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


Seyedyara Mohajerani
John R. Percy
Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada  (Correspondence should be addressed to Dr. Percy)

Received September 9, 2010; revised October  4, 2010; accepted October 4, 2010


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.

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