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1.
In this study we present the new R and I light curve solutions for the eclipsing binary systems RW CrB and VZ Leo, which for
VZ Leo is the first one in the literature. Our new observations have been analyzed using the Wilson-Devinney code from which
new geometric and photometric elements are derived. The geometry of both stars is that of a semi-detached binary system where
the secondary component fills its Roche lobe while the primary component is well inside. In the case of RW CrB, asymmetry
in the light curve was explained by a spot model. The orbital period changes of both systems were studied and the results
indicated a period decrease which can be explained by angular momentum loss. We also investigated the possibility of pulsations
of the primary components since these systems are mentioned as candidates of δ Sct type pulsation. However, a time-series analysis of the residual curves in the filter I does not indicate any evidence
of periodic light variation for both systems. Finally, we compared the results obtained for both binary stars to those of
similar systems. 相似文献
2.
Precursor techniques, in particular those using geomagnetic indices, often are used in the prediction of the maximum amplitude
for a sunspot cycle. Here, the year 2008 is taken as being the sunspot minimum year for cycle 24. Based on the average aa index value for the year of the sunspot minimum and the preceding four years, we estimate the expected annual maximum amplitude
for cycle 24 to be about 92.8±19.6 (1-sigma accuracy), indicating a somewhat weaker cycle 24 as compared to cycles 21 – 23.
Presuming a smoothed monthly mean sunspot number minimum in August 2008, a smoothed monthly mean sunspot number maximum is
expected about October 2012±4 months (1-sigma accuracy). 相似文献
3.
We demonstrate that a simple solar dynamo model, in the form of a Parker migratory dynamo with random fluctuations of the
dynamo governing parameters and algebraic saturation of dynamo action, can at least qualitatively reproduce all the basic
features of solar Grand Minima as they are known from direct and indirect data. In particular, the model successfully reproduces
such features as an abrupt transition into a Grand Minimum and the subsequent gradual recovery of solar activity, as well
as mixed-parity butterfly diagrams during the epoch of the Grand Minimum. The model predicts that the cycle survives in some
form during a Grand Minimum, as well as the relative stability of the cycle inside and outside of a Grand Minimum. The long-term
statistics of simulated Grand Minima appears compatible with the phenomenology of the Grand Minima inferred from the cosmogenic
isotope data. We demonstrate that such ability to reproduce the Grand Minima phenomenology is not a general feature of the
dynamo models but requires some specific assumption, such as random fluctuations in dynamo governing parameters. In general,
we conclude that a relatively simple and straightforward model is able to reproduce the Grand Minima phenomenology remarkably
well, in principle providing us with a possibility of studying the physical nature of Grand Minima. 相似文献
4.
John F. Hawley 《Astrophysics and Space Science》2009,320(1-3):107-114
Observations are providing increasingly detailed quantitative information about the accretion flows that power such high energy systems as X-ray binaries and Active Galactic Nuclei. These observations have been modeled in some detail by a variety of accretion scenarios, but such models rely on unavoidable assumptions such as regular flow geometry and a simple, parameterized stress. Global numerical simulations offer a way to investigate the basic physical dynamics of accretion flows without these assumptions. We are now carrying out fully three-dimensional general relativistic magnetohydrodynamic simulations of time-dependent inflows into Kerr black holes. The results from recent global simulations of black hole accretion disks will be reviewed, and some implications of those results for observations will be discussed. 相似文献
5.
In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC 189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the limiting radii of 7′, 12′, 6′ and 5′ which correspond to linear radii of 3.6 pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values E(B?V) obtained for the clusters are 0.85, 0.65–0.85, 0.6 and 0.53 and their true distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their structures, luminosity functions and mass functions (φ(M)=dN/dM ∝ M ?(1+χ)) to the parameter τ=t age /t relax to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times (τ≥1). These results suggest mass seggregation due to dynamical effects. The values of χ, which characterize the overall mass functions for the clusters are 0.96±0.11, 1.16±0.18, 0.55±0.14 and 0.66±0.31 respectively. The change in χ as a function of radius is a good indicator of the dynamical state of clusters. 相似文献
6.
A. M. Uralov V. V. Grechnev G. V. Rudenko I. G. Rudenko H. Nakajima 《Solar physics》2008,249(2):315-335
Neutral Line associated Sources (NLSs) are quasi-stationary microwave sources projected onto vicinities of the neutral line
of the photospheric magnetic field. NLSs are often precursors of powerful flares, but their nature is unclear. We endeavor
to reveal the structure of an NLS and to analyze a physical connection between such a source with a site of energy release
in the corona above NOAA 10488 (October/November 2003). Evolution of this AR includes emergence and collision of two bipolar
magnetic structures, rise of the main magnetic separator, and the appearance of an NLS underneath. The NLS appears at a contact
site of colliding sunspots, whose relative motion goes on, resulting in a large shear along a tangent. Then the nascent NLS
becomes the main source of microwave fluctuations in the AR. The NLS emission at 17 GHz is dominated by either footpoints
or the top of a loop-like structure, an NLS loop, which connects two colliding sunspots. During a considerable amount of time,
the emission dominates over that footpoint of the NLS loop, where the magnetic field is stronger. At that time, the NLS resembles
a usual sunspot–associated radio source, whose brightness center is displaced towards the periphery of a sunspot. Microwave
emission of an X2.7 flare is mainly concentrated in an ascending flare loop, initially coinciding with the NLS loop. The top
of this loop is located at the base of a non-uniform bar-like structure visible in soft X-rays and at 34 GHz at the flare
onset. We reveal i) upward lengthening of this bar before the flare onset, ii) the motion of the top of an apparently ascending flare loop along the axis of this bar, and iii) a non-thermal microwave source, whose descent along the bar was associated with the launching of a coronal ejection. We
connect the bar with a probable position of a nearly vertical diffusion region, a site of maximal energy release inside an
extended pre-flare current sheet. The top of the NLS loop is located at the bottom of this region. A combination of the NLS
loop and diffusion region constitutes the skeleton of a quasi-stationary microwave NLS. 相似文献
7.
S. Masson K.-L. Klein R. Bütikofer E. Flückiger V. Kurt B. Yushkov S. Krucker 《Solar physics》2009,257(2):305-322
The origin of relativistic solar protons during large flare/CME events has not been uniquely identified so far. We perform
a detailed comparative analysis of the time profiles of relativistic protons detected by the worldwide network of neutron
monitors at Earth with electromagnetic signatures of particle acceleration in the solar corona during the large particle event
of 20 January 2005. The intensity – time profile of the relativistic protons derived from the neutron monitor data indicates
two successive peaks. We show that microwave, hard X-ray, and γ-ray emissions display several episodes of particle acceleration within the impulsive flare phase. The first relativistic
protons detected at Earth are accelerated together with relativistic electrons and with protons that produce pion-decay γ rays during the second episode. The second peak in the relativistic proton profile at Earth is accompanied by new signatures
of particle acceleration in the corona within ≈1R
⊙ above the photosphere, revealed by hard X-ray and microwave emissions of low intensity and by the renewed radio emission
of electron beams and of a coronal shock wave. We discuss the observations in terms of different scenarios of particle acceleration
in the corona. 相似文献
8.
Donald C. Norquist 《Solar physics》2011,269(1):111-127
Designing a statistical solar flare forecasting technique can benefit greatly from knowledge of the flare frequency of occurrence
with respect to sunspot groups. This study analyzed sunspot groups and Hα and X-ray flares reported for the period 1997 – 2007.
Annual catalogs were constructed, listing the days that numbered sunspot groups were observed (designated sunspot group-days,
SSG-Ds) and for each day a record for each associated Hα flare of importance category one or greater and normal or bright
brightness and for each X-ray flare of intensity C 5 or higher. The catalogs were then analyzed to produce frequency distributions
of SSG-Ds by year, sunspot group class, likelihood of producing at least one flare overall and by sunspot group class, and
frequency of occurrence of numbers of flares per day and flare intensity category. Only 3% of SSG-Ds produced a substantial
Hα flare and 7% had a significant X-ray flare. We found that mature, complex sunspot groups were more likely than simple sunspot
groups to produce a flare, but the latter were more prevalent than the former. More than half of the SSG-Ds with flares had
a maximum intensity flare greater than the lowest category (C-class of intensity five and higher). The fact that certain sunspot
group classes had flaring probabilities significantly higher than the combined probabilities of the intensity categories when
all SSG-Ds were considered suggest that it might be best to first predict the flaring probability. For sunspot groups found
likely to flare, a separate diagnosis of maximum flare intensity category appears feasible. 相似文献
9.
10.
Subdwarf B stars (sdBs) can significantly change the ultraviolet spectra of populations at age t～1 Gyr, and have been even included in the evolutionary population synthesis (EPS) models by Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007). In this study we present the spectral energy distributions (SEDs) of binary stellar populations (BSPs) by combining the EPS models of Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007) and those of the Yunnan group (Zhang et al. in Astron. Astrophys. 415:117, 2004; Mon. Not. R. Astron. Soc. 357:1088, 2005), which have included various binary interactions (except sdBs) in EPS models. This set of SEDs is available upon request from the authors. Using this set of SEDs of BSPs we build the spectra of Burst, E, S0–Sd and Irr types of galaxies by using the package of Bruzual and Charlot (Mon. Not. R. Astron. Soc. 344:1000, 2003). Combined with the photometric data (filters and magnitudes), we obtain the photometric redshifts and morphologies of 1502 galaxies by using the Hyperz code of Bolzonella et al. (Astron. Astrophys. 363:476, 2000). This sample of galaxies is obtained by removing those objects, mismatched with the SDSS/DR7 and GALEX/DR4, from the catalogue of Fukugita et al. (Astron. J. 134:579, 2007). By comparison the results with the SDSS spectroscopic redshifts and the morphological index of Fukugita et al. (Astron. J. 134:579, 2007), we find that the photo-z fluctuate with the SDSS spectroscopic redshifts, while the Sa–Sc galaxies in the catalogue of Fukugita et al. (Astron. J. 134:579, 2007) are classified earlier as Burst-E galaxies. 相似文献
11.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2011,331(1):199-206
We investigate the late-time dynamics of a four-dimensional universe based on the effective action of a Brans-Dicke scalar field in the presence of the matter source term, conformal coupling of the scalar curvature to the scalar field, a dynamical cosmological constant and Gauss-Bonnet higher-order terms in the scalar curvature. Many new interesting features are revealed and discussed in some details. 相似文献
12.
We investigate coronal transients associated with a GOES M6.7 class flare and a coronal mass ejection (CME) on 13 July 2004. During the rising phase of the flare, a filament eruption, loop expansion, a Moreton wave, and an ejecta were observed. An EIT wave was detected later on. The main features in the radio dynamic spectrum were a frequency-drifting continuum and two type II bursts. Our analysis shows that if the first type II burst was formed in the low corona, the burst heights and speed are close to the projected distances and speed of the Moreton wave (a chromospheric shock wave signature). The frequency-drifting radio continuum, starting above 1 GHz, was formed almost two minutes prior to any shock features becoming visible, and a fast-expanding piston (visible as the continuum) could have launched another shock wave. A possible scenario is that a flare blast overtook the earlier transient and ignited the first type II burst. The second type II burst may have been formed by the same shock, but only if the shock was propagating at a constant speed. This interpretation also requires that the shock-producing regions were located at different parts of the propagating structure or that the shock was passing through regions with highly different atmospheric densities. This complex event, with a multitude of radio features and transients at other wavelengths, presents evidence for both blast-wave-related and CME-related radio emissions. 相似文献
13.
P. W. A. Roming C. Gronwall D. E. Vanden Berk M. J. Page P. T. Boyd 《Astrophysics and Space Science》2009,320(1-3):203-206
Currently there are four operating near-UV imaging space telescopes, one of which is the Swift Ultra-Violet/Optical Telescope (UVOT). Although the UVOT was primarily built for observations of γ-ray bursts, it has become a powerful instrument for studying other types of UV and optical astronomical phenomena. Here we discuss the properties of the UVOT, summarize some of the science undertaken with the UVOT, and present other possible science goals for the UVOT that have not yet been pursued. We also discuss some lessons learned that apply to future UV telescopes. 相似文献
14.
The Recovery of CME-Related Dimmings and the ICME’s Enduring Magnetic Connection to the Sun 总被引：1，自引：1，他引：0
G. D. R. Attrill L. van Driel-Gesztelyi P. Démoulin A. N. Zhukov K. Steed L. K. Harra C. H. Mandrini J. Linker 《Solar physics》2008,252(2):349-372
It is generally accepted that transient coronal holes (TCHs, dimmings) correspond to the magnetic footpoints of CMEs that
remain rooted in the Sun as the CME expands out into the interplanetary space. However, the observation that the average intensity
of the 12 May 1997 dimmings recover to their pre-eruption intensity in SOHO/EIT data within 48 hours, whilst suprathermal
unidirectional electron heat fluxes are observed at 1 AU in the related ICME more than 70 hours after the eruption, leads
us to question why and how the dimmings disappear whilst the magnetic connectivity is maintained. We also examine two other
CME-related dimming events: 13 May 2005 and 6 July 2006. We study the morphology of the dimmings and how they recover. We
find that, far from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data have a deep central core and a more
shallow extended dimming area. The dimmings recover not only by shrinking of their outer boundaries but also by internal brightenings.
We quantitatively demonstrate that the model developed by Fisk and Schwadron (Astrophys. J.
560, 425, 2001) of interchange reconnections between “open” magnetic field and small coronal loops is a strong candidate for the mechanism
facilitating the recovery of the dimmings. This process disperses the concentration of “open” magnetic field (forming the
dimming) out into the surrounding quiet Sun, thus recovering the intensity of the dimmings whilst still maintaining the magnetic
connectivity to the Sun.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
15.
Cyclic variations of the mean semi-annual intensities I
of the coronal green line 530.3 nm are compared with the mean semi-annual variations of the Wolf numbers W during the period of 1943–1999 (activity cycles 18–23). The values of I
in the equatorial zone proved to correlate much better with the Wolf numbers in a following cycle than in a given one (the correlation coefficient r is 0.86 and 0.755, respectively). Such increase of the correlation coefficient with a shift by one cycle differs in different phases of the cycle, being the largest at the ascending branch. The regularities revealed make it possible to predict the behaviour of W in the following cycle on the basis of intensities of the coronal green line in the preceding cycle. We predict the maximum semi-annual W in cycle 23 to be 110–122 and the epoch of minimum between cycles 23 and 24 to take place at 2006–2007. A slow increase of I
in the current cycle 23 permits us to forecast a low-Wolf-number cycle 24 with the maximum W50 at 2010–2011. A scheme is proposed on the permanent transformation of the coronal magnetic fields of different scales explaining the found phenomenon. 相似文献
16.
The thermal character of inner horizon in a Reissner-Nordstrom black hole is studied via Hamilton-Jacobi method. There is
“Hawking absorption” as a quantum effect near the inner horizon, and a negative temperature of the inner horizon was attained
by choosing an observer outside the black hole. Using a redefined entropy of the black hole, we give a new expression of Bekenstein-Smarr
formula. The redefined entropy satisfies Nernst Theorem, so it can be regarded as Planck absolute entropy of the Reissner-Nordstrom
black hole. 相似文献
17.
The high quality of the asteroseismic data provided by space missions such as CoRoT (Michel et al. in The CoRoT Mission, ESA Spec. Publ. vol. 1306, p. 39, 2006) or expected from new operating missions such as Kepler (Christensen-Dalsgaard et al. in Commun. Asteroseismol. 150:350, 2007) requires the capacity of stellar evolution codes to provide accurate models whose numerical precision is better than the expected observational errors (i.e. below 0.1 μHz on the frequencies in the case of CoRoT). We present a review of some thorough comparisons of stellar models produced by different evolution codes, involved in the CoRoT/ESTA activities (Monteiro in Evolution and Seismic Tools for Stellar Astrophysics, 2009). We examine the numerical aspects of the computations as well as the effects of different implementations of the same physics on the global quantities, physical structure and oscillations properties of the stellar models. We also discuss a few aspects of the input physics. 相似文献
18.
A. Noels J. Montalban A. Miglio M. Godart P. Ventura 《Astrophysics and Space Science》2010,328(1-2):227-236
Overshooting and semiconvection are two poorly known mechanisms which affect the extent and the efficiency of chemical mixing outside classical convection zones in stars. We discuss the uncertainties and the inferences of those processes in main sequence stars burning hydrogen in a convective core. We then focus on the asteroseismic signatures of partially or fully mixed zones surrounding the convective core, through the detailed shape of the induced chemical composition profile. We emphasize the potential power of asteroseismology to determine the internal structure of stars and thus to help us understand the physical processes at work inside the stars. 相似文献
19.
M. M. Bisi B. V. Jackson A. Buffington J. M. Clover P. P. Hick M. Tokumaru 《Solar physics》2009,256(1-2):201-217
We present initial 3D tomographic reconstructions of the inner heliosphere during the Whole Heliosphere Interval (WHI) – Carrington Rotation 2068 (CR2068) – using Solar-Terrestrial Environment Laboratory (STELab) Interplanetary Scintillation (IPS) observations. Such observations have been used for over a decade to visualise and investigate the structure of the solar wind and to study in detail its various features. These features include co-rotating structures as well as transient structures moving out from the Sun. We present global reconstructions of the structure of the inner heliosphere during this time, and compare density and radial velocity with multi-point in situ spacecraft measurements in the ecliptic; namely STEREO and Wind data, as the interplanetary medium passes over the spacecraft locations. 相似文献