Abstract
Context. Since about half of all main-sequence stars reside in multiple star systems, it is important to consider the effect of binarity on the evolution of planetesimal belts in these complex systems. Aims. We aim to see whether debris belts evolving between two stars may be impacted by the presence of the companion and whether this leaves any detectable signature that could be observed with current or future instruments. Methods. We consider a circumprimary parent body (PB) planetesimal belt that is placed just inside the stability limit between the two stars and we use the state-of-the-art DyCoSS code to follow the coupled dynamical and collisional evolution of the dust produced by this PB belt. We explore several free parameters, such as the belt’s mass and the binary’s mass ratio as well as its orbital eccentricity. We use the GraTeR package to produce 2D luminosity maps and system-integrated spectral energy distributions (SEDs). Results. We confirm a preliminary result obtained by previous DyCoSS studies, which is that the coupled effect of collisional activity, binary perturbations, and stellar radiation pressure is able to place and maintain a halo of small grains in the dynamically unstable region between the two stars. In addition, we identify several prominent spatial structures, notably, a single spiral arm stretching all the way from the PB belt to the companion star. We also identify a fainter and more compact disc around the secondary star, which is non-native and feeds off small grains from the unstable halo. The halo, spiral arm, and secondary disc should all be detectable on resolved images by instruments with capacities on the level of SPHERE. The system as a whole is depleted of small grains when compared to a companion-free case. This depletion leaves an imprint on the system’s integrated SED, which appears colder than for the same parent body belt around a single star. This new finding could explain why the SED-derived location, rdisc, of some unresolved discs-in-binaries places their primary belt in the dynamically ’forbidden’ region between the two stars: indeed, this apparent paradox could be due to an overestimation of rdisc when using empirical prescriptions that are valid for the case of a single star.
Highlights
Dusty debris discs have been detected around ∼15% to ∼30% of main-sequence stars in the K to A stellar-types range
We confirm a crucial result of TBO12, which is that the steady collisional production of small, radiation-pressure affected grains is able to maintain a significant level of dust in the dynamically unstable region beyond rout
Summary and conclusions In this work, we use the state-of-the-art DyCoSS code to investigate the maximum possible effect a companion star can have on a debris disc, that is, when the outer edge of its dust-producing parent body (PB) belt coincides with the instability limit rcrit due to companion perturbations
Summary
Dusty debris discs have been detected around ∼15% to ∼30% of main-sequence stars in the K to A stellar-types range (see reviews by Matthews et al 2014; Hughes et al 2018, and references therein). The link between disc incidence and binarity has been investigated by Trilling et al (2007); Rodriguez & Zuckerman (2012); Rodriguez et al (2015) and, more recently, in Yelverton et al (2019) with a sample of 341 binaries which they use to look for dust-induced excesses at 70 and 100 μm These studies have shown that while the incidence of discs in binaries of separation of ρ 100 au is similar to that of single stars, there is a strong depletion of discs in tighter binaries, with, for instance, no discs detected in binaries with 25 au ≤ ρ ≤ 135 au (Yelverton et al 2019). When using dust temperature estimates to infer disc radii, Trilling et al (2007) found that some discs seem to be located within these dynamically “forbidden” regions
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