Do Eclipsing Variable Stars Show Random Cycle-to-cycle Period Fluctuations?

Volume 39 number 1 (2011)

Download this article (pdf)

Seyedyara Mohajerani

Department of Astronomy and Astrophysics, University of Toronto, Toronto ON Canada M5S 3H4; correspondence should be addressed to Dr. Percy, john.percy@utoronto.ca

John R. Percy

Department of Astronomy and Astrophysics, University of Toronto, Toronto ON Canada M5S 3H4; correspondence should be addressed to Dr. Percy, john.percy@utoronto.ca

Abstract

AAVSO observers and others have measured the times of minima of hundreds of eclipsing binaries over many decades. These times can be used to construct (O-C) diagrams that can be used to refine the periods of the stars, and to look for changes or fluctuations in the periods. We have applied the Eddington-Plakidis (1929) model to the (O-C) data on 100 stars in the AAVSO-Eclipsing Binary Program, to determine whether the (O-C) diagrams can be explained by the cumulative effect of random, cycle-to-cycle fluctuations in period. The stars can be divided into three groups: 25-35% showing (O-C) fluctuations due only to measurement errors; 40-50% showing small, random cycle-to-cycle period fluctuations (typically a few times 10^4 of a cycle), and 20-30% showing (O-C) variations which do not fit the Eddington-Plakidis model and therefore cannot be explained by the accumulation of random fluctuations. We discuss possible explanations for these three groups.