Infrared Excesses from accretion

streams in circumbinary discs




We used Smoothed Particle Hydrodynamics to study the formation and evolution of mass streams that transfer material from a circumbinary disk to the stars of a close binary. These streams form when the disk is hot enough and/or viscous enough (thickness-to-radius ratio c>=0.05, for viscosity parameter alpha>0.01).

We modeled binaries with different mass ratios and eccentricities and calculated the spectral energy distribution of the binary-disk system, for an optically thick disk. We focused on the variation of the excess in the N band (effective wavelength ~11 microns). The result of the mass streams is a considerable infrared excess that varies over the binary period.This variability is observable and can be used as a diagnostic element in the study of very close binary systems, because its  presence  is a sign of stream accretion.There is a periodicity in this  variation, with a period equal to the binary period. The general pattern the excess follows is that it is larger at the periastron of the orbit.

We also examined the role of the temperature profile in the formation of the streams. We found that for a  hotter disk temperature profile (T~1/R^{1/2}) streams form even for moderate values of thickkness-to-radius ratio (c~0.03). Thus, systems like DQ Tau  (c ~0.03-0.045) may have such streams, something that previously was questioned.