Radiative transfer in protoplanetary disks

We present a new 3D continuum radiative transfer code, MCFOST, based on a Monte-Carlo method. The reliability and efficiency of the code is tested by comparison with five different radiative transfer codes previously tested by Pascucci et al., 2004, using a 2D disk configuration. When tested against the same disk configuration, no significant difference is found between the temperature and SED calculated with MCFOST and with the other codes. The computed values are well within the range of values computed by the other codes. The code-to-code differences are small, they rarely exceed 10% and are usually much smaller.Comment: 20 pages, 11 figures, GRETA conference : "Radiative transfer and Applications to Very Large Telescopes

A Herschel PACS survey of the dust and gas in Upper Scorpius disks

We present results of far-infrared photometric observations with Herschel PACS of a sample of Upper Scorpius stars, with a detection rate of previously known disk-bearing K and M stars at 70, 100, and 160 micron of 71%, 56%, and 50%, respectively. We fit power-law disk models to the spectral energy distributions of K & M stars with infrared excesses, and have found that while many disks extend in to the sublimation radius, the dust has settled to lower scale heights than in disks of the less evolved Taurus-Auriga population, and have much reduced dust masses. We also conducted Herschel PACS observations for far-infrared line emission and JCMT observations for millimeter CO lines. Among B and A stars, 0 of 5 debris disk hosts exhibit gas line emission, and among K and M stars, only 2 of 14 dusty disk hosts are detected. The OI 63 micron and CII 157 micron lines are detected toward [PZ99] J160421.7-213028 and [PBB2002] J161420.3-190648, which were found in millimeter photometry to host two of the most massive dust disks remaining in the region. Comparison of the OI line emission and 63 micron continuum to that of Taurus sources suggests the emission in the former source is dominated by the disk, while in the other there is a significant contribution from a jet. The low dust masses found by disk modeling and low number of gas line detections suggest that few stars in Upper Scorpius retain sufficient quantities of material for giant planet formation. By the age of Upper Scorpius, giant planet formation is essentially complete.Comment: 48 pages, 14 figures, accepted A&

Continuum and line modelling of discs around young stars. I. 300000 disc models for Herschel/GASPS

We have combined the thermo-chemical disc code ProDiMo with the Monte Carlo radiative transfer code MCFOST to calculate a grid of ~300000 circumstellar disc models, systematically varying 11 stellar, disc and dust parameters including the total disc mass, several disc shape parameters and the dust-to-gas ratio. For each model, dust continuum and line radiative transfer calculations are carried out for 29 far IR, sub-mm and mm lines of [OI], [CII], 12CO and o/p-H2O under 5 inclinations. The grid allows to study the influence of the input parameters on the observables, to make statistical predictions for different types of circumstellar discs, and to find systematic trends and correlations between the parameters, the continuum fluxes, and the line fluxes. The model grid, comprising the calculated disc temperatures and chemical structures, the computed SEDs, line fluxes and profiles, will be used in particular for the data interpretation of the Herschel open time key programme GASPS. The calculated line fluxes show a strong dependence on the assumed UV excess of the central star, and on the disc flaring. The fraction of models predicting [OI] and [CII] fine-structure lines fluxes above Herschel/PACS and Spica/SAFARI detection limits are calculated as function of disc mass. The possibility of deriving the disc gas mass from line observations is discussed.Comment: accepted by MNRAS. 5 pages, 4 figures, 3 table

HST Scattered Light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-Hα\alpha 569

We present new HST ACS observations and detailed models for a recently discovered edge-on protoplanetary disk around ESO H$\alpha$ 569 (a low-mass T Tauri star in the Cha I star forming region). Using radiative transfer models we probe the distribution of the grains and overall shape of the disk (inclination, scale height, dust mass, flaring exponent and surface/volume density exponent) by model fitting to multiwavelength (F606W and F814W) HST observations together with a literature compiled spectral energy distribution. A new tool set was developed for finding optimal fits of MCFOST radiative transfer models using the MCMC code emcee to efficiently explore the high dimensional parameter space. It is able to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in those derived properties. We confirm that ESO H$\alpha$ 569 is an optically thick nearly edge-on protoplanetary disk. The shape of the disk is well described by a flared disk model with an exponentially tapered outer edge, consistent with models previously advocated on theoretical grounds and supported by millimeter interferometry. The scattered light images and spectral energy distribution are best fit by an unusually high total disk mass (gas+dust assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.Comment: Accepted for publication in Ap

The Anatomy of an Unusual Edge-on Protoplanetary Disk. II. Gas temperature and a warm outer region

We present high-resolution $^{12}$CO and $^{13}$CO 2-1 ALMA observations, as well as optical and near-infrared spectroscopy, of the highly-inclined protoplanetary disk around SSTC2D J163131.2-242627. The spectral type we derive for the source is consistent with a $\rm 1.2 \, M_{\odot}$ star inferred from the ALMA observations. Despite its massive circumstellar disk, we find little to no evidence for ongoing accretion on the star. The CO maps reveal a disk that is unusually compact along the vertical direction, consistent with its appearance in scattered light images. The gas disk extends about twice as far away as both the submillimeter continuum and the optical scattered light. CO is detected from two surface layers separated by a midplane region in which CO emission is suppressed, as expected from freeze-out in the cold midplane. We apply a modified version of the Topographically Reconstructed Distribution method presented by Dutrey et al. 2017 to derive the temperature structure of the disk. We find a temperature in the CO-emitting layers and the midplane of $\sim$33 K and $\sim$20 K at $\rm R<200$ au, respectively. Outside of $\rm R>200$ au, the disk's midplane temperature increases to $\sim$30 K, with a nearly vertically isothermal profile. The transition in CO temperature coincides with a dramatic reduction in the sub-micron and sub-millimeter emission from the disk. We interpret this as interstellar UV radiation providing an additional source of heating to the outer part of the disk.Comment: 27 pages, 18 figures, 1 tabl

The compound machinery of government: The case of seconded officials in the European commission

This article explores the compound machinery of government. Attention is directed toward decision making within the core executive of the European Union - the European Commission. The article studies seconded national civil servants (SNEs) hired on short-term contracts. The analysis benefits from an original and rich body of surveys and interview data derived from current and former SNEs. The decision-making dynamics of SNEs are shown to contain a compound mix of departmental, epistemic, and supranational dynamics. This study clearly demonstrates that the socializing power of the Commission is conditional and only partly sustained when SNEs exit the Commission. Any long-lasting effect of socialization within European Union's executive machinery of government is largely absent. The compound decision-making dynamics of SNEs are explained by (1) the organizational affiliations of SNEs, (2) the formal organization of the Commission apparatus, and (3) only partly by processes of resocialization of SNEs within the Commission

Modelling the urban heat island : sensitivity to land cover data

The MOCCA (MOnitoring the City's Climate and Atmosphere) network is measuring since July 2016 the urban climate of Ghent by using high-accuracy weather stations installed in different urban environments. Urban canopy temperature observations clearly show that surface properties (e.g. land cover fraction, building height...) determine the urban heat island (UHI) intensity. This relationship is also expected in simulations of the UHI since the radiation and energy balance in a land surface model, coupled to an atmospheric model, is based upon the characteristics of the surface. In this study we illustrate how the use of more accurate land cover data in the SURFEX surface scheme leads to an improved simulation of the nocturnal UHI of Ghent. As the modelled UHI is very sensitive to the land cover fractions, it can be concluded that it is important to use accurate, up-to-date surface information based on the newest techniques of remote sensing for UHI modelling