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

Abstract

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 Te < 7.4) has been studied using line fluxes from the EUVE. Emission measure distributions for the lower transition region (3.8 < log Te < 5.3) have been found using emission-line fluxes obtained with IUE and the GHRS. Electron densities of ~1.6 × 1011 and ~5 × 1011 cm-3 have been determined at log Te = 7.0 and log Te = 4.7 respectively, using the density-sensitive Fe XXI λ128.7 and Si III] λ1892 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.