| 1. |
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| 2. |
- Kasper, M., et al.
(författare)
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NEAR: : Low-mass Planets in α Cen with VISIR
- 2017
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Ingår i: The Messenger. ; 169, s. 16-20
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Tidskriftsartikel (refereegranskat)abstract
- ESO, in collaboration with the Breakthrough Initiatives, is working to modify the Very Large Telescope mid-IR imager (VISIR) to greatly enhance its ability to search for potentially habitable planets around both components of the binary Alpha Centauri, part of the closest stellar system to the Earth. Much of the funding for the NEAR (New Earths in the Alpha Cen Region) project is provided by the Breakthrough Initiatives, and ESO mostly provides staff and observing time. The concept combines adaptive optics using the deformable secondary mirror at Unit Telescope 4, a new annular groove phase mask (AGPM) coronagraph optimised for the most sensitive spectral bandpass in the N-band, and a novel internal chopper system for noise filtering based on a concept for longer wavelengths invented by the microwave pioneer Robert Dicke. The NEAR experiment is relevant to the mid-infrared METIS instrument on the Extremely Large Telescope, as the knowledge gained and proof of concept will be transferable.
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| 3. |
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| 4. |
- Akiyama, E., et al.
(författare)
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DISCOVERY OF A DISK GAP CANDIDATE AT 20 AU IN TW HYDRAE
- 2015
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 802:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a new Subaru/HiCIAO high-contrast H-band polarized intensity (PI) image of a nearby transitional disk associated with TW Hydrae. The scattered light from the disk was detected from 0 ''.2 to 1 ''.5 (11-81 AU) and the PI image shows a clear axisymmetric depression in PI at similar to 0 ''.4 (similar to 20 AU) from the central star, similar to the similar to 80 AU gap previously reported from Hubble Space Telescope images. The azimuthal PI profile also shows that the disk beyond 0 ''.2 is almost axisymmetric. We discuss two possible scenarios explaining the origin of the PI depression: (1) a gap structure may exist at similar to 20 AU from the central star because of a shallow slope seen in the PI profile, and (2) grain growth may be occurring in the inner region of the disk. Multi-band observations at near-infrared and millimeter/submillimeter wavelengths play a complementary role in investigating dust opacity and may help reveal the origin of the gap more precisely.
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| 5. |
- Asensio-Torres, Ruben, et al.
(författare)
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Polarimetry and flux distribution in the debris disk around HD 32297
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 593
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Tidskriftsartikel (refereegranskat)abstract
- We present high-contrast angular differential imaging (ADI) observations of the debris disk around HD32297 in H-band, as well as the first polarimetric images for this system in polarized differential imaging (PDI) mode with Subaru/HICIAO. In ADI, we detect the nearly edge-on disk at > 5 sigma levels from similar to 0.45 '' to similar to 1.7 '' (50-192AU) from the star and recover the spine deviation from the midplane already found in previous works. We also find for the first time imaging and surface brightness (SB) indications for the presence of a gapped structure on both sides of the disk at distances of similar to 0.75 '' (NE side) and similar to 0.65 '' (SW side). Global forward-modelling work delivers a best-fit model disk and well-fitting parameter intervals that essentially match previous results, with high-forward scattering grains and a ring located at 110AU. However, this single ring model cannot account for the gapped structure seen in our SB profiles. We create simple double ring models and achieve a satisfactory fit with two rings located at 60 and 95AU, respectively, low-forward scattering grains and very sharp inner slopes. In polarized light we retrieve the disk extending from similar to 0.25-1.6 '', although the central region is quite noisy and high S/N are only found in the range similar to 0.75-1.2 ''. The disk is polarized in the azimuthal direction, as expected, and the departure from the midplane is also clearly observed. Evidence for a gapped scenario is not found in the PDI data. We obtain a linear polarization degree of the grains that increases from similar to 10% at 0.55 '' to similar to 25% at 1.6 ''. The maximum is found at scattering angles of similar to 90 degrees, either from the main components of the disk or from dust grains blown out to larger radii.
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| 6. |
- Fuzzi, Sandro, et al.
(författare)
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Overview of the inorganic and organic composition of size-segregated aerosol in Rondonia, Brazil, from the biomass-burning period to the onset of the wet season
- 2007
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Ingår i: Journal of Geophysical Research. - 2156-2202. ; 112:D1
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Tidskriftsartikel (refereegranskat)abstract
- The aerosol characterization experiment performed within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia-Smoke, Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) field experiment carried out in Rondonia, Brazil, in the period from September to November 2002 provides a unique data set of size-resolved chemical composition of boundary layer aerosol over the Amazon Basin from the intense biomass-burning period to the onset of the wet season. Three main periods were clearly distinguished on the basis of the PM10 concentration trend during the experiment: (1) dry period, with average PM10 well above 50 mu g m(-3); (2) transition period, during which the 24-hour-averaged PM10 never exceeded 40 mu g m(-3) and never dropped below 10 mg m(-3); (3) and wet period, characterized by 48-hour-averaged concentrations of PM10 below 12 mu g m(-3) and sometimes as low as 2 mu g m(-3). The trend of PM10 reflects that of CO concentration and can be directly linked to the decreasing intensity of the biomass- burning activities from September through November, because of the progressive onset of the wet season. Two prominent aerosol modes, in the submicron and supermicron size ranges, were detected throughout the experiment. Dry period size distributions are dominated by the fine mode, while the fine and coarse modes show almost the same concentrations during the wet period. The supermicron fraction of the aerosol is composed mainly of primary particles of crustal or biological origin, whereas submicron particles are produced in high concentrations only during the biomass-burning periods and are mainly composed of organic material, mostly water-soluble, and similar to 10% of soluble inorganic salts, with sulphate as the major anion. Size-resolved average aerosol chemical compositions are reported for the dry, transition, and wet periods. However, significant variations in the aerosol composition and concentrations were observed within each period, which can be classified into two categories: (1) diurnal oscillations, caused by the diurnal cycle of the boundary layer and the different combustion phase active during day (flaming) or night (smouldering); and (2) day-to-day variations, due to alternating phases of relatively wet and dry conditions. In a second part of the study, three subperiods representative of the conditions occurring in the dry, transition, and wet periods were isolated to follow the evolution of the aerosol chemical composition as a function of changes in rainfall rate and in the strength of the sources of particulate matter. The chemical data set provided by the SMOCC field experiment will be useful to characterize the aerosol hygroscopic properties and the ability of the particles to act as cloud condensation nuclei.
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| 7. |
- Grady, C., et al.
(författare)
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The outer disks of Herbig stars from the UV to NIR
- 2015
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Ingår i: Astrophysics and Space Science. - : Springer Science and Business Media LLC. - 0004-640X .- 1572-946X. ; 355:2, s. 253-266
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Forskningsöversikt (refereegranskat)abstract
- Spatially-resolved imaging of Herbig stars and related objects began with HST, but intensified with commissioning of high-contrast imagers on 8-m class telescopes. The bulk of the data taken from the ground have been polarized intensity imagery at H-band, with the majority of the sources observed as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey. Sufficiently many systems have been imaged that we discuss disk properties in scattered, polarized light in terms of groups defined by the IR spectral energy distribution. We find novel phenomena in many of the disks, including spiral density waves, and discuss the disks in terms of clearing mechanisms. Some of the disks have sufficient data to map the dust and gas components, including water ice dissociation products.
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| 8. |
- Helminiak, K. G., et al.
(författare)
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SEEDS DIRECT IMAGING OF THE RV-DETECTED COMPANION TO V450 ANDROMEDAE, AND CHARACTERIZATION OF THE SYSTEM
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 832:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the direct imaging detection of a low-mass companion to a young, moderately active star V450. And, that was previously identified with the radial velocity (RV) method. The companion was found in high-contrast images obtained with the Subaru Telescope equipped with the HiCIAO camera and AO188 adaptive optics system. From the public ELODIE and SOPHIE archives we extracted available high-resolution spectra and RV measurements, along with RVs from the Lick planet search program. We combined our multi-epoch astrometry with these archival, partially unpublished RVs, and found that the companion is a low-mass star, not a brown dwarf, as previously suggested. We found the best-fitting dynamical masses to be m(1) = 1.141(-0.091)(+0.037)and m(2) = 0.279(-0.020)(+0.023) M-circle dot. We also performed spectral analysis of the SOPHIE spectra with the iSpec code. Hipparcos time-series photometry shows a periodicity of P = 5.743 day, which is also seen in the SOPHIE spectra as an RV modulation of the star A. We interpret it as being caused by spots on the stellar surface, and the star to be rotating with the given period. From the rotation and level of activity, we found that the system is 380(-100)(+220) Myr old, consistent with an isochrone analysis (220(-90)(+2120) Myr). This work may serve as a test case for future studies of low-mass stars, brown dwarfs, and exoplanets by combination of RV and direct imaging data.
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| 9. |
- Mangiarotti, Franco J., et al.
(författare)
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Test of the First Full-Length Prototype of the HL-LHC D2 Orbit Corrector Based on Canted Cosine Theta Technology
- 2020
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Ingår i: IEEE transactions on applied superconductivity (Print). - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1051-8223 .- 1558-2515. ; 30:4
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Tidskriftsartikel (refereegranskat)abstract
- In the context of CERN's high-luminosity upgrade project (HL-LHC) for the Large Hadron Collider (LHC), a new double aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These 2.2 m long NbTi dipoles are built with the canted cosine theta (CCT) technique. The two independently powered apertures are oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A full-length double aperture prototype was built and tested at CERN in the SM18 test facility. Here we present the results of powering tests at 1.9 and 4.5 K: training of each aperture, magnetic field quality and cross-talk effects, quench detection system effectiveness, quench protection performance and quench-back with several energy extraction systems.
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| 10. |
- Mizuki, T., et al.
(författare)
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Orbital Characterization of GJ1108A System, and Comparison of Dynamical Mass with Model-derived Mass for Resolved Binaries
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 865:2
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Tidskriftsartikel (refereegranskat)abstract
- We report an orbital characterization of GJ1108Aab that is a low-mass binary system in the pre-main-sequence phase. Via the combination of astrometry using adaptive optics and radial velocity measurements, an eccentric orbital solution of e = 0.63 is obtained, which might be induced by the Kozai-Lidov mechanism with a widely separated GJ1108B system. Combined with several observed properties, we confirm that the system is indeed young. Columba is the most probable moving group, to which the GJ1108A system belongs, although its membership to the group has not been established. If the age of Columba is assumed for GJ1108A, the dynamical masses of both GJ1108Aa and GJ1108Ab (M-dynamical,M-GJ1108Aa= 0.72 +/- 0.04 M-circle dot and M-dynamical,M-GJ1108Ab = 0.30 +/- 0.03 M-circle dot) are more massive than what an evolutionary model predicts based on the age and luminosities. We consider that the discrepancy in mass comparison can be attributed to an age uncertainty; the system is likely older than stars in Columba, and effects that are not implemented in classical models such as accretion history and magnetic activity are not preferred to explain the mass discrepancy. We also discuss the performance of the evolutionary model by compiling similar low-mass objects in the evolutionary state based on the literature. Consequently, it is suggested that the current model on average reproduces the mass of resolved low-mass binaries without any significant offsets.
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| 11. |
- Schmid, Otmar, et al.
(författare)
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Derivation of the Density and Refractive Index of Organic Matter and Elemental Carbon from Closure between Physical and Chemical Aerosol Properties
- 2009
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 1520-5851 .- 0013-936X. ; 43:4, s. 1166-1172
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Tidskriftsartikel (refereegranskat)abstract
- Information on the density (p) and refractive index m(=n-ik) of elemental carbon (ECa) and organic matter (OMa), the main carbon components of atmospheric aerosols, has frequently been obtained from closure calculations between physical and chemical aerosol properties. However, this approach has suffered from large uncertainties since there were more unknown (or poorly known) parameters than defining equations. In this study, we propose a method that avoids this ambiguity mainly by considering both optical and mass closure and by expressing the three ECa parameters (p(Eca), n(Eca), k(ECa)) by a single (unknown) parameter. This allows mathematically rigorous determination of p(Eca), m(Eca), p(OMa) and m(OMa) from standard physico-chemical aerosol data and rigorous error analysis. The results are unambiguous and self-consistent, i.e., there is no difference between the chemically and physically derived p and m values of the atmospheric aerosol. Application of this method to our previously published data on biomass burning particles from Amazonia yields p(Eca) = 1.8(+/- 0.2) g/cm(3), m(ECa) = 1.9(+/- 0.1)-i0.20(-0.04/+0.02), p(OMa) = 1.39(+/- 0.13) g/cm(3) and m(OMa)=1.46(+/- 0.02), where the 1 sigma uncertainty limits given in parenthesis are based on the principles of error propagation. The relatively low imaginary part of mEca indicates the presence of only partially graphitized elemental carbon, which is consistent with biomass burning aerosol dominated bysmoldering combustion conditions.
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| 12. |
- Wingate, L., et al.
(författare)
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Interpreting canopy development and physiology using a European phenology camera network at flux sites
- 2015
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 12:20, s. 5995-6015
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Tidskriftsartikel (refereegranskat)abstract
- Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE < 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring 'green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future.
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