The Coronae of AB Doradus and V471 Tauri: Primordial Angular Momentum versus Tidal Spin‐up

The zero-age main-sequence star AB Dor and the K dwarf component of the V471Tau close binary have essentially identical rotation rates and spectral types.An analysis of their high resolution {\it Chandra} X-ray spectra revealsremarkably similar coronal characteristics in terms of both temperaturestructure and element abundances. Both stars show depletions of low FIPelements by factors of $\sim 3$, with higher FIP elements showing more milddepletions. No evidence for enhancements of very low FIP ($< 7$ eV) elements,such as Na, Al and Ca, as compared to other low FIP elements was found. Theabundance anomaly pattern for AB Dor and V471 Tau is similar to, though lessextreme than, the abundance anomalies exhibited by active RS-CVn-type binaries.While we find statistically significant structure in the underlyingdifferential emission measure distributions of these stars over narrowtemperature intervals, this structure is strongly dependent on the lines usedin the analysis and is probably spurious. Based on their X-ray similarities, weconclude that the exact evolutionary state of a star has little effect oncoronal characteristics, and that the parameters that dominate coronalstructure and composition are simply the rotation rate and spectral type.Comment: 23 pages, 10 figures. Accepted by Ap