Archival HST and IUE study of the dwarf novae AH Herculis and CM Delphini:: Exposed white dwarfs?

We have analyzed Hubble Space Telescope (HST) archival and IUE NEWSIPS archival SWP spectra of the dwarf novae CM Del and AH Her obtained when AAVSO light-curve data indicated the occurrence of dwarf nova quiescence. We have computed synthetic, high-gravity spectra in LTE with solar composition using TLUSTY195 and SYNSPEC42 and have carried out fits of these models to the far-UV continuum and narrow absorption line spectra. For CM Del, we find that the far-UV spectrum is dominated by a hot (T-eff = 22,000 K and log g = 8) white dwarf, but reliable information on the metal abundances is unavailable because of the quality of the data. For AH Her, we find evidence for a hot white dwarf with T-eff = 27,000 K and log g = 8, with subsolar abundance for Si. An HST spectrum (GHRS G160M) of AH Her reveals blue-asymmetric Si IV profiles. If this is due to wind outflow, we derive a single-scattering, upper limit, mass-loss rate of 10(-9) M-. yr(-1). Synthetic profile fits to 12 co-added HST medium-resolution G160M spectra of the Si IV (1393, 1402 Angstrom) resonance doublet of CM Del AZ) yield a white dwarf rotational velocity estimate of v sin i = 400(-30)(+70) km s(-1) and Si/H = 1(-0.3)(+0.5) times solar. ,The value of v sin i for CM Del is discussed in the context of angular momentum transfer and rotation rates for other cataclysmic variable, primary degenerate stars.