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Discovery of Non-radial pulsations in PQ Andromedae.pdf

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Discovery of Non-radial pulsations in PQ Andromedae

a r X i v : a s t r o - p h / 0 5 0 6 0 9 8 v 1 5 J u n 2 0 0 5 Discovery of Non-radial pulsations in PQ Andromedae Karen M. Vanlandingham Columbia University, Department of Astronomy, New York, NY 10027 kmv14@columbia.edu Greg J. Schwarz Steward Observatory, University of Arizona, Tucson, AZ 85721 gschwarz@as.arizona.edu and Steve B. Howell WIYN Observatory and National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85726 howell@noao.edu ABSTRACT We have detected pulsations in time-series photometry of the WZ Sge dwarf nova PQ And. The strongest peak in the power spectrum occurs at a period of 10.5 minutes. Similar periods have been observed in other WZ Sge systems and are attributed to ZZ Ceti type non-radial pulsations. There is no indication in the photometry of an approximately 1.7 hour orbital period as reported in previous spectroscopic observations. Subject headings: binaries: close — stars: dwarf novae — stars:individual(PQ And) 1. Introduction PQ And is a dwarf nova with three known outbursts in the last ～ 70 years (Richter 1990). The last outburst on 21 March, 1988 reached a visual magnitude of 10 (Hurst 1988). It had many of the characteristics of the WZ Sge class of dwarf novae including a large outburst amplitude and strong Balmer emission superimposed over broad absorption at quiescence (How- ell et al. 1995). However, to be in the WZ Sge class, PQ And must have an orbital period below the period gap. Time series optical spectra of PQ And were obtained 1 by Schwarz et al. (2004) to determine the orbital period of the system. They found a period of 1.7 hours from the fit to the ra- dial velocity curve as determined from the convolution of double Gaussians to the line profiles (Schafter 1985). Unfortunately the derived period was similar in length to the total observing time and couldn’t be clas- sified as a definite period due to under- sampling. Nevertheless the Hα emission showed a clear periodic change in its blue and red co