Netherlands Institute for Space Research

About: Netherlands Institute for Space Research is a facility organization based out in Utrecht, Netherlands. It is known for research contribution in the topics: Galaxy & Neutron star. The organization has 737 authors who have published 3026 publications receiving 106632 citations. The organization is also known as: SRON & Space Research Organisation Netherlands.

Water vapor toward starless cores: the Herschel view

Abstract: SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) 7000 AU and ~2x10^-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ~10^-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Herschel has provided the first measurement of water vapor in dark regions. Prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) are very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds.

Consistent dust and gas models for protoplanetary disks. III. Models for selected objects from the FP7 DIANA project

Abstract: The European FP7 project DIANA has performed a coherent analysis of a large set of observational data of 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, which probe the dust, polycyclic aromatic hydrocarbons (PAHs) and the gas in these objects. We define and apply a standardized modeling procedure to fit these data by state-of-the-art modeling codes (ProDiMo, MCFOST, MCMax), solving continuum and line radiative transfer (RT), disk chemistry, and the heating and cooling balance for both the gas and the dust. 3D diagnostic RT tools (e.g., FLiTs) are eventually used to predict all available observations from the same disk model, the DIANA-standard model. Our aim is to determine the physical parameters of the disks, such as total gas and dust masses, the dust properties, the disk shape, and the chemical structure in these disks. 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. It allows us to break some of the degeneracies arising from pure Spectral Energy Distribution (SED) modeling. 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. 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. 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. However, some line fluxes may deviate by a larger factor, and sometimes we find puzzling data which the models cannot reproduce. Some of these issues are 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 to the community through an online database (http://www.univie.ac.at/diana).

Retrieving Aerosol Characteristics From the PACE Mission, Part 2: Multi-Angle and Polarimetry

Abstract: The Plankton, Aerosol, Clouds, ocean Ecosystem (PACE) mission presents new opportunities and new challenges in applying observations of two complementary multi-angle polarimeters for the space-based retrieval of global aerosol properties.Aerosol remote sensing from multi-angle radiometric-only observations enables aerosol characterization to a greater degree than single-view radiometers, as demonstrated by nearly two decades of heritage instruments. Adding polarimetry to the multi-angle observations allows for the retrieval of aerosol optical depth, Angstrom exponent,parameters of size distribution, measures of aerosol absorption, complex refractive index and degree of non-sphericity of the particles, as demonstrated by two independent retrieval algorithms applied to the heritage POLarization and Directionality of the Earth's Reflectance (POLDER) instrument. The reason why this detailed particle characterization is possible is because a multi-angle polarimeter measurement contains twice the number of Degrees of Freedom of Signal (DFS) compared to an observation from a single-view radiometer. The challenges of making use of this information content involve separating surface signal from atmospheric signal, especially when the surface is optically complex and especially in the ultraviolet portion of the spectrum where we show the necessity of polarization in making that separation. The path forward is likely to involve joint retrievalsthat will simultaneously retrieve aerosol and surface properties, although advances will berequired in radiative transfer modeling and in representing optically complex constituents in those models. Another challenge is in having the processing capability that can keep pace with the output of these instruments in an operational environment. Yet, preliminaryalgorithms applied to airborne multi-angle polarimeter observations offer encouraging results that demonstrate the advantages of these instruments to retrieve aerosol layer height, particle single scattering albedo, size distribution and spectral optical depth, and also show the necessity of polarization measurements, not just multi-angle radiometricmeasurements, to achieve these results.

Herschel/HIFI observations of ionised carbon in the β Pictoris debris disk

Abstract: Context. The dusty debris disk around the 20 Myr old main-sequence A-star Pictoris is known to contain gas. Evidence points towards a secondary origin of the gas as opposed to being a direct remnant from the initial protoplanetary disk, although the dominant gas production mechanism is so far not identified. The origin of the observed overabundance of C and O compared with solar abundances of metallic elements such as Na and Fe is also unclear. Aims. Our goal is to constrain the spatial distribution of C in the disk, and thereby the gas origin and its abundance pattern. Methods. We used the HIFI instrument on board the Herschel Space Observatory to observe and spectrally resolve Cii emission at 158 m from the Pic debris disk. Assuming a disk in Keplerian rotation and a model for the line emission from the disk, we used the spectrally resolved line profile to constrain the spatial distribution of the gas. Results. We detect the Cii 158 m emission. Modelling the shape of the emission line shows that most of the gas is located at about 100 AU or beyond. We estimate a total C gas mass of 1:3 +1:3 0:5 10 2 M (central 90% confidence interval). The data suggest that more gas is located on the south-west side of the disk than on the north-east side. The shape of the emission line is consistent with the hypothesis of a well mixed gas (constant C/Fe ratio throughout the disk). Assuming instead a spatial profile expected from a simplified accretion disk model, we found it to give a significantly poorer fit to the observations. Conclusions. Since the bulk of the gas is found outside 30 AU, we argue that the cometary objects known as “falling evaporating bodies” are probably not the dominant source of gas; production from grain-grain collisions or photodesorption seems more likely. The incompatibility of the observations with a simplified accretion disk model might favour a preferential depletion explanation for the overabundance of C and O, although it is unclear how much this conclusion is a ected by the simplifications made. More stringent constraints on the spatial distribution will be available from ALMA observations of Ci emission at 609 m.

Evolution of the equatorial oscillation in Saturn's stratosphere between 2005 and 2010 from Cassini/CIRS limb data analysis

Abstract: We present an analysis of thermal infrared spectra acquired in limb viewing geometry by Cassini/CIRS in February 2010 We retrieve vertical profiles of Saturn's stratospheric temperature from 20 hPa to 10 (exp -2) hPa, at 9 latitudes between 20 deg N and 20 deg S Using the gradient thermal wind equation, we derive a map of the zonal wind field Both the temperature and the zonal wind vertical profiles exhibit an oscillation in the equatorial region These results are compared to the temperature and zonal wind maps obtained from 2005-2006 CIRS limb data, when this oscillation was first reported In both epochs, strong temperature anomalies at the equator (up to 20K) are consistent with adiabatic heating (cooling) due to a sinking (rising) motion at a speed of 01 - 02 mm/s Finally, we show that the altitude of the maximum eastward wind has moved downwards by 13 scale heights in 42 years, hence with a 'phase' speed of approximately 05 mm/s This rate is consistent with the estimated period of 147 years for the equatorial oscillation, and requires a local zonal acceleration of 11 x 10(exp -6) ms(exp -2) at the 25 hPa pressure level This downward propagation of the oscillation is consistent with it being driven by absorption of upwardly propagating waves