Realisation of a fully‐deterministic microlensing observing strategy for inferring planet populations     

M. Dominik  U.G. Jrgensen  N.J. Rattenbury  M. Mathiasen  T.C. Hinse  S. Calchi Novati  K. Harpse  V. Bozza  T. Anguita  M.J. Burgdorf  K. Horne  M. Hundertmark  E. Kerins  P. Kjrgaard  C. Liebig  L. Mancini  G. Masi  S. Rahvar  D. Ricci  G. Scarpetta  C. Snodgrass  J. Southworth  R.A. Street  J. Surdej  C.C. Thne  Y. Tsapras  J. Wambsganss  M. Zub 《Astronomische Nachrichten》2010,331(7):671-691

Within less than 15 years, the count of known planets orbiting stars other than the Sun has risen from none to more than 400 with detections arising from four successfully applied techniques: Doppler‐wobbles, planetary transits, gravitational microlensing, and direct imaging. While the hunt for twin Earths is on, a statistically well‐defined sample of the population of planets in all their variety is required for probing models of planet formation and orbital evolution so that the origin of planets that harbour life, like and including ours, can be understood. Given the different characteristics of the detection techniques, a complete picture can only arise from a combination of their respective results. Microlensing observations are well‐suited to reveal statistical properties of the population of planets orbiting stars in either the Galactic disk or bulge from microlensing observations, but a mandatory requirement is the adoption of strictly‐deterministic criteria for selecting targets and identifying signals. Here, we describe a fully‐deterministic strategy realised by means of the ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) system at the Danish 1.54‐m telescope at ESO La Silla between June and August 2008 as part of the MiNDSTEp (Microlensing Network for the Detection of Small Terrestrial Exoplanets) campaign, making use of immediate feedback on suspected anomalies recognized by the SIGNALMEN anomaly detector. We demonstrate for the first time the feasibility of such an approach, and thereby the readiness for studying planet populations down to Earth mass and even below, with ground‐based observations. While the quality of the real‐time photometry is a crucial factor on the efficiency of the campaign, an impairment of the target selection by data of bad quality can be successfully avoided. With a smaller slew time, smaller dead time, and higher through‐put, modern robotic telescopes could significantly outperform the 1.54‐m Danish, whereas lucky‐imaging cameras could set new standards for high‐precision follow‐up monitoring of microlensing events (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The Earth-Moon system during the late heavy bombardment period - Geochemical support for impacts dominated by comets     

Uffe Gråe Jørgensen  Peter W.U. Appel  Robert Frei  Yosuke Toh 《Icarus》2009,204(2):368-7225

The solid planets assembled 4.57 Gyr ago during a period of less than 100 Myr, but the bulk of the impact craters we see on the inner planets formed much later, in a narrow time interval between 3.8 and 3.9 Gyr ago, during the so-called late heavy bombardment (LHB). It is not certain what caused the LHB, and it has not been well known whether the impactors were comets or asteroids, but our present study lend support to the idea that it was comets. Due to the Earth’s higher gravity, the impactors will have hit the Earth with ∼twice the energy density that they hit the Moon, and the bombardment will have continued on Earth longer than on the Moon. All solid surface of the Earth will have been completely covered with craters by the end of the LHB.However, almost nothing of the Earth’s crust from even the end of this epoch, is preserved today. One of the very few remnants, though, is exposed as the Isua greenstone belt (IGB) and nearby areas in Western Greenland. During a field expedition to Isua, we sampled three types of metasedimentary rocks, deposited ∼3.8 billion years ago, that contain information about the sedimentary river load from larger areas of surrounding land surfaces (mica-schist and turbidites) and of the contemporaneous seawater (BIF). Our samples show evidence of the LHB impacts that took place on Earth, by an average of a seven times enrichment (150 ppt) in iridium compared to present-day ocean crust (20 ppt). The clastic sediments show slightly higher enrichment than the chemical sediments, which may be due to contamination from admixtures of mafic (proto-crustal) sources.We show that this enrichment is in agreement with the lunar cratering rate and a corresponding extraterrestrial LHB contribution to the Earth’s Hadean-Eoarchean crust, provided the bulk of the influx was cometary (i.e., of high velocity and low in CI abundance), but not if the impactors were meteorites (i.e. had velocities and abundances similar to present-day Earth-crossing asteroids). Our study is a first direct indication of the nature of the LHB impactors, and the first to find an agreement between the LHB lunar cratering rate and the Earth’s early geochemical record (and the corresponding lunar record). The LHB comets that delivered the iridium we see at Isua will at the same time have delivered the equivalent of a ∼1 km deep ocean, and we explain why one should expect a cometary ocean to become roughly the size of the Earth’s present-day ocean, not only in terms of depth but also in terms of the surface area it covers. The total impacting mass on the Earth during the LHB will have been ∼1000 tons/m².  相似文献   

Neotectonic deformation of a Late Weichselian outwash plain by deglaciation‐induced fault reactivation of a deep‐seated graben structure          下载免费PDF全文

Peter B. E. Sandersen  Flemming Jørgensen 《Boreas: An International Journal of Quaternary Research》2015,44(2):413-431

The Late Weichselian Tinglev outwash plain in southwestern Denmark slopes gently from east to west, but certain areas of the topography show unusual irregularities. Analysis of LiDAR data reveals a mosaic of smaller areas with pronounced changes in slope magnitude and orientation between neighbouring areas. The outwash plain also features notable changes in elevation across kilometre‐long lineaments and areas lying lower and higher than the expected level. The depressions in the area have previously been interpreted as the result of melting dead‐ice blocks left by the Late Weichselian ice sheet. However, borehole samples from Lake Tinglev on the outwash plain show that lake sedimentation did not start until the early Holocene (9000 years ago), which is more than 9000 years after the ice sheet had retreated. The topographical irregularities are located above the Tønder Graben structure, and we interpret these as the result of Holocene strike‐slip movements along the graben faults resulting in areas of both subsidence and uplift. The deformations of the outwash plain are interpreted as the effect of deglaciation tectonics acting within a limited time frame at the beginning of the Holocene. As the event can be related to stress release from the weight of the Scandinavian Ice Sheet, we expect that other fault zones in northern Europe would be equally prone to reactivation. Tectonic events related to deglaciation would most likely be recurrent, and the stress changes appear to have been able to induce short‐lived tectonic instability to areas normally considered tectonically stable. We conclude that this type of tectonics has had a significant impact on topography and sedimentation throughout the Quaternary.  相似文献   

Sulfate reduction below the sulfate-methane transition in Black Sea sediments     

Lars Holmkvist  Alexey Kamyshny Jr.  Christoph VogtKyriakos Vamvakopoulos  Timothy G. FerdelmanBo Barker Jørgensen 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):493-504

A sudden increase in salinity about 7000 years ago caused a shift in the deposited sediments of the Black Sea from limnic to brackish-marine. Due to the development of an anoxic deep water basin and a relatively high sulfate concentration, organic matter is mineralized primarily through sulfate reduction in modern Black Sea sediments. Earlier studies showed that sulfate-reducing bacteria are abundant within the limnic sub-surface sediment in spite of extremely low concentrations of sulfate and organic carbon. A main objective of the present study was therefore to understand the depth distribution of sulfate reduction across the different sediment units, even deep below the sulfate-methane transition. Our study combined experimental measurements of sulfate reduction using ³⁵S radiotracer with analyses of sulfur and iron geochemistry in pore water and sediment. Potential sulfate reduction rates were measured with ³⁵S in sediment samples that were amended with sulfate and organic substrates and incubated in time-series up to 48 h. Sulfate reduction could thereby be detected and quantified at depths where concentrations of sulfate were otherwise too low to enable calculation of the rates. The results demonstrate that sulfate-reducing bacteria are active several meters below the sulfate-methane transition in Black Sea sediments. The cryptic sulfate reduction below the sulfate-methane transition may be driven by sulfate produced from re-oxidation of reduced sulfur species with oxidized iron minerals buried in the deep limnic sediment.  相似文献   

Time-series spectroscopy of pulsating sdB stars – III. Line indices of PG 1605+072     

S. J. O'Toole  M. S. Jørgensen  H. Kjeldsen  T. R. Bedding  T. H. Dall  U. Heber 《Monthly notices of the Royal Astronomical Society》2003,340(3):856-862

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Biotransformation of polycyclic aromatic hydrocarbons in marine polychaetes   总被引：2，自引：0，他引：2  

Jørgensen A  Giessing AM  Rasmussen LJ  Andersen O 《Marine environmental research》2008,65(2):171-186

Deposit-feeding polychaetes constitute the dominant macrofauna in marine environments that tend to be depositional centers for organic matter and contaminants. Polychaetes are known to accumulate polycyclic aromatic hydrocarbons (PAHs) from both particulate and dissolved phases but less is known about the mechanisms underlying elimination of accumulated PAHs. An important pathway of elimination is through biotransformation which results in increased aqueous solubility of the otherwise hydrophobic PAHs. Biotransformation in marine polychaetes proceeds in a two phased process similar to those well studied in vertebrates, phase I enzymes belonging to the Cytochrome P450 (CYP) enzyme family, along with a few phase II enzymes have been identified in marine polychaetes. In this review we aim at highlighting advances in the mechanistic understanding of PAH biotransformation in marine polychaetes by including data obtained using analytical chemistry and molecular techniques. In marine polychaetes induction of CYP enzyme activity after exposure to PAHs and the mechanism behind this is currently not well established. Conflicting results regarding the inducibility of CYP enzymes from polychaetes have led to the suggestion that induction in polychaetes is mediated through a different mechanistic pathway, which is corroborated by the apparent lack of an AhR homologous in marine polychaetes. Also, none of the currently identified CYP genes from marine polychaetes are isoforms of those regulated by the AhR in vertebrates. Relatively few studies of phase II enzymes in marine polychaetes are currently available and most of these studies have not measured the activity of specific phase II enzymes and identified phase II metabolites but used an extraction technique only allowing determination of the overall amount of phase II metabolites. Studies in insects and various marine invertebrates suggest that in invertebrates, enzymes in the important phase II enzyme family, UDP-glucuronosyl transferases primarily use glucoside as co-substrate as opposed to the vertebrate cosubstrate glucuronic acid. Recent studies in marine polychaetes have however identified glucuronidation of PAHs indicating no mechanistic difference in co-substrate preference among UDP-glucuronosyl transferases between vertebrates and marine polychaetes but it might suggest a mechanistic difference between marine polychaetes and insects.  相似文献   

Virtual Environments Begin to Embrace Process‐based Geographic Analysis          下载免费PDF全文

Hui Lin  Michael Batty  Sven E Jørgensen  Bojie Fu  Milan Konecny  Alexey Voinov  Paul Torrens  Guonian Lu  A‐Xing Zhu  John P Wilson  Jianya Gong  Olaf Kolditz  Temenoujka Bandrova  Min Chen 《Transactions in GIS》2015,19(4):493-498

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Springtime coupling between chlorophyll a, sea ice and sea surface temperature in Disko Bay, West Greenland     

M.P. Heide-Jørgensen  K.L. Laidre  M.L. Logsdon 《Progress in Oceanography》2007,73(1):79-95

Alterations in sea ice and primary production are expected to have cascading influences on the food web in high Arctic marine ecosystems. This study spanned four years and examined the spring phytoplankton production bloom in Disko Bay, West Greenland (69°N, 53°W) (using chlorophyll a concentrations as a proxy) under contrasting sea ice conditions in 2001 and 2003 (heavy sea ice) and 2002 and 2004 (light sea ice). Satellite-based observations of chlorophyll a, sea ice and sea surface temperature were used together with in situ depth profiles of chlorophyll a fluorescence collected at 24 sampling stations along the south coast of Disko Island (5-30 km offshore) in May 2003 and 2004. Chlorophyll a and sea surface temperatures were also obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS: EOS-Terra and AQUA satellites) between March 2001 and July 2004. Daily SMMR/SSMI sea ice data were obtained in the same years. An empirical regional algorithm was developed to calibrate ratios of remotely sensed measurements of water leaving radiance with in situ chlorophyll a fluorescence. The optimal integration depth was 0-4 m, explaining between 70% and 91% of the variance. The spatial development of the phytoplankton bloom showed that the southwestern corner of the study area had the earliest and the largest spring phytoplankton bloom. The eastern part of Disko Bay, influenced by meltwater outflow from the glaciers, shows no signs of an early phytoplankton bloom and followed the general pattern of an accelerated bloom soon after the disappearance of sea ice. In all four years the coupling between phytoplankton and sea ice was bounded by average open water between 50% and 80%, likely due to the combined availability of light and stable open water. The daily incremental growth in both mean chlorophyll a density (chlorophyll a per volume water, μg l⁻¹) and abundance (density of chlorophyll a extrapolated to ice free areas, tons) estimated by linear regression (chlorophyll a vs. day) between 1 April and 15 May was highest in 2002 and 2004 (light ice years) and lowest in 2001 and 2003 (heavy ice years). In years with late sea ice retreat the chlorophyll a attained only slightly lower densities than in years with early sea ice retreat. However, the abundance of chlorophyll a in light ice years was considerably larger than in heavy ice years, and there was an obvious effect of more open water for light-induced stimulation of primary production. This observation demonstrates the importance of estimating chlorophyll a abundance rather than density in sea ice covered areas. This study also presents the first regional calibration of MODIS chlorophyll a data for Arctic waters.  相似文献   

Geophysical investigations of buried Quaternary valleys in Denmark: an integrated application of transient electromagnetic soundings, reflection seismic surveys and exploratory drillings   总被引：1，自引：0，他引：1  

Flemming Jrgensen  Holger Lykke-Andersen  Peter B. E. Sandersen  Esben Auken  Egon Nrmark 《Journal of Applied Geophysics》2003,53(4):215

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The poor cluster of galaxies S639     

Inger Jørgensen  & Helge Jønch-Sørensen 《Monthly notices of the Royal Astronomical Society》1998,297(3):968-976

We have studied the poor southern cluster of galaxies S639. Based on new Strömgren photometry of stars in the direction of the cluster, we confirm that the Galactic extinction affecting the cluster is large. We find the extinction in Johnson B to be A_B =0.75±0.03. We have obtained new photometry in Gunn r for E and S0 galaxies in the cluster. If the Fundamental Plane is used for determination of the relative distance and the peculiar velocity of the cluster, we find a distance, in velocity units, of (5706±350) km s⁻¹, and a substantial peculiar velocity, (839±350) km s⁻¹. However, the colours and the absorption line indices of the E and S0 galaxies indicate that the stellar populations in these galaxies are different from those in similar galaxies in the two rich clusters Coma and Hydra I. This difference may severely affect the distance determination and the derived peculiar velocity. The data are consistent with a non-significant peculiar velocity for S639 and the galaxies in the cluster being on average 0.2 dex younger than similar galaxies in Coma and Hydra I. The results for S639 caution that some large peculiar velocities may be spurious and caused by unusual stellar populations.  相似文献