共查询到20条相似文献，搜索用时 62 毫秒
1.
G.W. Lockwood 《Icarus》1977,32(4):413-430
The brightnesses of Titan, Uranus, and Neptune in b (4718 ÅA) and y (5508 ÅA) have increased linearly since 1972 at rates ranging from 0.005 to 0.025 mag yr?1. The observations were made differentially on a number of nights each season with respect to a network of comparison stars whose relative magnitudes were determined by independent measurements. Solar phase coefficients were derived for each object, and all observations have been normalized to zero solar phase angle and mean heliocentric distances. No explanation for the changes has been found, but a possible influence of solar activity upon planetary albedo is suggested by the fact that all of the objects observed have brightened during the declining half of the solar cycle. 相似文献
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E. T. Dunham A. Sheikh D. Opara N. Matsuda M.-C. Liu K. D. McKeegan 《Meteoritics & planetary science》2023,58(5):643-671
As the Sun was forming, calcium–aluminum-rich inclusions (CAIs) were the first rocks to have condensed in the hottest regions of the solar nebula disk. Carbonaceous chondrites (CCs) contain abundant CAIs but are thought to have accreted in the outer Solar System, requiring that CAIs must have been transported outward. Curiously, CAIs are rare in ordinary, enstatite, rumuruti, and kakangari chondrites, non-carbonaceous chondrites (NCs), that likely formed in the inner Solar System. Thus, CAI abundances and characteristics can provide constraints on the early dynamical evolution of the disk. In this work, we address whether the hypothesis of an early-formed proto-Jupiter “opening a gap” in the disk can explain the dichotomy in the relative abundance of CAIs in CC and NC chondrites. We searched 76 NC meteorite sections to find 232 CAIs which have an average apparent diameter of 46 μm and comprise 0.01 area%, about half the size of and ~200 times less abundant than CC CAIs on average. Unlike CC CAIs, only 4% of the NC CAIs contain melilite and most contain alteration features suggesting that NC CAIs underwent pervasive fluid-assisted thermal metamorphism on asteroidal parent bodies. However, based on NC CAI populations correlating with meteorite metamorphic grade, we argue that disk dynamics is likely the primary reason behind the existence of small (<100 μm) and rare NC CAIs. Our data support astrophysical models which suggest that, after outward transport of CAIs, formation of a gap in the disk trapped CAIs in the outer Solar System. 相似文献
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Here we present new adaptive optics observations of the Quaoar–Weywot system. With these new observations we determine an improved system orbit. Due to a 0.39 day alias that exists in available observations, four possible orbital solutions are available with periods of ～11.6, ～12.0, ～12.4, and ～12.8 days. From the possible orbital solutions, system masses of 1.3–1.5 ± 0.1 × 1021 kg are found. These observations provide an updated density for Quaoar of 2.7–5.0 g cm?3. In all cases, Weywot’s orbit is eccentric, with possible values ～0.13–0.16. We present a reanalysis of the tidal orbital evolution of the Quaoar–Weywot system. We have found that Weywot has probably evolved to a state of synchronous rotation, and has likely preserved its initial inclination over the age of the Solar System. We find that for plausible values of the effective tidal dissipation factor tides produce a very slow evolution of Weywot’s eccentricity and semi-major axis. Accordingly, it appears that Weywot’s eccentricity likely did not tidally evolve to its current value from an initially circular orbit. Rather, it seems that some other mechanism has raised its eccentricity post-formation, or Weywot formed with a non-negligible eccentricity. 相似文献
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Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,325(2):149-152
We investigate the cosmological dynamics of a four-dimensional Friedmann–Robertson–Walker homogenous and isotropic universe from Gauss–Bonnet higher-order curvature corrections, together with nonminimal coupling and with an infrared effective action of gravity based on a second-order gauge formulation for the Lorentz group. We study the evolution of the universe in such a model, identifying its key properties. Many new interesting features are revealed and discussed in some detail. 相似文献
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Emmanuel E. Etim Prasanta Gorai Ankan Das Elangannan Arunan 《Astrophysics and Space Science》2018,363(1):6
There are numerous complex organic molecules containing carbon and oxygen atoms which show either C–C–O or C–O–C bonding backbone. This paper examines altogether 51 C–C–O and C–O–C bonding backbone molecules from ten different isomeric groups (C2H2O, C3H2O, C2H4O, C2H4O2, C3H4O, C2H6O, C2H6O2, C3H6O, C3H6O2, C3H8O) to summarize the present astronomical status of these molecules. Accurate calculations of enthalpy of formation of these molecules show that the isomers with C–C–O backbone are more stable than the C–O–C backbone. Interestingly, a detailed analysis of relevant astromolecules indicates that most of the observed astromolecules have the C–C–O backbone. As a matter of fact, of all the molecules examined in this study, 80% of the astronomically observed species have the C–C–O backbone while only 20% have the C–O–C backbone. In general, interstellar abundance of a molecule is controlled by some factors such as kinetics, formation and destruction pathways,thermodynamics etc. A proper consideration of these factors could explain the observed abundances of these molecules. All these possible key factors are discussed in this paper. 相似文献
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In this article, we present a multi-wavelength and multi-instrument investigation of a halo coronal mass ejection (CME) from active region NOAA 12371 on 21 June 2015 that led to a major geomagnetic storm of minimum \(\mathrm{Dst} = -204\) nT. The observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot EUV channel of 94 Å confirm the CME to be associated with a coronal sigmoid that displayed an intense emission (\(T \sim6\) MK) from its core before the onset of the eruption. Multi-wavelength observations of the source active region suggest tether-cutting reconnection to be the primary triggering mechanism of the flux rope eruption. Interestingly, the flux rope eruption exhibited a two-phase evolution during which the “standard” large-scale flare reconnection process originated two composite M-class flares. The eruption of the flux rope is followed by the coronagraphic observation of a fast, halo CME with linear projected speed of 1366 km?s?1. The dynamic radio spectrum in the decameter-hectometer frequency range reveals multiple continuum-like enhancements in type II radio emission which imply the interaction of the CME with other preceding slow speed CMEs in the corona within \(\approx10\)?–?\(90~\mbox{R} _{\odot}\). The scenario of CME–CME interaction in the corona and interplanetary medium is further confirmed by the height–time plots of the CMEs occurring during 19?–?21 June. In situ measurements of solar wind magnetic field and plasma parameters at 1 AU exhibit two distinct magnetic clouds, separated by a magnetic hole. Synthesis of near-Sun observations, interplanetary radio emissions, and in situ measurements at 1 AU reveal complex processes of CME–CME interactions right from the source active region to the corona and interplanetary medium that have played a crucial role towards the large enhancement of the geoeffectiveness of the halo CME on 21 June 2015. 相似文献
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Lorenzo Iorio 《Celestial Mechanics and Dynamical Astronomy》2001,79(3):201-230
The general relativistic Lense—Thirring effect can be measured by inspecting a suitable combination of the orbital residuals of the nodes of LAGEOS and LAGEOS II and the perigee of LAGEOS II. The solid and ocean Earth tides affect the recovery of the parameter by means of which the gravitomagnetic signal is accounted for in the combined residuals. Thus an extensive analysis of the perturbations induced on these orbital elements by the solid and ocean Earth tides is carried out. It involves the l=2 terms for the solid tides and the l=2,3,4 terms for the ocean tides. The perigee of LAGEOS II turns out to be very sensitive to the l=3 part of the ocean tidal spectrum, contrary to the nodes of LAGEOS and LAGEOS II. The uncertainty in the solid tidal perturbations, mainly due to the Love number k
2, ranges from 0.4% to 1.5%, while the ocean tides are uncertain at 5–15% level. The obtained results are used in order to check in a preliminary way which tidal constituents the Lense-Thirring shift is sensitive to. In particular it is tested if the semisecular 18.6-year zonal tide really does not affect the combined residuals. It turns out that, if modeled at the level of accuracy worked out in the paper, the l=2,4 m=0 and also, to a lesser extent, the l=3, m=0 tidal perturbations cancel out.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
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We present a catalog of high-speed streams, along with their solar sources for solar cycle 23. We study their distribution
during different years and different phases of solar cycle after classifying them into different groups based on their source(s),
duration, and speed. We also study the average plasma/field properties of streams after dividing them into suitable groups
on the basis of their source(s), duration and speed. It is expected that the catalog and statistical results presented in
this work will further stimulate the space weather and solar-terrestrial studies involving high-speed streams. 相似文献
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D. M. Willis H. E. Coffey R. Henwood E. H. Erwin D. V. Hoyt M. N. Wild W. F. Denig 《Solar physics》2013,288(1):117-139
The measurements of sunspot positions and areas that were published initially by the Royal Observatory, Greenwich, and subsequently by the Royal Greenwich Observatory (RGO), as the Greenwich Photo-heliographic Results (GPR), 1874?–?1976, exist in both printed and digital forms. These printed and digital sunspot datasets have been archived in various libraries and data centres. Unfortunately, however, typographic, systematic and isolated errors can be found in the various datasets. The purpose of the present paper is to begin the task of identifying and correcting these errors. In particular, the intention is to provide in one foundational paper all the necessary background information on the original solar observations, their various applications in scientific research, the format of the different digital datasets, the necessary definitions of the quantities measured, and the initial identification of errors in both the printed publications and the digital datasets. Two companion papers address the question of specific identifiable errors; namely, typographic errors in the printed publications, and both isolated and systematic errors in the digital datasets. The existence of two independently prepared digital datasets, which both contain information on sunspot positions and areas, makes it possible to outline a preliminary strategy for the development of an even more accurate digital dataset. Further work is in progress to generate an extremely reliable sunspot digital dataset, based on the programme of solar observations supported for more than a century by the Royal Observatory, Greenwich, and the Royal Greenwich Observatory. This improved dataset should be of value in many future scientific investigations. 相似文献
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Photospheric and chromospheric spectroscopic Doppler rotation rates for the full solar disk are analyzed for the period July, 1966 to July, 1978. An approximately linear secular increase of the equatorial rate of 3.7% for these 12 years is found (in confirmation of Howard, 1976). The high latitude rates above 65 ° appear to vary with a peak-to-peak amplitude of 8%, or more, phased to the sunspot cycle such that the most rapid rotation occurs at, or following, solar maximum. The chromosphere, as indicated by H, has continued to rotate on the average 3% faster than the photosphere agreeing with past observations. Sources of error are discussed and evaluated.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
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The solar cycle appears to be remarkably synchronized with the gravitational torques exerted by the tidally dominant planets Venus, Earth and Jupiter. Recently, a possible synchronization mechanism was proposed that relies on the intrinsic helicity oscillation of the current-driven Tayler instability which can be stoked by tidal-like perturbations with a period of 11.07 years. Inserted into a simple \(\alpha \)–\(\Omega \) dynamo model these resonantly excited helicity oscillations led to a 22.14 years dynamo cycle. Here, we assess various alternative mechanisms of synchronization. Specifically we study a simple time-delay model of Babcock–Leighton type dynamos and ask whether periodic changes of either the minimal amplitude for rising toroidal flux tubes or the \(\Omega \) effect could eventually lead to synchronization. In contrast to the easy and robust synchronizability of Tayler–Spruit dynamo models, our answer for those Babcock–Leighton type models is less propitious. 相似文献
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Takeo Kosugi 《Solar physics》1976,48(2):339-356
The radio observations of type II–IV bursts on December 14, 1971 are analyzed. These radio events were associated with a H-spray or eruptive prominence, and later followed by several compact moving clouds observed with the NRL white-light coronagraph aboard OSO-7. There was also observed a diffuse expanding cloud behind the compact moving clouds.From the comparison of the interferometer observation of the bursts with the optical observation, it is strongly suggested that the compact moving clouds were likely to be the optical counterparts of the sources of moving type IV radio emission. This fact suggests that the magnetic bubbles were really produced in the flare process. The frequency-drift of the first group of type II bursts was so rapid, that we could neither identify the type II shock with the leading edge of the diffuse expanding cloud nor interpret it as the piston-driven shock of the latter. Because of the uncertainty of the velocities of the compact clouds due to the projection effect, the possibility that the type II shock was the piston-driven shock of the compact clouds cannot be excluded. Nevertheless we suggest that the type II shock was a blast type MHD shock and had no direct physical relation to the flare-associated mass-ejection processes. The relation between the type II–IV bursts and the interplanetary shock is also discussed. 相似文献
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Mutual quasi-periodicities near the solar-rotation period appear in time series based on the Earth’s magnetic field, the interplanetary
magnetic field, and signed solar-magnetic fields. Dominant among these is one at 27.03±0.02 days that has been highlighted
by Neugebauer et al. (J. Geophys. Res.
105, 2315, 2000). Extension of their study in time and to different data reveals decadal epochs during which the ≈ 27.0 days, or a ≈ 28.3 days,
or other quasi-periods dominate the signal. Space-time eigenvalue analyses of time series in 30 solar latitude bands, based
on synoptic maps of unsigned photospheric fields, lead to two maximally independent modes that account for almost 30% of the
data variance. One mode spans 45° of latitude in the northern hemisphere and the other one in the southern. The modes rotate
around the Sun rigidly, not differentially, suggesting connection with the subsurface dynamo. Spectral analyses yield familiar
dominant quasi-periods 27.04±0.03 days in the North and at 28.24±0.03 days in the South. These are replaced during cycle 23
by one at 26.45±0.03 days in the North. The modes show no tendency for preferred longitudes separated by ≈ 180°. 相似文献
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This paper will review the input of 65 years of radio observations to our understanding of solar and solar–terrestrial physics. It is focussed on the radio observations of phenomena linked to solar activity in the period going from the first discovery of the radio emissions to present days. We shall present first an overview of solar radio physics focussed on the active Sun and on the premices of solar–terrestrial relationships from the discovery to the 1980s. We shall then discuss the input of radioastronomy both at metric/decimetric wavelengths and at centimetric/millimetric and submillimetric wavelengths to our understanding of flares. We shall also review some of the radio, X-ray and white-light signatures bringing new evidence for reconnection and current sheets in eruptive events. The input of radio images (obtained with a high temporal cadence) to the understanding of the initiation and fast development in the low corona of coronal mass ejections (CMEs) as well as the radio observations of shocks in the corona and in the interplanetary medium will be reviewed. The input of radio observations to our knowledge of the interplanetary magnetic structures (ICMEs) will be summarized; we shall show how radio observations linked to the propagation of electron beams allow to identify small scale structures in the heliosphere and to trace the connection between the Sun and interplanetary structures as far as 4AU. We shall also describe how the radio observations bring useful information on the relationship and connections between the energetic electrons in the corona and the electrons measured in-situ. The input of radio observations on the forecasting of the arrival time of shocks at the Earth as well as on Space Weather studies will be described. In the last section, we shall summarize the key results that have contributed to transform our knowledge of solar activity and its link with the interplanetary medium. In conclusion, we shall indicate the instrumental radio developments at Earth and in space, which are from our point of view, necessary for the future of solar and interplanetary physics. 相似文献