Interferometric Studies of the extreme binary, $\epsilon$ Aurigae: Pre-eclipse Observations

TL;DR

This study uses interferometry to measure the size of the F supergiant in epsilon Aurigae before its eclipse, finding no pulsations or shrinkage, and confirming its large radius at a known distance.

Contribution

First interferometric measurement of epsilon Aurigae's F star diameter prior to eclipse, clarifying its size and ruling out pulsations or shrinkage.

Findings

No Cepheid-like pulsations detected.

F star diameter measured at 2.27 mas, consistent with a large supergiant.

No evidence of 6% per decade shrinkage.

Abstract

We report new and archival K-band interferometric uniform disk diameters obtained with the Palomar Testbed Interferometer for the eclipsing binary star $\epsilon$ Aurigae, in advance of the start of its eclipse in 2009. The observations were inteded to test whether low amplitude variations in the system are connected with the F supergiant star (primary), or with the intersystem material connecting the star with the enormous dark disk (secondary) inferred to cause the eclipses. Cepheid-like radial pulsations of the F star are not detected, nor do we find evidence for proposed 6% per decade shrinkage of the F star. The measured 2.27 +/- 0.11 milli-arcsecond K band diameter is consistent with a 300 times solar radius F supergiant star at the Hipparcos distance of 625 pc. These results provide an improved context for observations during the 2009-2011 eclipse.