  The synchronously rotating G stars in the detached, short-period (0.7 d),
partially eclipsing binary, ER Vul, are the most chromospherically active
solar-type stars known. We have monitored activity in the Ca II H & K reversals
for almost an entire orbit. Rucinski's Broadening Function Formalism allows the
photospheric contribution to be objectively subtracted from the highly blended
spectra. The power of the BF technique is also demonstrated by the good
agreement of radial velocities with those measured by others from less crowded
spectral regions. In addition to strong Ca II emission from the primary and
secondary, there appears to be a high-velocity stream flowing onto the
secondary where it stimulates a large active region on the surface 30 - 40
degrees in advance of the sub-binary longitude. A model light curve with a spot
centered on the same longitude also gives the best fit to the observed light
curve. A flare with approximately 13% more power than at other phases was
detected in one spectrum. We suggest ER Vul may offer a magnified view of the
more subtle chromospheric effects synchronized to planetary revolution seen in
certain `51 Peg'-type systems.
