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Session 76 - Exploding Stars.
Display session, Thursday, June 13
Great Hall,

[76.03] Hopkins Ultraviolet Telescope Observations of the Phase Dependent Variability in AM Herculis

B. W. Greeley, W. P. Blair (JHU), K. S. Long (STScI), J. C. Raymond (CfA), C. W. Mauche (LLNL)

AM Her is the prototypical ``polar'', a strongly magnetic white dwarf accreting matter from a red dwarf. We obtained phase resolved spectra of AM Her in the spectral region from the Lyman Limit to 1860 Å\ with a resolution of about 3 Å\ using the Hopkins Ultraviolet Telescope during the Astro-2 space shuttle mission in 1995 March. Three observations were made over 5 days, covering phases \phi = 0.97-0.26, 0.53-0.78, and 0.68-0.86 of the 186 minute orbital period. The data were accumulated in 2 second intervals and have good signal to noise when binned to one minute time resolution. The continuum increases by a factor of two from the \phi=0.97-0.26 observation to the \phi=0.68-0.86 observation, while the line fluxes decrease by about 30%. The spectrum consists of a blue continuum and strong lines of C III \lambda977,\lambda1176, O VI \lambda\lambda1032,1038, N V \lambda1240, Si IV \lambda\lambda1394,1402, C IV \lambda1549, and He II \lambda1640. The Si IV \lambda\lambda1394,1402 doublet ratio varies from 1.3 to 1.1 indicative of variable optical depth in these lines with orbital phase. The profiles of the lines also vary with phase, reflecting the motion of material through the accretion column. Fluctuations in the count rate on the order of 30% occured on timescales as short as a minute, implying very short timescale dynamic activity.

This work was supported by NASA contract NAS 5-27000 to the Johns Hopkins University.

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