Debris discs in binaries: morphology and photometric signatures

Thébault, P.; Kral, Quentin; Olofsson, Johan

doi:10.1051/0004-6361/202039582

Cited by 3 publications

(1 citation statement)

References 53 publications

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“…7.4; -Our results provide indirect support for models in which planetesimals are born large ( 10 km), such as those based on streaming instability. The general framework for the realistic treatment of planetesimal growth in binaries developed in this work can be applied to study a range of other problems: circumbinary planet formation in Ptype systems , collisional evolution of debris disks perturbed by planetary (Nesvold & Kuchner 2015;Sefilian et al 2021) or stellar (Thebault et al 2021) companions, and so on.…”

Section: Discussionmentioning

confidence: 99%

Planet formation in stellar binaries: global simulations of planetesimal growth

Silsbee

Rafikov

2021

A&A

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Planet formation around one component of a tight, eccentric binary system such as γ Cephei (with semimajor axis around 20 AU) is theoretically challenging because of destructive high-velocity collisions between planetesimals. Despite this fragmentation barrier, planets are known to exist in such (so-called S-type) orbital configurations. Here we present a novel numerical framework for carrying out multi-annulus coagulation-fragmentation calculations of planetesimal growth, which fully accounts for the specifics of planetesimal dynamics in binaries, details of planetesimal collision outcomes, and the radial transport of solids in the disk due to the gas drag-driven inspiral. Our dynamical inputs properly incorporate the gravitational effects of both the eccentric stellar companion and the massive non-axisymmetric protoplanetary disk in which planetesimals reside, as well as gas drag. We identify a set of disk parameters that lead to successful planetesimal growth in systems such as γ Cephei or α Centauri starting from 1 to 10 km size objects. We identify the apsidal alignment of a protoplanetary disk with the binary orbit as one of the critical conditions for successful planetesimal growth: It naturally leads to the emergence of a dynamically quiet location in the disk (as long as the disk eccentricity is of order several percent), where favorable conditions for planetesimal growth exist. Accounting for the gravitational effect of a protoplanetary disk plays a key role in arriving at this conclusion, in agreement with our previous results. These findings lend support to the streaming instability as the mechanism of planetesimal formation. They provide important insights for theories of planet formation around both binary and single stars, as well as for the hydrodynamic simulations of protoplanetary disks in binaries (for which we identify a set of key diagnostics to verify).

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Section: Discussionmentioning

confidence: 99%

Planet formation in stellar binaries: global simulations of planetesimal growth

Silsbee

Rafikov

2021

A&A

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Flybys in debris disk systems withGaiaeDR3

Bertini

Roccatagliata

Kim

2023

A&A

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Context. Debris disks represent the last phase of the evolution of protoplanetary disks around young stellar objects where planetary systems had most likely already been formed. Resolved systems show peculiar structures, such as asymmetries or spirals, which may be associated with either the presence of a low-mass companion or dynamical interactions with a perturber during a flyby event.Aims. We aim to observationally and statistically constrain the influence of flybys in the formation and evolution of debris disks. Methods. We compiled a sample of 254 debris disks with ages between 2 Myr and 8 Gyr that are either part of an association or isolated, drawing the binary and planetary companions of the systems mainly from the literature. Using the Gaia eDR3 astrometric data and radial velocities of our sample, as well as all the sources in a specific region of the sky, we reconstructed the relative linear motions in the last 5 Myr and made predictions for the next 2 Myr. Relating the Hill radius of each debris disk system and the closest distances reached by the two sources, we defined the flyby events in terms of position and time.Results. We find that in the period between the last 5 Myrs and the next 2 Myrs, 90% of the analyzed systems have experienced at least a close flyby, while 7% of them have experienced flybys at distances greater than 0.5R Hill . In particular, 75% of them have experienced at least one past close encounter and 36% multiple past close encounters. From the sub-sample of resolved debris disk (41 out of 94), 80% of the analyzed systems experience at least an encounter within 0.8 pc. From the subsample of 10 debris disks with planets, half of these systems do show misalignments between disk and planet, stirring, or asymmetries. Systems with a misalignment between the planetary orbit and the disk do indeed experience at least one flyby event. In particular, when the planet orbits have a difference with the disk inclination higher than about 20 • , as in the case of HD 38529, we find that multiple close encounters have taken place in the last 5 Myr, as theoretically predicted. Conclusions. The high incidence of encounters, particularly close encounters, experienced by the systems in the last 5 Myr suggests the fundamental impact of flybys on the evolution of debris disks. Moreover, despite the low statistics, it is interesting to highlight that flybys that have been theoretically predicted so far in peculiar resolved systems have also been observationally constrained.

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A reinvestigation of debris disc halos

Thébault¹,

Olofsson²,

Kral³

2023

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Context. Scattered-light images reveal that a significant fraction of debris discs consist of a bright ring beyond which extends a wide halo. This halo is expected and should be made of small grains collisionally produced in the ring of parent bodies (PBs) and pushed on high-eccentricity orbits by radiation pressure. It has been shown that, under several simplifying assumptions, the surface brightness (SB) of this halo should radially decrease as r−3.5 in scattered light Aims. We aim to revisit the halo phenomenon and focus on two unexplored issues: (1) how the unavoidable presence of small unbound grains, non-isotropic scattering phase functions (SPFs), and finite instrument resolution affect scattered-light SB profiles, and (2) how the halo phenomenon manifests itself at longer wavelengths in thermal emission, both on resolved images and on system-integrated spectral energy distributions (SEDs). Methods. We use a collisional evolution code to estimate the size-dependent spatial distribution of grains in a belt+halo system at steady state. We use the GRaTeR radiative-transfer code to derive synthetic images in scattered light and thermal emission, as well as SEDs. Results. We find that unbound grains account for a significant fraction of the halo’s luminosity in scattered light, and can significantly flatten the SB radial profile for the densest and brightest discs. Because halos are strongly size-segregated with radial distance, realistic size-dependent SPFs also have an effect, resulting here again in shallower SB profiles. For edge-on discs, non-resolving the vertical profile can also significantly flatten the projected SB profile. We show that roughly half of the observationally derived halo profiles found in the literature are compatible with our new results, and that roughly half of the remaining systems are probably shaped by additional processes (planets, stellar companions, etc.). We also propose that, in future observational studies, the characteristics of the PB belts and the halos should be fitted separately. In thermal emission, we find that wide halos should remain detectable up to the far-infrared (far-IR) and that, with the exception of the ~8–15 µm domain, the halo accounts for more than half of the system’s total flux up to λ ~ 80–90 µm. The contribution from the halo strongly decreases in the submm to mm but still represents a few percent of the system’s luminosity at λ ~ 1 mm. For unresolved systems, the presence of a halo can also affect the determination of the radius of the disc from its SED.

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Debris discs in binaries: morphology and photometric signatures

Cited by 3 publications

References 53 publications

Planet formation in stellar binaries: global simulations of planetesimal growth

Planet formation in stellar binaries: global simulations of planetesimal growth

Flybys in debris disk systems withGaiaeDR3

A reinvestigation of debris disc halos

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