Epsilon Aurigae : deriving a Baade-Wesselink distance

Abstract

Epsilon Aurigae is a third magnitude, long-period binary that eclipses every 27.1 years and has been continuously observed for more than 160 years. The observed spectrum is that of an apparently normal F supergiant. The duration of the eclipse and the amplitude of the derived radial velocity orbit imply the presence of a massive companion; however, this eclipsing companion is dark. In addition to the strange nature of this binary, previous distance estimates to this system have provided inaccurate results. The HIPPARCOS satellite measured a parallax of 1:53 [plus or minus] 1:29 mas, which gives a nominal distance of 0:35--4:2 pc (van Leeuwen, 2007). Without an understanding of the distance to the system, absolute parameters, such as the mass and evolutionary state, of the system cannot be determined. This thesis project focuses on a spectroscopic and photometric analysis of the F0 supergiant in this enigmatic, long period eclipsing binary. Archival U, B, V, R, I, J, and H photometric data compiled by Hopkins (2012), and radial velocity data from Stefanik et al. (2010), Chadima et al. (2010), and Eaton (2013) were used to analyze the irregular variability of the supergiant. Using a variation of the Baade-Wesselink method, commonly used for Cepheid distance determination, an estimate of the distance to this system can be derived. A more complete data set, selected for simultaneous optical and infrared photometric and radial velocity coverage, is necessary to provide accurate results with this proposed method. Suggestions for future observations and analysis are discussed.