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[13.01] HST Observations of the Pulsations in WZ Sagittae on the Decline from Outburst

W. F. Welsh (San Diego State University), E. M. Sion (Villanova University)

We present time series analysis of HST observations of WZ Sge during its decline from its 2001 July outburst. STIS observations were carried out at four epochs, roughly equally spaced between 2001 September and December. The temperature of the white dwarf drops dramatically during this post-outburst transition back into quiescence, from roughly 29,000 K to 15,000 K (Sion et al., Godon et al. 2003). At each epoch we detect the well-known 29 s oscillation. The presence of a quasi-stable 29 s oscillation as the white dwarf cools by over 10,000 K provides compelling evidence against the white dwarf pulsation interpretation of the oscillation. In addition, we detect a quasi-periodic oscillation (QPO) with period near 18 s in the September observations. The 28 s oscillation is not seen at any epoch, nor the 15 s oscillation that was detected early in the outburst (Knigge et al. 2002).

This work is supported by NASA through grants GO-9304 from the Space Telescope Science Institute, which is operated by the AURA, Inc., under NASA Contract NAS5-26555.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.