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.

Correlations between the stellar, planetary, and debris components of exoplanet systems observed by Herschel

Abstract: Context. Stars form surrounded by gas- and dust-rich protoplanetary discs. Generally, these discs dissipate over a few (3–10) Myr, leaving a faint tenuous debris disc composed of second-generation dust produced by the attrition of larger bodies formed in the protoplanetary disc. Giant planets detected in radial velocity and transit surveys of main-sequence stars also form within the protoplanetary disc, whilst super-Earths now detectable may form once the gas has dissipated. Our own solar system, with its eight planets and two debris belts, is a prime example of an end state of this process. Aims. TheHerschel DEBRIS, DUNES, and GT programmes observed 37 exoplanet host stars within 25 pc at 70, 100, and 160 μm with the sensitivity to detect far-infrared excess emission at flux density levels only an order of magnitude greater than that of the solar system’s Edgeworth-Kuiper belt. Here we present an analysis of that sample, using it to more accurately determine the (possible) level of dust emission from these exoplanet host stars and thereafter determine the links between the various components of these exoplanetary systems through statistical analysis. Methods. We have fitted the flux densities measured from recent Herschel observations with a simple two parameter (Td, LIR/L� ) black-body model (or to the 3σ upper limits at 100 μm). From this uniform approach we calculated the fractional luminosity, radial extent and dust temperature. We then plotted the calculated dust luminosity or upper limits against the stellar properties, e.g. effective temperature, metallicity, and age, and identified correlations between these parameters. Results. A total of eleven debris discs are identified around the 37 stars in the sample. An incidence of ten cool debris discs around the Sun-like exoplanet host stars (29 ± 9%) is consistent with the detection rate found by DUNES (20.2 ± 2.0%). For the debris disc systems, the dust temperatures range from 20 to 80 K, and fractional luminosities (LIR/L� ) between 2.4 ×10 −6 and 4.1 ×10 −4 . In the case of non-detections, we calculated typical 3σ upper limits to the dust fractional luminosities of a few ×10 −6 . Conclusions. We recover the previously identified correlation between stellar metallicity and hot-Jupiter planets in our data set. We find a correlation between the increased presence of dust, lower planet masses, and lower stellar metallicities. This confirms the recently identified correlation between cold debris discs and low-mass planets in the context of planet formation by core accretion.

A clumpy-cloud photon-dominated regions model of the global far-infrared line emission of the Milky Way

Abstract: Context. The fractal structure of the interstellar medium suggests that the interaction of UV radiation with the ISM as described in the context of photon-dominated regions (PDR) dominates most of the physical and chemical conditions, and hence the far-infrared and submm emission from the ISM in the Milky Way. Aims. We investigate to what extent the Galactic FIR line emission of the important species CO, C, C + , and O, as observed by the Cosmic Background Explorer (COBE) satellite can be modeled in the framework of a clumpy, UV-penetrated cloud scenario. Methods. The far-infrared line emission of the Milky Way is modeled as the emission from an ensemble of clumps with a power law clump mass spectrum and mass-size relation with power-law indices consistent with the observed ISM structure. The individual clump line intensities are calculated using the KOSMA-τ PDR-model for spherical clumps. The model parameters for the cylindrically symmetric Galactic distribution of the mass density and volume filling factor are determined by the observed radial distributions. A constant FUV intensity, in which the clumps are embedded, is assumed. Results. We show that this scenario can explain, without any further assumptions and within a factor of about 2, the absolute FIR-line intensities and their distribution with Galactic longitude as observed by COBE.

Molecular line mapping of the giant molecular cloud associated with RCW 106 – III. Multimolecular line mapping

Abstract: We present multimolecular line maps obtained with the Mopra telescope towards the southern giant molecular cloud (GMC) complex G333, associated with the H ii region RCW 106. We have characterized the GMC by decomposing the 3D data cubes with gaussclumps, and investigated spatial correlations among different molecules with principal component analysis (PCA). We find no correlation between clump size and linewidth, but a strong correlation between emission luminosity and linewidth. PCA classifies molecules into high- and low-density tracers, and reveals that HCO+ and N2H+ are anticorrelated.

The X‐ray properties of young radio‐loud AGN

Abstract: We present XMM–Newton observations of a complete sample of five archetypal young radioloud active galactic nucleus (AGN), also known as Compact Symmetric Objects (CSO) or Gigahertz Peaked Spectrum (GPS) sources. They are among the brightest and best studied GPS/CSO sources in the sky, with radio powers in the range L5 GHz = 1043-44 erg s−1 and with four sources having measured kinematic ages of 570–3000 yr. All five sources are detected, and have 2-10 keV luminosities ranging from 0.5 to 4.8 × 1044 erg s−1. A detailed analysis was performed, comparing the X-ray luminosities and NH absorption column densities of the GPS/CSO galaxies with their optical and radio properties, and with those of the general population of radio galaxies. We find the following. (i) GPS/CSO galaxies show a wide range in absorption column densities with a distribution not different from that of the general population of radio galaxies.We therefore find no evidence that GPS/CSO galaxies could reside in a significantly more dense circumnuclear environment such that they could be ‘frustrated’ radio sources – hampered in their development. (ii) The ratio of radio to X-ray luminosity is significantly higher for GPS/CSO sources than for classical radio sources. This is consistent with an evolution scenario in which young, compact radio sources are more efficient radio emitters than large extended objects, at a constant accretion power. (iii) Taking the X-ray luminosity of radio sources as a measure of their ionization power, we find that GPS/CSO sources are significantly underluminous in their [O III]5007A line luminosity, including a weak trend with age. This is consistent with the fact that the Str¨omgren sphere should still be expanding in these young objects. If true, this would mean that here we are witnessing the birth of the narrow-line region of radio-loud AGN.

Modelling the role of fires in the terrestrial carbon balance by incorporating SPITFIRE into the global vegetation model ORCHIDEE – Part 2: Carbon emissions and the role of fires in the global carbon balance

Abstract: . Carbon dioxide emissions from wild and anthropogenic fires return the carbon absorbed by plants to the atmosphere, and decrease the sequestration of carbon by land ecosystems. Future climate warming will likely increase the frequency of fire-triggering drought, so that the future terrestrial carbon uptake will depend on how fires respond to altered climate variation. In this study, we modelled the role of fires in the global terrestrial carbon balance for 1901–2012, using the ORCHIDEE global vegetation model equipped with the SPITFIRE model. We conducted two simulations with and without the fire module being activated, using a static land cover. The simulated global fire carbon emissions for 1997–2009 are 2.1 Pg C yr−1, which is close to the 2.0 Pg C yr−1 as estimated by GFED3.1. The simulated land carbon uptake after accounting for emissions for 2003–2012 is 3.1 Pg C yr−1, which is within the uncertainty of the residual carbon sink estimation (2.8 ± 0.8 Pg C yr−1). Fires are found to reduce the terrestrial carbon uptake by 0.32 Pg C yr−1 over 1901–2012, or 20% of the total carbon sink in a world without fire. The fire-induced land sink reduction (SRfire) is significantly correlated with climate variability, with larger sink reduction occurring in warm and dry years, in particular during El Nino events. Our results suggest a "fire respiration partial compensation". During the 10 lowest SRfire years (SRfire = 0.17 Pg C yr−1), fires mainly compensate for the heterotrophic respiration that would occur in a world without fire. By contrast, during the 10 highest SRfire fire years (SRfire = 0.49 Pg C yr−1), fire emissions far exceed their respiration partial compensation and create a larger reduction in terrestrial carbon uptake. Our findings have important implications for the future role of fires in the terrestrial carbon balance, because the capacity of terrestrial ecosystems to sequester carbon will be diminished by future climate change characterized by increased frequency of droughts and extreme El Nino events.