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

TL;DR

This study analyzes over a century of photometric data of epsilon Aurigae outside of eclipse, revealing multiperiodic variations and suggesting the F-star behaves more like a supergiant than a post-AGB star.

Contribution

It provides a comprehensive analysis of historic photometry outside eclipse, identifying evolving multiperiodic variations and offering new insights into the star's evolutionary status.

Findings

F-star variations are multiperiodic with at least two evolving periods.

Detected near-sinusoidal variations at approximately 3,200-day intervals.

Photometric behavior suggests the F-star is more like a supergiant.

Abstract

The lure of a 50 percent 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 multiperiodic with at least two periods that evolve in time at delta(Period) approximately -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.