Amplitude variations in the sdBV star PG 1605+072: Another beating time scale?^*

¹ Centro Multidisciplinar de Astrofísica, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal e-mail: tiago.pereira@ist.utl.pt
² Department of Physics, Denys Wilkinson Building, Keble Road, Oxford University, OX1 3RH, UK e-mail: lopes@astro.ox.ac.uk

Received: 3 March 2004
Accepted: 3 May 2004

Abstract

PG 1605+072 has an unique and complex oscillation spectrum amongst the pulsating members of the EC 14026 stars. It has the longest periods and the richest, most puzzling frequency spectrum. We present a quantitative analysis of the photometric time-series obtained at 1-m telescope of the South African Astronomical Observatory. Thirteen oscillation parameters, frequencies, amplitudes and initial phases were determined from a 45 h time-series. Our work confirm previous observational results. The observed frequencies are within a difference smaller than 2.7% of the theoretical values, and less than 0.1% of other previous studies. We also infer the existence of variation of a periodicity of 4–5 days on the amplitude of the observed modes, similar to the yearly time-scale variation found by previous studies. Furthermore, we found a new frequency of 2133 which has not been previously reported, its origin being yet unclear.