The phase 0.5 absorption in V1315 Aquilae, SW Sextantis, and DW Ursae Majoris

Abstract

Medium-resolution (1.5-2.5-A) spectra of three eclipsing novalike cataclysmic variables (V1315 Aql, SW Sex, and DW UMa) have been obtained on several nights throughout the 0.4-0.7 phase interval. These spectra are used to study the time scale and velocity of the absorption feature which appears near phase 0.5 in these three systems. The results show that the absorption feature appears at slightly changing times from night to night within the phase interval of 0.39-0.42, and disappears in the interval 0.57-0.67. The time scale for the feature to emerge and disappear is within 0.025 phase. All the absorption velocities are displaced to the red with respect to the emission wings, while the best data (for DW UMa) show a systematic excursion of the absorption velocities with respect to the emission. While the general results are consistent with absorbing gas associated with the outer disk, at least two components are necessary to explain the velocity behavior of the lines in DW UMa.