Testing the Binary Trigger Hypothesis in FUors

Abstract

We present observations of three FU Orionis objects (hereafter, FUors) with nonredundant aperture-mask interferometry (NRM) at 1.59 um and 2.12 um that probe for binary companions on the scale of the protoplanetary disk that feeds their accretion outbursts. We do not identify any companions to V1515 Cyg or HBC 722, but we do resolve a close binary companion to V1057 Cyg that is at the diffraction limit (rho = 58.3 +/- 1.4 mas or 30 +/- 5 AU) and currently much fainter than the outbursting star (delta(K') = 3.34 +/- 0.10 mag). Given the flux excess of the outbursting star, we estimate that the mass of the companion (M ~ 0.25 Msun) is similar to or slightly below that of the FUor itself, and therefore it resembles a typical T Tauri binary system. Our observations only achieve contrast limits of delta(K') ~ 4 mag, and hence we are only sensitive to companions that were near or above the pre-outburst luminosity of the FUors. It remains plausible that FUor outbursts could be tied to the presence of a close binary companion. However, we argue from the system geometry and mass reservoir considerations that these outbursts are not directly tied to the orbital period (i.e., occurring at periastron passage), but instead must only occur infrequently.

6 pages, 2 figures

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• The Rate, Amplitude and Duration of Outbursts from Class 0 Protostars in Orion
• A 1.3 mm SMA Survey of 29 Variable Young Stellar Objects
• On the rise times in FU Orionis events
• Sustained FU Orionis-type outbursts from colliding discs in stellar flybys
• The role of turbulence during the formation of circumbinary discs
• The dependence of episodic accretion on eccentricity during the formation of binary stars
• A study of the photometric and spectroscopic variations of the prototypical FU Orionis-type star V1057 Cyg