AAS 201st Meeting, January, 2003
Session 120. Cataclysmic Variables
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

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[120.01] New Ultraviolet Observations of AM CVn

R.A. Wade, M. Eracleous (Penn State)

AM CVn is an ultra-short-period Helium cataclysmic variable. An interesting question is whether the accretion disk or the accreting white dwarf dominates the ultraviolet spectrum from this object. We obtained HST/STIS observations of the UV spectrum of AM CVn on 2002 Feb 21. We used the NUV MAMA with grating G230L to obtain 1925 s of time--tagged data covering 1600--3150~Å, and in the following spacecraft orbit we used the FUV MAMA with grating G140L to obtain 2400 s of time--tagged data covering 1140--1710~Å. We thus have complete orbital coverage of the binary star, but not coverage of the 13.4 h precessional period of the eccentric disk. In this contribution we will describe the mean spectrum. In addition we will discuss ``white light'' variations in the time domain, in particular, any variations at the orbital (1029 s) or superhump (1051 s) periods.

The spectrum is approximately flat in f\nu. The absorption profiles of the resonance lines of N V, Si IV, C IV, and N IV are blue-shifted, evidencing a wind that is partly occulted by the accretion disk. There is weak emission at N V, which also shows the deepest absorption. The He II 1640Å\ line is asymmetric. Numerous weaker spectral features of various widths are found, which will be the subject of modeling as an accretion disk. Sharp (interstellar) absorption lines are also seen. The light curve shows both short--term fluctuations and a long--term decline by ~15% over the span of the observations.

Supported by STScI.

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