Debris Discs in Binaries Numerical modelling Philippe Thébault Thebault, Marzari & Augereau, 2010, A&A Thebault, P., 2011 (submitted)

Debris Discs in binaries why bother? a majority of stars in multiple systems >80 detected exoplanets in binaries Planet formation in binaries is a very fashionable topic right now debris discs are the most easily observable components of an extrasolar planetary system

They rather look like this They rarely look like this Imaged debris discs show pronounced structures They rather look like this They rarely look like this ”something” is shaping them: planets? ...or planets? ...or maybe planets? What about a companion star?

imaged discs in binaries HD141569 (Krist et al.) HR4796A (Schneider et al.)

In principle, it’s simple: (Holman&Wiegert, 1999) acrit …N-body code but... steady collisional production of small grains placed on high-e orbits by radiation pressure reaching far beyond rcrit need to model the coupled dynamical & collisional evolution of the disc (Krivov, 2010)

a new code to study the collisional and dynamical evolution of perturbed discs at steady state Set up Parent Body Ring  = 10-3 (~ Pic)

3 steps 1) Parent Body run: for =0 particles, until dynamical steady state is reached. Save10 PB disc profiles for 10 ≠ positions of the companion on its orbit separated by dtsav=torb/10 2) Collisional Runs: From each of the10 PB discs, 105 small grains are released following dN s-3.5ds. They are assigned a collision destruction probability as a function of size and location. All particle positions are recorded at each dtsav. Runs are stopped when all particles have been removed by ejection or collisions 3) Recombining: Use all collisional runs to reconstruct the dust distribution, at steady state, for each orbital position of the perturber.

Azimuthally averaged radial profiles Always small grains in the ”forbidden” region. Amount of matter beyond rcrit increases with increasing eB. Only very diffuse discs can present sharp outer edges. unstable region (Thebault et al. 2010)

Spatial Structures: density maps at steady state acrit eB=0.2 precessing spirals for half the orbit eB=0 precessing spiral structures eB=0.75 Invariant asymmetric disc eB=0.5 spiral at periastron passages (Thebault, 2011)

Radial cuts Azimuthal cuts eB=0 eB=0.2 eB=0.75

Depletion of small >0.15 grains Size distribution within < rcrit Depletion of small >0.15 grains

Synthetic SEDs

(not) fitting the HR4796A disc Observational constraints on the companion: eB>0.45 in order to truncate a PB disc at 70AU r>510AU

SUMMARY New model to study the combined effects of Dynamical Perturbations, Collisions and Radiation Pressure in collisionally active perturbed debris discs A binary can never fully truncate a debris disc: Circumprimary discs extend far outside the limit for orbital stability Small grains are underabundant within the orbital stability limit Discs can appear colder than what they should Depending on eB, precessing, transient (spirals) or fixed asymmetries can develop in the dynamically “forbidden” regions