Coronal and transition region structure in the RS Canum Venaticorum binaries V711 Tauri, AR Lacertae, and II Pegasi. I. Data analysis and emission measure distributions

We present a study of the transition regions and coronae of the RS CVn binaries V711 Tau, AR Lac, and II Peg. Archival data from the Extreme Ultraviolet Explorer (EUVE), International Ultraviolet Explorer (IUE), Goddard High-Resolution Spectrograph (GHRS), and a variety of X-ray telescopes have been analyzed and modeled. Emission measure distributions have been determined for the transition region of each system. The upper transition region (6.1 < log T-e < 7.4) has been studied using line fluxes from the EUVE. Emission measure distributions for the lower transition region (3.8 < log T-e < 5.3) have been found using emission-line fluxes obtained with IUE and the GHRS. Electron densities of similar to 1.6 x 10(11) and similar to 5 x 10(11) cm(-3) have been determined at log T-e = 7.0 and log T-e = 4.7 respectively, using the density-sensitive Fe XXI lambda 128.7 and Si III] lambda 1892 lines. The total pressure (gas + turbulent) is smaller at the lower temperature, indicating that the high- and low-temperature material originates in physically unconnected regions. The emission measure distributions derived from the EUVE line spectra are compared with emission measures found from spectral fits to a variety of low-resolution X-ray spectra, including our reanalysis of archival EXOSAT spectra. Although the emission measure distribution is continuous, both types of analysis lead to two distinct peaks in the high-temperature emission measure distribution, suggesting that there may be two classes of structure in the upper transition region and corona, e.g., two families of loops.