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High-resolution Observations (high-resolution + observation)
Selected AbstractsInvestigating the Fate and Transport of Escherichia coli in the Charles River, Boston, Using High-Resolution Observation and Modeling,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2008Ferdi L. Hellweger Abstract:, The processes affecting the fate and transport of Escherichia coli in surface waters were investigated using high-resolution observation and modeling. The concentration patterns in Boston's Charles River were observed during four sampling events with a total of 757 samples, including two spatial surveys with two along-river (1,500 m length) and three across-river (600 m length) transects at approximately 25-m intervals, and two temporal surveys at a fixed location (Community Boating) over seven days at hourly intervals. The data reveal significant spatial and temporal structure at scales not resolved by typical monitoring programs. A mechanistic, time-variable, three-dimensional coupled hydrodynamic and water quality model was developed using the ECOMSED and RCA modeling frameworks. The computational grid consists of 3,066 grid cells with average length dimension of 25 m. Forcing functions include upstream and downstream boundary conditions, Stony Brook, and Muddy River (major tributaries) combined sewer overflow (CSO) and non-CSO discharge and wind. The model generally reproduces the observed spatial and temporal patterns. This includes the presence and absence of a plume in the study area under similar loading, but different hydrodynamic conditions caused by operation of the New Charles River Dam (downstream) and wind. The model also correctly predicts an episode of high concentrations at the time-series station following seven days of no rainfall. The model has an overall root mean square error (RMSE) of 250 CFU/100 ml and an error rate (above or below the USEPA-recommended single sample criteria value of 235 CFU/100 ml) of 9.4%. At the time series station, the model has an RMSE of 370 CFU/100 ml and an error rate of 15%. [source] High-resolution observations of SN 2001gd in NGC 5033MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005M. A. Pérez-Torres ABSTRACT We report on 8.4-GHz very-long-baseline interferometry (VLBI) observations of SN 2001gd in the spiral galaxy NGC 5033 made on 2002 June 26 (2002.48) and 2003 April 8 (2003.27). We used the interferometric visibility data to estimate angular diameter sizes for the supernova by model fitting. Our data nominally suggest a relatively strong deceleration for the expansion of SN 2001gd, but we cannot dismiss the possibility of a free supernova expansion. From our VLBI observations on 2003 April 8, we inferred a minimum total energy in relativistic particles and magnetic fields in the supernova shell of Emin= (0.3,14) × 1047 erg, and a corresponding equipartition average magnetic field of Bmin= 50,350 mG. We also present multiwavelength Very Large Array (VLA) measurements of SN 2001gd made at our second VLBI epoch at frequencies of 1.4, 4.9, 8.4, 15.0, 22.5 and 43.3 GHz. The VLA data are well fitted by an optically thin, synchrotron spectrum (,=,1.0 ± 0.1; S,,,,), partially absorbed by thermal plasma. We obtain a supernova flux density of 1.02 ± 0.05 mJy at the observing frequency of 8.4 GHz for the second epoch, which results in an isotropic radio luminosity of (6.0 ± 0.3) × 1036 erg s,1 between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we report on an XMM,Newton X-ray detection of SN 2001gd on 2002 December 18. The supernova X-ray spectrum is consistent with optically thin emission from a soft component (associated with emission from the reverse shock) at a temperature of around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of LX= (1.4 ± 0.4) × 1039 erg s,1 in the 0.3,5 keV band. We suggest that both radio and X-ray observations of SN 2001gd indicate that a circumstellar interaction similar to that displayed by SN 1993J in M 81 is taking place. [source] High-resolution observations of interstellar Na i and Ca ii towards the southern opening of the ,Local Interstellar Chimney': probing the disc,halo connectionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002I. A. Crawford ABSTRACT We present high-resolution (R= 400 000) observations of interstellar Ca ii and Na i absorption lines towards seven stars in the direction of the southern opening of the recently identified Local Interstellar Chimney. These lines of sight probe the lower Galactic halo (0.3 ,|z|, 2.5 kpc), without the complication of sampling dense foreground interstellar material. In addition to components with velocities expected from Galactic rotation, these stars also exhibit components with negative local standard of rest velocities, which are contrary to the sense of Galactic rotation for the sightlines observed. After a discussion of possible origins for these peculiar velocities, we conclude that at least some of them result from gas falling towards the Galactic plane from distances of |z|, 300 pc. The narrow linewidths are generally inconsistent with temperatures as high as the ,6000 K generally assumed for the so-called Lockman layer. Rather, the picture that emerges is one of a scattered, generally infalling, population of high- |z| diffuse clouds, seemingly not very different from those encountered in the local interstellar medium. Overall, we argue that our results are most consistent with a ,Galactic fountain' model. [source] Instrument and data analysis challenges for imaging spectropolarimetryASTRONOMISCHE NACHRICHTEN, Issue 6 2010C. Denker Abstract The next generation of solar telescopes will enable us to resolve the fundamental scales of the solar atmosphere, i.e., the pressure scale height and the photon mean free path. High-resolution observations of small-scale structures with sizes down to 50 km require complex post-focus instruments, which employ adaptive optics (AO) and benefit from advanced image restoration techniques. The GREGOR Fabry-Pérot Interferometer (GFPI) will serve as an example of such an instrument to illustrate the challenges that are to be expected in instrumentation and data analysis with the next generation of solar telescopes (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigating the Fate and Transport of Escherichia coli in the Charles River, Boston, Using High-Resolution Observation and Modeling,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2008Ferdi L. Hellweger Abstract:, The processes affecting the fate and transport of Escherichia coli in surface waters were investigated using high-resolution observation and modeling. The concentration patterns in Boston's Charles River were observed during four sampling events with a total of 757 samples, including two spatial surveys with two along-river (1,500 m length) and three across-river (600 m length) transects at approximately 25-m intervals, and two temporal surveys at a fixed location (Community Boating) over seven days at hourly intervals. The data reveal significant spatial and temporal structure at scales not resolved by typical monitoring programs. A mechanistic, time-variable, three-dimensional coupled hydrodynamic and water quality model was developed using the ECOMSED and RCA modeling frameworks. The computational grid consists of 3,066 grid cells with average length dimension of 25 m. Forcing functions include upstream and downstream boundary conditions, Stony Brook, and Muddy River (major tributaries) combined sewer overflow (CSO) and non-CSO discharge and wind. The model generally reproduces the observed spatial and temporal patterns. This includes the presence and absence of a plume in the study area under similar loading, but different hydrodynamic conditions caused by operation of the New Charles River Dam (downstream) and wind. The model also correctly predicts an episode of high concentrations at the time-series station following seven days of no rainfall. The model has an overall root mean square error (RMSE) of 250 CFU/100 ml and an error rate (above or below the USEPA-recommended single sample criteria value of 235 CFU/100 ml) of 9.4%. At the time series station, the model has an RMSE of 370 CFU/100 ml and an error rate of 15%. [source] Gas dynamics of the central few parsec region of NGC 1068 fuelled by the evolving nuclear star clusterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010M. Schartmann ABSTRACT Recently, high-resolution observations with the help of the near-infrared adaptive optics integral field spectrograph Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) at the Very Large Telescope proved the existence of massive and young nuclear star clusters in the centres of a sample of Seyfert galaxies. With the help of three-dimensional high-resolution hydrodynamical simulations with the Pluto code, we follow the evolution of such clusters, especially focusing on stellar mass loss feeding gas into the ambient interstellar medium and driving turbulence. This leads to a vertically wide distributed clumpy or filamentary inflow of gas on large scales (tens of parsec), whereas a turbulent and very dense disc builds up on the parsec scale. In order to capture the relevant physics in the inner region, we treat this disc separately by viscously evolving the radial surface density distribution. This enables us to link the tens of parsec-scale region (accessible via SINFONI observations) to the (sub-)parsec-scale region (observable with the mid-infrared interferometer instrument and via water maser emission). Thereby, this procedure provides us with an ideal testbed for data comparison. In this work, we concentrate on the effects of a parametrized turbulent viscosity to generate angular momentum and mass transfer in the disc and additionally take star formation into account. Most of the input parameters are constrained by available observations of the nearby Seyfert 2 galaxy NGC 1068, and we discuss parameter studies for the free parameters. At the current age of its nuclear starburst of 250 Myr, our simulations yield disc sizes of the order of 0.8,0.9 pc, gas masses of 106 M, and mass transfer rates of 0.025 M, yr,1 through the inner rim of the disc. This shows that our large-scale torus model is able to approximately account for the disc size as inferred from interferometric observations in the mid-infrared and compares well to the extent and mass of a rotating disc structure as inferred from water maser observations. Several other observational constraints are discussed as well. [source] Observation and modelling of main-sequence star chromospheres , X. Radiative budgets on Gl 867A and AU Mic (dM1e), and a two-component model chromosphere for Gl 205 (dM1),MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010E. R. Houdebine ABSTRACT We report on high-resolution observations of two dM1 stars: Gl 867A, an active dM1e star, and Gl 205, a less active dM1 star. The wavelength coverage is from 3890 to 6820 Ĺ with a resolving power of about 45 000. The difference spectrum of these two stars allows us to make a survey of spectral lines sensitive to magnetic activity. We chose these two stars because, to within measurement errors, they have very close properties: Gl 867A has R= 0.726 R,, [M/H]= 0.080 dex and Teff= 3416 K, and Gl 205 has R= 0.758 R,, [M/H]= 0.101 dex and Teff= 3493 K. We find that besides traditional chromospheric lines, many photospheric lines are ,filled-in' in the active star spectrum. These differences are, most of the time, weak in absolute fluxes but can be large in terms of differences in the spectral-line equivalent widths. We calculate the differences in surface fluxes between these two stars for many spectral lines. We derive the radiative budgets for two dM1e stars: Gl 867A and AU Mic. We show that the sum of the numerous spectral lines represents a significant fraction of the radiative cooling of the outer atmosphere. We also re-investigate the cooling from the continuum from the visible to the extreme ultraviolet; we find that earlier predictions of the calculations of Houdebine et al. (Paper V) are in good agreement with observations. We emphasize that if this radiative cooling is chromospheric in character, then in chromospheric model calculations, we should include the radiative losses in Ca i, Cr i, V i, Ti i and Fe i. From simple constraints, we derive model chromospheres for quiescent and active regions on Gl 205. We show that the quiescent regions have a strong absorption H, profile. The plage regions show a filled-in intermediate activity H, profile. We also present possible spectral line profiles of quiescent and active regions on Gl 867A. [source] A homogeneous sample of sub-damped Lyman systems , IV.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Global metallicity evolution ABSTRACT An accurate method to measure the abundance of high-redshift galaxies involves the observation of absorbers along the line of sight towards a background quasar. Here, we present abundance measurements of 13 z, 3 sub-damped Lyman , (sub-DLA) systems (quasar absorbers with H i column density in the range 19 < log N(H i) < 20.3 cm,2) based on high-resolution observations with the VLT UVES spectrograph. These observations more than double the amount of metallicity information for sub-DLAs available at z > 3. These new data, combined with other sub-DLA measurements from the literature, confirm the stronger evolution of metallicity with redshift for sub-DLAs than for the classical damped Lyman , absorbers. In addition, these observations are used to compute for the first time, using photoionization modelling in a sample of sub-DLAs, the fraction of gas that is ionized. Based on these results, we calculate that sub-DLAs contribute no more than 6 per cent of the expected amount of metals at z, 2.5. We therefore conclude that, even if sub-DLAs are found to be more metal-rich than classical DLAs, their contribution is insufficient to solve the so-called ,missing-metals' problem. [source] Structural parameters of Mayall II = G1 in M31MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007J. Ma ABSTRACT Mayall II = G1 is one of the most luminous globular clusters (GCs) known in M31. New deep, high-resolution observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate photometric data to the smallest radii yet. In particular, we present the precise variation of ellipticity and position angle, and of surface brightness for the core of the object. Based on these accurate photometric data, we redetermine the structural parameters of G1 by fitting a single-mass isotropic King model. We derive a core radius, rc= 0.21 ± 0.01 arcsec (= 0.78 ± 0.04 pc), a tidal radius, rt= 21.8 ± 1.1 arcsec (= 80.7 ± 3.9 pc), and a concentration index c= log (rt/rc) = 2.01 ± 0.02. The central surface brightness is 13.510 mag arcsec,2. We also calculate the half-light radius, at rh= 1.73 ± 0.07 arcsec (= 6.5 ± 0.3 pc). The results show that, within 10 core radii, a King model fits the surface brightness distribution well. We find that this object falls in the same region of the MV versus log Rh diagram as , Centauri, M54 and NGC 2419 in the Milky Way. All three of these objects have been claimed to be the stripped cores of now defunct dwarf galaxies. We discuss in detail whether GCs, stripped cores of dwarf spheroidals and normal dwarf galaxies form a continuous distribution in the MV versus log Rh plane, or if GCs and dwarf spheroidals constitute distinct classes of objects; we present arguments in favour of this latter view. [source] The effects of thermal conduction on the intracluster medium of the Virgo clusterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2005Edward C. D. Pope ABSTRACT Thermal conduction has been suggested as a possible mechanism by which sufficient energy is supplied to the central regions of galaxy clusters to balance the effect of radiative cooling. Recent high-resolution observations of the nearby Virgo cluster make it an ideal subject for an attempt to reproduce the properties of the cluster by numerical simulations, because most of the defining parameters are comparatively well known. Here, we present the results of a simulated high-resolution, 3D Virgo cluster for different values of thermal conductivity ( times the full Spitzer value). Starting from an initially isothermal cluster atmosphere, we allow the cluster to evolve freely over time-scales of roughly 1.3,4.7 × 109 yr. Our results show that thermal conductivity at the Spitzer value can increase the central intracluster medium (ICM) radiative cooling time by a factor of roughly 3.6. In addition, for larger values of thermal conductivity, the simulated temperature and density profiles match the observations significantly better than for the lower values. However, no physically meaningful value of thermal conductivity was able to postpone the cooling catastrophe (characterized by a rapid increase in the central density) for longer than a fraction of the Hubble time nor explain the absence of a strong cooling flow in the Virgo cluster today. We also calculate the effective adiabatic index of the cluster gas for both simulation and observational data and compare the values with theoretical expectations. Using this method, it appears that the Virgo cluster is being heated in the cluster centre by a mechanism other than thermal conductivity. Based on this and our simulations, it is also likely that the thermal conductivity is suppressed by a factor of at least 10 and probably more. Thus, we suggest that thermal conductivity, if present at all, has the effect of slowing down the evolution of the ICM, by radiative cooling, but only by a factor of a few. [source] Convective-scale assimilation of radar data: progress and challengesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 613 2005Juanzhen Sun Abstract Active research has been carried out in recent years to assimilate high-resolution observations into numerical models to improve precipitation forecasting. Considerable progress has been made although great scientific and technological challenges still exist. This paper reviews techniques used in convective-scale data assimilation research. Experiences in the assimilation of radar observations into high-resolution numerical models are presented. A number of future challenges in convective-scale data assimilation are discussed. Copyright © 2005 Royal Meteorological Society [source] Night-time science with large solar telescopes: The magnetic Sun through timeASTRONOMISCHE NACHRICHTEN, Issue 6 20102Article first published online: 18 JUN 2010, S.C. Marsden Abstract Today the Sun has a regular magnetic cycle driven by a dynamo action. But how did this regular cycle develop? How do basic parameters such as rotation rate, age, and differential rotation affect the generation of magnetic fields? Zeeman Doppler imaging (ZDI) is a technique that uses high-resolution observations in circularly polarised light to map the surface magnetic topology on stars. Utilising the spectropolarimetric capabilities of future large solar telescopes it will be possible to study the evolution and morphology of the magnetic fields on a range of Sun-like stars from solar twins through to rapidly-rotating active young Suns and thus study the solar magnetic dynamo through time. In this article I discuss recent results from ZDI of Sun-like stars and how we can use night-time observations from future solar telescopes to solve unanswered questions about the origin and evolution of the Sun's magnetic dynamo (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||