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Binary star-formation theory predicts that close binaries (a<100 AU) willexperience periodic pulsed accretion events as streams of material form at theinner edge of a circumbinary disk, cross a dynamically cleared gap, and feedcircumstellar disks or accrete directly onto the stars. The archetype for thepulsed-accretion theory is the eccentric, short-period, classical T Tauribinary DQ Tau. Low-cadence (~daily) broadband photometry has shown brighteningevents near most periastron passages, just as numerical simulations wouldpredict for an eccentric binary. Magnetic reconnection events (flares) duringthe collision of stellar magnetospheres near periastron could, however, producethe same periodic, broadband behavior when observed at a one-day cadence. Toreveal the dominate physical mechanism seen in DQ Tau's low-cadenceobservations, we have obtained continuous, moderate-cadence, multi-bandphotometry over 10 orbital periods, supplemented with 27 nights ofminute-cadence photometry centered on 4 separate periastron passages. Whileboth accretion and stellar flares are present, the dominant timescale andmorphology of brightening events are characteristic of accretion. On average,the mass accretion rate increases by a factor of 5 near periastron, in goodagreement with recent models. Large variability is observed in the morphologyand amplitude of accretion events from orbit-to-orbit. We argue this is due tothe absence of stable circumstellar disks around each star, compounded byinhomogeneities at the inner edge of the circumbinary disk and within theaccretion streams themselves. Quasi-periodic apastron accretion events are alsoobserved, which are not predicted by binary accretion theory.

Accretion and Magnetic Reconnection in the Classical T Tauri Binary DQ Tau