共查询到20条相似文献,搜索用时 31 毫秒
1.
We present a code for solving the nonlinear force-free equations in spherical polar geometry, with the motivation of modeling the magnetic field in the corona. The code is an implementation of the Grad–Rubin method. Our method is applicable to a spherical domain of arbitrary angular size. The implementation is based on a global spectral representation for the magnetic field that makes no explicit assumptions about the form of the magnetic field at the transverse boundaries of the domain. We apply the code to a bipolar test case with analytic boundary conditions, and demonstrate the convergence of the Grad–Rubin method and the self-consistency of the resulting numerical solution. 相似文献
2.
Late-type stars in general possess complicated magnetic surface fields which makes their detection and in particular their modeling and reconstruction challenging. In this work we present a new Zeeman-Doppler imaging code which is especially designed for the application to late-type stars. This code uses a new multi-line cross-correlation technique by means of a principal component analysis to extract and enhance the quality of individual polarized line profiles. It implements the full polarized radiative transfer equation and uses an inversion strategy that can incorporate prior knowledge based on solar analogies. Moreover, our code utilizes a new regularization scheme which is based on local maximum entropy to allow a more appropriate reproduction of complex surface fields as those expected for late-type stars. In a first application we present Zeeman-Doppler images of II Pegasi which reveal a surprisingly large scale surface structure with one predominant (unipolar) magnetic longitude which is mainly radially oriented. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Markus J. Aschwanden 《Solar physics》2010,262(2):399-423
We develop a new numerical code with automated feature extraction, customized for tracing of coronal loops, a method we call Oriented Coronal CUrved Loop Tracing (OCCULT), which for the first time breaks even with the results of visual tracing. The method used is based on oriented-directivity tracing of curvi-linear features, but in contrast to other general feature-extraction algorithms, it is customized for solar EUV and SXR images by taking advantage of the specific property that coronal loops have large curvature radii compared with their widths. We evaluate the performance of this new code by comparing the cumulative distribution of loop lengths, the median and maximum loop lengths, the completeness of detection, and the congruency of the detected features with other numerical codes and visual tracings. We find that the new code closely approaches the results of visual perception and outperforms the other existing numerical codes. This algorithm is useful for the 3D reconstruction of the geometry, motion, and oscillations of coronal loops, with single or stereoscopic spacecraft, as well as for modeling of the loop hydrodynamics and the coronal magnetic field. 相似文献
4.
Michael Bauer 《Astrophysics and Space Science》2005,296(1-4):255-260
A method is presented to include irradiation effects in the modeling of over-contact binaries. The Roche potential is numerically
modified in a way to account for mechanical effects of the mutual irradiation of the two binary components. The efficiency
of radiative interaction is parametrized by means of the fraction of radiative over gravitational forces for each component
of the binary. The modified Roche geometry is implemented as binary model in an eclipse light curve solution code, which is
based on the general Wilson–Devinney scheme. As an example the method is applied to the early-type over-contact system V606
Cen. 相似文献
5.
E. Oblak 《Astrophysics and Space Science》1988,142(1-2):31-37
Summary The catalogue gives the parameters of theUBV, uvby, and Geneva photometries for more than 200 stars.
It gives also the first statistics with respect to the different caracteristics of visual systems: separation, difference
of the magnitude of components,... etc.
For 11713 components of stellar systems the catalogue, in its actual form, gives the parameters of theUBV, uvbyβ and Geneva photometric systems.
A concise statistics presents the distribution of the stars in the different photometric systems and the relations between
the difference in the magnitudes and separation of the components.
CNRS UA 040389. 相似文献
6.
Zhang Qing Wang Li-fan Hu Jing-yao P. A. Mazzali Wang Zhen-ru 《Chinese Astronomy and Astrophysics》1995,19(4):426-431
We present the modeling of the ultraviolet and optical spectra obtained simultaneously on 1993 April 15 with the HST and at Lick Observatory. A Monte Carlo code is employed in the modeling and a comparison is made between models reported by different groups. With an atmosphere similar to the Sun in chemical composition, the observed spectral lines are well reproduced by a power law density structure of index around 20 except the strong H and HeI λ5876 lines which have peculiar absorption profiles. The photospheric velocity is found to be 9500 km/s and the blackbody temperature of the spectrum is 7990 K. For H and HeI λ5876, we suggest a two-component density structure which has a smoother layer located immediately outside the steeply decreasing inner envelope. The power law indices are most probably 20 and 3, respectively, with the transition point at about 13 000 km/s. In addition, this outer smooth layer serves to flatten the far UV spectrum as observed. 相似文献
7.
Alain Hui-Bon-Hoa 《Astrophysics and Space Science》2008,316(1-4):55-60
In the framework of the CoRoT-ESTA, we present the Toulouse–Geneva Evolution Code (TGEC) at its present stage. 相似文献
8.
Magnetic flux tubes are considered to be a possible source of observed brightness variations on the extreme limb of the Sun. A computer code to simulate the brightness fluctuations is developed. It follows from numerical modeling that a filling factor of f=4% is required to explain the observed fine structure. Such a value is typical for the boundaries of supergranules. Tubes produce a local maximum of intensity just inside the limb. 相似文献
9.
The light curve modeling of binary stars has continued to evolve since its founding by Henry Norris Russell (see Russell and Merrill 1952 and citations therein) nearly a century ago, accelerated in the 1950s by Kopal's introduction of Roche geometry into models and by the development of synthetic light curve computer code in the 1970's. Improved physics and the use of more kinds of observational input are providing another round of important advances that promise to enlarge our knowledge of both binary stars and ensembles containing them. Here we discuss the newer horizons of light curve modeling and the steps being taken toward them. 相似文献
10.
D. John Hillier 《Astrophysics and Space Science》2011,336(1):87-93
We have developed a radiative transfer code, cmfgen, which allows us to model the spectra of massive stars and supernovae. Using cmfgen we can derive fundamental parameters such as effective temperatures and surface gravities, derive abundances, and place constraints
on stellar wind properties. The last of these is important since all massive stars are losing mass via a stellar wind that
is driven from the star by radiation pressure, and this mass loss can substantially influence the spectral appearance and
evolution of the star. Recently we have extended cmfgen to allow us to undertake time-dependent radiative transfer calculations of supernovae. Such calculations will be used to
place constraints on the supernova progenitor, to place constraints on the supernova explosion and nucleosynthesis, and to
derive distances using a physical approach called the “Expanding Photosphere Method”. We describe the assumptions underlying
the code and the atomic processes involved. A crucial ingredient in the code is the atomic data. For the modeling we require
accurate transition wavelengths, oscillator strengths, photoionization cross-sections, collision strengths, autoionization
rates, and charge exchange rates for virtually all species up to, and including, cobalt. Presently, the available atomic data
varies substantially in both quantity and quality. 相似文献
11.
Byurakan Astrophysical Observatory; University of Geneva, Switzerland. Translated from Astrofizika, Vol. 33, No. 3, pp. 329–344, November–December, 1990. 相似文献
12.
G. M. Tovmasyan R. Kh. Oganesyan R. A. Epremyan M. A. Mkrtchyan Yu. M. Khodzhayants M. N. Krmoyan A. L. Kashin D. Huguenin Yu. V. Romanenko A. P. Aleksandrov V. G. Titov M. Kh. Manarov A. A. Volkov S. K. Krikalev 《Astrophysics》1990,32(2):105-109
Byurakan Astrophysical Observatory; SKB Granit; Geneva Observatory; Cosmonaut Preparation Center. Translated from Astrofizika, Vol. 32, No. 2, pp. 197–202, March–April, 1990. 相似文献
13.
Byurakan Astrophysical Observatory and Geneva Observatory. Translated from Astrofizika, Vol. 36, No. 1, pp. 35–54, January–Feburary, 1993. 相似文献
14.
Abstract The first inventory of the meteorite collection of the Muséum d'Histoire Naturelle of Geneva is given. The collection, which was initiated early in the nineteenth century and thus is one of the oldest in the world, numbers at present 164 fragments of 102 individual meteorites including the largest fragment (22 kg) of the North Chile hexahedrite. During 1991 the collection was updated and several new specimens were acquired. 相似文献
15.
Byurakan Astrophysical Observatory; Geneva Observatory. Translated from Astrofizika, Vol. 34, No. 3, pp. 301–314, May–June, 1991. 相似文献
16.
G. M. Tovmasyan R. Kh. Oganesyan R. A. Epremyan S. E. Nersesyan M. A. Mkrtchyan Yu. M. Khodzhayants M. N. Krmoyan A. L. Kashin D. Huguenin S. I. Serova Yu. V. Romanenko A. P. Aleksandrov V. G. Titov M. Kh. Manarov 《Astrophysics》1990,32(1):1-5
Byurakan Astrophysical Observatory; SKB Granit; Geneva Observatory; Flight Control Center. Translated from Astrofizika, Vol. 32, No. 1, p. 5–13, January–February, 1990. 相似文献
17.
The absolute radii of 78 Scuti variables in the Catalogue of the Geneva Observatory have been computed. A PRC relation among the period, radius and color has been obtained. 相似文献
18.
Christiaan P. A. van Buchem Yamila Miguel Mantas Zilinskas Wim van Westrenen 《Meteoritics & planetary science》2023,58(8):1149-1161
To date, over 500 short-period rocky planets with equilibrium temperatures above 1500 K have been discovered. Such planets are expected to support magma oceans, providing a direct interface between the interior and the atmosphere. This provides a unique opportunity to gain insight into their interior compositions through atmospheric observations. A key process in doing such work is the vapor outgassing from the lava surface. LavAtmos is an open-source code that calculates the equilibrium chemical composition of vapor above a dry melt for a given composition and temperature. Results show that the produced output is in good agreement with the partial pressures obtained from experimental laboratory data as well as with other similar codes from literature. LavAtmos allows for the modeling of vaporization of a wide range of different mantle compositions of hot rocky exoplanets. In combination with atmospheric chemistry codes, this enables the characterization of interior compositions through atmospheric signatures. 相似文献
19.
M. Haberreiter 《Solar physics》2011,274(1-2):473-479
We present spectral synthesis calculations of the solar extreme UV (EUV) in spherical symmetry carried out with the ‘Solar Modeling in 3D’ code. The calculations are based on one-dimensional atmospheric structures that represent a temporal and spatial mean of the chromosphere, transition region, and corona. The synthetic irradiance spectra are compared with the recent calibration spectrum taken with the EUV Variability Experiment during the Whole Heliospheric Interval. The good agreement between the synthetic and observed quiet Sun spectrum shows that the employed atmospheric structures are suitable for irradiance calculations. The validation of the quiet Sun spectrum for the present solar minimum is the first step toward the modeling of the EUV variations. 相似文献
20.
E. PIERAZZO N. ARTEMIEVA E. ASPHAUG E. C. BALDWIN J. CAZAMIAS R. COKER G. S. COLLINS D. A. CRAWFORD T. DAVISON D. ELBESHAUSEN K. A. HOLSAPPLE K. R. HOUSEN D. G. KORYCANSKY K. WÜNNEMANN 《Meteoritics & planetary science》2008,43(12):1917-1938
Abstract— Over the last few decades, rapid improvement of computer capabilities has allowed impact cratering to be modeled with increasing complexity and realism, and has paved the way for a new era of numerical modeling of the impact process, including full, three‐dimensional (3D) simulations. When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS‐MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum‐on‐aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter‐code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well‐characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter‐code variability. 相似文献