Astron. Astrophys. 326, 698-708 (1997)

Period changes of AR Lacertae between 1900 and 1989

L. Jetsu ¹, I. Pagano ², D. Moss ³, M. Rodonò ^{2, 4}, A.F. Lanza ² and I. Tuominen <sup>5

1</sup> NORDITA, Blegdamsvej 17, DK-2100 Copenhagen, Denmark
² Osservatorio Astrofisico di Catania, Città Universitaria, I-95125, Catania, Italy
³ Mathematics Department, The University, Manchester M13 9PL, UK
⁴ Istituto di Astronomia, Università degli Studi, Viale A. Doria, 6, I-95125 Catania, Italy
⁵ Department of Geosciences and Astronomy, University of Oulu, P.O. Box 333, FIN-90571 Oulu, Finland

Received 6 June 1996 / Accepted 29 April 1997

Abstract

The epochs of the primary and secondary minima of AR Lac  between 1900 and 1989 are analysed with two nonparametric methods of searching for periodicity in a weighted time point series. An analytical model for transforming the  data of eclipsing binaries into the period domain is presented and is applied to AR Lac. The abrupt period changes of AR Lac  reported in several previous studies are most probably a consequence of an oversimplified interpretation of the  data, since these changes are as likely to be continuous, and even the possibility of a 36 cycle in the period cannot be definitely ruled out.

Key words: stars: AR Lacertae -- binaries: eclipsing -- methods: analytical; statistical

Send offprint requests to: L. Jetsu (jetsu@nordita.dk)

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Contents

• 1. Introduction
• 2. Observations
• 3. The ephemeris of AR Lac
• 4. The model
  • 4.1. The  variations
  • 4.2. The variations
  • 4.3. The variations
  • 4.4. Some special cases of the  variations
  • 4.5. Linear trend in
• 5. Discussion and conclusions
  • 5.1. The direct results of the modelling
  • 5.2. The physical interpretation
• Acknowledgements
• Appendix A
  • Appendix A
  • References

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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