Abstract
ABSTRACT The recently discovered exoplanets in binary or higher order multiple stellar systems sparked a new interest in the study of protoplanetary 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.
Highlights
About a half of the main-sequence stars are part of binary or higherorder multiple stellar systems (e.g., Raghavan et al 2010; Moe & Di Stefano 2017) and this fraction is expected to increase significantly in the case of pre-main-sequence stars (e.g., Duchêne & Kraus 2013; Chen et al 2013)
Our aim is showing that, when radial drift is taken into account, the disc dust sizes predicted
To deal with the observations consistently, we analysed Cox et al (2017) data in the visibility plane in order to compute disc dust sizes as Manara et al (2019) did in Taurus. This allowed for a study of the disc sizes and the flux-radius correlation in binary discs
Summary
About a half of the main-sequence stars are part of binary or higherorder multiple stellar systems (e.g., Raghavan et al 2010; Moe & Di Stefano 2017) and this fraction is expected to increase significantly in the case of pre-main-sequence stars (e.g., Duchêne & Kraus 2013; Chen et al 2013). The angular resolution of the latter survey (∼ 0.20 arcsec) is high-enough to resolve the primary component of all binaries and, at least marginally, several secondaries For this reason, to be consistent with the analysis in Manara et al (2019), we fit the dust continuum emission in Cox et al (2017) discs in multiple stellar systems in the visibility plane employing the state-of-the-art techniques used in Taurus (Tazzari et al 2018). In single-star discs Tripathi et al (2017), using results from SMA, reported a correlation between (sub-)millimetre disc dust sizes (the radius enclosing 68 per cent of the total dust emission) and dust fluxes, R68,obs ∝ Lm0.m5 , known as the flux-radius correlation This correlation was later confirmed by Tazzari et al (2017); Andrews et al (2018) and Tazzari et al (2020b) in Lupus, by Long et al (2019) in Taurus and by Barenfeld et al (2017) in Upper Scorpius, using ALMA data (see Hendler et al 2020 for a summary view).
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