Ly$\alpha$ Absorption in Quiescent Dwarf Novae

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Session 63 -- Intrinsic and Cataclysmic Variables
Display presentation, Thursday, 9:20-4:00, Heller Lounge Room

[63.11] Ly$\alpha$ Absorption in Quiescent Dwarf Novae

A. Holm, H. Lanning (CSC), J. Mattei (AAVSO), E. Nelan (U. Texas)

International Ultraviolet Explorer (IUE) observations of dwarf novae RX And, TZ Per, WZ Sge, and SS Cyg in quiescence show broad absorption at Ly$\alpha$. These features can be modeled reasonably well by the predicted spectrum of a hydrogen atmosphere white dwarf. RX And is best fit by a 35,000$\deg$K model, TZ Per by a 18,000$\deg$K model modified by an empirically determined disk contribution, and SS Cyg by a 34,000$\deg$K model. The spectrum of WZ Sge following its December 1978 outburst is fit by a series of successively cooler white dwarf atmospheres, starting at 28,000$\deg$K on 1979 Jan 1 and decreasing to 14,000$\deg$K on 1987 July 5. Other dwarf novae, including SU UMa, EX Hya, and Z Cam, did not show absorption at Ly$\alpha$ at minimum.

RX And, WZ Sge, and TZ Per also show strong absorption at 1400\AA. If the observed far ultraviolet spectrum and the temperatures derived from the Ly$\alpha$ fitting are assumed to correspond to the white dwarf component, the 1400\AA\ feature could be Si IV in RX And, but both WZ Sge and TZ Per would be too cool for Si IV. This raises questions about a photospheric origin for any of these features.

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