dust drastically increases, and varies rapidly. Near the plane, techniques are needed that measure the reddening and absorption directly from the target RRL. Conrad Sturch (1966) noticed that all RRL far from the plane have roughly the same color, measured as the difference in apparent magnitude between a blue filter and a visual/green filter (B-V). By measuring the apparent (B-V) color of an RRL near the plane and comparing it to the un-reddened or "intrinsic" color of variable stars far from the plane, Sturch was able to measure the reddening due to interstellar dust absorbing star light. Mario Mateo et al. (1995) suggested that the difference between visual and infrared filters (V-I) colors might be better suited to measuring reddening tools since they should be less affected by metal-abundance differences among stars. Our hypothesis is that the (V-I) filters will produce a more tightly constrained reddening measuring tool, as suggested by Mateo et al. The specific goal of this project is to use the images of several RRL stars, taken with the BGSU 0.5-meter telescope and CCD camera, to determine the intrinsic, unreddened (V-I) colors of typical RRL. We will correct our images for electronic and optical distortions, and measure star brightnesses using the software program IRAF. We will determine the pulsation period of each star and "fold" the brightness observations to generate a light curve showing intrinsic (V-I) color as a function of pulsation phase. We will study the stars' (V-I) colors (in comparison with the (B-V) color relationship) as a function of metal abundance and pulsation period to determine a statistical relationship that can be used as a reddening measurement tool.
Advisor: Dr. Andrew Layden, Associate Professor, Department of Physics & Astronomy, Bowling Green State University, Bowling Green, OH