Searching for planets by differential astrometry with large telescopes     

Richard Dekany  Roger Angel  Keith Hege  Dave Wittman 《Astrophysics and Space Science》1994,212(1-2):299-319

Traditional astrometric methods are limited in accuracy by the atmosphere in a way that does not show much improvement with increased telescope aperture. However, there is the potential for very high accuracy with large telescopes if advantage can be taken of these factors: First, the differential atmospheric distortion of images of closely adjacent stars is less with larger aperture; second, the diffraction limit is sharper, and third, photon statistics are improved. In this paper we analyze and give experimental tests of techniques that could be applied to the detection of planets with the mass of Jupiter or Uranus, if they are present in nearby binary star systems.The atmospheric perturbation of the relative position of the energy centroids measured in short exposure images of binary stars depends on the effective height of the turbulent distortion. For a 4-meter telescope, the error in centroid determination of a 4-arcsec binary can be as small as 20 milliarcsec (mas) in a single 20-millisecond (msec) exposure. The relative position measured by cross-correlation of short exposure speckle images, as suggested by McAlister (1977b), may give even higher accuracy. In this case, Roddier (Roddieret al., 1980) has shown that the atmospheric error depends on the thickness rather than the height of the layers that make the dominant contribution to the turbulence. Through Monte Carlo analysis we show that on occasions when the turbulence arises largely in a thin layer, a single 20-msec exposure of a 4-arcsec binary taken with a 4-m aperture can yield an astrometric accuracy of order 0.5 mas.We report on experiments made at the Steward Observatory 2.3-m telescope which achieved accuracies corresponding to 1.7 mas in a 2.24-arcsec binary and 16.1 mas in a 6.0-arcsec binary with only 15 and 18 specklegram pairs respectively. We plan to use the 6.5-m converted MMT to obtain much higher performance, between 4.0 mas and 0.40 masper independent specklegram pair, depending upon atmospheric conditions, for binaries of 4-arcsec separation. By cycling rapidly through perhaps 100 binaries, thus calibrating systematic errors through the average change in binary separation, Jupiter-mass planets may be detectable with small but regular access to the telescope.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

Local people unprotected by protected (depopulated) natural areas: the case of Sierra Norte Guadalajara,Spain     

Angel Paniagua 《GeoJournal》2018,83(5):993-1004

The aim of this study is to place the current geographical debate on nature in the context of protected natural areas severely affected by depopulation processes, in which the daily lives of the inhabitants have been altered by changes in the traditional balance between human and non-human populations. A significantly humanized area within the Sierra Norte de Guadalajara National Park in central Spain is considered as an example. The qualitative methodology followed is based on documentary analysis and interviews with key inhabitants in the area, revealing narratives with a productive or consumer view of the nature. The national park appears as a container of a cultural nature, initially created by the traditional inhabitants, which generates an artificial, excessive nature and accelerates regressive sociodemographic dynamics.  相似文献   

Deformation and Gravity Change: Indicators of Isostasy, Tectonics, Volcanism and Climate Change, Volume III. Introduction     

Detlef Wolf  Miguel Angel Santoyo  José Fernández 《Pure and Applied Geophysics》2012,169(8):1329-1330

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March 1, 2005 Daylight Fireball Over Galicia (NW of Spain) and Minho (N. Portugal)     

José Angel Docobo  Josep Maria Trigo-Rodríguez  Jiri Borovicka  Vakhtang S. Tamazian  Vera Assis Fernandes  Jordi Llorca 《Earth, Moon, and Planets》2008,102(1-4):537-542

A daylight bolide was observed over Galicia (NW Spain) and Minho (N. Portugal) on March 1, 2005 at 15 h10 min ± 3 min UTC. We interviewed 23 eyewitnesses of the event in order to obtain the azimuth, altitude, and slope of the fireball’s trajectory. Reports suggest an atmospheric ending height below 20 km, indicating that meteorite survival was likely. From the reconstructed trajectory and the fireball’s duration, we obtained the approximate heliocentric orbits for the meteoroid. Assuming an entry velocity higher than 20 km s⁻¹ which is consistent with its estimated duration, the meteoroid originated in the asteroid belt.  相似文献   

Assessment of soft-bottom Polychaeta assemblage affected by a spatial confluence of impacts: Sewage and brine discharges     

Del-Pilar-Ruso Yoana  De-la-Ossa-Carretero Jose Antonio  Loya-Fernández Angel  Ferrero-Vicente Luis Miguel  Giménez-Casalduero Francisca  Sánchez-Lizaso Jose Luis 《Marine pollution bulletin》2009,58(5):776-782

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Effects of Physical Processes and Sampling Resolution on Fault Displacement Versus Length Scaling: The Case of the Cantarell Complex Oilfield,Gulf of Mexico     

Shunshan Xu  Angel F. Nieto-Samaniego  Gustavo Murillo-Muñetón  Susana A. Alaniz-Álvarez  José M. Grajales-Nishimura  Luis G. Velasquillo-Martinez 《Pure and Applied Geophysics》2016,173(4):1125-1142

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Spatial assessment of fishing effort around European marine reserves: implications for successful fisheries management   总被引：7，自引：0，他引：7  

Stelzenmüller V  Maynou F  Bernard G  Cadiou G  Camilleri M  Crec'hriou R  Criquet G  Dimech M  Esparza O  Higgins R  Lenfant P  Pérez-Ruzafa A 《Marine pollution bulletin》2008,56(12):2018-2026

We examined the spatial dynamic of artisanal fishing fleets around five European marine protected areas (MPAs) to derive general implications for the evaluation of MPAs as fisheries management tools. The coastal MPAs studied were located off France, Malta and Spain and presented a variety of spatial designs and processes of establishment. We developed a standardized methodology to define factors influencing effort allocation and to produce fishing effort maps by merging GIS with geostatistical modelling techniques. Results revealed that in most cases the factors “distance to the no-take”, “water depth”, and “distance to the port” had a significant influence on effort allocation by the fishing fleets. Overall, we found local concentration of fishing effort around the MPA borders. Thus, neglecting the pattern of fishing effort distribution in evaluating MPA benefits, such as spillover of biomass, could hamper sound interpretation of MPAs as fisheries management tools.  相似文献   

Using M-AMBI in assessing benthic quality within the Water Framework Directive: some remarks and recommendations   总被引：1，自引：1，他引：0  

Borja A  Mader J  Muxika I  Rodríguez JG  Bald J 《Marine pollution bulletin》2008,56(7):1377-1379

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Scale effects on modelling the seismic signature of gas: results from an outcrop analogue          下载免费PDF全文

Maria‐Daphne Mangriotis  Colin MacBeth  Angel Briceño 《Geophysical Prospecting》2018,66(6):1159-1179

Numerous examples of reservoir fields from continental and marine environments involve thin‐bedded geology, yet, the inter‐relationship between thin‐bedded geology, fluid flow and seismic wave propagation is poorly understood. In this paper, we explore the 4D seismic signature due to saturation changes of gas within thin layers, and address the challenge of identifying the relevant scales and properties, which correctly define the geology, fluid flow and seismic wave propagation in the field. Based on the study of an outcrop analogue for a thin‐bedded turbidite, we model the time‐lapse seismic response to fluid saturation changes for different levels of model scale, and explore discrepancies in quantitative seismic attributes caused by upscaling. Our model reflects the geological complexity associated with thin‐bedded turbidites, and its coupling to fluid flow, which in turn affects the gas saturation distribution in space, and its time‐lapse seismic imprint. Rock matrix and fluid properties are modelled after selected fields to reproduce representative field models with realistic impedance contrasts. In addition, seismic modelling includes multiples, in order to assess their contribution in seismic propagation through thin gas layers. Our results show that multiples could contribute significantly to the measured amplitudes in the case of thin‐bedded geology. This suggests that forward/inverse modelling involving the flow simulation and seismic domains used in time‐lapse seismic interpretation should account for thin layers, when these are present in the geological setting.  相似文献   

Is delta-aminolevulinic acid dehydratase activity in bivalves from south-west Iberian Peninsula a good biomarker of lead exposure?     

Kalman J  Riba I  Blasco J  DelValls TA 《Marine environmental research》2008,66(1):38-40

The coast of Huelva is considered as a heavily contaminated area where the Tinto and Odiel rivers discharge after running through a metalliferous mining area in the Iberian Pyrite Belt and end in common estuary called Ría of Huelva. Lead is a highly toxic and widely distributed element in the aquatic environment; therefore there is a great interest in assessing the impact of this contaminant on aquatic organisms. To study the bioavailability and sources of lead, the bivalve species Chamelea gallina was collected from six sampling sites along the coast of Huelva. Besides the effect of this metal on the enzyme activity, delta-aminolevulinic acid dehydratase (ALA-D) was determined in the whole tissue. Results show the inverse relationship between the lead concentration and the activity of ALA-D measured in whole tissues (r2=0.7). Individuals collected from the Ría of Huelva estuary had the highest levels of total lead concentrations and the lowest activity of ALA-D. Lead isotope analyses demonstrated the different sources of lead contamination and also confirmed the influence of Ría of Huelva on the metal input to the marine environment.  相似文献