An Analysis of the Long-term Photometric Behavior of epsilon Aurigae

Volume 40 number 2 (2012)

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Brian K. Kloppenborg

Department of Physics and Astronomy, University of Denver, 2112 East Wesley Avenue, Denver, CO 80208; bkloppen@du.edu

Jeffrey L. Hopkins

Hopkins Phoenix Observatory, 7812 West Clayton Drive, Phoenix, AZ 85033; phxjeff@hposoft.com

Robert E. Stencel

University of Denver, Department of Physics and Astronomy, 2112 E. Wesley Avenue, Denver, CO 80208; rstencel@du.edu

Abstract

The lure of a 50% reduction in light has brought a multitude of observers and researchers to e 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 e 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 e 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.