Investigating CaiiEmission in the RS Canum Venaticorum Binary ER Vulpeculae Using the Broadening Function Formalism

The synchronously rotating G stars in the detached, short-period (0.7 d),partially eclipsing binary, ER Vul, are the most chromospherically activesolar-type stars known. We have monitored activity in the Ca II H & K reversalsfor almost an entire orbit. Rucinski's Broadening Function Formalism allows thephotospheric contribution to be objectively subtracted from the highly blendedspectra. The power of the BF technique is also demonstrated by the goodagreement of radial velocities with those measured by others from less crowdedspectral regions. In addition to strong Ca II emission from the primary andsecondary, there appears to be a high-velocity stream flowing onto thesecondary where it stimulates a large active region on the surface 30 - 40degrees in advance of the sub-binary longitude. A model light curve with a spotcentered on the same longitude also gives the best fit to the observed lightcurve. A flare with approximately 13% more power than at other phases wasdetected in one spectrum. We suggest ER Vul may offer a magnified view of themore subtle chromospheric effects synchronized to planetary revolution seen incertain `51 Peg'-type systems.Comment: Accepted to AJ; 17 pages and 16 figure