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SONS: the JCMT Legacy Survey of Debris Discs in the Submillimetre

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SONS: the JCMT Legacy Survey of Debris Discs in the Submillimetre MNRAS 000,1{47 (2016) Preprint 6 June 2017 Compiled using MNRAS LATEX style file v3.0 SONS: The JCMT legacy survey of debris discs in the submillimetre Wayne S. Holland,1;2? Brenda C. Matthews,3;4 Grant M. Kennedy,5 Jane S. Greaves,6y Mark C. Wyatt,5 Mark Booth,7;8 Pierre Bastien,9 Geoff Bryden,10 Harold Butner,11 Christine H. Chen,12 Antonio Chrysostomou,13z Claire L. Davies,6x William R. F. Dent,14 James Di Francesco,3;4 Gaspard Duch^ene,15;16 Andy G. Gibb,17 Per Friberg;18{ Rob J. Ivison;2;19 Tim Jenness;18k JJ Kavelaars,3;4 Samantha Lawler,3;4 Jean-Fran¸cois Lestrade;20 Jonathan P. Marshall,21;22;23 Amaya Moro-Martin;12;24 Olja Pani´c;5?? Neil Phillips,14 Stephen Serjeant,25 Gerald H. Schieven;3;4 Bruce Sibthorpe;26yy Laura Vican,27 Derek Ward-Thompson,28 Paul van der Werf,29 Glenn J. White;25;30 David Wilner,31 Ben Zuckerman27 Affiliations are listed at the end of the paper. Accepted XXX. Received YYY; in original form ZZZ ABSTRACT Debris discs are evidence of the ongoing destructive collisions between planetesi- mals, and their presence around stars also suggests that planets exist in these systems. In this paper, we present submillimetre images of the thermal emission from debris discs that formed the SCUBA-2 Observations of Nearby Stars (SONS) survey, one of seven legacy surveys undertaken on the James Clerk Maxwell telescope between 2012 and 2015. The overall results of the survey are presented in the form of 850 µm (and 450 µm, where possible) images and fluxes for the observed fields. Excess thermal emission, over that expected from the stellar photosphere, is detected around 49 stars out of the 100 observed fields. The discs are characterised in terms of their flux density, size (radial distribution of the dust) and derived dust properties from their spectral energy distributions. The results show discs over a range of sizes, typically 1{10 times the diameter of the Edgeworth-Kuiper Belt in our Solar System. The mass of a disc, for particles up to a few millimetres in size, is uniquely obtainable with submillimetre observations and this quantity is presented as a function of the host stars' age, show- ing a tentative decline in mass with age. Having doubled the number of imaged discs at submillimetre wavelengths from ground-based, single dish telescope observations, one of the key legacy products from the SONS survey is to provide a comprehen- arXiv:1706.01218v1 [astro-ph.SR] 5 Jun 2017 sive target list to observe at high angular resolution using submillimetre/millimetre interferometers (e.g., ALMA, SMA). Key words: circumstellar matter { submillimetre: stars ? E-mail: [email protected] { Present address: East Asian Observatory, 660 N. A‘oh¯ok¯u y Present address: School of Physics & Astronomy, Cardiff Uni- Place, University Park, Hilo, HI 96720, USA versity, 5 The Parade, Cardiff, CF24 3AA, UK k Present address: LSST Project Office, 950 N. Cherry Avenue, z Present address: SKA Organisation, Jodrell Bank Observatory, Tucson, AZ 85719, USA Lower Withington, Macclesfield, Chesire, SK11 9DL, UK ?? Present address: School of Physics and Astronomy, E C Stoner x Present address: School of Physics, University of Exeter, Building, University of Leeds, Leeds, LS2 9JT, UK Physics Building, Stocker Road, Exeter, EX4 4QL, UK c 2016 The Authors 2 W. S. Holland et al. 1 INTRODUCTION due to structure in the debris disc through scattered light imaging before the planet was found (Mouillet et al. 1997; Debris discs represent the longest-lived phase in the lifetime Heap et al. 2000). Whilst scattered light observations are of circumstellar discs. Following the decline of the gas-rich sensitive to the small grains around a given star, the bulk protoplanetary phase when agglomeration processes prevail, of the mass resides in the largest grains most detectable at the remnant mass of circumstellar discs is dominated by submillimetre to centimetre wavelengths. These grains are planetesimals, which undergo collisional grinding down to most likely to be located in or near the planetesimal belts, smaller and smaller bodies, until particles reach the blow- and hence may show evidence of perturbed geometries due out size determined by the radiation pressure from the host to resonances with long-period planets (Wyatt 2006). star (e.g. Wyatt 2008; Krivov 2010). The presence of these unseen planetesimals can be inferred through scattered light The James Clerk Maxwell telescope (JCMT) has a long or thermal emission from micron to millimetre-sized dust history of debris disc studies (e.g., Zuckerman & Beckin grains. The dust must be continuously replenished, by on- 1993), including some of the earliest imaging using the going collisions between the aforementioned planetesimals, SCUBA camera (Holland et al. 1999). At the time of its since the timescales for dust grains to be removed from the decommissioning in 2005, half of the resolved images of de- system are significantly shorter than the ages of the stars bris discs (about a dozen in total) were due to submillimetre around which they are observed (Backman & Paresce 1993). imaging with SCUBA (e.g., Holland et al. 1998; Greaves et It appears to be the case that debris discs can persist over all al. 2005). Subsequent surveys in the mid-far IR (e.g. using stages following the pre-main-sequence phase of stellar evo- Spitzer, AKARI and Herschel) identified a large sample of lution (e.g. Bonsor et al. 2013), even including white dwarfs discs in the solar vicinity (to a distance of ∼100 pc). For (e.g. Farihi 2016). example, the Herschel DEBRIS (Disk Emission via a Bias- Observations at submillimetre/millimetre wavelengths Free Reconnaissance in the Infrared/Submillimetre) survey are immensely valuable to the study of debris discs in that observed the nearest ∼90 stars in each of the spectral type they trace the Rayleigh-Jeans tail of the outer cold dust in groups A, F, G, K and M, obtaining a disc detection rate of a system (Matthews et al. 2014). For example, they probe 17 per cent based on 100 µm and 160 µm results, correspond- substantially different (thermal) emission mechanisms than ing to 77 out of a total of 446 targets detected (Matthews scattered light observations, and lower characteristic tem- et al. 2014). Similarly, the Herschel DUNES (DUst around peratures for the material than far-infrared (far-IR) data. NEarby Stars) survey detected an incidence of 20 per cent These long wavelengths also provide an important anchor to for nearby Sun-like stars, probing to the photospheric level the flux energy distribution (loosely referred to in this paper (Eiroa et al. 2013; Montesinos et al. 2016). In terms of limits as the spectral energy distribution, or SED) in an otherwise to the detectable flux, Spitzer and Herschel achieved average poorly constrained wavelength range, and can indicate the sensitivities, expressed as fractional dust luminosities (see presence of any (cold) disc components not detectable at Section 4.4) of ∼10−5 and ∼10−6, respectively. These lev- shorter wavelengths. By probing the Rayleigh-Jeans tail of els compare to ∼10−7 for the Edgeworth-Kuiper belt in our the spectrum, the effect of any possible bias introduced by Solar System. Crucially, the surveys by Herschel spatially modelling the dust temperatures from the observed data is resolved half of the detected discs, many for the first time. minimised, thus allowing information to be derived on the Other surveys, in the near-mid IR with AKARI, have probed radial distribution of the disc and the size distribution of \warmer" debris discs (T > 150 K), i.e. material to be found the emitting grains (Ertel et al. 2012; Marshall et al. 2014b). closer to the central star, with incidence rates typically 3 The slope of the spectrum constrains the dust size distribu- per cent, much lower than for the \cooler" discs detected at tion, providing a test of whether or not the solids in the disc longer wavelengths (Fujiwara et al. 2013). are undergoing a steady-state collisional cascade. Critically, since the emission is optically thin, the dust mass for grain The SCUBA-2 Observations of Nearby Stars (SONS) sizes up to ∼1 mm is uniquely determined from submillime- survey was one of the seven original legacy surveys under- tre data. taken on the James Clerk Maxwell telescope between 2012 The disc component (in millimetre-sized grains) probed and 2015 (Chrysostomou 2010). The survey set out to tar- in the submillimetre is also unique from the perspective of get 115 known disc host stars (within 100 pc of the Sun) understanding disc dynamics. These relatively large dust searching for debris signatures in the form of dust emission grains are less affected by the radiation or stellar wind pres- at 850 µm. The aim of the SONS survey was to characterise sure (Burns et al. 1979) and therefore trace the location of these discs to the fullest extent possible by: (1) providing di- their parent planetesimal belts more reliably than smaller rect dust masses that cannot be obtained from shorter wave- grains at shorter wavelengths. Debris discs act as impor- lengths alone; (2) adding to the far-IR/submillimetre spec- tant pointers to planetary systems (K´osp´al et al. 2009) with trum to constrain the dust size distribution; (3) using the features in the discs having the potential to highlight the power of a 15 m telescope to resolve disc structures around presence of planets, even in cases where the planet is as the nearest systems, and (4) looking for evidence of reso- yet undetected, or would be difficult to detect by any other nant clumps and other features in resolved structures that method, including direct imaging (e.g.
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