TheROSATAll‐Sky Survey of Active Binary Coronae. III. Quiescent Coronal Properties for the BY Draconis–Type Binaries

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Abstract
We present X-ray observations of 35 active late-type BY Draconis dwarf binary systems and 28 evolved binary systems, similar in nature to the RS Canum Venaticorum systems, obtained with the Position Sensitive Proportional Counter (PSPC) during the ROSAT All-Sky Survey phase of the mission. Of this sample, 52 targets were detected in exposures of roughly 600 s or less. When these new data are combined with the earlier results from Dempsey et al. (1993b), this survey represents the largest sample of active binary systems observed to date at any wavelength, including X-rays. We expand our investigation of how coronal properties (e.g., surface flux, luminosity, etc.) correlate with stellar parameters (e.g., rotation period, color, etc.) and confirm the conclusions of Dempsey et al. (1993b). Rotation period provides the best correlation with X-ray surface flux with FX ~P for the entire sample. We find no evidence for a "basal" or nonmagnetic X-ray flux component. We model the low-resolution pulse-height spectra for 12 systems with two-temperature thermal plasmas. The derived temperatures for the BY Dra systems are identical to those previously derived for active evolved giants and subgiants in close binaries (Dempsey et al. 1993c). We also show that the dependence of temperature and emission measures on rotation period is the same for the dwarf, subgiant, and giant binaries.