Ultraviolet spectral behavior of IP Peg and DW UMa in high, intermediate and low states from the HST and IUE satellites

• We confirmed the existence of line flux variations for IP Peg & DW UMa in the UV.
• The variations of line fluxes are attributed to the variations of both density and temperature.
• The line fluxes of IP Peg are greater than the line fluxes of DW UMa.
• These variations can be explained by a white dwarf model atmospheres.
• Conversion to absorption lines in an unusual low state occurs for DW UMa.

Ultraviolet spectra of IP Peg and DW UMa observed with Hubble Space Telescope Space Telescope Imaging Spectrograph & Faint Object Spectrograph (HST STIS FOS) and International Ultraviolet Explorer (IUE) satellites were analyzed during the period between 1989–1994 and 1985–2004. Different profiles of two systems showing variations of line fluxes at different orbital phases are presented. Both IP Peg and DW UMa are characterized by emission lines in high, intermediate and low states. DW UMa is characterized by absorption lines in an unusual low state. This paper focuses on the C IV emission line at 1550 Å produced in an accretion disk for two systems (Saito et al., 2005 and Knigge et al., 2000), by calculating spectral line fluxes. Our results show that there are significant variations of line fluxes with time for two systems. The variations of line fluxes are attributed to the variations of both density and temperature as a result of a changing rate of mass transfer from the secondary star to the white dwarf (Saito et al., 2005 and Knigge et al., 2000). These results from the IUE and HST observations support a white dwarf model atmospheres of IP Peg and DW UMa producing sufficient UV flux for orbital modulations.