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

2. 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

3. 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?

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

5. 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)

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

7. 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.

8. 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)

9. 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)

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

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

12. Synthetic SEDs

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

14. 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