The post-outburst photometric behaviour of V838 Mon     

Lisa A. Crause  Warrick A. Lawson  David Kilkenny  Francois van Wyk  Fred Marang  Albert F. Jones 《Monthly notices of the Royal Astronomical Society》2003,341(3):785-791

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GMRT and VLA observations at 49 cm and 20 cm of the HII region near <Emphasis Type="Italic">l</Emphasis> = 24.8°, <Emphasis Type="Italic">b</Emphasis> = 0.1°     

N. G. Kantharia  W. M. Goss  D. Anish Roshi  Niruj R. Mohan  Francois Viallefond 《Journal of Astrophysics and Astronomy》2007,28(1):41-53

We report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near l = 24.8°, b = 0.1° using the Giant Metrewave Radio Telescope (GMRT) at 1.28 GHz (n = 172), 0.61 GHz (n = 220) and the Very Large Array (VLA) at 1.42 GHz (n = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at l = 24.83° and b = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ∼550 M_⊙ with a linear size of 7 pc and an rms electron density of ∼110 cm⁻³ at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type O5.5. We also report detection of hydrogen recombination lines from the HII region at l = 24.83° and b = 0.1° at all observed frequencies near V _lsr = 100 km s⁻¹. We model the observed integrated line flux density as arising in the diffuse HII region and find that the best fitting model has an electron density comparable to that derived from the continuum. We also report detection of hydrogen recombination lines from two other HII regions in the field.  相似文献   

First Lunar Flashes Observed from Morocco (ILIAD Network): Implications for Lunar Seismology     

Mamoun Ait Moulay Larbi  Ahmed Daassou  David Baratoux  Sylvain Bouley  Zouhair Benkhaldoun  Mohamed Lazrek  Raphael Garcia  Francois Colas 《Earth, Moon, and Planets》2015,115(1-4):1-21

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A spectroscopic study of the surfaces of Saturn's large satellites: H₂O ice, tholins, and minor constituents     

Dale P. Cruikshank  Tobias C. Owen  Thomas R. Geballe  Catherine de Bergh  Francois Poulet  Joshua P. Emery 《Icarus》2005,175(1):268-283

We present spectra of Saturn's icy satellites Mimas, Enceladus, Tethys, Dione, Rhea, and Hyperion, 1.0-2.5 μm, with data extending to shorter (Mimas and Enceladus) and longer (Rhea and Dione) wavelengths for certain objects. The spectral resolution (R=λ/Δλ) of the data shown here is in the range 800-1000, depending on the specific instrument and configuration used; this is higher than the resolution (R=225 at 3 μm) afforded by the Visual-Infrared Mapping Spectrometer on the Cassini spacecraft. All of the spectra are dominated by water ice absorption bands and no other features are clearly identified. Spectra of all of these satellites show the characteristic signature of hexagonal H₂O ice at 1.65 μm. We model the leading hemisphere of Rhea in the wavelength range 0.3-3.6 μm with the Hapke and the Shkuratov radiative transfer codes and discuss the relative merits of the two approaches to fitting the spectrum. In calculations with both codes, the only components used are H₂O ice, which is the dominant constituent, and a small amount of tholin (Ice Tholin II). Tholin in small quantities (few percent, depending on the mixing mechanism) appears to be an essential component to give the basic red color of the satellite in the region 0.3-1.0 μm. The quantity and mode of mixing of tholin that can produce the intense coloration of Rhea and other icy satellites has bearing on its likely presence in many other icy bodies of the outer Solar System, both of high and low geometric albedos. Using the modeling codes, we also establish detection limits for the ices of CO₂ (a few weight percent, depending on particle size and mixing), CH₄ (same), and NH₄OH (0.5 weight percent) in our globally averaged spectra of Rhea's leading hemisphere. New laboratory spectral data for NH₄OH are presented for the purpose of detection on icy bodies. These limits for CO₂, CH₄, and NH₄OH on Rhea are also applicable to the other icy satellites for which spectra are presented here. The reflectance spectrum of Hyperion shows evidence for a broad, unidentified absorption band centered at 1.75 μm.  相似文献   

Climatic change in Central Asia during MIS 3/2: a case study using biological responses from Lake Baikal   总被引：5，自引：0，他引：5  

George E.A. Swann  Anson W. Mackay  Melanie J. Leng  Francois Demory 《Global and Planetary Change》2005,46(1-4):235

A Marine Isotope Stage (MIS) 3/early MIS 2 section from a structural high along the east coast of the North Basin of Lake Baikal was analysed for diatoms, C/N ratios, and organic carbon isotope ratios. Diatoms were present throughout MIS 3 and early MIS 2, with high concentrations of the planktonic taxa Cyclotella sp. c.f. gracilis between 54 and 51.5 kyr BP indicating relatively warm, interstadial, conditions. Following a %TOC inferred climatic cooling between 43.2 and 39.1 kyr BP, evidence of a more muted δ¹³C_(organic) and %TOC inferred climatic warming from c. 39.1–34.7 kyr BP coincides with a period of very high diatom concentrations, indicating high aquatic productivity, at the Buguldeika Saddle in the South Basin of Lake Baikal. No evidence exists for a ‘Kuzmin’ catchment erosional event in the North Basin during MIS 3. This, however, may reflect the location of the coring site away from major riverine inputs. Abrupt climatic cooling at the culmination of both warm phases in the North Basin are associated, on the basis of the palaeomagnetic age-model and correlations to existing sites in Lake Baikal, with the initiation of Heinrich events 5 (c. 50 kyr BP) and 4 (c. 35 kyr BP), respectively, in the North Atlantic. The amount of organic material declines across the MIS 3/MIS 2 transition while constant C/N ratios suggest organic material to be predominantly derived from phytoplankton. An increase in δ¹³C_(organic) at the MIS 3/MIS 2 transition may therefore indicate changes in aquatic productivity, pCO₂ or the inorganic carbon pool.  相似文献   

The self-organizing map,a new approach to apprehend the Madden–Julian Oscillation influence on the intraseasonal variability of rainfall in the southern African region     

Pascal Oettli  Tomoki Tozuka  Takeshi Izumo  Francois A. Engelbrecht  Toshio Yamagata 《Climate Dynamics》2014,43(5-6):1557-1573

The Madden–Julian Oscillation (MJO) is the major mode of intraseasonal variability (30–60 days) in the tropics, having large rainfall impacts globally, and possibly on southern Africa. However, the latter impact is not well understood and needs to be further explored. The life cycle of the MJO, known to be asymmetric, has been nevertheless analyzed usually through methods constrained by both linearity and orthogonality, such as empirical orthogonal function analysis. Here we explore a non-linear classification method, the self-organizing map (SOM), a type of artificial neural network used to produce a low-dimensional representation of high-dimensional datasets, to capture more accurately the life cycle of the MJO and its global impacts. The classification is applied on intraseasonal anomalies of outgoing longwave radiation within the tropical region over the 1980–2009 period. Using the SOM to describe the MJO is a new approach, complimentary to the usual real-time multivariate MJO index. It efficiently captures this propagative phenomenon and its seasonality, and is shown to provide additional temporal and spatial information on MJO activity. For each node, the subtropical convection is analyzed, with a particular focus on the southern Africa region. Results show that the convection activity over the central tropical Indian Ocean is a key factor influencing the intraseasonal convective activity over the southern African region. Enhanced (suppressed) convection over the central Indian Ocean tends to suppress (enhance) convection over the southern African region with a 10-day lag by modulating the moisture transport.  相似文献   

Impacts of convection schemes on simulating tropical-temperate troughs over southern Africa     

Tomoki Tozuka  Babatunde J. Abiodun  Francois A. Engelbrecht 《Climate Dynamics》2014,42(1-2):433-451

This study examines southern African summer rainfall and tropical temperate troughs (TTTs) simulated with three versions of an atmospheric general circulation model differing only in the convection scheme. All three versions provide realistic simulations of key aspects of the summer (November–February) rainfall, such as the spatial distribution of total rainfall and the percentage of rainfall associated with TTTs. However, one version has a large bias in the onset of the rainy season. Results from self-organizing map (SOM) analysis on simulated daily precipitation data reveals that this is because the occurrence of TTTs is underestimated in November. This model bias is not related to westerly wind shear that provides favorable conditions for the development of TTTs. Rather, it is related to excessive upper level convergence and associated subsidence over southern Africa. Furthermore, the model versions are shown to be successful in capturing the observed drier (wetter) conditions over the southern African region during El Niño (La Niña) years. The SOM analysis reveals that nodes associated with TTTs in the southern (northern) part of the domain are observed less (more) often during El Niño years, while nodes associated with TTTs occur more frequently during La Niña years. Also, nodes associated with dry conditions over southern Africa are more (less) frequently observed during El Niño (La Niña) years. The models tend to perform better for La Niña events, because they are more successful in representing the observed frequency of different synoptic patterns.  相似文献   

关于“含水中基性大陆下地壳部分熔融能形成C型埃达克岩吗？”的回复     

张超  马昌前  Francois HOLTZ 《高校地质学报》2013,19(2):381

焦永玲等对笔者发表在《高校地质学报》2012年第18 卷第1 期的“含水大陆下地壳的部分熔融：大别山C型埃达克 岩成因探讨”一文提出质疑。针对他们的问题,笔者进行了回复,并提出：（1）大别山C 型埃达克岩的源岩可能是基性的 （SiO2 含量50% 左右）,但是比较准确的成分估计还需要进一步研究;（2）变质含水基性岩（角闪岩）在1.0~1.2 GPa 压力下（相当于35~40 km）可以形成含石榴石20% 以上的残余体;（3）中钾的角闪岩（K2O 含量1% 左右）部分熔融可以形成高钾钙碱性长英质熔体（K2O 含量3.5%~5%）。  相似文献   

Dust tail of the active distant Comet C/2003 WT42 (LINEAR) studied with photometric and spectroscopic observations     

Pavlo P. Korsun  Irina V. Kulyk  Oleksandra V. Ivanova  Viktor L. Afanasiev  Francois Kugel  Claudine Rinner  Yuriy M. Ivashchenko 《Icarus》2010,210(2):916-929

We present the study of dust environment of dynamically new Comet C/2003 WT42 (LINEAR) based on spectroscopic and photometric observations. The comet was observed before and after the perihelion passage at heliocentric distances from 5.2 to 9.5 AU. Although the comet moved beyond the zone where water ice sublimation could be significant, its bright coma and extended dust tail evidenced the high level of physical activity. Afρ values exceeded 3000 cm likely reaching its maximum before the perihelion passage. At the same time, the spectrum of the comet did not reveal molecular emission features above the reflected continuum. Reddening of the continuum derived from the cometary spectrum is nonlinear along the dispersion with the steeper slop in the blue region. The pair of the blue and red continuum images was analyzed to estimate a color of the comet. The mean normalized reflectivity gradient derived from the innermost part of the cometary coma equals to 8% per 1000 Å that is typical for Oort cloud objects. However, the color map shows that the reddening of the cometary dust varies over the coma increasing to 15% per 1000 Å along the tail axis. The photometric images were fitted with a Monte Carlo model to construct the theoretical brightness distribution of the cometary coma and tail and to investigate the development of the cometary activity along the orbit. As the dust particles of distant comets are expected to be icy, we propose here the model, which describes the tail formation taking into account sublimation of grains along their orbits. The chemical composition and structure of these particles are assumed to correspond with Greenberg’s interstellar dust model of comet dust. All images were fitted with the close values of the model parameters. According to the results of the modeling, the physical activity of the comet is mainly determined by two active areas with outflows into the wide cones. The obliquity of the rotation axis of the nucleus equals to 20° relative to the comet’s orbital plane. The grains occupying the coma and tail are rather large amounting to 1 mm in size, with the exponential size distribution of a^−4.5. The outflow velocities of the dust particles vary from a few centimeters to tens of meters per second depending on their sizes. Our observations and the model findings evidence that the activity of the nucleus decreased sharply to a low-level phase at the end of April–beginning of May 2007. About 190 days later, in the first half of November 2007 the nucleus stopped any activity, however, the remnant tail did not disappear for more than 1.5 years at least.  相似文献   

Changes in the South Pacific Convergence Zone in IPCC AR4 future climate projections   总被引：1，自引：0，他引：1  

Josephine R. Brown  Aurel F. Moise  Francois P. Delage 《Climate Dynamics》2012,39(1-2):1-19

The response of the South Pacific Convergence Zone (SPCZ) to climate change is examined using simulations from 16 coupled climate models under the A2 emission scenario carried out for the Intergovernmental Panel on Climate Change Fourth Assessment Report. Characteristics of the austral summer SPCZ in the late twenty-first century are compared with the late twentieth century: the orientation and latitude of the SPCZ precipitation band; the area and intensity of precipitation within the SPCZ; and the eastern extent of the SPCZ. Changes in the SPCZ position are examined using a simple linear fit to the band of maximum precipitation and using a “pattern matching” technique. Both techniques find no consistent shift in the slope or mean latitude of the austral summer SPCZ. However, many models simulate a westward shift in the eastern edge of the SPCZ in austral summer, with reduced precipitation to the east of around 150°W. The westward contraction of the SPCZ is associated with a strengthening of the trade winds in the southeast Pacific and an increased zonal sea surface temperature gradient across the South Pacific. The majority of models simulate an increase in the area of the SPCZ and in mean and maximum precipitation within the SPCZ, defined by a 6?mm/day precipitation threshold, consistent with increased moisture convergence in a warmer climate. Changes in the SPCZ response to ENSO are examined using ENSO precipitation composites. The SPCZ has a reduced slope and is shifted towards the equator in the A2 multi-model mean El Ni?o composite.  相似文献