共查询到20条相似文献，搜索用时 46 毫秒
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A.A. Stanislavsky A.A. Konovalenko H.O. Rucker E.P. Abranin M.L. Kaiser V.V. Dorovskyy V.N. Mel'nik A. Lecacheux 《Astronomische Nachrichten》2009,330(7):691-697
Decameter wavelength radio emission is finely structured in solar bursts. For their research it is very important to use a sufficient sensitivity of antenna systems. In this paper we study an influence of the radiotelescope‐antenna effective area on the results of decameter solar radio observations. For this purpose we compared the solar bursts received by the array of 720 ground‐based dipoles and the single dipole of the radiotelescope UTR‐2. It is shown that a larger effective area of the ground‐based antenna allows us to measure a weaker solar emission and to distinguish a fine structure of strong solar events. This feature has been also verified by simultaneous ground‐ and space‐based observations in the overlapping frequency range (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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We compared the microwave bursts with short timescale fine structure observed at 2.84 GHZ at Beijing Astronomical Observatory with the hard X-ry bursts (HXB) observed by the YOHKOH satellite during the period 1991 Oct–1992 Dec, and found that of the 20 microwave events, 12 had HXB counterparts. For the typical event of 1992-06-07, we analyzed the common quasi-period oscillations on the order of 102 s and calculated the parameters of the source region, together with a brief discussion. 相似文献
4.
During the type IV burst on 24 April, 1985 we observed at 234 MHz an untypical, strong, nearly six hours lasting continuum emission incorporating several groups of broadband pulsations, zebra patterns, fiber bursts, and a new fine structure phenomenon. The power spectra of the groups of broadband pulsations reveal no simple structure. There is only one common periodic component between 0.3 s and 0.4 s. Slowly drifting chains of narrowband fiber bursts are described as a new fine structure by spectrograms and simultaneously recorded single frequency intensity profiles. A qualitative model of this new fine structure is suggested. 相似文献
5.
In order to study a model‐dependence of the results achieved in the previous investigations of the Pleiades luminosity function using D'Antona and Mazzitelli (1994) evolutionary tracks, we repeated the computations with the new track system by D'Antona and Mazzitelli (1997). The following main conclusions can be drawn: the new models agree better with observations; the helium abundance needed to fit the Hipparcos distance modulus is reduced to a more reasonable value of Y = 0.31; the cluster age becomes slightly higher and the slope of the initial mass function somewhat lower. The conclusions on the fine structure of the luminosity function do not change significantly due to the application of the new models. 相似文献
6.
Ly α and Ly β line profiles in a solar prominence were observed with high spatial and spectral resolution with SOHO/SUMER.
Within a 60-arcsec scan, we measure a very large variety of profiles: not only reversed and nonreversed profiles but also
red-peaked and blue-peaked ones in both lines. Such a spatial variability is probably related to both the fine structure in
prominences and the different orientations of mass motions. The usage of integrated-intensity cuts along the SUMER slit allowed
us to categorize the prominence in three regions. We computed average profiles and integrated intensities in these lines in
the range 2.36 – 42.3 W m−2 sr−1 for Ly α and 0.027 – 0.237 W m−2 sr−1 for Ly β. As shown by theoretical modeling, the Ly α/Ly β ratio is very sensitive to geometrical and thermodynamic properties
of fine structure in prominences. For some pixels, and in both lines, we found agreement between observed intensities and
those predicted by one-dimensional models. But a close examination of the profiles indicated a rather systematic disagreement
concerning their detailed shapes. The disagreement between observations and thread models (with ambipolar diffusion) leads
us to speculate about the importance of the temperature gradient between the cool and coronal regions. This gradient could
depend on the orientation of field lines as proposed by Heinzel, Anzer, and Gunár (Astron. Astrophys.
442, 331, 2005). 相似文献
7.
H. Bhringer 《Astronomische Nachrichten》2008,329(2):135-138
8.
H. Kjeldsen 《Astrophysics and Space Science》2003,284(1):1-12
Measuring eigenfrequencies and identifying eigenmodes provide the observational basis for a significant improvement in our understanding of stellar evolution and structure.Development throughout the last few years show that we may be at the dawn of a `Golden Age'for Asteroseismology. For this to become a reality we only need two things:Better data and better models. In this paper I describe some aspectsof how one detects stellar oscillations. 相似文献
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B. E. J. Pagel & L. Portinari 《Monthly notices of the Royal Astronomical Society》1998,298(3):747-752
The slope Δ Y /Δ Z is a quantity of interest in relation to stellar evolution, the initial mass function and the determination of the primordial helium abundance. In this paper we estimate Δ Y /Δ Z from fine structure in the main sequence of nearby stars from Hipparcos data for stars with Z ≤ Z⊙. We find a value of about 3, which is consistent with what has been found in extragalactic H II regions and with stellar models for suitable upper limits to the initial masses of supernovae according to the initial mass function slope adopted. 相似文献
10.
G. P. Chernov R. A. Sych Yihua Yan Qijun Fu Chengming Tan Guangli Huang De-Yu Wang Hongao Wu 《Solar physics》2006,237(2):397-418
We present results of the first simultaneous observations of zebra patterns (ZPs) with super-fine spiky structure in the microwave range made at two observatories ～1000 km apart (Beijing and Nanjing, China). The fine structure was recorded by a spectra polarimeter in the 5.2 – 7.6 and 2.8 – 3.6 GHz ranges at the Huairou station and by the spectrometer in the 4.5 – 7.5 GHz range at the Purple Mountain Observatory. Simultaneously, the locations of radio sources were observed by the Siberian Solar Radio Telescope (SSRT) at 5.7 GHz. For a general analysis of the April 10, 2001 event, the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) data and Transition Region and Coronal Explorer (TRACE) images in EUV 171 Å line were used. The circular polarization degree was very weak for the burst background radio emission and moderate to strong for the fine structure. The polarization sign in all the cases probably corresponds to the extraordinary wave mode. Estimations of the magnetic field values in the whistler model for fine structure agree well with the extrapolated values from magnetic maps. Given the possibility of wave transformation in the perpendicular magnetic field and the spiky structure of the ZP, the whistler wave model appears to be the most appropriate explanation for the zebra stripe phenomenon. 相似文献
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O. Engvold 《Solar physics》1980,67(2):351-355
Observed H brightness versus size of emission substructures of quiescent prominences are compared with values predicted from thermodynamical models. The measured size of an emission element of a given brightness is substantially less than the theoretical value.Two possible causes for the discrepancy are suggested: (1) The partial filling of a recording aperture, due to the prominence fine structure, may affect the measurements seriously. Caution is therefore urged against using face values of observed brightness vs ratios in model calculations in cases of partly optically thick lines. (2) Changes of individual fine structure elements on a time scale of a few minutes implies that the prominence plasma may be in a non-stationary radiative state. 相似文献
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Oddbjörn Engvold 《Solar physics》1972,23(2):346-352
A study has been made of fine structure wavelength shift in the K line spectra from quiescent prominences. A persistent small scale motion is found in the prominence main body. In places where we see the characteristic thread like fine structure in the accompanying H filtergrams the average line-of-sight velocity amplitude is about 1 km s–1. A higher velocity ( 4 km s–1) is associated with a slightly coarser, mottled prominence fine structure. In the low lying regions, connecting the prominence body and the chromosphere, we do not detect any fine structure line shift (v 1/2 km s–1). 相似文献
13.
We studied the properties of fine structures in 23 type II bursts recorded at the Trieste Astronomical Observatory at frequencies above 200 MHz.The lifetime of a single fine structure is a fraction of a second. The ratio of fine structures intensity vs bulk flux density is different in different type II bursts and it changes during the evolution of a single event; the reported maximum ratio is 3. The polarization of fine structures is nearly the same during the lifetime of an event. There is also no essential difference in polarization between fine structures and bulk emission; this holds also for an example of high-polarization (about 80%) event.At frequencies lower than 200 MHz the analogy between herringbone structure and type III bursts is frequently mentioned in the literature. From the observations we studied, it results, however, that the time profile of single fine-structure elements and their polarization are substantially different from the morphology of type III bursts.The observed fine structures and their characteristics are discussed in the framework of the model by Holman and Pesses (1983).Paper presented at the 4th CESRA Workshop in Ouranopolis (Greece) 1991. 相似文献
14.
T. M. Lawlor T. R. Young T. A. Johnson J. MacDonald 《Monthly notices of the Royal Astronomical Society》2008,384(4):1533-1543
We present stellar evolution calculations for Population III stars for both single- and binary-star evolutions. Our models include 10- and 16.5-M⊙ single stars and a 10-M⊙ model star that undergoes an episode of accretion resulting in a final mass of 16.1 M⊙ . For comparison, we present the evolution of a solar heavy element abundance model. We use the structure from late-stage evolution models to calculate simulated supernova light curves. Light curve comparisons are made between accretion and non-accretion progenitor models, and models for single-star evolution of comparable masses. Where possible, we make comparisons to previous works. Similar investigations have been carried out, but primarily for solar or near-solar heavy metal abundance stars and not including both the evolution and the supernova explosions in one work. 相似文献
15.
We investigate the structure of convective flows in the solar photosphere on subgranulation scales. The solar granulation pattern is reproduced by solving the inverse problem of nonequilibrium radiation transfer on the basis of the profiles of the neutral iron line λ 523.42 nm. The wave motions are excluded by the k-ω filtration. The line-of-sight velocity has an asymmetric distribution inside the convective flows in large granules (1.5″ and larger) in the lower photosphere and at the bottom of the middle photosphere. This asymmetry is weaker in the upper photosphere. For smaller flows the distribution is more symmetric at all heights. The asymmetry of the temperature distribution is less pronounced. Large convective flows were found to have a fine structure: they are fragmentized into several smaller flows. The fine structure of large flows and spatial smearing are responsible for the observed asymmetry of the convection velocity distribution inside flows. 相似文献
16.
In order to obtain the internal structure of a main-sequence star such as the Sun usually one has to solve the detailed structure equations numerically. This paper is an attempt to construct analytic models for the stellar nuclear energy generation. We give closed-form analytic results for the stellar luminosity and stellar neutrino emission rate when the radial matter density of the spherical star under consideration is linear. For the numerical estimation of the neutrino flux of a specified stellar nuclear reaction we take into account parameters of the standard solar model. The present paper gives for the first time the connection between stellar structure parameters and neutrino fluxes in an analytic stellar model. 相似文献
17.
The predictions of a time-dependent, three-dimensional model of the high-latitude ionosphere have been compared with the diurnal variations of plasma convection velocities and electron densities observed at Chatanika on geomagnetically quiet and disturbed days near equinox. The model predictions for the quiet day are in good agreement, both qualitatively and quantitatively, with the measurements. The model predictions for the disturbed day are in qualitative agreement with the measurements, but at certain local times there are significant quantitative differences. Also, the model cannot produce the detailed fine structure in the electron density that was observed on the disturbed day owing to the lack of fine structure in the model convection pattern and auroral precipitation fluxes. For the quiet day, the gross features of plasma convection are consistent with a symmetric two-cell pattern with a cross-polar cap potential of 52 kV. For the disturbed day, on the other hand, the observed plasma convection is consistent with an asymmetric two-cell pattern with enhanced plasma flow in the dusk sector and a cross-polar cap potential of 90 kV. For both the quiet and disturbed days, the lower latitude region of the high-latitude ionosphere was found to be sensitive to the competition between the vertical components of the electrodynamic and wind-induced ion drifts. For both days, horizontal plasma transport was found to be very important. One consequence of transport is that on the dayside the peak density at a given altitude occurs at a later local time as altitude increases. Another consequence of transport is that high electron densities are maintained in regions devoid of ionization sources, particularly on the disturbed day. 相似文献
18.
MARIO TRIELOFF ALEXANDER DEUTSCH ELMAR K. JESSBERGER 《Meteoritics & planetary science》1998,33(2):361-372
Abstract— For the ～65 km sized Kara impact structure close to the polar Ural, we report an age of 70.3 ± 2.2 Ma (2s?), defined by the mean of 40Ar-39Ar plateau ages for three glassy or crystalline impact melt rocks cleaned from mineral and rock clasts. The fine structure of the age spectra of these samples can quantitatively be simulated by modeling taking into account 39Ar recoil effects, without assuming the presence of excess Ar. The calculations corroborate our age results by showing that 39Ar recoil does not affect the plateau fractions. Previously, Kara has been proposed as a probable K/T impact site or was related to the Campanian-Maastrichtian boundary at 73 Ma. At the 2s? level, both suggestions are ruled out by the well-constrained age for the Kara impact structure. 相似文献
19.
As a first step in constructing three-dimensional decaying sunspot models we select the relevant observational data. From these we conclude:
- sunspots, except the smallest, obey a radial and evolutionary similarity;
- sunspots may be considered as isolated, fairly well defined flux tubes, wrapped in thin current sheets;
- a substantial number among stable regular spots show a phase of slowest decay whose rate is independent of the spot's area.
20.
Volker Springel Simon D. M. White 《Monthly notices of the Royal Astronomical Society》1999,307(1):162-178
We study the formation of tidal tails in pairs of merging disc galaxies with structural properties motivated by current theories of cold dark matter (CDM) cosmologies. In a recent study, Dubinski, Mihos & Hernquist showed that the formation of prominent tidal tails can be strongly suppressed by massive and extended dark haloes. For the large halo-to-disc mass ratio expected in CDM cosmologies their sequence of models failed to produce strong tails like those observed in many well-known pairs of interacting galaxies. In order to test whether this effect can constrain the viability of CDM cosmologies, we construct N ‐body models of disc galaxies with structural properties derived in analogy to the recent analytical work of Mo, Mao & White. With a series of self-consistent collisionless simulations of galaxy–galaxy mergers we demonstrate that even the discs of very massive dark haloes have no problems developing long tidal tails, provided the halo spin parameter is large enough. For our class of models, the halo-to-disc mass ratio is not a good indicator of the ability to produce tails. Instead, the relative size of disc and halo or, alternatively, the ratio of circular velocity to local escape speed at the half mass radius of the disc is a more useful criterion. This result holds in all CDM models. While tidal tails can provide useful information on the structure of galaxies, it thus appears unlikely that they are able to constrain the values of the cosmological parameters within these models. 相似文献