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Recent spectra of protoplanetary disks around very low-mass stars (VLMS), captured by the Mid-InfraRed Instrument (MIRI) on board the James Webb Space Telescope (JWST), reveal a rich carbon chemistry. Current interpretations of these spectra are based on 0D slab models and provide valuable estimates for molecular emission temperatures and column densities in the innermost disk. However, the established fitting procedures and simplified models are challenged by the many overlapping gas features. We aim to simultaneously determine the molecular and the dust composition of the disk around the VLMS Sz28 in a Bayesian way. We model the JWST/MIRI spectrum of Sz28 up to $17\,\rm \mu m$ using the Dust Continuum Kit with Line emission from Gas (DuCKLinG). Systematically excluding different molecules from the Bayesian analysis allows for an evidence determination of all investigated molecules and isotopologues. We continue by examining the emission conditions and locations of all molecules, analysing the differences to previous 0D slab fitting, and analysing the dust composition. We find very strong Bayesian evidence for the presence of C2H2, HCN, C6H6, CO2, HC3N, C2H6, C3H4, C4H2, and CH4 in the JWST/MIRI spectrum of Sz28. Additionally, we identify CH3 and find tentative indications for NH3. There is no evidence for water in the spectrum. However, we show that column densities of up to $2\times10^{17}\,\rm cm^{-2}$ could be hidden in the observational noise if assuming similar emission conditions of water as the detected hydrocarbons. Contrary to previous 0D slab results, a C4H2 quasi-continuum is robustly identified. We expect some of the stated differences to previous 0D slab fitting results to arise from an updated data reduction of the spectrum, but also due to the different modelling process. The latter reason underpins the need for more advanced models and fitting procedures., Comment: accepted by Astronomy & Astrophysics

Understanding the formation history of planets is one of the goals of studying exoplanet atmospheres. The atmospheric composition of planets can provide insights into the formation pathways of planets. Even though the mapping of the atmospheric composition onto a formation pathway is not unambiguous, with the increasing sensitivity of modern instruments, we can derive promising constraints. In this work, we aim to understand the formation pathway of WASP-39b. We discuss whether the detection of SO2 in its atmosphere would impact our understanding of the formation of the planet and whether it enables us to determine the formation pathway of the planet with greater accuracy. We used the JWST transit observation of the planet together with the available HST and Spitzer observations. We used a formation model coupled with a radiative transfer retrieval model to derive the planet's atmospheric characteristics and formation history. Furthermore, we used a photochemical model to derive the impact of photochemistry on the atmosphere of the planet. In this work, we show that the planet is most likely to have initiated beyond the CO2 ice line of its natal disk. Furthermore, the planet is likely to have have accreted some planetesimals during its formation. We show that the sulfur abundance in the atmosphere of the planet is probably lower than $2.27 \times 10^{-4}$. This abundance indicates that the planet is likely to exhibit a lower metallicity than suggested by the retrievals. Furthermore, such an abundance for sulfur is more likely if WASP-39b had been formed beyond the CO ice line of its natal disk., Comment: 10 pages, 7 figures, 5 tables

The Mid-InfraRed Instrument (MIRI) on board the James Webb Space Telescope (JWST) probes the chemistry and dust mineralogy of the inner regions of protoplanetary disks. The observed spectra are unprecedented in their detail, complicating interpretations which are mainly based on manual continuum subtraction and 0D slab models. We investigate the physical conditions under which the gas emits in protoplanetary disks. Based on MIRI spectra, we apply a full Bayesian analysis that provides the posterior distributions of dust and molecular properties. For doing so, we introduce the Dust Continuum Kit with Line emission from Gas (DuCKLinG), a model describing the molecular line emission and the dust continuum simultaneously without large computational cost. The dust model is based on work by Juhasz et al. (2009, 2010). The molecular emission is based on LTE slab models, but with radial gradients in column densities and temperatures. The model is compared to observations using Bayesian analysis. We benchmark this model to a complex thermo-chemical ProDiMo model and fit the MIRI spectrum of GWLup. We find that the retrieved molecular conditions from DuCKLinG fall within the true values from ProDiMo. The column densities retrieved by Grant et al. (2023) fall within the retrieved ranges in this study for all examined molecules (CO2, H2O, HCN, and C2H2). Similar overlap is found for the temperatures with only the temperature range of HCN not including the previously found value. This discrepancy may be due to the simultaneous fitting of all molecules compared to the step-by-step fitting of the previous study. There is statistically significant evidence for radial temperature and column density gradients for H2O and CO2 compared to the constant temperature and column density assumed in the 0D slab models. Additionally, HCN and C2H2 emit from a small region with near constant conditions., Comment: accepted by Astronomy & Astrophysics

The first JWST observations of hot Jupiters showed an unexpected detection of SO2 in their hydrogen-rich atmospheres. We investigate how much sulphur can be expected in the atmospheres of rocky exoplanets and which sulphur molecules can be expected to be most abundant and detectable by transmission spectroscopy. We run thermo-chemical equilibrium models at the crust-atmosphere interface, considering surface temperatures 500 to 5000 K, surface pressures 1 to 100 bar, and various sets of element abundances based on common rock compositions. Between 1000 K and 2000 K, we find gaseous sulphur concentrations of up to 25 percent above the rock in our models. SO2, SO, H2S and S2 are by far the most abundant sulphur molecules. SO2 shows potentially detectable features in transmission spectra at about 4 micron, between 7 and 8 micron, and beyond 15 micron. In contrast, the sometimes abundant H2S molecule is difficult to detect in these spectra, which are mostly dominated by H2O and CO2. Although the molecule PS only occurs with concentrations below 300 ppm, it can cause a strong absorption feature between 0.3 and 0.65 micron in some of our models for high surface pressures. The detection of sulphur molecules would enable a better characterisation of the planetary surface., Comment: Typos have been corrected compared to version 1

ABRIDGED. The analysis of spectral energy distributions (SEDs) of protoplanetary disks to determine their physical properties is known to be highly degenerate. Hence, a Bayesian analysis is required to obtain parameter uncertainties and degeneracies. The challenge here is computational speed, as one radiative transfer model requires a couple of minutes to compute. We performed a Bayesian analysis for 30 well-known protoplanetary disks to determine their physical disk properties, including uncertainties and degeneracies. To circumvent the computational cost problem, we created neural networks (NNs) to emulate the SED generation process. We created two sets of radiative transfer disk models to train and test two NNs that predict SEDs for continuous and discontinuous disks. A Bayesian analysis was then performed on 30 protoplanetary disks with SED data collected by the DIANA project to determine the posterior distributions of all parameters. We ran this analysis twice, (i) with old distances and additional parameter constraints as used in a previous study, to compare results, and (ii) with updated distances and free choice of parameters to obtain homogeneous and unbiased model parameters. We evaluated the uncertainties in the determination of physical disk parameters from SED analysis, and detected and quantified the strongest degeneracies. The NNs are able to predict SEDs within 1ms with uncertainties of about 5% compared to the true SEDs obtained by the radiative transfer code. We find parameter values and uncertainties that are significantly different from previous values obtained by $\chi^2$ fitting. Comparing the global evidence for continuous and discontinuous disks, we find that 26 out of 30 objects are better described by disks that have two distinct radial zones. Also, we created an interactive tool that instantly returns the SED predicted by our NNs for any parameter combination., Comment: 40 pages, 22 figures, the online tool is available at https://tillkaeufer.github.io/sedpredictor

(abridged) Stable circumbinary discs around evolved post-Asymptotic Giant branch (post-AGB) binary systems show many similarities with protoplanetary discs around young stellar objects. These discs can provide constraints on both binary evolution and the formation of macrostructures within circumstellar discs. Here we focus on one post-AGB binary system: IRAS08544-4431. We aim to refine the physical model of IRAS08544-4431 with a radiative transfer treatment and continue the near-infrared and mid-infrared interferometric analysis covering the H-, K-, L-, and N-bands. We aim to capture the previously detected amount of over-resolved flux and the radial intensity profile at and beyond the inner dust disc rim to put constraints on the physical processes in the inner disc regions. We used a Monte Carlo radiative transfer code to investigate the physical structure of the disc by reproducing both the photometry and the multi-wavelength infrared interferometric data set. We developed a strategy to identify the models which perform best to reproduce our data set. We found a family of models that successfully fit the infrared photometric and interferometric data in all bands. Some over-resolved flux component was recovered in all bands but the optimised models still fall short to explain all the over-resolved flux. This suggests that another dusty structure within the system plays a role. Multi-wavelength infrared interferometric observations of circumstellar discs allow to study the inner disc regions in unprecedented detail. The refined physical models can reproduce most of the investigated features, including the photometric characteristics, the radial extent, and the overall shape of the visibility curves. Our multi-wavelength interferometric observations combined with photometry show that the disc is similar to protoplanetary discs with similar dust masses and efficient dust growth., Comment: 18 pages, 13 figures (including apppendix), accepted for publication in A&A

The high cosmic abundance and the intermediate volatility and chemical properties of sulfur allow the use of sulfur-bearing species as a tracer of the chemical processes in the atmospheres of hot Jupiter exoplanets. Nevertheless, despite its properties and relevance as a tracer of the giant planets' formation history, little attention has been paid to this species in the context of hot Jupiter atmospheres. Here we provide an overview of the abundances of sulfur-bearing species in hot Jupiter atmospheres under different conditions and explore their observability. We use the photochemical kinetics code VULCAN to model hot Jupiter atmospheric disequilibrium chemistry. Transmission spectra for these atmospheres are created using the modelling framework ARCiS. We vary model parameters such as the diffusion coefficient, and we study the importance of photochemistry on the resulting mixing ratios. Furthermore, we vary the chemical composition of the atmosphere by increasing the metallicity from solar to ~10 times solar. We also explore different C/O ratios. We find that H2S and SO2 are the best candidates for detection between 1 and 10 micron, using a spectral resolution that is representative of the instruments on board the JWST. H2S is easiest to detect at an equilibrium temperature of ~1500 K and C/O ratios between 0.7 and 0.9, with the ideal value increasing slightly for increasing metallicity. SO2 is most likely to be detected at an equilibrium temperature of ~1000 K at low C/O ratios and high metallicities. Nevertheless, among these two molecules, we expect SO2 detection to be more common, as it is detectable in scenarios more favoured by formation models. We conclude that H2S and SO2 will most likely be detected in the coming years with the JWST and that the detection of these species will provide information on atmospheric processes and planet formation scenarios., Comment: Accepted for publication in A&A

Direct observations of young stellar objects are important to test established theories of planet formation. PDS 70 is one of the few cases where robust evidence favours the presence of two planetary mass companions inside the gap of the transition disk. Those planets are believed to be going through the last stages of accretion from the protoplanetary disk, a process likely mediated by a circumplanetary disk (CPD). We aim to develop a three dimensional radiative transfer model for the dust component of the PDS 70 system which reproduces the system's global features observed at two different wavelengths: 855 $\mu\, \mathrm{m}$ with ALMA and 1.25 $\mu\, \mathrm{m}$ with VLT/SPHERE. We use this model to investigate the physical properties of the planetary companion PDS 70 c and its potential circumplanetary disk. We select initial values for the physical properties of the planet and CPD through appropriate assumptions about the nature and evolutionary stage of the object. We modify iteratively the properties of the protoplanetary disk until the predictions retrieved from the model are consistent with both data sets. We provide a model that jointly explains the global features of the PDS 70 system seen in submillimeter and polarised-scattered light. Our model suggests that spatial segregation of dust grains is present in the protoplanetary disk. The submillimeter modelling of the PDS 70 c source favours the presence of an optically thick CPD and places an upper limit to its dust mass of 0.7 $M_\oplus$. Furthermore, analysis of the thermal structure of the CPD demonstrates that the planet luminosity is the dominant heating mechanism of dust grains inside 0.6 au from the planet while heating by stellar photons dominates at larger planetocentric distances., Comment: accepted for publication in A&A

We present a basic, fast, and flexible planet formation model, called SimAb (Simulating Abundances), to form giant planets and study their primary atmospheric composition soon after their formation. In SimAb we introduce parameters to simplify the assumptions about the complex physics involved in the formation of a planet. This approach allows us to trace and understand the influence of complex physical processes on the formed planets. We focus on the C/O ratio and the metallicity of the planetary atmosphere as an indicator of their compositions. We show that the initial protoplanet core mass does not influence the final composition of the planetary atmosphere in the context of our model. The initial orbital distance affects the C/O ratio due to the different C/O ratios in the gas phase and the solid phase at different orbital distances. Additionally, the initial orbital distance together with the amount of accreted planetesimals cause the planet to have sub-solar or super-solar metallicity. Furthermore, the C/O ratio is affected by the dust grain fraction and the planetesimal fraction. Planets that accrete most of their heavy elements through dust grains will have a C/O ratio close to the solar C/O ratio, while planets that accrete most of their heavy elements from the planetesimals in the disk will end up with a C/O ratio closer to the C/O ratio in the solid phase of the disk. By using the C/O ratio and metallicity together we can put a lower and upper boundary on the initial orbital distance where super-solar metallicity planets are formed. We show that planetesimals are the main source for reaching super-solar metallicity planets. On the other hand, planets that mainly accrete dust grains will show a more solar composition. Super-solar metallicity planets that initiate their formation farther than the CO ice line have a C/O ratio closer to the solar value., Comment: 14 pages,11 figures, Submitted to A&A

The presence of stable, compact circumbinary discs of gas and dust around post-asymptotic giant branch (post-AGB) binary systems has been well established. We focus on one such system: IRAS 08544-4431. We present an interferometric multi-wavelength analysis of the circumstellar environment of IRAS 08544-4431. The aim is to constrain different contributions to the total flux in the H, K, L, and N-bands in the radial direction. The data from VLTI/PIONIER, VLTI/GRAVITY, and VLTI/MATISSE range from the near-infrared, where the post-AGB star dominates, to the mid-infrared, where the disc dominates. We fitted two geometric models to the visibility data to reproduce the circumbinary disc: a ring with a Gaussian width and a flat disc model with a temperature gradient. The flux contributions from the disc, the primary star (modelled as a point-source), and an over-resolved component are recovered along with the radial size of the emission, the temperature of the disc as a function of radius, and the spectral dependencies of the different components. The trends of all visibility data were well reproduced with the geometric models. The near-infrared data were best fitted with a Gaussian ring model while the mid-infrared data favoured a temperature gradient model. This implies that a vertical structure is present at the disc inner rim, which we attribute to a rounded puffed-up inner rim. The N-to-K size ratio is 2.8, referring to a continuous flat source, analogues to young stellar objects. By combining optical interferometric instruments operating at different wavelengths we can resolve the complex structure of circumstellar discs and study the wavelength-dependent opacity profile. A detailed radial, vertical, and azimuthal structural analysis awaits a radiative transfer treatment in 3D to capture all non-radial complexity., Comment: 8 pages, 5 figures, accepted for publication in A&A Letters

Ultra-hot Jupiters are the hottest exoplanets discovered so far. Observations begin to provide insight into the composition of their extended atmospheres and their chemical day/night asymmetries. Both are strongly affected by cloud formation. We explore trends in cloud properties for a sample of five giant gas planets: WASP-43b, WASP-18b, HAT-P-7b, WASP-103b, and WASP-121b. This provides a reference frame for cloud properties for the JWST targets WASP-43b and WASP-121b. We further explore chemically inert tracers to observe geometrical asymmetries, and if the location of inner boundary of a 3D GCM matters for the clouds that form. The large day/night temperature differences of ultra-hot Jupiters cause large chemical asymmetries: cloud-free days but cloudy nights, atomic vs. molecular gases and respectively different mean molecular weights, deep thermal ionospheres vs. low-ionised atmospheres, undepleted vs enhanced C/O. WASP-18b, as the heaviest planet in the sample, has the lowest global C/O. The global climate may be considered as similar amongst ultra-hot Jupiters, but different to that of hot gas giants. The local weather, however, is individual for each planet since the local thermodynamic conditions, and hence the local cloud and gas properties, differ. The morning and the evening terminator of ultra-hot Jupiters will carry signatures of their strong chemical asymmetry such that ingress/egress asymmetries can be expected. An increased C/O ratio is a clear sign of cloud formation, making cloud modelling a necessity when utilizing C/O (or other mineral ratios) as tracer for planet formation. The changing geometrical extension of the atmosphere from the day to the nightside may be probed through chemically inert species like helium. Ultra-hot Jupiters are likely to develop deep atmospheric ionospheres which may impact the atmosphere dynamics through MHD processes., Comment: 38 pages, accepted for publication in A&A

The processes by which red supergiants lose mass are not fully understood thus-far and their mass-loss rates lack theoretical constraints. The ambient surroundings of the nearby M0.5 Iab star Antares offers an ideal environment to obtain detailed empirical information on the outflow properties at its onset, and hence indirectly, on the mode(s) of mass loss. We present and analyse optical VLT/SPHERE/ZIMPOL polarimetric imaging with angular resolution down to 23 milli-arcsec, sufficient to spatially resolve both the stellar disk and its direct surroundings. We detect a conspicuous feature in polarised intensity that we identify as a clump containing dust, which we characterise through 3D radiative transfer modelling. The clump is positioned behind the plane of the sky, therefore has been released from the backside of the star, and its inner edge is only 0.3 stellar radii above the surface. The current dust mass in the clump is $1.3^{+0.2}_{-1.0} \times 10^{-8}$ M$_{\odot}$, though its proximity to the star implies that dust nucleation is probably still ongoing. The ejection of clumps of gas and dust makes a non-negligible contribution to the total mass lost from the star which could possibly be linked to localised surface activity such as convective motions or non-radial pulsations., Comment: 15 pages, accepted for publication in MNRAS

With the advent of interferometric instruments with 4 telescopes at the VLTI and 6 telescopes at CHARA, the scientific possibility arose to routinely obtain milli-arcsecond scale images of the observed targets. Such an image reconstruction process is typically performed in a Bayesian framework where the function to minimize is made of two terms: the datalikelihood and the Bayesian prior. This prior should be based on our prior knowledge of the observed source. Up to now,this prior was chosen from a set of generic and arbitrary functions, such as total variation for example. Here, we present an image reconstruction framework using generative adversarial networks where the Bayesian prior is defined using state-of-the-art radiative transfer models of the targeted objects. We validate this new image reconstruction algorithm on synthetic data with added noise. The generated images display a drastic reduction of artefacts and allow a more straight forward astrophysical interpretation. The results can be seen as a first illustration of how neural networks can provide significant improvements to the image reconstruction of a variety of astrophysical sources., Comment: SPIE Astronomical Telescopes + Instrumentation 2020 conference Paper No. 11446-110

Having a short orbital period and being tidally locked makes WASP-43b an ideal candidate for JWST observations. Phase curve observations of an entire orbit will enable the mapping of the atmospheric structure across the planet, with different wavelengths of observation allowing different atmospheric depths to be seen. We provide insight into the details of the clouds that may form on WASP-43b in order to prepare the forthcoming interpretation of the JWST and follow-up data. We utilize 3D GCM results as input for a kinetic, non-equilibrium model for mineral cloud particles, and for a kinetic model to study a photochemicaly-driven hydrocarbon haze component. Mineral condensation seeds form throughout the atmosphere of WASP-43b. This is in stark contrast to the ultra-hot Jupiters, like WASP-18b and HAT-P-7b. The dayside is loaded with few but large mineral cloud particles in addition to hydrocarbon haze particles of comparable abundance. Photochemically driven hydrocarbon haze appears on the dayside, but does not contribute to the cloud formation on the nightside. The geometrical cloud extension differs across the globe due to the changing thermodynamic conditions. Day and night differ by 6000km in pressure scale height. As reported for other planets, the C/O is not constant throughout the atmosphere. The mean molecular weight is approximately constant in a H2-dominated WASP-43b. WASP-43b is expected to be fully covered in clouds which are not homogeneously distributed throughout the atmosphere. The dayside and the terminator clouds will be a combination of mineral particles of locally varying size and composition, and of hydrocarbon hazes. The optical depth of hydrocarbon hazes is considerably lower than that of mineral cloud particles such that a wavelength-dependent radius measurement of WASP-43b would be determined by the mineral cloud particles but not by hazes., Comment: 22 pages, accepted for publication A&A (correcting auto-correct)

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. The achievements obtained thus far with SPHERE (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. The SPHERE+ project capitalizes on the expertise and lessons learned from SPHERE to push high contrast imaging performance to its limits on the VLT 8m-telescope. The scientific program of SPHERE+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and WFIRST). While SPHERE has sampled the outer parts of planetary systems beyond a few tens of AU, SPHERE+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. Building on SPHERE's scientific heritage and resounding success, SPHERE+ will be a dedicated survey instrument which will strengthen the leadership of ESO and the European community in the very competitive field of direct imaging of exoplanetary systems. With enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei., Comment: White paper submitted to ESO on Feb. 20th, 2020

Our aim was to directly detect the thermal emission of the putative exoring system responsible for the complex deep transits observed in the light curve for the young Sco-Cen star 1SWASP J140747.93-394542.6 (V1400 Cen, hereafter J1407), confirming it as the occulter seen in May 2007, and to determine its orbital parameters with respect to the star. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the field centred on J1407 in the 340 GHz (Band 7) continuum in order to determine the flux and astrometric location of the ring system relative to the star. We used the VLT/NACO camera to observe the J1407 system in March 2019 and to search for the central planetary mass object at thermal infrared wavelengths. We detect no point source at the expected location of J1407, and derive an upper limit $3\sigma$ level of $57.6~\mu\rm{Jy}$. There is a point source detected at an angular separation consistent with the expected location for a free-floating ring system that occulted J1407 in May 2007, with a flux of $89~\mu\rm{Jy}$ consistent with optically thin dust surrounding a massive substellar companion. At 3.8 microns with the NACO camera, we detect the star J1407 but no other additional point sources within 1.3 arcseconds of the star, with a lower bound on the sensitivity of $6M_{Jup}$ at the location of the ALMA source, and down to $4M_{Jup}$ in the sky background limit. The ALMA upper limit at the location of J1407 implies that a hypothesised bound ring system is composed of dust smaller than $1\rm{~mm}$ in size, implying a young ring structure. The detected ALMA source has multiple interpretations, including: (i) it is an unbound substellar object surrounded by warm dust in Sco-Cen with an upper mass limit of $6M_{Jup}$, or (ii) it is a background galaxy., Comment: Accepted for publication in A&A (6 pages, 5 figures). Reduced data and reduction scripts on GitHub at https://github.com/mkenworthy/j1407_alma_detection

Post-AGB binaries are surrounded by circumbinary disks of gas and dust that are similar to protoplanetary disks found around young stars. We aim to understand the structure of these disks and identify the physical phenomena at play in their very inner regions. We want to understand the disk-binary interaction and to further investigate the comparison with protoplanetary disks. We have conducted an interferometric snapshot survey of 23 post-AGB binaries in the near-infrared (H-band) using VLTI/PIONIER. We have fitted the multiwavelength visibilities and closure phases with purely geometrical models with an increasing complexity in order to retrieve the sizes, temperatures and flux ratios of the different components All sources are resolved and the different components contributing to the H-band flux are dissected. The environment of these targets is very complex: 13/23 targets need models with thirteen or more parameters to fit the data. We find that the inner disk rims follow and extend the size-luminosity relation established for disks around young stars with an offset toward larger sizes. The measured temperature of the near-infrared circumstellar emission of post-AGB binaries is lower (Tsub~1200K) than for young stars, probably due to a different dust mineralogy and/or gas density in the dust sublimation region. The dusty inner rims of the circumbinary disks around post-AGB binaries are ruled by dust sublimation physics. Additionally, a significant amount of the circumstellar H-band flux is over-resolved (14 targets have more than 10% of their non-stellar flux over-resolved) hinting for more structure from a yet unknown origin (disk structure or outflow). The amount of over-resolved flux is larger than around young stars. Due to the complexity of these targets, interferometric imaging is a necessary tool to reveal the interacting inner regions in a model-independent way., Comment: Accepted for publication in A&A, 40 pages

The scattering properties of the dust originating from debris discs are still poorly known. The analysis of scattered light is however a powerful remote-sensing tool to understand the physical properties of dust particles orbiting other stars. Scattered light is indeed widely used to characterise the properties of cometary dust in the solar system. We aim to measure the morphology and scattering properties of the dust from the debris ring around HR4796A in polarised optical light. We obtained high-contrast polarimetric images of HR4796A in the wavelength range 600-900nm with the SPHERE / ZIMPOL instrument on the Very Large Telescope. We measured for the first time the polarised phase function of the dust in a debris system over a wide range of scattering angles in the optical. We confirm that it is incompatible with dust particles being compact spheres under the assumption of the Mie theory, and propose alternative scenarios compatible with the observations, such as particles with irregular surface roughness or aggregate particles., Comment: 12 pages, 11 figures

Consistent modeling of protoplanetary disks requires the simultaneous solution of both continuum and line radiative transfer, heating/cooling balance between dust and gas and, of course, chemistry. Such models depend on panchromatic observations that can provide a complete description of the physical and chemical properties and energy balance of protoplanetary systems. Along these lines we present a homogeneous, panchromatic collection of data on a sample of 85 T Tauri and Herbig Ae objects for which data cover a range from X-rays to centimeter wavelengths. Datasets consist of photometric measurements, spectra, along with results from the data analysis such as line fluxes from atomic and molecular transitions. Additional properties resulting from modeling of the sources such as disc mass and shape parameters. dust size and PAH properties are also provided for completeness. Targets were selected based on their properties data availability. Data from more than 50 different telescopes and facilities were retrieved and combined in homogeneous datasets directly from public data archives or after being extracted from more than 100 published articles. X-ray data for a subset of 56 sources represent an exception as they were reduced from scratch and are presented here for the first time. Compiled datasets along with a subset of continuum and emission-line models are stored in a dedicated database and distributed through a publicly accessible online system. All datasets contain metadata descriptors that allow to backtrack them to their original resources. The graphical user interface of the online system allows the user to visually inspect individual objects but also compare between datasets and models. It also offers to the user the possibility to download any of the stored data and metadata for further processing., Comment: 32 pages, 11 figures, A&A accepted

The European FP7 project DIANA has performed a coherent analysis of a large set of observations from protoplanetary disks by means of thermo-chemical disk models. The collected data include extinction-corrected stellar UV and X-ray input spectra (as seen by the disk), photometric fluxes, low and high resolution spectra, interferometric data, emission line fluxes, line velocity profiles and line maps. We define and apply a standardized modelling procedure to simultaneously fit all these data by state-of-the-art modelling codes (ProDiMo, MCFOST, MCMax) which solve the continuum and line radiative transfer, disk chemistry, and the heating & cooling balance for both the gas and the dust. We allow for up to two radial disk zones to obtain our best-fitting models that have about 20 free parameters. This approach is novel and unique in its completeness and level of consistency. In this paper, we present the results from pure SED fitting for 27 objects and from the all inclusive DIANA-standard models for 14 objects. We fit most infrared to millimeter emission line fluxes within a factor better than 3, simultaneously with SED, PAH features and radial brightness profiles extracted from images at various wavelengths. Our analysis shows a number of Herbig Ae and T Tauri stars with very cold and massive outer disks which are situated at least partly in the shadow of a tall and gas-rich inner disk. The disk masses derived are often in excess to previously published values, since these disks are partially optically thick even at millimeter wavelength and so cold that they emit less than in the Rayleigh-Jeans limit. Some line observations cannot be reproduced by the models, probably caused by foreground cloud absorption or object variability. Our data collection, the fitted physical disk parameters as well as the full model output are available at an online database (http://www.univie.ac.at/diana)., Comment: 70 pages, 35 figures, 22 tables, accepted by PASP

Context. Kepler observations have revealed a class of short period exoplanets, of which Kepler-1520 b is the prototype, which have comet-like dust tails thought to be the result of small, rocky planets losing mass. The shape and chromaticity of the transits constrain the properties of the dust particles originating from the planet's surface, offering a unique opportunity to probe the composition and geophysics of rocky exoplanets. Aims. We aim to approximate the average Kepler long-cadence light curve of Kepler-1520 b and investigate how the optical thickness and transit cross-section of a general dust tail can affect the observed wavelength dependence and depth of transit light curves. Methods. We developed a new 3D model that ejects sublimating particles from the planet surface to build up a dust tail, assuming it to be optically thin, and used 3D radiative transfer computations that fully treat scattering using the distribution of hollow spheres (DHS) method, to generate transit light curves between 0.45 and 2.5 $\mu$m. Results. We show that the transit depth is wavelength independent for optically thick tails, potentially explaining why only some observations indicate a wavelength dependence. From the 3D nature of our simulated tails, we show that their transit cross-sections are related to the component of particle ejection velocity perpendicular to the planet's orbital plane and use this to derive a minimum ejection velocity of 1.2 kms$^{-1}$. To fit the average transit depth of Kepler-1520 b of 0.87%, we require a high dust mas-loss rate of 7 $-$ 80 M$_\oplus$ Gyr$^{-1}$ which implies planet lifetimes that may be inconsistent with the observed sample. Therefore, these mass-loss rates should be considered to be upper limits., Comment: 22 pages, 22 figures, accepted for publication in A&A

We introduce a new modelling framework called FLiTs to simulate infrared line emission spectra from protoplanetary discs. This paper focuses on the mid-IR spectral region between 9.7 um to 40 um for T Tauri stars. The generated spectra contain several tens of thousands of molecular emission lines of H2O, OH, CO, CO2, HCN, C2H2, H2 and a few other molecules, as well as the forbidden atomic emission lines of SI, SII, SIII, SiII, FeII, NeII, NeIII, ArII and ArIII. In contrast to previously published works, we do not treat the abundances of the molecules nor the temperature in the disc as free parameters, but use the complex results of detailed 2D ProDiMo disc models concerning gas and dust temperature structure, and molecular concentrations. FLiTs computes the line emission spectra by ray tracing in an efficient, fast and reliable way. The results are broadly consistent with R=600 Spitzer/IRS observational data of T Tauri stars concerning line strengths, colour, and line ratios. In order to achieve that agreement, however, we need to assume either a high gas/dust mass ratio of order 1000, or the presence of illuminated disc walls at distances of a few au. The molecules in these walls cannot be photo-dissociated easily by UV because of the large densities in the walls which favour their re-formation. Most observable molecular emission lines are found to be optically thick, rendering a standard analysis with column densities difficult. We find that the difference between gas and dust temperatures in the disc surface is important for the line formation. We briefly discuss the effects of C/O ratio and choice of chemical rate network on these results. Our analysis offers new ways to infer the chemical and temperature structure of T Tauri discs from future JWST/MIRI observations, and to possibly detect secondary illuminated disc walls based on their specific mid-IR molecular signature., Comment: accepted by A&A, 13 figures, 4 tables

Context: Post-Asymptotic Giant Branch (AGB) binaries are surrounded by stable dusty and gaseous disks similar to the ones around young stellar objects. Whereas significant effort is spent on modeling observations of disks around young stellar objects, the disks around post-AGB binaries receive significantly less attention, even though they pose significant constraints on theories of disk physics and binary evolution. Aims: We want to examine the structure of and phenomena at play in circumbinary disks around post-AGB stars. We continue the analysis of our near-infrared interferometric image of the inner rim of the circumbinary disk around IRAS08544-4431. We want to understand the physics governing this inner disk rim. Methods: We use a radiative transfer model of a dusty disk to reproduce simultaneously the photometry as well as the near-infrared interferometric dataset on IRAS08544-4431. The model assumes hydrostatic equilibrium and takes dust settling self-consistently into account. Results: The best-fit radiative transfer model shows excellent agreement with the spectral energy distribution up to mm wavelengths as well as with the PIONIER visibility data. It requires a rounded inner rim structure, starting at a radius of 8.25 au. However, the model does not fully reproduce the detected over-resolved flux nor the azimuthal flux distribution of the inner rim. While the asymmetric inner disk rim structure is likely to be the consequence of disk-binary interactions, the origin of the additional over-resolved flux remains unclear. Conclusions: As in young stellar objects, the disk inner rim of IRAS08544-4431 is ruled by dust sublimation physics. Additional observations are needed to understand the origin of the extended flux and the azimuthal perturbation at the inner rim of the disk., Comment: Accepted for publication in A&A, 13 figures, 13 pages

The study of extrasolar planets and of the Solar System provides complementary pieces of the mosaic represented by the process of planetary formation. Exoplanets are essential to fully grasp the huge diversity of outcomes that planetary formation and the subsequent evolution of the planetary systems can produce. The orbital and basic physical data we currently possess for the bulk of the exoplanetary population, however, do not provide enough information to break the intrinsic degeneracy of their histories, as different evolutionary tracks can result in the same final configurations. The lessons learned from the Solar System indicate us that the solution to this problem lies in the information contained in the composition of planets. The goal of the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL), one of the three candidates as ESA M4 space mission, is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres, which should show minimal condensation and sequestration of high-Z materials and thus reveal their bulk composition across all main cosmochemical elements. In this work we will review the most outstanding open questions concerning the way planets form and the mechanisms that contribute to create habitable environments that the compositional information gathered by ARIEL will allow to tackle, Comment: 20 pages, 6 figures, accepted for publication on Experimental Astronomy, to appear in the special issue on the ESA space mission ARIEL

Context. Multi-wavelength observations are indispensable in studying disk geometry and dust evolution processes in protoplanetary disks. Aims. We aimed to construct a 3-dimensional model of HD 163296 capable of reproducing simultaneously new observations of the disk surface in scattered light with the SPHERE instrument and thermal emission continuum observations of the disk midplane with ALMA. We want to determine why the SED of HD 163296 is intermediary between the otherwise well-separated group I and group II Herbig stars. Methods. The disk was modelled using the Monte Carlo radiative transfer code MCMax3D. The radial dust surface density profile was modelled after the ALMA observations, while the polarized scattered light observations were used to constrain the inclination of the inner disk component and turbulence and grain growth in the outer disk. Results. While three rings are observed in the disk midplane in millimeter thermal emission at $\sim$80, 124 and 200 AU, only the innermost of these is observed in polarized scattered light, indicating a lack of small dust grains on the surface of the outer disk. We provide two models capable of explaining this difference. The first model uses increased settling in the outer disk as a mechanism to bring the small dust grains on the surface of the disk closer to the midplane, and into the shadow cast by the first ring. The second model uses depletion of the smallest dust grains in the outer disk as a mechanism for decreasing the optical depth at optical and NIR wavelengths. In the region outside the fragmentation-dominated regime, such depletion is expected from state-of-the-art dust evolution models. We studied the effect of creating an artificial inner cavity in our models, and conclude that HD 163296 might be a precursor to typical group I sources., Comment: 15 pages, 12 figures

Meteorites contain minerals from Solar System asteroids with different properties (like size, presence of water, core formation). We provide new mid-IR transmission spectra of powdered meteorites to obtain templates of how mid-IR spectra of asteroidal debris would look like. This is essential for interpreting mid-IR spectra of past and future space observatories, like the James Webb Space Telescope. We show that the transmission spectra of wet and dry chondrites, carbonaceous and ordinary chondrites and achondrite and chondrite meteorites are distinctly different in a way one can distinguish in astronomical mid-IR spectra. The two observables that spectroscopically separate the different meteorites groups (and thus the different types of parent bodies) are the pyroxene-olivine feature strength ratio and the peak shift of the olivine spectral features due to an increase in the iron concentration of the olivine.

The X-ray luminosities of T Tauri stars are about two to four orders of magnitude higher than the luminosity of the contemporary Sun. As these stars are born in clusters, their disks are not only irradiated by their parent star but also by an X-ray background field produced by the cluster members. We aim to quantify the impact of X-ray background fields produced by young embedded clusters on the chemical structure of disks. Further, we want to investigate the importance of the dust for X-ray radiative transfer in disks. We present a new X-ray radiative transfer module for the radiation thermo-chemical disk code ProDiMo, which includes X-ray scattering and absorption by both the gas and dust component. For the X-ray radiative transfer, we consider irradiation by the star and by X-ray background fields. To study the impact of X-rays on the chemical structure of disks we use the well-established disk ionization tracers N2H+ and HCO+. For evolved dust populations, X-ray opacities are mostly dominated by the gas; only for photon energies $E\gtrsim5-10\,$keV, dust opacities become relevant. Consequently, the local disk X-ray radiation field is only affected in dense regions close to the disk midplane. X-ray background fields can dominate the local X-ray disk ionization rate for disk radii $r\gtrsim20\,$au. However, the N2H+ and HCO+ column densities are only significantly affected in case of low cosmic-ray ionization rates, or if the background flux is at least a factor of ten higher than the flux level expected for clusters typical for the solar vicinity. Observable signatures of X-ray background fields in low-mass star-formation regions, like Taurus, are only expected for cluster members experiencing a strong X-ray background field. For the majority of the cluster members, the X-ray background field has only little impact on the disk chemical structure., Comment: 16 pages, 12 figures, accepted for publication in A&A

Exoplanet Proxima b will be an important laboratory for the search for extraterrestrial life for the decades ahead. Here we discuss the prospects of detecting carbon dioxide at 15 um using a spectral filtering technique with the Medium Resolution Spectrograph (MRS) mode of the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). At superior conjunction, the planet is expected to show a contrast of up to 100 ppm with respect to the star. At a spectral resolving power of R=1790-2640, about 100 spectral CO2 features are visible within the 13.2-15.8 um (3B) band, which can be combined to boost the planet atmospheric signal by a factor 3-4, depending on the atmospheric temperature structure and CO2 abundance. If atmospheric conditions are favorable (assuming an Earth-like atmosphere), with this new application to the cross-correlation technique carbon dioxide can be detected within a few days of JWST observations. However, this can only be achieved if both the instrumental spectral response and the stellar spectrum can be determined to a relative precision of <= 1e-4 between adjacent spectral channels. Absolute flux calibration is not required, and the method is insensitive to the strong broadband variability of the host star. Precise calibration of the spectral features of the host star may only be attainable by obtaining deep observations of the system during inferior conjunction that serve as a reference. The high-pass filter spectroscopic technique with the MIRI MRS can be tested on warm Jupiters, Neptunes, and super-Earths with significantly higher planet/star contrast ratios than the Proxima system., Comment: 11 Pages, 4 Figures: Published in AJ - revision: corrected typo in author name

We present experimental phase functions of three types of millimeter-sized dust grains consisting of enstatite, quartz and volcanic material from Mount Etna, respectively. The three grains present similar sizes but different absorbing properties. The measurements are performed at 527 nm covering the scattering angle range from 3 to 170 degrees. The measured phase functions show two well defined regions i) soft forward peaks and ii) a continuous increase with the scattering angle at side- and back-scattering regions. This behavior at side- and back-scattering regions are in agreement with the observed phase functions for the Fomalhaut and HR 4796A dust rings. Further computations and measurements (including polarization) for millimeter sized-grains are needed to draw some conclusions about the fluffy or compact structure of the dust grains.

Shadows in transitional disks are generally interpreted as signs of a misaligned inner disk. This disk is usually beyond the reach of current day high contrast imaging facilities. However, the location and morphology of the shadow features allow us to reconstruct the inner disk geometry. We derive analytic equations of the locations of the shadow features as a function of the orientation of the inner and outer disk and the height of the outer disk wall. In contrast to previous claims in the literature, we show that the position angle of the line connecting the shadows cannot be directly related to the position angle of the inner disk. We show how the analytic framework derived here can be applied to transitional disks with shadow features. We use estimates of the outer disk height to put constraints on the inner disk orientation. In contrast with the results from Long et al. (2017), we derive that for the disk surrounding HD100453 the analytic estimates and interferometric observations result in a consistent picture of the orientation of the inner disk. The elegant consistency in our analytic framework between observation and theory strongly support both the interpretation of the shadow features as coming from a misaligned inner disk as well as the diagnostic value of near infrared interferometry for inner disk geometry., Comment: Accepted in A&A Letters

Temperature changes in the planet forming disc midplanes carry important physico-chemical consequences, such as the effect on the locations of the condensation fronts of molecules - the snowlines. Snowlines impose major chemical gradients and possibly foster grain growth. The aim of this paper is to understand how disc midplane temperature changes with gas and dust evolution, and identify trends that may influence planet formation or allow to constrain disc evolution observationally. We calculate disc temperature, hydrostatic equilibrium and dust settling in a mutually consistent way from a grid of disc models at different stages of gas loss, grain growth and hole opening. We find that the CO snowline location depends very strongly on disc properties. The CO snowline location migrates closer to the star for increasing degrees of gas dispersal and dust growth. Around a typical A type star, the snowline can be anywhere between several tens and a few hundred au, depending on the disc properties such as gas mass and grain size. In fact, gas loss is as efficient as dust evolution in settling discs, and flat discs may be gas-poor counterparts of flared discs. Our results, in the context of different pre-main sequence evolution of the luminosity in low- and intermediate-mass stars suggests very different thermal (and hence chemical) histories in these two types of discs. Discs of T Tauri stars settle and cool down while discs of Herbig Ae stars may remain rather warm throughout the pre-main sequence., Comment: 12 pages, 6 figures

To understand the chemical composition of planets, it is important to know the chemical composition of the region where they form in protoplanetary disks. Due to its fundamental role in chemical and biological processes, carbon is a key element to trace. We aim to identify the carriers and processes behind the extended NIR flux observed around several Herbig stars. We compare the extended NIR flux from objects in the PIONIER Herbig Ae/Be survey with their flux in the PAH features. HD 100453 is used as a benchmark case to investigate the influence of quantum heated particles, like PAHs or very small carbonaceous grains, in more detail. We use the Monte Carlo radiative transfer code MCMax to do a parameter study of the QHP size and scale- height and examine the influence of quantum heating on the amount of extended flux in the NIR visibilities. There is a correlation between the PAH feature flux of a disk and the amount of its extended NIR flux. We find that very small carbonaceous grains create the observed extended NIR flux around HD 100453 and still lead to a realistic SED. These results can not be achieved without using quantum heating effects, e.g. only with scattered light and grains in thermal equilibrium. It is possible to explain the extended NIR emission around Herbig stars with the presence of carbonaceous, quantum heated particles. Interferometric observations can be used to constrain the spatial distribution and typical size of carbonaceous material in the terrestrial planet forming region., Comment: 10 pages, 6 figures, 2 tables, accepted for publication at A&A

Understanding the diversity of planets requires to study the morphology and the physical conditions in the protoplanetary disks in which they form. We observed and spatially resolved the disk around the ~10 Myr old protoplanetary disk HD 100453 in polarized scattered light with SPHERE/VLT at optical and near-infrared wavelengths, reaching an angular resolution of ~0.02", and an inner working angle of ~0.09". We detect polarized scattered light up to ~0.42" (~48 au) and detect a cavity, a rim with azimuthal brightness variations at an inclination of 38 degrees, two shadows and two symmetric spiral arms. The spiral arms originate near the location of the shadows, close to the semi major axis. We detect a faint spiral-like feature in the SW that can be interpreted as the scattering surface of the bottom side of the disk, if the disk is tidally truncated by the M-dwarf companion currently seen at a projected distance of ~119 au. We construct a radiative transfer model that accounts for the main characteristics of the features with an inner and outer disk misaligned by ~72 degrees. The azimuthal brightness variations along the rim are well reproduced with the scattering phase function of the model. While spirals can be triggered by the tidal interaction with the companion, the close proximity of the spirals to the shadows suggests that the shadows could also play a role. The change in stellar illumination along the rim, induces an azimuthal variation of the scale height that can contribute to the brightness variations. Dark regions in polarized images of transition disks are now detected in a handful of disks and often interpreted as shadows due to a misaligned inner disk. The origin of such a misalignment in HD 100453, and of the spirals, is unclear, and might be due to a yet-undetected massive companion inside the cavity, and on an inclined orbit., Comment: A&A, accepted

We present a mid-IR interferometric survey of the circumstellar environment of a specific class of post-Asymptotic Giant Branch (post-AGB) binaries. For this class the presence of a compact dusty disk has been postulated on the basis of various spatially unresolved measurements. Our interferometric survey was performed with the MIDI instrument on the VLTI. In total 19 different systems were observed using variable baseline configurations. Combining all the visibilities at a single wavelength at 10.7 micron, we fitted two parametric models to the data: a uniform disk (UD) and a ring model mimicking a temperature gradient. We compared our observables of the whole sample, with synthetic data computed from a grid of radiative transfer models of passively irradiated disks in hydrostatic equilibrium. These models are computed with a Monte Carlo code that has been widely applied to describe the structure of protoplanetary disks around young stellar objects (YSO). The spatially resolved observations show that the majority of our targets cluster closely together in the distance-independent size-colour diagram, and have extremely compact N-band emission regions. The typical uniform disk diameter of the N-band emission region is about 40 mass which corresponds to a typical brightness temperature of 400-600~K. The resolved objects display very similar characteristics in the interferometric observables and in the spectral energy distributions. Therefore, the physical properties of the disks around our targets must be similar. The grid of protoplanetary disk models covers very well the observed objects. Much like for young stars, the spatially resolved N-band emission region is determined by the hot inner rim of the disk. Continued comparisons between post-AGB and protoplanetary disks will help to understand grain growth and disk evolution processes, Comment: 30 pages, 21 figures, in press in Astronomy and Astrophysics

Whether BP Piscium (BP Psc) is either a pre-main sequence T Tauri star at d ~ 80 pc, or a post-main sequence G giant at d ~ 300 pc is still not clear. As a first-ascent giant, it is the first to be observed with a molecular and dust disk. Alternatively, BP Psc would be among the nearest T Tauri stars with a protoplanetary disk (PPD). We investigate whether the disk geometry resembles typical PPDs, by comparing polarimetric images with radiative transfer models. Our VLT/SPHERE/ZIMPOL observations allow us to perform Polarimetric Differential Imaging; Reference Star Differential Imaging; and Richardson-Lucy deconvolution. We present the first visible light polarization and intensity images of the disk of BP Psc. Our deconvolution confirms the disk shape as detected before, mainly showing the southern side of the disk. In polarized intensity the disk is imaged at larger detail and also shows the northern side, giving it the typical shape of high inclination flared disks. We explain the observed disk features by retrieving the large-scale geometry with MCMax radiative transfer modeling, which yields a strongly flared model, atypical for disks of T Tauri stars., Comment: MNRAS Letter, 6 pages, 4 figures

High-contrast scattered light observations have revealed the surface morphology of several dozens of protoplanetary disks at optical and near-infrared wavelengths. Inclined disks offer the opportunity to measure part of the phase function of the dust grains that reside in the disk surface which is essential for our understanding of protoplanetary dust properties and the early stages of planet formation. We aim to construct a method which takes into account how the flaring shape of the scattering surface of an (optically thick) protoplanetary disk projects onto the image plane of the observer. This allows us to map physical quantities (scattering radius and scattering angle) onto scattered light images and retrieve stellar irradiation corrected (r^2-scaled) images and dust phase functions. We apply the method on archival polarized intensity images of the protoplanetary disk around HD 100546 that were obtained with VLT/SPHERE in R'-band and VLT/NACO in H- and Ks-band. The brightest side of the r^2-scaled R'-band polarized intensity image of HD 100546 changes from the far to the near side of the disk when a flaring instead of a geometrically flat disk surface is used for the r^2-scaling. The decrease in polarized surface brightness in the scattering angle range of ~40-70 deg is likely a result of the dust phase function and degree of polarization which peak in different scattering angle regimes. The derived phase functions show part of a forward scattering peak which indicates that large, aggregate dust grains dominate the scattering opacity in the disk surface. Projection effects of a protoplanetary disk surface need to be taken into account to correctly interpret scattered light images. Applying the correct scaling for the correction of stellar irradiation is crucial for the interpretation of the images and the derivation of the dust properties in the disk surface layer., Comment: Accepted for publication in A&A, 6 pages, 3 figures

We studied the well known circumstellar disk around the Herbig Ae/Be star HD 97048 with high angular resolution to reveal undetected structures in the disk, which may be indicative of disk evolutionary processes such as planet formation. We used the IRDIS near-IR subsystem of the extreme adaptive optics imager SPHERE at the ESO/VLT to study the scattered light from the circumstellar disk via high resolution polarimetry and angular differential imaging. We imaged the disk in unprecedented detail and revealed four ring-like brightness enhancements and corresponding gaps in the scattered light from the disk surface with radii between 39 au and 341 au. We derived the inclination and position angle as well as the height of the scattering surface of the disk from our observational data. We found that the surface height profile can be described by a single power law up to a separation ~270 au. Using the surface height profile we measured the scattering phase function of the disk and found that it is well consistent with theoretical models of compact dust aggregates. We discuss the origin of the detected features and find that low mass (< 1 M_Jup) nascent planets are a possible explanation., Comment: 11 pages, 8 Figures, accepted for publication in A&A as of September 13th 2016 (submitted July 7th)

Evaporating rocky exoplanets, such as KIC 12557548b, eject large amounts of dust grains, which can trail the planet in a comet-like tail. When such objects occult their host star, the resulting transit signal contains information about the dust in the tail. We aim to use the detailed shape of the Kepler light curve of KIC 12557548b to constrain the size and composition of the dust grains that make up the tail, as well as the mass loss rate of the planet. Using a self-consistent numerical model of the dust dynamics and sublimation, we calculate the shape of the tail by following dust grains from their ejection from the planet to their destruction due to sublimation. From this dust cloud shape, we generate synthetic light curves (incorporating the effects of extinction and angle-dependent scattering), which are then compared with the phase-folded Kepler light curve. We explore the free-parameter space thoroughly using a Markov chain Monte Carlo method. Our physics-based model is capable of reproducing the observed light curve in detail. Good fits are found for initial grain sizes between 0.2 and 5.6 micron and dust mass loss rates of 0.6 to 15.6 M_earth/Gyr (2-sigma ranges). We find that only certain combinations of material parameters yield the correct tail length. These constraints are consistent with dust made of corundum (Al2O3), but do not agree with a range of carbonaceous, silicate, or iron compositions. Using a detailed, physically motivated model, it is possible to constrain the composition of the dust in the tails of evaporating rocky exoplanets. This provides a unique opportunity to probe to interior composition of the smallest known exoplanets., Comment: 18 pages, 11 figures, A&A accepted

The presence or absence of ice in protoplanetary disks is of great importance for the formation of planets. By enhancing the solid surface density and increasing the sticking efficiency, ice catalyzes the rapid formation of planetesimals and decreases the time scale for giant planet core accretion. Aims: In this paper we analyse the composition of the outer disk around the Herbig star HD~142527. We focus on the composition of the water ice, but also analyse the abundances of previously proposed minerals. Methods: We present new Herschel far infrared spectra and a re-reduction of archival data from the Infrared Space Observatory (ISO). We model the disk using full 3D radiative transfer to obtain the disk structure. Also, we use an optically thin analysis of the outer disk spectrum to obtain firm constraints on the composition of the dust component. Results: The water ice in the disk around HD~142527 contains a large reservoir of crystalline water ice. We determine the local abundance of water ice in the outer disk (i.e. beyond 130\,AU). The re-reduced ISO spectrum differs significantly from that previously published, but matches the new Herschel spectrum at their common wavelength range. In particular, we do not detect any significant contribution from carbonates or hydrous silicates, in contrast to earlier claims. Conclusions: The amount of water ice detected in the outer disk requires $\sim80\,$\% of the oxygen atoms. This is comparable to the water ice abundance in the outer solar system, in comets and in dense interstellar clouds. The water ice is highly crystalline while the temperatures where we detect it are too low to crystallize the water on relevant time scales. We discuss the implications of this finding., Comment: Accepted for publication in A&A

We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study the photosphere, the warm molecular layer, and the inner wind of the close-by oxygen-rich AGB star R Doradus. We present observations in filters V, cntH$\alpha$, and cnt820 and investigate the surface brightness distribution of the star and of the polarised light produced in the inner envelope. Thanks to second-epoch observations in cntH$\alpha$, we are able to see variability on the stellar photosphere. We find that in the first epoch the surface brightness of R Dor is asymmetric in V and cntH$\alpha$, the filters where molecular opacity is stronger, while in cnt820 the surface brightness is closer to being axisymmetric. The second-epoch observations in cntH$\alpha$ show that the morphology of R Dor changes completely in a timespan of 48 days to a more axisymmetric and compact configuration. The polarised intensity is asymmetric in all epochs and varies by between a factor of 2.3 and 3.7 with azimuth for the different images. We fit the radial profile of the polarised intensity using a spherically symmetric model and a parametric description of the dust density profile, $\rho(r)=\rho_\circ r^{-n}$. On average, we find exponents of $- 4.5 \pm 0.5$ that correspond to a much steeper density profile than that of a wind expanding at constant velocity. The dust densities we derive imply an upper limit for the dust-to-gas ratio of $\sim 2\times10^{-4}$ at 5.0 $R_\star$. Given the uncertainties in observations and models, this value is consistent with the minimum values required by wind-driving models for the onset of a wind, of $\sim 3.3\times10^{-4}$. However, if the steep density profile we find extends to larger distances from the star, the dust-to-gas ratio will quickly become too small for the wind of R Dor to be driven by the grains that produce the scattered light., Comment: 10 pages, 8 figures, 4 tables

We investigate the effect that the turbulent mixing strength parameter $\alpha_{\rm{turb}}$ plays on near-infrared polarimetric and sub-millimetre interferometric imaging observations of transitional discs (TDs) with a gap carved by a planet. We generate synthetic observations of these objects with ALMA and VLT/SPHERE-ZIMPOL by combining hydrodynamical, dust evolution, radiative transfer and instrument models for values of $\alpha_{\rm{turb}}=[10^{-4}, 10^{-3}, 10^{-2}]$. We find that, through a combination of effects on the viscosity of the gas, the turbulent mixing and dust evolution processes, $\alpha_{\rm{turb}}$ strongly affects the morphology of the dust distribution that can be traced with these observations. We constrain the value of $\alpha_{\rm{turb}}$ to be within an order of magnitude of $10^{-3}$ in TD sources that show cavities in sub-mm continuum images while featuring continuous distribution of dust or smaller cavities in NIR-polarimetric images., Comment: Accepted 2016 March 21, MNRAS Letters. Monthly Notices of the Royal Astronomical Society: Letters 2016