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.

Uncertainties in the space-based measurements of CO2 columns due to scattering in the Earth's atmosphere

Abstract: During the next decade satellites may be expected to provide a promising new source of CO 2 data However, in order for the column-integrated CO 2 measurements to be useful for sources/sinks inversions, the requirements on these measurements are very demanding In this paper we therefore quantify the largest error source for such CO 2 measurements in the near-infrared wavelength range ( ∼ 16 μ m ) , namely the effect of aerosols and thin cirrus clouds in the atmosphere The errors are provided for the most common used observation geometries, nadir observations over land and sunglint observations over the ocean It is estimated that for dust aerosols the aerosol optical thickness must be known within ± 005 for errors below ± 05 % in the CO 2 total column For other aerosol types the requirements are less strict (eg ± 015 for sulfate aerosols) In the case of thin cirrus clouds over land the cirrus optical thickness must be known to ± 005 over land surfaces and ± 0015 for sunglint observations over the ocean in case of moderate windspeed

Optical to near-infrared transit observations of super-Earth GJ 1214b: water-world or mini-Neptune?

Abstract: Context. GJ 1214b, the 6.55 Earth-mass transiting planet recently discovered by the MEarth team, has a mean density of ~35% of that of the Earth. It is thought that this planet is either a mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water.Aims. In the case of a hydrogen-rich atmosphere, molecular absorption and scattering processes may result in detectable radius variations as a function of wavelength. The aim of this paper is to measure these variations.Methods. We have obtained observations of the transit of GJ 1214b in the r - and I -band with the Isaac Newton Telescope (INT), in the g -, r -, i - and z -bands with the 2.2 m MPI/ESO telescope, in the K s -band with the Nordic Optical Telescope (NOT), and in the K c -band with the William Herschel Telescope (WHT). By comparing the transit depth between the the different bands, which is a measure for the planet-to-star size ratio, the atmosphere is investigated.Results. We do not detect clearly significant variations in the planet-to-star size ratio as function of wavelength. Although the ratio at the shortest measured wavelength, in g -band, is 2σ larger than in the other bands. The uncertainties in the K s and K c bands are large, due to systematic features in the light curves. Conclusions. The tentative increase in the planet-to-star size ratio at the shortest wavelength could be a sign of an increase in the effective planet-size due to Rayleigh scattering, which would require GJ 1214b to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have both clouds, to suppress planet-size variations at red optical wavelengths, as well as a sub-solar metallicity, to suppress strong molecular features in the near- and mid-infrared. However, star spots, which are known to be present on the host-star’s surface, can (partly) cancel out the expected variations in planet-to-star size ratio, because the lower surface temperature of the spots causes the effective size of the star to vary with wavelength. A hypothetical spot-fraction of ~10%, corresponding to an average stellar dimming of ~5% in the i -band, would be able to raise the near- and mid-infrared points sufficiently with respect to the optical measurements to be inconsistent with a water-dominated atmosphere. Modulation of the spot fraction due to the stellar rotation would in such case cause the observed flux variations of GJ 1214.

Galaxy And Mass Assembly (GAMA): Panchromatic Data Release (far-UV --- far-IR) and the low-z energy budget

Abstract: We present the Galaxy And Mass Assembly (GAMA) Panchromatic Data Release (PDR) constituting over 230 deg2 of imaging with photometry in 21 bands extending from the far-UV to the far-IR. These data complement our spectroscopic campaign of over 300k galaxies, and are compiled from observations with a variety of facilities including: GALaxy Evolution eXplorer, Sloan Digital Sky Survey, Visible and Infrared Telescope for Astronomy (VISTA), Wide-field Infrared Survey Explorer, and Herschel, with the GAMA regions currently being surveyed by VLT Survey Telescope (VST) and scheduled for observations by Australian Square Kilometer Array Pathfinder (ASKAP). These data are processed to a common astrometric solution, from which photometry is derived for ∼221 373 galaxies with r < 19.8 mag. Online tools are provided to access and download data cutouts, or the full mosaics of the GAMA regions in each band. We focus, in particular, on the reduction and analysis of the VISTA VIsta Kilo-degree INfrared Galaxy data, and compare to earlier data sets (i.e. 2MASS and UKIDSS) before combining the data and examining its integrity. Having derived the 21-band photometric catalogue, we proceed to fit the data using the energy balance code magphys. These measurements are then used to obtain the first fully empirical measurement of the 0.1–500 μm energy output of the Universe. Exploring the cosmic spectral energy distribution across three time-intervals (0.3–1.1, 1.1–1.8, and 1.8–2.4 Gyr), we find that the Universe is currently generating (1.5 ± 0.3) × 1035 h70 W Mpc−3, down from (2.5 ± 0.2) × 1035 h70 W Mpc−3 2.3 Gyr ago. More importantly, we identify significant and smooth evolution in the integrated photon escape fraction at all wavelengths, with the UV escape fraction increasing from 27(18) per cent at z = 0.18 in NUV(FUV) to 34(23) per cent at z = 0.06. The GAMA PDR can be found at: http://gama-psi.icrar.org/.

Evidence of a Nonequilibrium Distribution of Quasiparticles in the Microwave Response of a Superconducting Aluminum Resonator

Abstract: In a superconductor, absorption of photons with an energy below the superconducting gap leads to redistribution of quasiparticles over energy and thus induces a strong nonequilibrium quasiparticle energy distribution. We have measured the electrodynamic response, quality factor, and resonant frequency of a superconducting aluminium microwave resonator as a function of microwave power and temperature. Below 200 mK, both the quality factor and resonant frequency decrease with increasing microwave power, consistent with the creation of excess quasiparticles due to microwave absorption. Counterintuitively, above 200 mK, the quality factor and resonant frequency increase with increasing power. We demonstrate that the effect can only be understood by a nonthermal quasiparticle distribution.

Probing the turbulent mixing strength in protoplanetary disks across the stellar mass range: no significant variations

Abstract: Context. Dust settling and grain growth are the first steps in the planet-formation process in protoplanetary disks. These disks are observed around stars with different spectral types, and there are indications that the disks around lower mass stars are significantly flatter, which could indicate that they settle and evolve faster, or in a different way. Aims. We aim to test this hypothesis by modeling the median spectral energy distributions (SEDs) of three samples of protoplanetary disks: around Herbig stars, T Tauri stars and brown dwarfs. We focus on the turbulent mixing strength to avoid a strong observational bias from disk and stellar properties that depend on stellar mass. Methods. We generated SEDs with the radiative transfer code MCMax, using a hydrostatic disk structure and settling the dust in a self-consistent way with the alpha-prescription to probe the turbulent mixing strength. Results. We are able to fit all three samples with a disk with the same input parameters, scaling the inner edge to the dust evaporation radius and disk mass to millimeter photometry. The Herbig stars require a special treatment for the inner rim regions, while the T Tauri stars require viscous heating, and the brown dwarfs lack a good estimate of the disk mass because only few millimeter detections exist. Conclusions. We find that the turbulent mixing strength does not vary across the stellar mass range for a fixed grain size distribution and gas-to-dust ratio. Regions with the same temperature have a self-similar vertical structure independent of stellar mass, but regions at the same distance from the central star appear more settled in disks around lower mass stars. We find a relatively low turbulent mixing strength of alpha = 10(-4) for a standard grain size distribution, but our results are also consistent with alpha = 10(-2) for a grain size distribution with fewer small grains or a lower gas-to-dust ratio.