An Analysis of the Long-term Photometric Behavior of epsilon Aurigae
Brian K. Kloppenborg
Department of Physics and Astronomy, University of Denver, 2112 East Wesley Avenue, Denver, CO 80208
Jeffrey L. Hopkins
Hopkins Phoenix Observatory, 7812 West Clayton Drive, Phoenix, AZ 85033
Robert E. Stencel
University of Denver, Department of Physics and Astronomy, 2112 E. Wesley Avenue, Denver, CO 80208
Received June 1, 2012; revised October 4, 2012; accepted October 4, 2012
Abstract
The lure of a 50% reduction in light has brought a multitude of observers and researchers to epsilon Aur every twenty-seven years, but few have paid attention to the system outside of eclipse. As early as the late 1800s, it was clear that the system undergoes some form of quasi-periodic variation outside of totality, but few considered this effect in their research until the mid-1950s. In this work we focus exclusively on the out-of-eclipse (OOE) variations seen in this system. We have digitized twenty-seven sources of historic photometry from eighty-one different observers. Two of these sources provide twenty-seven years of inter-eclipse UBV photometry which we have analyzed using modern period finding techniques. We have discovered the F-star variations are multi-periodic with at least two periods that evolve in time at DP ≈ –1.5 day/year. These periods are detected when they manifest as near-sinusoidal variations at 3,200-day intervals. We discuss our work in an evolutionary context by comparing the behavior found in epsilon Aur with bona-fide supergiant and post-AGB stars of similar spectral type. Based upon our qualitative comparison, we find the photometric behavior of the F-star in the epsilon Aur system is more indicative of supergiant behavior. Therefore the star is more likely to be a “traditional supergiant’’ than a post-AGB object. We encourage continued photometric monitoring of this system to test our predictions.