This work was by the European Research Council under the European Commission's Seventh Framework Programme (FP7/2007-2013 Grant Agreement No. 339248). The calculation discussed in this paper was performed on the University of Exeter Supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS, and the University of Exeter, and on the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). The latter equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure. The calculation was conducted as part of the award ‘The formation of stars and planets: Radiation hydrodynamical and magnetohydrodynamical simulations’ made under the European Heads of Research Councils and European Science Foundation EURYI (European Young Investigator) Awards scheme, was supported by funds from the Participating Organisations of EURYI and the EC Sixth Framework Programme.

On the diversity and statistical properties of protostellar discs

Discs around young planets, so-called circumplanetary discs (CPDs), are essential for planet growth, satellite formation, and planet detection. We study the millimetre and centimetre emission from accreting CPDs by using the simple $\alpha$ disc model. We find that it is easier to detect CPDs at shorter radio wavelengths (e.g. $\lambda\lesssim$ 1 mm). For example, if the system is 140 pc away from us, deep observations (e.g. 5 hours) at ALMA Band 7 (0.87 mm) are sensitive to as small as 0.03 lunar mass of dust in CPDs. If the CPD is around a Jupiter mass planet 20 AU away from the host star and has $\alpha\lesssim 0.001$, ALMA can detect this disc when it accretes faster than $10^{-10} M_{\odot}/yr$. ALMA can also detect the "minimum mass sub-nebulae" disc if such a disc exists around a young planet in YSOs. However, to distinguish the embedded compact CPD from the circumstellar disc material, we should observe circumstellar discs with large gaps/cavities using the highest resolution possible. We also calculate the CPD fluxes at VLA bands, and discuss the possibility of detecting radio emission from jets/winds launched in CPDs. Finally we argue that, if the radial drift of dust particles is considered, the drifting timescale for millimetre dust in CPDs can be extremely short. It only takes 10$^2$-10$^{3}$ years for CPDs to lose millimetre dust. Thus, for CPDs to be detectable at radio wavelengths, mm-sized dust in CPDs needs to be replenished continuously, or the disc has a significant fraction of micron-sized dust or a high gas surface density so that the particle drifting timescale is long, or the radial drift is prevented by other means (e.g. pressure traps).

/pdf/on-the-radio-detectability-of-circumplanetary-discs-1vgm4nfcdp.pdf

On the Radio Detectability of Circumplanetary Discs

DHF gratefully acknowledges support from the ECOGAL project, grant agreement 291227, funded by the European Research Council (ERC) under ERC-2011-ADG. This project has received funding from ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 681601). The research leading to these results also received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 313014 (ETAEARTH). WKMR acknowledges the support of the UK Science and Technology Facilities Council through grant number ST/M001229/1. FM acknowledges support from The Leverhulme Trust and the Isaac Newton Trust.

Towards a population synthesis model of self-gravitating disc fragmentation and tidal downsizing II: The effect of fragment-fragment interactions

Context. Young giant planets and brown dwarf companions emit near-infrared radiation that can be linearly polarized up to several percent. This polarization can reveal the presence of an (unresolved) circumsubstellar accretion disk, rotation-induced oblateness of the atmosphere, or an inhomogeneous distribution of atmospheric dust clouds.Aims. We aim to measure the near-infrared linear polarization of 20 known directly imaged exoplanets and brown dwarf companions.Methods. We observed the companions with the high-contrast imaging polarimeter SPHERE-IRDIS at the Very Large Telescope. We reduced the data using the IRDAP pipeline to correct for the instrumental polarization and crosstalk of the optical system with an absolute polarimetric accuracy We report the first detection of polarization originating from substellar companions, with a polarization of several tenths of a percent for DH Tau B and GSC 6214-210 B in H -band. By comparing the measured polarization with that of nearby stars, we find that the polarization is unlikely to be caused by interstellar dust. Because the companions have previously measured hydrogen emission lines and red colors, the polarization most likely originates from circumsubstellar disks. Through radiative transfer modeling, we constrain the position angles of the disks and find that the disks must have high inclinations. For the 18 other companions, we do not detect significant polarization and place subpercent upper limits on their degree of polarization. We also present images of the circumstellar disks of DH Tau, GQ Lup, PDS 70, β Pic, and HD 106906. We detect a highly asymmetric disk around GQ Lup and find evidence for multiple scattering in the disk of PDS 70. Both disks show spiral-like features that are potentially induced by GQ Lup B and PDS 70 b, respectively.Conclusions. The presence of the disks around DH Tau B and GSC 6214-210 B as well as the misalignment of the disk of DH Tau B with the disk around its primary star suggest in situ formation of the companions. The non-detections of polarization for the other companions may indicate the absence of circumsubstellar disks, a slow rotation rate of young companions, the upper atmospheres containing primarily submicron-sized dust grains, and/or limited cloud inhomogeneity.

pdf/a-survey-of-the-linear-polarization-of-directly-imaged-ucrr1bzity.pdf

A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS. First polarimetric detections revealing disks around DH Tau B and GSC 6214-210 B

Debris disks are the intrinsic by-products of the star and planet formation processes. Most likely due to instrumental limitations and their natural faintness, little is known about debris disks around low-mass stars, especially when it comes to spatially resolved observations. We present new VLT/SPHERE IRDIS Dual-Polarization Imaging (DPI) observations in which we detect the dust ring around the M2 spectral type star TWA\,7. Combined with additional Angular Differential Imaging observations we aim at a fine characterization of the debris disk and setting constraints on the presence of low-mass planets. We model the SPHERE DPI observations and constrain the location of the small dust grains, as well as the spectral energy distribution of the debris disk, using the results inferred from the observations, and perform simple N-body simulations. We find that the dust density distribution peaks at 25 au, with a very shallow outer power-law slope, and that the disk has an inclination of 13 degrees with a position angle of 90 degrees East of North. We also report low signal-to-noise detections of an outer belt at a distance of ~52 au from the star, of a spiral arm in the Southern side of the star, and of a possible dusty clump at 3.9 au. These findings seem to persist over timescales of at least a year. Using the intensity images, we do not detect any planets in the close vicinity of the star, but the sensitivity reaches Jovian planet mass upper limits. We find that the SED is best reproduced with an inner disk at 7 au and another belt at 25 au. We report the detections of several unexpected features in the disk around TWA\,7. A yet undetected 100 M$_\oplus$ planet with a semi-major axis at 20-30 au could possibly explain the outer belt as well as the spiral arm. We conclude that stellar winds are unlikely to be responsible for the spiral arm.

/pdf/resolving-faint-structures-in-the-debris-disk-around-twa7-1grnnj5ca5.pdf

Resolving faint structures in the debris disk around TWA7

OTS44 is one of only four free-floating planets known to have a disk. We have previously shown that it is the coolest and least massive known free-floating planet ($\sim$12 M$_{\rm Jup}$) with a substantial disk that is actively accreting. We have obtained Band 6 (233 GHz) ALMA continuum data of this very young disk-bearing object. The data shows a clear unresolved detection of the source. We obtained disk-mass estimates via empirical correlations derived for young, higher-mass, central (substellar) objects. The range of values obtained are between 0.07 and 0.63 M$_{\oplus}$ (dust masses). We compare the properties of this unique disk with those recently reported around higher-mass (brown dwarfs) young objects in order to infer constraints on its mechanism of formation. While extreme assumptions on dust temperature yield disk-mass values that could slightly diverge from the general trends found for more massive brown dwarfs, a range of sensible values provide disk masses compatible with a unique scaling relation between $M_{\rm dust}$ and $M_{*}$ through the substellar domain down to planetary masses.

/pdf/first-millimeter-detection-of-the-disk-around-a-young-2hreytwmvm.pdf

First millimeter detection of the disk around a young, isolated, planetary-mass object

Proyecto Fondecyt Iniciacion [11140572]; Science Foundation Ireland [13/ERC/12907]; NSFC [11503087]; Natural Science Foundation of Jiangsu Province of China [BK20141046]; German Academic Exchange Service; China Scholarship Council; UV; European Science Council under the Horizon 2020 framework program via the ERC Consolidator grant [CSF-648505]; NASA through Hubble Fellowship - Space Telescope Science Institute [HST-HF2-51380.001-A]; NASA [NAS 5-26555]

/pdf/first-millimeter-detection-of-the-disk-around-a-young-25sm22oqwh.pdf

First Millimeter Detection of the Disk around a Young, Isolated, Planetary-mass Object

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First millimeter detection of the disk around a young, isolated, planetary-mass object

First Millimeter Detection of the Disk around a Young, Isolated, Planetary-mass Object