Flaring and self-shadowed disks around Herbig Ae stars: simulations for 10 micron interferometers

We present simulations of the interferometric visibilities of Herbig Ae star disks. We investigate whether interferometric measurements in the 10 micrometer atmospheric window are sensitive to the presence of an increased scale height at the inner disk edge, predicted by recent models. Furthermore, we investigate whether such measurements can discriminate between disks with a ``flaring'' geometry and disks with a ``flat'' geometry. We show that both these questions can be addressed, using measurements at a small number of appropriately chosen baselines. The classification of Herbig Ae stars in two groups, based on the appearance of the spectral energy distribution (SED), has been attributed to a difference in disk geometry. Sources with a group I SED would have a flaring outer disk geometry, whereas the disk of group II sources is proposed to be flat (or ``self-shadowed''). We show that this hypothesis can be tested using long-baseline interferometric measurements in the micrometer atmospheric window.Comment: 10 pages, 7 figures, accepted for publiction in Astronomy and Astrophysic

petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval

We present the easy-to-use, publicly available, Python package petitRADTRANS, built for the spectral characterization of exoplanet atmospheres. The code is fast, accurate, and versatile; it can calculate both transmission and emission spectra within a few seconds at low resolution ($\lambda/\Delta\lambda$ = 1000; correlated-k method) and high resolution ($\lambda/\Delta\lambda = 10^6$; line-by-line method), using only a few lines of input instruction. The somewhat slower correlated-k method is used at low resolution because it is more accurate than methods such as opacity sampling. Clouds can be included and treated using wavelength-dependent power law opacities, or by using optical constants of real condensates, specifying either the cloud particle size, or the atmospheric mixing and particle settling strength. Opacities of amorphous or crystalline, spherical or irregularly-shaped cloud particles are available. The line opacity database spans temperatures between 80 and 3000 K, allowing to model fluxes of objects such as terrestrial planets, super-Earths, Neptunes, or hot Jupiters, if their atmospheres are hydrogen-dominated. Higher temperature points and species will be added in the future, allowing to also model the class of ultra hot-Jupiters, with equilibrium temperatures $T_{\rm eq} \gtrsim 2000$ K. Radiative transfer results were tested by cross-verifying the low- and high-resolution implementation of petitRADTRANS, and benchmarked with the petitCODE, which itself is also benchmarked to the ATMO and Exo-REM codes. We successfully carried out test retrievals of synthetic JWST emission and transmission spectra (for the hot Jupiter TrES-4b, which has a $T_{\rm eq}$ of $\sim$ 1800 K). The code is publicly available at http://gitlab.com/mauricemolli/petitRADTRANS, and its documentation can be found at https://petitradtrans.readthedocs.io.Comment: 17 pages, 7 figures, published in A&

Onderzoek naar de oorzaken van de slechte bespeelbaarheid van enkele sportvelden in Den Haag

De dienst gemeente-plantsoenen van 's-Gravenhage heeft verzocht aandacht te besteden aan de slechte bespeelbaarheid van verscheidene van hun sportvelden (voetbal en hockey). Het probleem is , dat in natte perioden in herfst en winter te lang water op het veld blijft staan of de toplaag van het terrein te zacht wordt, waardoor het sportveld te vaak voor wedstrijden moet worden afgekeurd. Ook een te gladde toplaag wordt vaak, vooral bij hockey, als minder gewenst beschouwd. Het verzoek om enig onderzoek hield ook verband met het feit dat men de indruk had, dat het bodemkundige aspect bij aanleg en onderhoud van sportvelden nog een verwaarloosd terrein van onderzoek is

Scattered light images of spiral arms in marginally gravitationally unstable discs with an embedded planet

Scattered light images of transition discs in the near-infrared often show non-axisymmetric structures in the form of wide-open spiral arms in addition to their characteristic low-opacity inner gap region. We study self-gravitating discs and investigate the influence of gravitational instability on the shape and contrast of spiral arms induced by planet-disc interactions. Two-dimensional non-isothermal hydrodynamical simulations including viscous heating and a cooling prescription are combined with three-dimensional dust continuum radiative transfer models for direct comparison to observations. We find that the resulting contrast between the spirals and the surrounding disc in scattered light is by far higher for pressure scale height variations, i.e. thermal perturbations, than for pure surface density variations. Self-gravity effects suppress any vortex modes and tend to reduce the opening angle of planet-induced spirals, making them more tightly wound. If the disc is only marginally gravitationally stable with a Toomre parameter around unity, an embedded massive planet (planet-to-star mass ratio of $10^{-2}$) can trigger gravitational instability in the outer disc. The spirals created by this instability and the density waves launched by the planet can overlap resulting in large-scale, more open spiral arms in the outer disc. The contrast of these spirals is well above the detection limit of current telescopes.Comment: Accepted for publication in MNRAS; 13 pages, 8 figure

Invloed van organische stof op de bodemstructuur : verslag van ruim 25 jaar onderzoek op de 'Drie Miniatuur Organische-Stofbedrijven (IB 0006)' op het proefbedrijf 'Dr. Lovinkhoeve' te Marknesse

Report of more than 25 years of research on an experimental farm in the Netherland

Betekenis van groenbemesting voor de structuur van de grond

Green manuring can be quite effective only on soils that are very susceptible to slaking due to low calcium content and/or poor drainag