共查询到20条相似文献,搜索用时 0 毫秒
1.
Yu. Yurovsky 《Solar physics》2001,201(2):389-392
It is shown that for burst bandwidth B considered in the time-frequency domain, the distribution of w(B
−1) is the probability density of radiation of radio emission of a given relative frequency bandwidth, while the distribution
w(B) is the density of bursts, arrangement on axis B. Using this remark, we find that solar decimetric spikes and type III bursts, and metric noise storms, have a `radiation
probability' approximately 10 times higher for large-bandwidth bursts than for small-bandwidth bursts. 相似文献
2.
P. Zucca E. P. Carley J. McCauley P. T. Gallagher C. Monstein R. T. J. McAteer 《Solar physics》2012,280(2):591-602
The Rosse Solar-Terrestrial Observatory (RSTO; www.rosseobservatory.ie ) was established at Birr Castle, Co. Offaly, Ireland (53°05′38.9″, 7°55′12.7″) in 2010 to study solar radio bursts and the response of the Earth’s ionosphere and geomagnetic field. To date, three Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy in Transportable Observatory (CALLISTO) spectrometers have been installed, with the capability of observing in the frequency range of 10?–?870 MHz. The receivers are fed simultaneously by biconical and log-periodic antennas. Nominally, frequency spectra in the range of 10?–?400 MHz are obtained with four sweeps per second over 600 channels. Here, we describe the RSTO solar radio spectrometer set-up, and present dynamic spectra of samples of type II, III and IV radio bursts. In particular, we describe the fine-scale structure observed in type II bursts, including band splitting and rapidly varying herringbone features. 相似文献
3.
The properties of a sample of IR galaxies from the Point Source Catalog z (PSCz) Survey were investigated using the correlation gamma function [(r) and *(r)]. The results with different volume-limited subsamples indicate that the regions of strong correlations (a power-law decrease in density with distance with an exponent 1 1) are limited to a scale of 10-15 Mpc. A break is present at this scale in the dependences of log() on log(r) and of log(*) on log(r). Such a break is also observed for various other samples of galaxies and clusters (at different scales). After the break the density dependence changes to another regime, corresponding to a fully uniform distribution for bright galaxies in the northern Galactic hemisphere. For some subsamples of the southern and northern hemispheres the latter regime corresponds to some decrease in density with distance. Indications of significant differences between the distributions of objects in the southern and northern hemispheres are obtained. It is shown that the section of the gamma function after the break, even when its extent is small, is a significant indicator of actual correlation properties of the distributions. The results of the analysis are in good agreement, on the whole, with preceding studies of the PSCz survey. 相似文献
4.
5.
The intensity distribution of solar radio bursts observed in the frequency band 0.245–17 GHz has heen derived statistically. The distribution law has been found to be quite different from that of a power law as reported by earlier workers. This distribution leads to the error function, when the total number of bursts in any intensity range is found out. The generalized distribution law can be approximated to the power law only in the frequency band 0.65–2.8 GHz. 相似文献
6.
We investigate quantitatively how the peak emission frequency of the overall energy spectrum is at work in distinguishing
RBL-like and XBL-like objects. We employ the sample of Giommi et al. (1995) to study the distribution of BL Lacertae objects with various locations of the cutoff of the overall energy spectrum.
We find that the sources with the cutoff located at lower frequency are indeed sited in the RBL region of the αro-αoxplane, while those with the cutoff located at higher frequency are distributed in the XBL region. For a more quantitative
study, we employ the BL Lacerta esamples presented by Sambruna et al. (1996), where the peak emission frequency, νp, of each source is estimated by fitting the data with a parabolic function. In the plot of αrx -log νp we find that, in the four different regions divided by the αrx = 0.75 line and thelogνp = 14.7 line, all the RBL-like objects are inside the upper left region, while most XBL-like objects are within the lower
right region. A few sources are located in the lower left region. No sources are in the upper right region. This result is
rather quantitative. It provides an evidence supporting what Giommi et al. (1995) suggested: RBL-like and XBL-like objects can be distinguished by the difference of the peak emission frequency of
the overall energy spectrum.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
8.
Kuiper带天体的轨道分布特性 总被引:3,自引:1,他引:2
1992年9月,夏威夷大学的D.Jewitt和加利福尼亚大学的J.Lun发现了海王星外绕太阳运行的第一个小天体1992QB1[1],开创了人类对于海王星外天体的实际观测的研究.近10年的接连不断发现,已经证实了海王星轨道外面存在着一个由大量的环绕太阳运动的小天体组成的环带[2].由于G.P.Kuiper曾在1951年的文章中提出过在冥王星的外边可能存在小天体的问题,因此人们一般把这个环带称为Kuiper带,你这些天体为“KuiperBelt Objects”(KBOs),或从逻辑上称它们为“Trans-NeptunianObjects”(TNOs)[3] 相似文献
9.
Ke-Feng Sun Ji Yang Shao-Guang Luo Min Wang Li-Cai Deng Xu Zhou Jian-Sheng Chen Department of Astronomy Peking University Beijing sunkf Chinese Academy of Sciences-Peking University Joint Beijing Astrophysical Center Beijing Purple Mountain Observatory Chinese Academy of Sciences Nanjing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(5):458-468
We report our new results on Herbig-Haro (HH) objects in the star forming region of Taurus from a wide-field survey with the 60/90 cm Schmidt telescope of the Beijing Astronomical Observatory. This survey using CCD imaging with a narrow band [SII] filter and an intermediate band [BATC10] filter covered approximately 30 square degrees in Taurus. Besides confirming the known HH Objects in the region, we discovered seven new HH candidates, and groups. Six of these are HH 701A-B, HH 702A-D, HH 703, HH 704A-D, HH 705, HH 706 and the seventh is a group, a new component of HH 319, labeled HH 319B-D. Based on the large-scale distribution of pre-main-sequence (PMS) stars in Taurus, we analyze statistically the most probable distance from the HH objects to each PMS star, from which we estimate the typical timescale of these HH objects to be between (1.3 - 2.0) ×104 yrs; and we also obtain the birth rates of HH objects: 0.447±0.198 for Class Ⅰ PMS stars, 0.360±0.222 for Class Ⅱ PMS stars, and -0.148±0.234 fo 相似文献
10.
The metric spectral data obtained at the Yunnan Observatory from July 1990 to December 1991 are analysed and some type III bursts associated with millisecond spikes are found. Their different morphologies reveal the relation between the type III bursts and the millisecond spikes. Based on the occurrence time and the characteristics of continuity and changes of the morphologies in the spikes and the type III bursts of two typical events, we verify that the acceleration region of the coronal electrons is located above the emitting region of the millisecond spikes and the type III bursts. The observations show that the interface frequency of a pair of type III bursts lies near 250 MHz. Finally the authors attempt to explain qualitatively the generating mechanism of the metric millisecond spike-type III bursts by means of the plasma hypothesis. 相似文献
11.
Singh Dayal Sasikumar Raja K. Subramanian Prasad Ramesh R. Monstein Christian 《Solar physics》2019,294(8):1-19
Solar Physics - In early September 2017, a series of solar flares and coronal mass ejections (CMEs) erupted from the Sun. The Cor2a coronagraph, a unit of the Sun Earth Connection Coronal and... 相似文献
12.
William F. Bottke Jr.Alessandro Morbidelli Robert JedickeJean-Marc Petit Harold F. LevisonPatrick Michel Travis S. Metcalfe 《Icarus》2002,156(2):399-433
The orbital and absolute magnitude distribution of the near-Earth objects (NEOs) is difficult to compute, partly because only a modest fraction of the entire NEO population has been discovered so far, but also because the known NEOs are biased by complicated observational selection effects. To circumvent these problems, we created a model NEO population which was fit to known NEOs discovered or accidentally rediscovered by Spacewatch. Our method was to numerically integrate thousands of test particles from five source regions that we believe provide most NEOs to the inner Solar System. Four of these source regions are in or adjacent to the main asteroid belt, while the fifth one is associated with the transneptunian disk. The nearly isotropic comets, which include the Halley-type comets and the long-period comets, were not included in our model. Test bodies from our source regions that passed into the NEO region (perihelia q<1.3 AU and aphelia Q≥0.983 AU) were tracked until they were eliminated by striking the Sun or a planet or were ejected out of the inner Solar System. These integrations were used to create five residence time probability distributions in semimajor axis, eccentricity, and inclination space (one for each source). These distributions show where NEOs from a given source are statistically most likely to be located. Combining these five residence time probability distributions with an NEO absolute magnitude distribution computed from previous work and a probability function representing the observational biases associated with the Spacewatch NEO survey, we produced an NEO model population that could be fit to 138 NEOs discovered or accidentally rediscovered by Spacewatch. By testing a range of possible source combinations, a best-fit NEO model was computed which (i) provided the debiased orbital and absolute magnitude distributions for the NEO population and (ii) indicated the relative importance of each NEO source region.Our best-fit model is consistent with 960±120 NEOs having H<18 and a<7.4 AU. Approximately 44% (as of December 2000) have been found so far. The limits on this estimate are conditional, since our model does not include nearly isotropic comets. Nearly isotropic comets are generally restricted to a Tisserand parameter (with respect to Jupiter) of T<2, such that few are believed to have a<7.4 AU. Our computed NEO orbital distribution, which is valid for bodies as faint as H<22, indicates that the Amor, Apollo, and Aten populations contain 32±1%, 62±1%, and 6±1% of the NEO population, respectively. We estimate that the population of objects completely inside Earth's orbit (IEOs) arising from our source regions is 2% the size of the NEO population. This value does not include the putative Vulcanoid population located inside Mercury's orbit. Overall, our model predicts that ∼61% of the NEO population comes from the inner main belt (a<2.5 AU), ∼24% comes from the central main belt (2.5<a<2.8 AU), ∼8% comes from the outer main belt (a>2.8 AU), and ∼6% comes from the Jupiter-family comet region (2<T?3). The steady-state population in each NEO source region, as well as the influx rates needed to replenish each region, were calculated as a by-product of our method. The population of extinct comets in the Jupiter-family comet region was also computed. 相似文献
13.
根据1994年lslike&Benz给出的1-3GHz频带上的微波III型爆发和微波尖峰辐射的分类定义,分析北京天文台26-3.8GHz频带上观测到的微波爆发的精细结构.通过分析发现该定义有局限性.本文重新定义了该波段上的微波III型爆发和微波尖峰辐射,并讨论了这种分类定义与设备时间分辨率的关系 相似文献
14.
Wen-Long Zhang Xiu-Juan Li Yu-Peng Yang Shuang-Xi Yi Cheng-Kui Li Qing-Wen Tang Ying Qin Fa-Yin Wang 《天文和天体物理学研究(英文版)》2023,(11):114-119
As one class of the most important objects in the universe,magnetars can produce a lot of different frequency bursts including X-ray bursts.In Cai et al.,75 X-ray bursts produced by magnetar SGR J1935+2154 during an active period in 2020 are published,including the duration and net photon counts of each burst,and waiting time based on the trigger time difference.In this paper,we utilize the power-law model,dN(x)/dx ∝(x+x0)((-α)x),to fit the cumulative distributio... 相似文献
15.
It is well known that galaxies accumulating large quantities of gas undergo violent bursts of star formation. This is believed to be due to tidal interactions of galaxies leading to the infall of gas into their central regions. Bursts of star formation in this scenario are transitory phenomena and can be induced only by external sources.However, in some cases there is no direct evidence of tidal interactions in starburst galaxies.We discuss another possibility of bursting phenomena in galaxies connected with nonlinear feedback processes in mass-exchange between components of star-forming region. We consider a three-component model including cold clouds, warm gas and massive stars and take into account the delay processes in the transformation of hot gas ejected by massive stars and evaporated from cold phase, into the warm phase. Self-regulating mechanism of phase transition of small clouds into warm gas due to heating radiation of massive stars is also taken into account.The analysis of stability of the system shows that it could be unstable even in case of a small efficiency in the birth of massive stars. The evolution of unstable nonlinear perturbations leads to the development of self-sustained nonlinear oscillations of star formation. 相似文献
16.
17.
Umeda H 《The Astrophysical journal》2000,536(2):L89-L92
We present 1 μm Hubble Space Telescope/near-infrared camera and multiobject spectrometer resolved imaging polarimetry of the GG Tau circumbinary ring. We find that the ring displays east-west asymmetries in surface brightness as well as several pronounced irregularities but is smoother than suggested by ground-based adaptive optics observations. The data are consistent with a 37 degrees system inclination and a projected rotational axis at a position angle of 7 degrees east of north, determined from millimeter imaging. The ring is strongly polarized, up to approximately 50%, which is indicative of Rayleigh-like scattering from submicron dust grains. Although the polarization pattern is broadly centrosymmetric and clearly results from illumination of the ring by the central stars, departures from true centrosymmetry and the irregular flux suggest that binary illumination, scattering through unresolved circumstellar disks, and shading by these disks may all be factors influencing the observed morphology. We confirm a approximately 0&farcs;25 shift between the inner edges of the near-infrared and millimeter images and find that the global morphology of the ring and the polarimetry provide strong evidence for a geometrically thick ring. A simple Monte Carlo scattering simulation is presented that reproduces these features and supports the thick-ring hypothesis. We cannot confirm filamentary streaming from the binary to the ring, also observed in the ground-based images, although it is possible that there is material inside the dynamically cleared region that might contribute to filamentary deconvolution artifacts. Finally, we find a faint fifth point source in the GG Tau field that, if it is associated with the system, is almost certainly a brown dwarf. 相似文献
18.
A. A. Kuznetsov 《Solar physics》2006,237(1):153-171
The plasma mechanism of radio emission generation in an inhomogeneous medium is investigated. In the model under study, the
electron beam with loss-cone distribution generates upper-hybrid waves that, in turn, are transformed into radio emission.
It is shown that the influence of the plasma density inhomogeneity limits the plasma waves’ intensity considerably due to
variation in their wave vector. The results are used to interpret the intermediate drift (IMD) bursts. A model is proposed
in which these bursts are reflections of propagating small-scale (with amplitudes of about 1% and sizes of hundreds of kilometers)
magnetohydrodynamic (MHD) disturbances of magnetic tubes. It is shown that this model allows us to explain the spectral parameters
of the bursts in question. At present, the lack of precise and independent data about the magnetic field does not allow us
to decide definitively between the existing models (whistler or MHD waves) of the IMD bursts; nevertheless, if the proposed
model is correct, it can be used to determine the characteristics of the coronal MHD waves. 相似文献
19.
定位快速射电暴(Fast Radio Burst, FRB)以及确认其寄主星系至今仍是一个具有挑战性的难题,截至2021年4月已确认13个快速射电暴的寄主星系,其中只有3个重复暴,其余都是非重复暴.快速射电暴的寄主星系对快速射电暴起源的探索起着非常重要的作用,约束着快速射电暴前身星模型.对这些已确认寄主星系的FRB进行研究,发现FRB寄主星系对色散量(Dispersion Measure, DM)的贡献在一定范围内波动(0–240 pc·cm-3),并且寄主星系对DM的贡献与寄主星系的性质(恒星形成率、金属丰度)也可能具有关联性.寄主星系恒星形成率、金属丰度与色散量的统计关系对FRB邻近环境的研究有着重要意义. 相似文献