CoRoT 223992193: Investigating the variability in a low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk

CoRoT 223992193: Investigating the variability in a low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk

Authors:

Gillen et al

Abstract:

CoRoT 223992193 is the only known low-mass, pre-main sequence eclipsing binary that shows evidence of a circumbinary disk. The system displays complex photometric and spectroscopic variability over a range of timescales and wavelengths. Using two optical CoRoT runs, and infrared Spitzer 3.6 and 4.5 μm observations (simultaneous with the second CoRoT run), we model the out-of-eclipse light curves. The large scale structure in both CoRoT light curves is consistent with the constructive and destructive interference of starspot signals at two slightly different periods. Using the stellar vsini 's, we infer different rotation periods: the primary is consistent with synchronisation and the secondary is slightly supersynchronous. Comparison of the raw data to the residuals of our spot model in colour-magnitude space indicates additional contributions consistent with variable dust emission and obscuration. We also identify short-duration flux dips preceding secondary eclipse in all three CoRoT and Spitzer bands. We construct a model of the inner regions of the binary and propose that these dips could be caused by partial occultation of the central binary by the accretion stream onto the primary star. Analysis of 15 VLT/FLAMES Hα profiles reveal an emission profile associated with each star: the majority is consistent with chromospheric emission but higher velocity emission is also seen, which could be due to prominences or accretion-related phenomena. In addition, simultaneous u and r-band observations from CFHT/MEGACam reveal a short-lived u-band excess consistent with either an accretion hot spot or stellar flare. The photometric and spectroscopic variations are complex but are consistent with the picture of two active stars possibly undergoing non-steady, low-level accretion; the system's very high inclination provides a new view of such variability.

On the energy dissipation rate at the inner edge of circumbinary disks

On the energy dissipation rate at the inner edge of circumbinary discs

Authors:

Tarquem et al

Abstract:

We study, by means of numerical simulations and analysis, the details of the accretion process from a disc onto a binary system. We show that energy is dissipated at the edge of a circumbinary disc and this is associated with the tidal torque that maintains the cavity: angular momentum is transferred from the binary to the disc through the action of compressional shocks and viscous friction. These shocks can be viewed as being produced by fluid elements which drift into the cavity and, before being accreted, are accelerated onto trajectories that send them back to impact the disc. The rate of energy dissipation is approximately equal to the product of potential energy per unit mass at the disc's inner edge and the accretion rate, estimated from the disc parameters just beyond the cavity edge, that would occur without the binary. For very thin discs, the actual accretion rate onto the binary may be significantly less. We calculate the energy emitted by a circumbinary disc taking into account energy dissipation at the inner edge and also irradiation arising there from reprocessing of light from the stars. We find that, for tight PMS binaries, the SED is dominated by emission from the inner edge at wavelengths between 1-4 and 10 μm. This may apply to systems like CoRoT 223992193 and V1481 Ori.

Eclipsing Binary CoRoT 223992193 Appears to Have a Circumpibary Protoplanetary Disk

A circumbinary disc model for the variability of the eclipsing binary CoRoT 223992193

Authors:

Terquem et al

Abstract:

We calculate the flux received from a binary system obscured by a circumbinary disc. The disc is modelled using two dimensional hydrodynamical simulations, and the vertical structure is derived by assuming it is isothermal. The gravitational torque from the binary creates a cavity in the disc's inner parts. If the line of sight along which the system is observed has a high inclination I, it intersects the disc and some absorption is produced. As the system is not axisymmetric, the resulting light curve displays variability. We calculate the absorption and produce light curves for different values of the dust disc aspect ratio H/r and mass of dust in the cavity Mdust. This model is applied to the high inclination (I=85∘) eclipsing binary CoRoT 223992193, which shows 5-10% residual photometric variability after the eclipses and a spot model are subtracted. We find that such variations for I∼85∘ can be obtained for H/r=10−3 and Mdust≥10−12 M⊙. For higher H/r, Mdust would have to be close to this lower value and I somewhat less than 85∘. Our results show that such variability in a system where the stars are at least 90% visible at all phases can be obtained only if absorption is produced by dust located inside the cavity. If absorption is dominated by the parts of the disc located close to or beyond the edge of the cavity, the stars are significantly obscured.