On dust evolution in planet-forming discs in binary systems – II. Comparison with Taurus and ρ Ophiuchus (sub-)millimetre observations: discs in binaries have small dust sizes

Abstract

The recently discovered exoplanets in binary or higher-order multiple stellar systems sparked a new interest in the study of proto-planetary discs in stellar aggregations. Here we focus on disc solids, as they make up the reservoir out of which exoplanets are assembled and dominate (sub-)millimetre disc observations. These observations suggest that discs in binary systems are fainter and smaller than in isolated systems. In addition, disc dust sizes are consistent with tidal truncation only if they orbit very eccentric binaries. In a previous study we showed that the presence of a stellar companion hastens the radial migration of solids, shortening disc lifetime and challenging planet formation. In this paper we confront our theoretical and numerical results with observations: disc dust fluxes and sizes from our models are computed at ALMA wavelengths and compared with Taurus and ρ Ophiuchus data. A general agreement between theory and observations is found. In particular, we show that the dust disc sizes are generally smaller than the binary truncation radius due to the combined effect of grain growth and radial drift: therefore, small disc sizes do not require implausibly high eccentricities to be explained. Furthermore, the observed binary discs are compatible within 1σ with a quadratic flux-radius correlation similar to that found for single-star discs and show a close match with the models. However, the observational sample of resolved binary discs is still small and additional data are required to draw more robust conclusions on the flux-radius correlation and how it depends on the binary properties.

Stellar multiplicity affects the correlation between proto-planetary disc masses and accretion rates: binaries explain high-accretors in Upper Sco

“…6) would suggest that the most eccentric pairs would be those with larger 𝑎 p . As long as the bulk of the population has relatively smaller eccentricities (𝑒 ≈ 0.3 as expected in the field, e.g., Duchêne & Kraus 2013), this is not in tension with the fact that the the dust disc sizes in Taurus and 𝜌 Ophiuchus can be well explained assuming low eccentric orbits (Zagaria et al 2021b andRota et al 2022).…”

“…A passively irradiated time-independent disc temperature profile (Chiang & Goldreich 1997) is considered, radially decaying as 𝑅 −1/2 and with reference temperature 𝑇 0 = 88.23 K at 10 au, calibrated on a Solar-mass star. The Shakura & Sunyaev (1973) prescription is used for viscosity: we set 10 −4 ≤ 𝛼 ≤ 10 −3 , both for consistency with previous works (Sellek et al 2020b) and because at these viscosities similar models reproduce the flux-radius correlation most closely (Rosotti et al 2019a;Zagaria et al 2021b;Zormpas et al 2022).…”

“…For 𝑡 0, this trend is determined by binary discs both being fainter and accreting more. The former effect is due to the faster drift of grains for smaller values of 𝑅 trunc (Zagaria et al 2021a), which precipitates mass depletion (Zagaria et al 2021b); the latter is a consequence of the smaller viscous time scale of truncated discs (Rosotti & Clarke 2018). Remarkably, while in the case of singlestar models, evolutionary tracks are limited by 𝑡 acc = 0.1 Myr for 𝑅 0 = 10 au (Sellek et al 2020b), when 𝑅 trunc ≤ 100 au, the binary models are able to populate the region of the data-plane with shorter accretion time scales, where many of the observed sources lie.…”

Observational constraints on gas disc sizes in the protoplanetary discs of multiple systems in the Taurus region

“…However, the analysis above was performed using the dust disc radii estimates, because the data available did not cover the gas emission in these discs, which is nevertheless the component that we need to compare with current models of tidal truncation as this is the one that best responds to the disc dynamics. By considering the effect of dust growth and drift in truncated systems, Zagaria et al (2021b) recently showed that the results by Manara et al (2019) can be reconciled with tidal truncation models without the need to invoke extremely high eccentric orbits. This result must however be confirmed also observationally by measuring the sizes of the gas discs around multiple systems.…”

Demographics of young stars and their protoplanetary disks: lessons learned on disk evolution and its connection to planet formation

“…Full table available at http://ppvii.org/chapter/15/.SEDs. The resolution was also sufficient to extend earlier studies on the strong effect of stellar multiplicity on disk lifetime and masses (e.g., Harris et al 2012) to sizes and radial profiles (e.g.,Akeson et al 2019;Manara et al 2019b;Zurlo et al 2020Zurlo et al , 2021Zagaria et al 2021).A notable, and unfortunate, exception is Taurus. As a northern target, it was the best-surveyed region in the mm pre-ALMA(Beckwith et al 1990;Andrews and Williams…”