The triple-mode pulsating variable V823 Cassiopeiae

¹ Konkoly Observatory of the Hungarian Academy of Sciences. PO Box 67, 1525 Budapest, Hungary e-mail: jurcsik@konkoly.hu
² Department of Experimental Physics and Astronomical Observatory, University of Szeged, 6720 Szeged, Dóm tér 9, Hungary
³ Universities Space Research Association/US Naval Observatory, PO Box 1149, Flagstaff, 86002-1149, Arizona, USA e-mail: aah@nofs.navy.mil
⁴ Eötvös Loránd University, Department of Astronomy, PO Box 32, 1518 Budapest, Hungary

Received: 14 February 2005
Accepted: 23 August 2005

Abstract

Using extended multicolour CCD photometry of the triple-mode radial pulsator V823 Cas we studied the properties of the coupling frequencies invoked by nonlinear processes. Our results support that a resonance connection affects the mode coupling behaviour. The P1/P0 period ratio of V823 Cas has an “out of range” value if compared with the period ratios of the known double mode pulsators, while the P2/P1 period ratio is normal. The periods and period ratios cannot be consistently interpreted without conflict with pulsation and/or evolution models. We describe this failure with the suggestion that at present, the periods of V823 Cas are in a transient, resonance affected state, thus do not reflect the true parameters of the object. The anomalous period change behaviour of the fundamental and second overtone modes supports this idea. We have also raised the possibility that a resonance may act in triple mode pulsators.