HUBBLE-SPACE-TELESCOPE AND R-BAND ECLIPSE MAPS OF THE UX URSAE-MAJORIS ACCRETION DISK

Hubble Space Telescope time-resolved spectroscopic and ground-based R-band photometric data of UX UMa during eclipse are presented and discussed. The spectroscopy covers the C IV lambda 1550 and He II lambda 1640 spectral regions. The eclipses in the UV continuum are deep, nearly reaching the zero level at mid-eclipse phases. Sharp ingress and egress features reveal the occultation of the white dwarf at disk center but there is no evidence of the orbital hump or of the bright spot. The steep ultraviolet eclipse light curves are used to estimate the radius of the white dwarf and to constrain the binary parameters. We find M(1) = M(2) = 0.47 M. and i = 71.degrees 0 +/- 0.degrees 6. The white dwarf contributes with similar or equal to 25% of the light at 1600 Angstrom. If the inner disk is optically thick it has a temperature of T-wd greater than or similar to 65,000 K. Velocity-resolved light curves in the C IV lambda 1550 line show evidence of rotational disturbance and a strong orbital modulation is seen in the line center light curve. Maximum-entropy eclipse mapping techniques are used to solve for a map of the disk brightness distribution and for fluxes of an additional uneclipsed component in 18 narrow UV bands and in the R band. The angular scale of the disk and the distance to UX UMa are estimated from a color-magnitude diagram by a method similar to cluster main-sequence fitting. We find D = 345 +/- 34 pc. The radial temperature profiles derived from the UV continuum maps range from 8000 K in the outer disk regions to 30,000 K in the inner disk and reasonably follow the T proportional to R(-3/4) law for steady mass accretion at a rate of M = 10(-8.0+/-0.2) M. yr(-1). The comparison of R-band eclipse maps from observations 2 months apart indicates changes in the structure of the outer disk which are probably due to small changes (less than or similar to 20%) in the mass transfer rate from the secondary star. The maps in the C IV and He II line profiles are affected by emission from the disk wind. The radial temperature profiles of both line center maps show a flat slope. It is suggested that at low velocities the eclipsed part of the line emission arises from an opaque and extended region with a rather uniform spatial intensity distribution as projected in the plane of the sky. When plotted as a sequence of spatially resolved spectra these lines appear in absorption at disk center and change to emission in the outer disk regions besides showing large uneclipsed components. This behavior is similar to that found by Rutten et al. for the Balmer lines and suggests that these optical lines may also have a wind component. We obtain a revised ephemeris for the times of minimum and an upper limit for secular period changes of \P\ < 1.3 x 10(-12) s s(-1). The mass transfer rate inferred from this limit is an order of magnitude smaller than the value derived from the eclipse mapping, suggesting that the high mass transfer rate of UX UMa is not the consequence of its secular period decrease.