Hubble Space Telescope survey of the Perseus Cluster – I. The structure and dark matter content of cluster dwarf spheroidals     

Samantha J. Penny  Christopher J. Conselice  Sven De Rijcke  Enrico V. Held 《Monthly notices of the Royal Astronomical Society》2009,393(3):1054-1062

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Metal-rich carbon stars in the Sagittarius dwarf spheroidal galaxy     

Eric Lagadec  Albert A. Zijlstra  G. C. Sloan  Peter R. Wood  Mikako Matsuura  Jeronimo Bernard-Salas  J. A. D. L. Blommaert  M.-R. L. Cioni  M. W. Feast  M. A. T. Groenewegen  Sacha Hony  J. W. Menzies  J. Th. van Loon  P. A. Whitelock 《Monthly notices of the Royal Astronomical Society》2009,396(1):598-608

We present spectroscopic observations from the Spitzer Space Telescope of six carbon-rich asymptotic giant branch (AGB) stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) and two foreground Galactic carbon stars. The band strengths of the observed C₂H₂ and SiC features are very similar to those observed in Galactic AGB stars. The metallicities are estimated from an empirical relation between the acetylene optical depth and the strength of the SiC feature. The metallicities are higher than those of the Large Magellanic Cloud, and close to Galactic values. While the high metallicity could imply an age of around 1 Gyr, for the dusty AGB stars, the pulsation periods suggest ages in excess of 2 or 3 Gyr. We fit the spectra of the observed stars using the dusty radiative transfer model and determine their dust mass-loss rates to be in the range  1.0–3.3 × 10⁻⁸ M_⊙ yr⁻¹  . The two Galactic foreground carbon-rich AGB stars are located at the far side of the solar circle, beyond the Galactic Centre. One of these two stars shows the strongest SiC feature in our present Local Group sample.  相似文献   

Intranight polarization variability in radio-loud and radio-quiet AGN     

Carolin Villforth  Kari Nilsson  Roy Østensen  Jochen Heidt  Sami-Matias Niemi  Janine Pforr 《Monthly notices of the Royal Astronomical Society》2009,397(4):1893-1908

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Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations     

Robert P. C. Wiersma  Joop Schaye  Tom Theuns  Claudio Dalla Vecchia  Luca Tornatore 《Monthly notices of the Royal Astronomical Society》2009,399(2):574-600

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On the Tomographic Reconstruction of the 3D Electron Density for the Solar Corona from STEREO COR1 Data     

M. Kramar  S. Jones  J. Davila  B. Inhester  M. Mierla 《Solar physics》2009,259(1-2):109-121

We present for the first time a three-dimensional reconstruction of the electron density in the corona at distances from 1.5R _⊙ to 4R _⊙ using COR1 STEREO observations. The reconstruction is performed using a regularized tomography inversion method for two biweekly periods corresponding to Carrington Rotations 2058 and 2066. Images from the two STEREO spacecraft are used to compare the reconstructed density structures with coronal features located by triangulation. We find that the location of a bright tip of a helmet streamer obtained from the tomographic reconstruction is in good agreement with the location obtained by triangulation. The reconstructed density structure of the equatorial streamer belt is largely consistent with the variation of the current sheet derived from a potential magnetic field extrapolation for most of the equatorial region and for an MHD model of the corona. A zero-value density region in the reconstruction is identified with a low-density region seen in an EUVI image below the reconstruction domain.  相似文献   

On 3D Reconstruction of Coronal Mass Ejections: I. Method Description and Application to SECCHI-COR Data     

M. Mierla  B. Inhester  C. Marqué  L. Rodriguez  S. Gissot  A. N. Zhukov  D. Berghmans  J. Davila 《Solar physics》2009,259(1-2):123-141

The data from SECCHI-COR1 and SECCHI-COR2 coronagraphs onboard the STEREO mission, which was launched in October 2006, provide us with the first-ever stereoscopic images of the Sun’s corona. These observations were found to be useful in inferring the three-dimensional structure of coronal mass ejections (CMEs) and their propagation direction in space. We apply four methods for reconstructing CMEs: i) Forward modeling technique; ii) Local correlation tracking (to identify the same feature in COR Ahead and COR Behind images) plus tie-point reconstruction technique; iii) Center of mass of the structures in a given epipolar plane plus tie-point reconstruction technique; iv) Polarization ratio technique. The four techniques are applied to three structured CMEs observed by COR1 and COR2 instruments, respectively, on 15 May 2007, 31 August 2007, and 25 March 2008. A comparison of the results obtained from the application of the four reconstruction algorithms is presented and discussed.  相似文献   

Experimental and theoretical radiative decay rates for highly excited ruthenium atomic levels and the solar abundance of ruthenium     

V. Fivet  P. Quinet  P. Palmeri  É. Biémont  M. Asplund  N. Grevesse  A. J. Sauval  L. Engström  H. Lundberg  H. Hartman  H. Nilsson 《Monthly notices of the Royal Astronomical Society》2009,396(4):2124-2132

The solar photospheric abundance of ruthenium is revised on the basis of a new set of oscillator strengths derived for Ru  i transitions with wavelengths in the spectral range 2250–4710 Å. The new abundance value (in the usual logarithmic scale where the solar hydrogen abundance is equal to 12.00),   A _Ru= 1.72 ± 0.10  , is in agreement with the most recent meteoritic result,   A _Ru= 1.76 ± 0.03  . The accuracy of the transition probabilities, obtained using a relativistic Hartree–Fock model including core-polarization effects, has been assessed by comparing the theoretical lifetimes with previous experimental results. A comparison is also made with new measurements performed in this work by the time-resolved laser-induced fluorescence spectroscopy for 10 highly excited odd-parity levels of Ru  i .  相似文献   

Reflection Driven MHD Turbulence in the Solar Atmosphere and Wind     

A. Verdini  M. Velli  E. Buchlin 《Earth, Moon, and Planets》2009,104(1-4):121-125

Alfvénic turbulence is usually invoked and used in many solar wind models (Isenberg and Hollweg, 1982, J. Geophys. Res. 87:5023; Tu et al. 1984, J. Geophys. Res. 89:9695; Hu et  al. 2000, J. Geophys. Res. 105:5093; Li 2003, Astron. Astrphys. 406:345; Isenberg 2004, J. Geophys. Res. 109:3101) as a process responsible for the transfer of energy, released at large scale in the photosphere, towards small scale in the corona, where it is dissipated. Usually an initial spectrum is prescribed since the closest constraint to the spectrum is given by Helios measurements at 0.3 AU. With this work we intend to study the efficiency of the reflection as a driver for the nonlinear interactions of Alfvén waves, the development of a turbulent spectrum and its evolution in the highly stratified solar atmosphere inside coronal holes. Our main finding is that the perpendicular spectral slope changes substantially at the transition region because of the steep density gradient. As a result a strong turbulent heating occurs, just above the transition region, as requested by current solar wind models.  相似文献   

Elemental and organic carbon in atmospheric aerosols at downtown and suburban sites in Prague   总被引：1，自引：0，他引：1  

Jaroslav Schwarz  Xuguang Chi  Willy Maenhaut  Martin Civi&#x;  Jan Hovorka  Ji&#x;í Smolík 《Atmospheric Research》2008,90(2-4):287-ICNAA07

Organic and elemental carbon (OC and EC) content in PM₁₀ was studied at two sites in Prague, which were located in a suburb and in the downtown. Similar overall average levels were found for both species and also for the PM₁₀ mass at the two sites (i.e., 5.5 and 4.8 μg/m³ for OC, 0.74 and 0.80 μg/m³ for EC, and 33 μg/m³ and 37 μg/m³ for the PM₁₀ mass at the suburb and downtown site, respectively), but substantial differences were observed between the two sites in some seasons and/or meteorological situations. Approximately three times higher values were found for OC in winter compared to summer, with a higher winter/summer ratio for the suburban site. The differences for EC were smaller, but still, compared to summer, more than two times higher EC levels were observed during autumn at the suburban site and 1.5 higher EC levels in winter and autumn at the downtown site. The lowest OC to EC ratios at the suburban site were 3.4, while they were around 1.3 for the downtown site. It was found that the origin of the air masses had a major impact on the observed PM₁₀ mass and OC levels, with largest concentrations noted for air masses recirculating over central Europe and arriving from southeastern Europe in winter. Trajectories coming from the west and northwest originating above the Atlantic Ocean and the Artic brought the cleanest air masses to the sites. For EC the largest difference between the two sites was observed for northwesterly winds during the non-heating season when the suburban site was upwind of Prague.  相似文献   

The Southern Westerlies during the last glacial maximum in PMIP2 simulations   总被引：1，自引：1，他引：0  

Maisa Rojas  Patricio Moreno  Masa Kageyama  Michel Crucifix  Chris Hewitt  Ayako Abe-Ouchi  Rumi Ohgaito  Esther C. Brady  Pandora Hope 《Climate Dynamics》2009,32(4):525-548

The Southern Hemisphere westerly winds are an important component of the climate system at hemispheric and global scales. Variations in their intensity and latitudinal position through an ice-age cycle have been proposed as important drivers of global climate change due to their influence on deep-ocean circulation and changes in atmospheric CO₂. The position, intensity, and associated climatology of the southern westerlies during the last glacial maximum (LGM), however, is still poorly understood from empirical and modelling standpoints. Here we analyse the behaviour of the southern westerlies during the LGM using four coupled ocean-atmosphere simulations carried out by the Palaeoclimate Modelling Intercomparison Project Phase 2 (PMIP2). We analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks. The models suggest that changes were most significant during winter and over the Pacific ocean. For this season and region, three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere. Although the LGM atmosphere is colder and the equator to pole surface temperature gradient generally increases, the tropospheric temperature gradients actually decrease, explaining the weaker circulation. We evaluated the atmospheric influence on the Southern Ocean by examining the effect of wind stress on the Ekman pumping. Again, three of the models indicate decreased upwelling in a latitudinal band over the Southern Ocean. All models indicate a drier LGM than at present with a clear decrease in precipitation south of 40°S over the oceans. We identify important differences in precipitation anomalies over the land masses at regional scale, including a drier climate over New Zealand and wetter over NW Patagonia.  相似文献