Three Selected Low-Amplitude Variables

Volume 22 number 2 (1993)

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Imants Platais

Department of Astronomy, Yale University, New Haven, CT

Georgi Mandushev

Department of Astronomy and Physics, St. Mary's University, Halifax, NS, Canada

Abstract

A recent publication concerning the continuing decrease in the pulsation amplitude of Polaris, and the prediction that this star will soon become nonvariable raises the question of  similar behavior in other low-amplitude Cepheids (delta V < 0.5 magnitude). In this paper we use the Fourier decomposition of light curves to obtain rigorous estimates of the pulsational amplitude. A limited sample of three s-Cepheids, SU Cas, SZ Tau, and V1726 Cyg, was chosen to demonstrate the capabilities of this technique. The pulsation amplitude shows no decisive changes as a function of time in any of the three Cepheids. Adequate follow-up photoelectric photometry of these and other low-amplitude Cepheids is clearly needed to make more definite conclusions as to their pulsational (in)stability. Another issue we briefly address here is whether other parameters derived from the Fourier decomposition, like the phase difference vs. period, do unambiguously indicate the pulsational mode. The answer is probably negative since in the case of SU Cas and V1726 Cyg the pulsational mode deduced from the Cepheids' cluster/star association membership is different from that suggested by their Fourier parameters.