共查询到20条相似文献,搜索用时 31 毫秒
1.
G. Trottet J.-P. Raulin G. Giménez de Castro T. Lüthi A. Caspi C. H. Mandrini M. L. Luoni P. Kaufmann 《Solar physics》2011,273(2):339-361
Solar flares observed in the 200 – 400 GHz radio domain may exhibit a slowly varying and time-extended component which follows
a short (few minutes) impulsive phase and can last for a few tens of minutes to more than one hour. The few examples discussed
in the literature indicate that such long-lasting submillimeter emission is most likely thermal bremsstrahlung. We present
a detailed analysis of the time-extended phase of the 27 October 2003 (M6.7) flare, combining 1 – 345 GHz total-flux radio
measurements with X-ray, EUV, and Hα observations. We find that the time-extended radio emission is, as expected, radiated
by thermal bremsstrahlung. Up to 230 GHz, it is entirely produced in the corona by hot and cool materials at 7 – 16 MK and
1 – 3 MK, respectively. At 345 GHz, there is an additional contribution from chromospheric material at a few 104 K. These results, which may also apply to other millimeter–submillimeter radio events, are not consistent with the expectations
from standard semiempirical models of the chromosphere and transition region during flares, which predict observable radio
emission from the chromosphere at all frequencies where the corona is transparent. 相似文献
2.
Small ballistic ranges were used to perform controlled laboratory shock experiments on 12 selected silicates [quartz (30–310
kb), oligoclase (30–340 kb), andesine (40–100 kb), olivine (80–500 kb), forsterite (50–150 kb), enstatite (60–150 kb), biotite
(10–90 kb), hornblende (50–150 kb, garnet (40–160 kb), kunzite (60–150 kb), beryl (60–140 kb), topaz (60–150 kb)]. At least
4 pressure points per mineral are available.
Debye-Scherrer investigations of shocked materials revealed a gradual lattice breakdown of crystalline matter under shock.
Individual mineral species behave selectively. Sheet silicates break down very easily, followed by tecto-silicates. Chain-,
ino- and ortho-silicates are of considerably higher shock resistance. Depending on the mineral species, the first sign of
shock damage is evidenced in the long range order at 20–70 kb. At intermediate pressures (100–200 kb) the long range order
is essentially destroyed with the short range order heavily disturbed. At pressures exceeding 300 kb tecto-silicates are completely
collapsed. The degree of internal fragmentation is strongly related to shock pressure, thus providing a sensitive tool for
absolute pressure calibration of shocked materials.
The internal fragmentation is structurally controlled, leading to polycrystalline aggregates of strongly preferred orientation.
The grain size distribution of the fragmentation products is highly heterogeneous. The mechanisms leading to fragmentation
as evidenced by the X-ray patterns are highly complex. The formation of high pressure polymorphs is discussed.
Though application of the new results to naturally shocked rocks may have some limitations, the usefulness of Debye-Scherrer
investigations in the study of shocked materials is demonstrated.
Lunar Science Institute Contribution, No 2. 相似文献
3.
The characteristics of galaxies with and without a bar in the infrared range are compared, using two complete samples that
we have compiled. The data obtained show that star formation occurs more actively in barred galaxies than in galaxies without
a bar, which it is natural to believe is a consequence of the presence of the bar itself.
Translated from Astrofizika, Vol. 41, No. 3, pp. 349–358, July–September, 1998. 相似文献
4.
F. Delplancke F. Derie F. Paresce A. Glindemann F. Lévy S. Lévêque S. Ménardi 《Astrophysics and Space Science》2003,286(1-2):99-104
The four main scientific objectives of PRIMA – the Phase-Referenced Imaging and Micro-arc second Astrometry facility for the
VLTI – will be described:– extra-solar system characterization with astrometry, to detect planets and evaluate their mass,
and imaging of the dust accretion disk,– galactic center study with astrometry(dynamics of the bulge stars) and imaging at
10μm (piercing the gas and dust clouds surrounding the galactic center),– observations of AGNs and other extra-galactic objects,
too faint to be observed without PRIMA, for which partial imaging is needed to constrain their structuremodels,– micro-gravitational
lensing event resolution (imaging and astrometry of their photo-center) in the Galactic Bulge and Magellanic Clouds, helping
to determine directly the lens mass and distance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Xin-Fa Deng 《Astronomy Letters》2019,45(11):740-749
In this work, I construct a LRG sample with the redshift of 0.6 ≤ z ≤ 0.75 from the Sloan Digital Sky Survey Data Release 15 (SDSS DR15), which contains 184172 CMASS LRGs and 27158 eBOSS LRGs and examine the environmental dependence of the u–r, u–g, g–r, r–i, and i–z colors in this galaxy sample. I divide this LRG sample into subsamples with a redshift binning size of Δz = 0.01, and analyze the environmental dependence of the u–r, u–g, g–r, r–i, and i–z colors for these subsamples in each redshift bin. Overall, the u–r, u–g, g–r, and r–i colors of galaxies in LRG sample with the redshift of 0.6 ≤ z ≤ 0.75 are very weakly correlated with the local environment, which shows that minimal environmental dependence of galaxy parameters can continue to higher redshifts. It is noteworthy that i–z color of this CMASS + eBOSS LRG sample shows substantial correlation with the local environment in the redshift region 0.70 ≤ z ≤ 0.75. 相似文献
6.
Kotaro Kohno Koichiro Nakanishi Tomoka Tosaki Kazuyuki Muraoka Rie Miura Hajime Ezawa Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):279-285
Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0)
and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component
is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions
of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby
spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging
of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between
the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on
the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed
in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in
the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation
rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these
ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these
molecular lines are free from dust extinction. 相似文献
7.
A standard problem of radiative transfer theory — calculating the diffuse reflection and transmission of radiation by a plane
scattering atmosphere — is considered. The recently proposed albedoshift method is used to calculate the X and Y functions
(and the H function) for the case of anisotropic scattering with a Henyey-Greenstein indicatrix. The method enables one to
“suppress” scattering and obtain iterative solutions of high accuracy in only a few iterations, even when the mean number
of photon scatterings in the atmosphere is very large.
Translated from Astrofizika, Vol. 41. No. 4, pp. 623–646, October–December, 1998. 相似文献
8.
A.A. V’uga 《Astrophysics》1999,42(4):460-466
A random quantity ξ, the number of pairwise mergings in a finite set of particles, is constructed in a sequential scheme of
complex trials. Let T0, T1,T2,…, Tm,…be a sequence of times. We then have a discrete approximation of the process of mergings
by a uniform Markov chain.
Translated from Astrofizika, Vol. 42, No. 4, pp. 609–616, October–December, 1999. 相似文献
9.
Bojan Vršnak Manuela Temmer Astrid Veronig Marian Karlický Jun Lin 《Solar physics》2006,234(2):273-299
We analyze the evolution of the flare/postflare-loop system in the two-ribbon flare of November 3, 2003, utilizing multi-wavelength
observations that cover the temperature range from several tens of MK down to 104 K. A non-uniform growth of the loop system enables us to identify analogous patterns in the height–time, h(t), curves measured at different temperatures. The “knees,” “plateaus,” and “bends” in a higher-temperature curve appear after
a certain time delay at lower heights in a lower-temperature curve. We interpret such a shifted replication as a track of
a given set of loops (reconnected field lines) while shrinking and cooling after being released from the reconnection site.
Measurements of the height/time shifts between h(t) curves of different temperatures provide a simultaneous estimate of the shrinkage speed and cooling rate in a given temperature
domain, for a period of almost ten hours after the flare impulsive phase. From the analysis we find the following: (a) Loop
shrinkage is faster at higher temperatures – in the first hour of the loop-system growth, the shrinkage velocity at 5 MK is
20 – 30 km s−1, whereas at 1 MK it amounts to 5 km s−1; (b) Shrinking becomes slower as the flare decays – ten hours after the impulsive phase, the shrinkage velocity at 5 MK becomes
5 km s−1; (c) The cooling rate decreases as the flare decays – in the 5 MK range it is 1 MK min−1 in the first hour of the loop-system growth, whereas ten hours later it decreases to 0.2 MK min−1; (d) During the initial phase of the loop-system growth, the cooling rate is larger at higher temperatures, whereas in the
late phases the cooling rate apparently does not depend on the temperature; (e) A more detailed analysis of shrinking/cooling
around one hour after the impulsive phase reveals a deceleration of the loop shrinkage, amounting to ā ≈ 10 m s−2 in the T < 5 MK range; (f) In the same interval, conductive cooling dominates down to T ≈ 3 MK, whereas radiation becomes dominant below T ≈ 2 MK; (g) A few hours after the impulsive phase, radiation becomes dominant across the whole T < 5 MK range. These findings are compared with results of previous studies and discussed in the framework of relevant models. 相似文献
10.
N. Barrière P. von Ballmoos H. Halloin N. Abrosimov J. M. Alvarez K. Andersen P. Bastie S. Boggs P. Courtois T. Courvoisier M. Harris M. Hernanz J. Isern P. Jean J. Knödlseder G. Skinner B. Smither P. Ubertini G. Vedrenne G. Weidenspointner C. Wunderer 《Experimental Astronomy》2005,20(1-3):269-278
The next generation of instrumentation for nuclear astrophysics will have to achieve a factor of 10–100 improvement in sensitivity over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge: combining unprecedented sensitivity with high spectral and angular resolution, and the capability of measuring the polarization of the incident photons. The feasibility of such a crystal diffraction gamma-ray lens has recently been demonstrated with the prototype lens CLAIRE. MAX is a proposed mission which will make use of satellite formation flight to achieve 86 m focal length, with the Laue lens being carried by one satellite and the detector by the other. In the current design, the Laue diffraction lens of MAX will consist of 13740 copper and germanium (Ge1−x
Si
x
, x ∼ 0.02) crystal tiles arranged on 36 concentric rings. It simultaneously focuses in two energy bands, each centred on one of the main scientific objectives of the mission: the 800–900 keV band is dedicated to the study of nuclear gamma-ray lines from type Ia supernovae (e.g. 56 Co decay line at 847 keV) while the 450–530 keV band focuses on electron-positron annihilation (511 keV emission) from the Galactic centre region with the aim of resolving potential point sources. MAX promises a breakthrough in the study of point sources at gamma-ray energies by combining high narrow-line sensitivity (better than 10−6 cm−2 s−1) and high energy resolution (E/dE ∼ 500). The mission has successfully undergone a pre-phase A study with the French Space Agency CNES, and continues to evolve: new diffracting materials such as bent or composite crystals seem very promising.
PACS: 95.55.Ka, 29.30.Kv, 61.10.-i 相似文献
11.
Given the complexity involved in a flux-transport-type dynamo driven by both Babcock – Leighton and tachocline α effects, we present here a step-by-step procedure for building a flux-transport dynamo model calibrated to the Sun as a guide
for anyone who wishes to build this kind of model. We show that a plausible sequence of steps to reach a converged solution
in such a dynamo consists of (i) numerical integration of a classical α – ω dynamo driven by a tachocline α effect, (ii) continued integration with inclusion of meridional circulation to convert the model into a flux-transport dynamo
driven by only a tachocline α effect, (iii) final integration with inclusion of a Babcock – Leighton surface α effect, resulting in a flux-transport dynamo that can be calibrated to obtain a close fit of model output with solar observations. 相似文献
12.
A. V. Dudnik V. K. Persikov I. I. Zalyubovsky T. G. Timakova E. V. Kurbatov Yu. D. Kotov V. N. Yurov 《Solar System Research》2011,45(3):212-220
The STEP-F satellite telescope for measuring electrons and protons of the Photon scientific equipment is described. Its design
features are given. The device detects electrons, protons, and α-particles in the energy range 0.18–2.3, 7.4–55.2, and 298–160.0
MeV, respectively. Geometric factors vary in the range of 12.4–21.7 cm2 sr, depending on the energy of the particles. In addition, there are three channels of mixed recording of particles of different
types and channels of recording of the secondary electromagnetic radiation generated in the construction materials of the
device and spacecraft. Methods and results of the computer simulation of the passage of the particle through detector materials
are presented, along with configuration, calibration measurements, and tests (both standalone and integrated) within the complex
of scientific instrumentation and spacecraft. Updated data on geometric factors of the device and energy ranges of the direct
detection of charged high-energy particles and of channels of mixed recording of several types of particles are given. Special
software is described for the rapid analysis of the processed data of the STEP-F telescope, and the visualization of time
variations of particle fluxes with different time resolution in some periods of high solar activity and in its absence. 相似文献
13.
The north – south (N – S) asymmetry of solar activity is investigated by using the data on coronal green-line brightness and
total number and total area of sunspots over the period of 1939 – 2001. Typical time variations of the N – S asymmetry are
found to be consonant in these indices. Quasi-biennial oscillations (QBO) of solar activity are well recognizable in the N – S
asymmetry of the examined indices. Moreover, the QBO are much better manifested in the N – S asymmetry of the individual indices
than in the original (N plus S) indices. The time variations of relative QBO power are synchronous for the N – S asymmetry
of various solar activity indices whereas such a synchronization is weaker for the indices themselves. It is revealed that
the relative QBO power found in the N – S asymmetry of the studied indices has a negative correlation with the value of the
N – S asymmetry itself. The findings indicate that the N – S asymmetry should be regarded as a fundamental phenomenon of solar
activity similarly manifested in different activity indices. These findings should be taken into account when any dynamo theory
of solar activity is constructed. 相似文献
14.
Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the
observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an
amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum
is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant
light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation. 相似文献
15.
In this paper, we investigate the dynamics of generalized Chaplygin gas (GCG) model with or without viscosity in the w–w′ plane, which is defined by the equation of state parameter and its time derivative with respect to the logarithm of the
scale factor. We show that GCG model without viscosity approaches to a late time de Sitter attractor (w
g
=−1) and behaves like a “freezing” scalar field for the parameter α constrained by the latest observational data. However, introducing viscosity exerts an influence on the evolution of w and affects the location of the late time attractor (w
g
>−1) in viscous GCG model. We also find numerically such a transition from w′>0 to w′<0 as the universe expands in viscous GCG model different from GCG model without viscosity (w′<0) in the w–w′ plane. 相似文献
16.
A classical problem in the theory of radiative transfer is considered: calculating the radiation field within a plane scattering
atmosphere. The recently proposed albedo-shifting method is used to calculate the source function both in a semi-infinite
atmosphere and in an atmophere of finite optical depth, illuminated by parallel rays. The method enables one to “suppress”
scattering and obtain iterative solutions of the integral equation for the source function in only a few direct lambda iterations,
even when the average number of photon scatterings in the atmosphere is very large.
Translated from Astrofizika, Vol. 42, No. 4, pp. 485–500, October–December, 1999. 相似文献
17.
C. E. DeForest J. T. Hoeksema J. B. Gurman B. J. Thompson S. P. Plunkett R. Howard R. C. Harrison D. M. Hasslerz 《Solar physics》1997,175(2):393-410
On 7 and 8 March 1996, the SOHO spacecraft and several other space- and ground-based observatories cooperated in the most
comprehensive observation to date of solar polar plumes. Based on simultaneous data from five instruments, we describe the
morphology of the plumes observed over the south pole of the Sun during the SOHO observing campaign. Individual plumes have
been characterized from the photosphere to approximately 15 R⊙ yielding a coherent portrait of the features for more quantitative
future studies. The observed plumes arise from small (∼ 2-5 arc sec diameter) quiescent, unipolar magnetic flux concentrations,
on chromospheric network cell boundaries. They are denser and cooler than the surrounding coronal hole through which they
extend, and are seen clearly in both Feix and Fexii emission lines, indicating an ionization temperature between 1.0–1.5 x
106 K. The plumes initially expand rapidly with altitude, to a diameter of 20–30 Mm about 30 Mm off the surface. Above 1.2 R⊙
plumes are observed in white light (as ‘coronal rays’) and extend to above 12 R⊙. They grow superradially throughout their
observed height, increasing their subtended solid angle (relative to disk center) by a factor of ∼10 between 1.05 R⊙ and 4–5
R⊙ and by a total factor of 20–40 between 1.05 R⊙ and 12 R⊙. On spatial scales larger than 10 arc sec, plume structure in
the lower corona (R < 1.3 R⊙) is observed to be steady-state for periods of at least 24 hours; however, on spatial scales
smaller than 10 arc sec, plume XUV intensities vary by 10–20% (after background subtraction) on a time scale of a few minutes.
(Dr. Hassler is now employed by Southwest Research Institute, Boulder, CO) 相似文献
18.
We investigate the dependence of the line number density in the Lyman α forest on cosmological and evolutionary parameters. Recent data from eight high-redshift quasars obtained with VLT/UVES imply that either there is very strong evolution in the absorber population, or we live in a “nearly flat” closed universe which is more heavily vacuum-dominated than standard ΛCDM models.Wolfgang Priester (22 April 1924–9 July 2005) 相似文献
19.
The radio and xray properties of spiral galaxies with and without a bar are discussed on the basis of complete samples that
we have compiled. The two types of spirals are shown not to differ from one another in emission power in the two indicated
ranges. In the case of SB galaxies, the luminosities in the IR, radio, and xray ranges are closely related. The spectral indices
of SB and SA galaxies in the 1.4–5 GHz range are the same, on the average. In the case of barred galaxies, however, a definite
dependence is observed between the spectral index and both the IR and × ray luminosities, i.e., the spectral index increases
as both luminosities increase. It is assumed that this is caused by the bar itself, which stimulates star formation in a barred
galaxy.
Translated from Astrofizika, Vol. 41. No. 4, pp. 599–608, October–December, 1998. 相似文献
20.
We study a time – latitudinal distribution of CMEs observed by the SOHO spacecraft, their projected speeds and associated
magnetic fields, as well as the north – south (N – S) asymmetry of solar surface magnetic fields, and the coronal green line
intensities. We have found that (a) there exists an intricate relation between the average projected velocity of CMEs and
the mean value of large-scale magnetic fields; (b) there exists a pronounced N – S asymmetry in both the distribution and
the number of CMEs; (c) this asymmetry is in favor of the northern hemisphere at the beginning of the cycle, and of the southern
hemisphere from 2001 onward, being, in fact, (d) closely related with the N – S asymmetry in the distribution of large-scale
magnetic fields and the coronal green line intensities. 相似文献