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

We have analyzed 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. HST archival outburst data for AH Her is examined as well. We have computed synthetic, high gravity spectra in LTE with solar composition using TLUSTY195 and SYNSPEC42 and 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, log g = 8) white dwarf with subsolar Si abundance and all other observed metal transitions at essentially their solar values. For AH Her, we find evidence for a hot white dwarf with T-eff = 27,000 K, log g = 8 and subsolar Si abundances. An HST spectrum (GHRS G160M) of AH Her reveals blue-asymmetric SiIV profiles. If 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 coadded HST medium resolution G160M spectra of the Si IV (1393Angstrom, 1402Angstrom) resonance doublet of CM Del yield a white dwarf rotational velocity estimate of v sin i = 400 +70/-30 km/s(-1), T-wd = 27, 000K +/- 1000K and Si/H = 1 +0.5/-0.3 x solar. This value of v sin i is discussed in the context of angular momentum transfer and rotation rates for other CV primary degenerate stars