共查询到20条相似文献，搜索用时 31 毫秒
1.
David A. Juckett 《Solar physics》2010,262(1):3-17
Wolff (Astrophys. J.
193, 721, 1974) introduced the concept of g-mode coupling within the solar interior. Subsequently, Wolff developed a more quantitative model invoking a reciprocal interaction
between coupled g modes and burning in the solar core. Coupling is proposed to occur for constant values of the spherical harmonic degree [ℓ] creating rigidly rotating structures denoted as sets(ℓ). Power would be concentrated near the core and the top of radiative zone [RZ] in narrow intervals of longitude on opposite
sides of the Sun. Sets(ℓ) would migrate retrograde in the RZ as function of ℓ and their intersections would deposit extra energy at the top of the RZ. It is proposed that this enhances sunspot eruptions
at particular longitudes and at regular time intervals. Juckett and Wolff (Solar Phys.
252, 247, 2008) detected this enhancement by viewing selected spherical harmonics of sunspot patterns within stackplots twisted into the
relative rotational frames of various sets(ℓ). In subsequent work, the timings of the set(ℓ) intersections were compared to the sub-decadal variability of the sunspot cycle. Seventeen sub-decadal intersection frequencies
(0.63 – 7.0 year) were synchronous with 17 frequencies in the sunspot time-series with a mean correlation of 0.96. Six additional
non-11-year frequencies (periods of 8.0 to 28.7 year) are now shown to be nearly synchronous between sunspot variability and
the model. Two additional intersections have the same frequency as the solar cycle itself and peak during the rising phase
of the solar cycle. This may be partly responsible for cycle asymmetry. These results are evidence that some of the solar-cycle
variability may be attributable to deterministic components that are intermixed with a broad-spectrum stochastic and long-term
chaotic background. 相似文献
2.
The aim of this paper is to determine the flux emergence rate due to small-scale magnetic features in the quiet Sun using
high-resolution Hinode SOT NFI data. Small-scale magnetic features are identified in the data using two different feature identification methods
(clumping and downhill); then three methods are applied to detect flux emergence events. The distribution of the intranetwork
peak emerged fluxes is determined. When combined with previous emergence results, from ephemeral regions to sunspots, the
distribution of all fluxes are found to follow a power-law distribution which spans nearly seven orders of magnitude in flux
(1016 – 1023 Mx) and 18 orders of magnitude in frequency. The power-law fit to all these data is of the form
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\fracdNdY = \fracn0Y0\fracYY0-2.7,\frac{\mathrm{d}N}{\mathrm{d}\Psi} = \frac{n_0}{\Psi_0}\frac{\Psi}{\Psi _0}^{-2.7}, 相似文献
3.
M. R. Setare 《Astrophysics and Space Science》2010,326(1):27-31
In this paper, we study a cosmological application of the new agegraphic dark energy density in the f(R) gravity framework. We employ the new agegraphic model of dark energy to obtain the equation of state for the new agegraphic
energy density in a spatially flat universe. Our calculations show, taking n<0, that it is possible to have w
Λ crossing −1. This implies that one can generate a phantom-like equation of state from a new agegraphic dark energy model
in a flat universe in the modified gravity cosmology framework. Also, we develop a reconstruction scheme for the modified
gravity with f(R) action. 相似文献
4.
Leif Kahl Kristensen 《Celestial Mechanics and Dynamical Astronomy》2009,105(4):275-287
Initial orbit determination by least squares of N observations is essentially a linear problem if the coordinates x
0 and x
1 at two standard epochs are used as elements. The orbit of a main belt object is approximated within the observational errors
by a third degree polynomial during a month. A 4-observation orbit is useful for the initial linking between two nights. Parallax
is treated rigorously and future simultaneous space and Earth based observations determine the critical distance directly.
The N-observation method is a great simplification of the classical 3-observation orbit followed by a differential correction by
N observations. 相似文献
5.
Ulysses was launched in October 1990, and its Solar X-ray/Cosmic Gamma-Ray Burst Experiment (GRB) has provided more than 13 years
of uninterrupted observations of solar X-ray flare activity. Due to the large variation of the relative solar latitude and
longitude of the spacecraft orbit with respect to the Earth, the perspective of the GRB instrument often differed significantly
from that of X-ray instruments on Earth-orbiting satellites. During extended periods the GRB experiment made direct observations
of flares on the hidden face of the Sun, providing a unique record of events not visible to other instruments. The small detector
area of GRB and its optimization for very high counting rates minimized the effects of pulse pile-up. We interpret the spectra,
time histories, and occurrence distribution patterns of GRB data in terms of “thermal feed-through”, the confusion of thermal
soft X-rays and non-thermal hard X-rays. This effect is a systematic problem for scintillation-counter spectrometers observing
the solar hard X-ray spectrum. This paper provides a definitive catalog of the Ulysses X-ray flare observations and discusses various features of this unique database. For the equivalent GOES range X2 – X25,
we find a power-law fit for the (differential) occurrence frequency at >25 keV with slope −1.61±0.04, with no evidence for
a downturn at the highest event magnitudes (for the relatively small sample of such events available in this study). If the
nine most intense events are excluded because of concerns about the effects of pulse pile-up, the slope steepens to −1.75±0.08. 相似文献
6.
The twin STEREO spacecraft have been observing the Sun since 2006. Even though STEREO has only been active during solar minimum
conditions so far, an important number of coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) have
been observed. Many of the ICMEs can be linked back to the corresponding CMEs on the Sun through the combination of remote-sensing
and in situ observations. This paper aims to answer the question whether a CME observed by a coronagraph will be detected in situ by a spacecraft in a specific location in the heliosphere. We use a flux-rope-like model fit to the STEREO SECCHI/COR2 data
to obtain the direction of CME propagation and its geometrical configuration in three dimensions. Based on model parameters,
we then calculate their angular widths and determine whether they should have been detected by STEREO-A, STEREO-B, Wind or ACE. We compare the results with corresponding in situ observations of ICMEs. We find that predictions of ICME detections on the base of COR2 data generally match well the actual
in situ observations. 相似文献
7.
The abundances of 22 heavy elements from Sr to Pb have been determined for the halo star HD 29907 (T
eff = 5500 K, log g = 4.64) with [Fe/H] = −1.55 using high-quality VLT/UVES spectra (ESO, Chile). The star has a moderate enhancement of r-process elements (Eu-Tm) with [r/Fe] = 0.63. In the range from Ba to Yb, the derived abundance pattern agrees well with those for strongly r-process enhanced stars (r-II stars with [Eu/Fe] > 1 and [Ba/Eu] < 0), such as CS 22892-052 and CS 31082-001, as well as with
the scaled solar r-process curve and the r-process model HEW. Thus, Ba-Yb in HD 29907 originate in the r-process. Just as other moderately r-process enhanced stars studied in the literature, HD 29907 exhibits higher Sr, Y, and Zr abundances than those for r-II stars.
These results confirm the assumption by other authors about the existence of an additional Sr-Zr synthesis mechanism in the
early Galaxy before the onset of nucleosynthesis in asymptotic giant branch (AGB) stars. The same mechanism can be responsible
for the enhancement of Mo-Ag in the star being investigated compared to r-II stars. There are no grounds to suggest the presence
of s-nuclei of lead in the material of the star being investigated, because its measured abundance ratio log ɛ(Pb/Eu) = 1.20 lies within the range for the comparison stars: from log ɛ(Pb/Eu) = 0.17 (CS 31082-001) to < 1.55 (HE 1219-0312). Thus, even if there was a contribution of AGB stars to the heavy-element
enrichment of the interstellar medium at the epoch with [Fe/H] = −1.55, it was small, at the level of the abundance error. 相似文献
8.
The most detailed information on the seasonal evolution of water vapor distribution in the Martian atmosphere was obtained by the Mars Atmospheric Water Detector (MAWD), which was a five-channel spectrometer operating aboard the Viking 1 and 2 spacecraft in 1977–1980, and from the very recent observations by the Thermal Emission Spectrometer (TES) on the Mars Global Surveyor spacecraft. The TES results show a considerably larger amount of water vapor near the perihelion of Mars (summer in the southern hemisphere) than the estimates based on the MAWD data for this season, which is characterized by the development of global dust storms. The TES and MAWD instruments operated in different spectral regions (20–50 m and 1.38 m, respectively), and this could result in the aforementioned difference because of the effect of aerosol scattering on the intensity of the H2O bands, which becomes significant at short wavelengths. We considered the effect of aerosol scattering on the water vapor content measured in the 1.38-m band, taking into account the different geometries of observations, and restored the H2O content from the MAWD data with allowance for multiple scattering. We obtained a seasonal and spatial distribution of water vapor that showed better agreement with the TES data and, thus, indicated the stability of the hydrological cycle on Mars. Periodic structures, which could possibly be associated with the influence of the stationary planetary waves, are reliably revealed in the zonal distribution of the atmospheric water vapor. The seasonal variability of the wave structures correlates with variations of the latitude gradient of water vapor. This could indicate that wave processes contribute considerably to the meridional water transport in the Martian atmosphere.Translated from Astronomicheskii Vestnik, Vol. 38, No. 6, 2004, pp. 483–496.Original Russian Text Copyright © 2004 by Fedorova, Rodin, Baklanova. 相似文献
9.
P. Saint-Hilaire G. J. Hurford G. Keating G. C. Bower C. Gutierrez-Kraybill 《Solar physics》2012,277(2):431-445
We present the first observations of the Sun with the Allen Telescope Array (ATA). We used up to six frequencies, from 1.43 to 6 GHz, and baselines from 6 to 300 m. To our knowledge, these are the first simultaneous multi-frequency full-Sun maps obtained at microwave frequencies without mosaicing. The observations took place when the Sun was relatively quiet, although at least one active region was present each time. We present multi-frequency flux budgets for each of the sources on the Sun. Outside of active regions, assuming optically thin bremsstrahlung (free–free) coronal emission on top of an optically thick ≈?10?000 K chromosphere, the multi-frequency information can be condensed into a single, frequency-independent, “coronal bremsstrahlung contribution function” \([\mathrm{EM}/\sqrt{T}]\) map. This technique allows the separation of the physics of emission as well as a measurement of the density structure of the corona. Deviations from this simple relationship usually indicate the presence of an additional gyroresonance-emission component, as is typical in active regions. 相似文献
10.
Any calibration of the present value of the Hubble constant (H
0) requires recession velocities and distances of galaxies. While the conversion of observed velocities into true recession
velocities has only a small effect on the result, the derivation of unbiased distances which rest on a solid zero point and
cover a useful range of about 4–30 Mpc is crucial. A list of 279 such galaxy distances within v < 2,000 km s−1 is given which are derived from the tip of the red-giant branch (TRGB), from Cepheids, and/or from supernovae of type Ia
(SNe Ia). Their random errors are not more than 0.15 mag as shown by intercomparison. They trace a linear expansion field
within narrow margins, supported also by external evidence, from v = 250 to at least 2,000 km s−1. Additional 62 distant SNe Ia confirm the linearity to at least 20,000 km s−1. The dispersion about the Hubble line is dominated by random peculiar velocities, amounting locally to <100 km s−1 but increasing outwards. Due to the linearity of the expansion field the Hubble constant H
0 can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of 78 galaxies above this limit give H
0 = 63.0 ± 1.6 at an effective distance of 6 Mpc. They compensate the effect of peculiar motions by their large number. Support
for this result comes from 28 independently calibrated Cepheids that give H
0 = 63.4 ± 1.7 at 15 Mpc. This agrees also with the large-scale value of H
0 = 61.2 ± 0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of H
0 = 62.3 ± 1.3 is adopted. Because the value depends on two independent zero points of the distance scale its systematic error
is estimated to be 6%. Other determinations of H
0 are discussed. They either conform with the quoted value (e.g. line width data of spirals or the D
n
−σ method of E galaxies) or are judged to be inconclusive. Typical errors of H
0 come from the use of a universal, yet unjustified P–L relation of Cepheids, the neglect of selection bias in magnitude-limited
samples, or they are inherent to the adopted models. 相似文献
11.
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more
than 60 000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of stars in the range 4500≲T
eff≲9000 K. Our preliminary results indicate that the majority of the sample is formed by main sequence F- and G-type stars,
with metallicity [M/H]≳−1 dex. 相似文献
12.
I. D. Karachentsev D. I. Makarov V. E. Karachentseva O. V. Melnyk 《Astrophysical Bulletin》2011,66(1):1-27
We present a catalog of 520 most isolated nearby galaxies with angular velocities V
LG
< 3500 km/s, covering the entire sky. This population of “space orphans” makes up 4.8% among 10 900 galaxies with measured
radial velocities. We describe the isolation criterion used to select our sample, called the “Local Orphan Galaxies”(LOG),
and discuss their basic optical and HI properties. A half of the LOG catalog is occupied by the Sdm, Im and Ir morphological
type galaxies without a bulge. The median ratio M
gas/M
star in the LOG galaxies exceeds 1. The distribution of the catalog galaxies on the sky looks uniform with some signatures of
a weak clustering on the scale of about 0.5 Mpc. The LOG galaxies are located in the regions where the mean local density
of matter is approximately 50 times lower than the mean global density. We indicate a number of LOG galaxies with distorted
structures, which may be the consequence of interaction of isolated galaxies with massive dark objects. 相似文献
13.
V. I. Burnashev B. A. Burnasheva 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):63-67
From the results of long-term observations, data on the energy distribution in the spectra of 116 variable stars of different
types have been obtained. From the published response curves of the UBV system, the magnitudes and color indexes were calculated. The mean accuracy of the calculated values is σ
v
≃ 0.
m
04, σ
bv
≃ 0.
m
03, and σ
ub
≃ 0.
m
06. 相似文献
14.
A. N. Gerashchenko 《Astronomy Letters》2009,35(9):625-632
We describe a method for simultaneous determination of the metallicity and interstellar reddening of globular clusters that
uses parameters of the giant branch on the V vs. (B-R) color-magnitude diagram: the slope of the giant branch, its color at the level of the horizontal branch, and the apparent
magnitude V of the horizontal branch. Applying this method to the globular cluster NGC 7006 gives the metallicity [Fe/H] = −1.78 ± 0.11
and interstellar reddening E
B-R
= 0.25 ± 0.02. 相似文献
15.
We study the space – time distributions of intensity fluctuations in 2 – 3 hour sequences of multi-spectral, high-resolution,
high-cadence, broad-band filtergram images of the Sun made by the SOT – FG system aboard the Hinode spacecraft. In the frequency
range 5.5<f<8.0 mHz both G-band and Ca ii H-line oscillations are suppressed in the presence of magnetic fields, but the suppression disappears for f>10 mHz. By looking at G-band frequencies above 10 mHz we find that the oscillatory power, both at these frequencies and at
lower frequencies, lies in a mesh pattern with cell scale 2 – 3 Mm, clearly larger than normal granulation, and with correlation
times on the order of hours. The mesh pattern lies in the dark lanes between stable cells found in time-integrated G-band
intensity images. It also underlies part of the bright pattern in time-integrated H-line emission. This discovery may reflect
dynamical constraints on the sizes of rising granular convection cells together with the turbulence created in strong intercellular
downflows. 相似文献
16.
Data on HII regions, molecular clouds, and methanol masers have been used to estimate the Sun’s distance from the symmetry plane z ⊙ and the vertical disk scale height h. Kinematic distance estimates are available for all objects in these samples. The Local-arm (Orion-arm) objects are shown to affect noticeably the pattern of the z distribution. The deviations from the distribution symmetry are particularly pronounced for the sample of masers with measured trigonometric parallaxes, where the fraction of Local-arm masers is large. The situation with the sample of HII regions in the solar neighborhood is similar. We have concluded that it is better to exclude the Local arm from consideration. Based on the model of a self-gravitating isothermal disk, we have obtained the following estimates from objects located in the inner region of the Galaxy (R ≤ R 0): z ⊙ = ?5.7 ± 0.5 pc and h 2 = 24.1 ± 0.9 pc from the sample of 639 methanol masers, z ⊙ = ?7.6±0.4 pc and h 2 = 28.6±0.5 pc from 878HII regions, z ⊙ = ?10.1 ± 0.5 pc and h 2 = 28.2 ± 0.6 pc from 538 giant molecular clouds. 相似文献
17.
Luciana Bianchi 《Astrophysics and Space Science》2011,335(1):51-60
Wide-field far-UV (FUV, 1344–1786 Å) and near-UV (NUV, 1771–2831 Å) imaging from GALEX provides a deep, comprehensive view of the young stellar populations in hundreds of nearby galaxies, shedding new light on the process of star formation (SF) in different environments, and on the interplay between dust and SF. GALEX’s FUV-NUV color is extremely sensitive to stellar populations of ages up to a few hundred Myrs, unambiguously probing their presence and enabling age-dating and stellar mass estimate, together with the characterization of interstellar dust extinction. The deep sensitivity, combined with the wide field-of-view, made possible in particular the discovery and characterization of star formation in extremely low-density, diffuse gas environments such as outer galaxy disks, tidal tails, low-surface-brightness galaxies (LSB) and dwarf Irregular galaxies, and of rejuvenation episodes in early-type galaxies. Such results provide several missing links for interpreting galaxy classes in an evolutionary context, extend our knowledge of the star-formation process to previously unexplored conditions, constrain models of galaxy disk formation, and clarify the mutual role of dust and star formation. We review a variety of star-forming environments studied by GALEX, and provide some model analysis tools useful for interpretation of GALEX measurements, and potentially as basic science planning tools for next-generation UV instruments. 相似文献
18.
K. E. Papadakis 《Astrophysics and Space Science》2009,323(3):261-272
In this paper we study the asymptotic solutions of the (N+1)-body ring planar problem, N of which are finite and ν=N−1 are moving in circular orbits around their center of masses, while the Nth+1 body is infinitesimal. ν of the primaries have equal masses m and the Nth most-massive primary, with m
0=β
m, is located at the origin of the system. We found the invariant unstable and stable manifolds around hyperbolic Lyapunov
periodic orbits, which emanate from the collinear equilibrium points L
1 and L
2. We construct numerically, from the intersection points of the appropriate Poincaré cuts, homoclinic symmetric asymptotic
orbits around these Lyapunov periodic orbits. There are families of symmetric simple-periodic orbits which contain as terminal
points asymptotic orbits which intersect the x-axis perpendicularly and tend asymptotically to equilibrium points of the problem spiraling into (and out of) these points.
All these families, for a fixed value of the mass parameter β=2, are found and presented. The eighteen (more geometrically simple) families and the corresponding eighteen terminating
homo- and heteroclinic symmetric asymptotic orbits are illustrated. The stability of these families is computed and also presented. 相似文献
19.
O. I. Korablev A. V. Bondarenko I. V. Dokuchaev A. Yu. Ivanov O. E. Kozlov V. A. Kottsov A. B. Kiselev J. -P. Bibring J. -J. Fourmond 《Solar System Research》2010,44(5):403-408
Microscopy and spectroscopy are important methods of studies. The use of a microscope onboard a spacecraft is connected with
the fact that the closer approach to the objects and the switch to the in situ measurement methods have become possible. The
combination of taking an image and performing a spectral analysis forms a new type of instrument, so-called videospectrometers.
The scientific payload of the Phobos-Grunt spacecraft includes the microscope spectrometer designed to analyze the composition of the surface regolith of Phobos in
detail. 相似文献
20.
We investigate the properties of acoustic events (AEs), defined as spatially concentrated and short duration energy flux,
in the quiet Sun, using observations of a 2D field of view (FOV) with high spatial and temporal resolution provided by the
Solar Optical Telescope (SOT) onboard Hinode. Line profiles of Fe i 557.6 nm were recorded by the Narrow-band Filter Imager (NFI) on a 82″×82″ FOV during 75 min with a time step of 28.75 s
and 0.08″ pixel size. Vertical velocities were computed at three atmospheric levels (80, 130, and 180 km) using the bisector
technique, allowing the determination of energy flux to be made in the range 3 – 10 mHz using two complementary methods (Hilbert
transform and Fourier power spectrum). Horizontal velocities were computed using local correlation tracking (LCT) of continuum
intensities providing divergences. We found that the net energy flux is upward. In the range 3 – 10 mHz, a full FOV space
and time averaged flux of 2700 W m−2 (lower layer 80 – 130 km) and 2000 W m−2 (upper layer 130 – 180 km) is concentrated in less than 1 % of the solar surface in the form of narrow (0.3″) AE. Their total
duration (including rise and decay) is of the order of 103 s. Inside each AE, the mean flux is 1.6×105 W m−2 (lower layer) and 1.2×105 W m−2 (upper). Each event carries an average energy (flux integrated over space and time) of 2.5×1019 J (lower layer) to 1.9×1019 J (upper). More than 106 events could exist permanently on the Sun, with a birth and decay rate of 3500 s−1. Most events occur in intergranular lanes, downward velocity regions, and areas of converging motions. 相似文献
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