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991.
992.
Marcelo Samuel Berman 《Astrophysics and Space Science》2011,336(2):337-339
We show how to prove the two Pioneers Anomalies by means of the Godlowski et al. (, 2004) idea for a rotating General Relativistic Universe. The so-called clock effect is calculated. 相似文献
993.
The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150–2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the far ultraviolet range. The addition of the λ < 1200 Å wavelengths is critical as it contains important diagnostic lines for mass loss and shocks in the wind, as found by FUSE-based analyses.WSO will enable quantitative spectroscopic analyses of blue massive stars in the Local Group beyond the Magellanic Clouds. The results will lead to the characterization of their winds as a function of metallicity, and shed new light on current urging questions regarding radiation driven winds. 相似文献
994.
Rodica Roman 《Astrophysics and Space Science》2011,335(2):475-483
A new equivalence relation, named relation of ‘similarity’ is defined and applied in the restricted three-body problem. Using
this relation, a new class of trajectories (named ‘similar’ trajectories) are obtained; they have the theoretical role to
give us new details in the restricted three-body problem. The ‘similar’ coordinate systems allow us in addition to obtain
a unitary and an elegant demonstration of some analytical relations in the Roche geometry. As an example, some analytical
relations published by Seidov (in Astrophys. J. 603:283, 2004) are demonstrated. 相似文献
995.
In the present article a model of well behaved charged superdense star with surface density 2×1014 gm/cm3 is constructed by considering a static spherically symmetric metric with t=const hypersurfaces as hyperboloid. So far well behaved model described by such metric could not be obtained. Maximum mass
of the star is found to be 0.343457M
⊙ and the corresponding radius is 9.57459 km. The red shift at the centre and on the surface are given as 0.068887 and 0.031726
respectively. 相似文献
996.
Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate
through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the
first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era
were very massive, 25–500 solar masses, with H(II) regions of up to 30,000 light-years in diameter. We present three-dimensional
radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent
instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which
supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation
of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation
hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs,
introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given
calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of
both cosmological and galactic ionization fronts. 相似文献
997.
Dragan Slavkov Hajdukovic 《Astrophysics and Space Science》2011,334(2):215-218
Assuming that a particle and its antiparticle have the gravitational charge of the opposite sign, the physical vacuum may
be considered as a fluid of virtual gravitational dipoles. Following this hypothesis, we present the first indications that
dark matter may not exist and that the phenomena for which it was invoked might be explained by the gravitational polarization
of the quantum vacuum by the known baryonic matter. 相似文献
998.
Nancy S. Brickhouse 《Astrophysics and Space Science》2011,336(1):75-79
Young T Tauri stars exhibit strong solar-type magnetic activity, with extremely high temperature coronae and energetic flares.
In a few systems discovered with Chandra and XMM-Newton there is also evidence for X-ray emission produced by shocks associated
with magnetically channeled accretion. A recent 489 ksec Chandra HETG/ACIS-S observation of the classical T Tauri star TW
Hydrae has provided a wealth of spectroscopic diagnostics not available in lower signal-to-noise ratio observations. Using
line ratios for electron temperature, electron density, and column density we have found that the shock produced by the accelerating
material in the accretion stream behaves as predicted by standard theory. However, the properties of the post-shock plasma
differ substantially from the predictions of standard 1D shock models (Brickhouse et al. in Astrophys. J. 710:1835, 2010). The accretion process apparently heats the stellar atmosphere up to soft X-ray emitting temperatures, providing hot ions
to populate the magnetic corona, in loops, stellar wind, and/or jets. This gas is highly turbulent, as evidenced by non-thermal
line broadening. The observed properties of the accretion-fed corona should constrain theoretical models of an accretion-driven
dynamo. 相似文献
999.
Adolfo L. Méndez Berhondo Ramón E. Rodríguez Taboada Paolo Zlobec 《Astrophysics and Space Science》2008,318(1-2):73-78
Pulsating structures recorded at 237 MHz that are associated to decimetric continuum enhancement during the September 9, 2001 solar radio burst are described. We analyzed the radiopolarimetric data recorded at the Trieste Solar Radio System (INAF—Trieste Astronomical Observatory—Basovizza Observing Station) with very high time resolution (1 ms) at metric frequencies. Two different types of pulsations that occur in about 4 minutes at the same frequency are described. The possible mechanisms are analyzed and some parameters of the associated magnetic structure are estimated. 相似文献
1000.
Markus J. Aschwanden Jong Kwan Lee G. Allen Gary Michael Smith Bernd Inhester 《Solar physics》2008,248(2):359-377
The three-dimensional (3D) modeling of coronal loops and filaments requires algorithms that automatically trace curvilinear
features in solar EUV or soft X-ray images. We compare five existing algorithms that have been developed and customized to
trace curvilinear features in solar images: i) the oriented-connectivity method (OCM), which is an extension of the Strous pixel-labeling algorithm (developed by Lee,
Newman, and Gary); ii) the dynamic aperture-based loop-segmentation method (developed by Lee, Newman, and Gary); iii) unbiased detection of curvilinear structures (developed by Steger, Raghupathy, and Smith); iv) the oriented-direction method (developed by Aschwanden); and v) ridge detection by automated scaling (developed by Inhester). We test the five existing numerical codes with a TRACE image
that shows a bipolar active region and contains over 100 discernable loops. We evaluate the performance of the five codes
by comparing the cumulative distribution of loop lengths, the median and maximum loop length, the completeness or detection
efficiency, the accuracy, and flux sensitivity. These algorithms are useful for the reconstruction of the 3D geometry of coronal
loops from stereoscopic observations with the STEREO spacecraft, or for quantitative comparisons of observed EUV loop geometries
with (nonlinear force-free) magnetic field extrapolation models. 相似文献