共查询到20条相似文献，搜索用时 31 毫秒
1.
Spectroheliograms were obtained simultaneously in the He ii 304 Å emission line and the He i 10 830 Å absorption line with an angular resolution of approximately 5″. A negative print of the 304 Å image is matched with a positive print of the 10 830 Å image so that corresponding features of the chromospheric network (including active regions) appear identical in the two images. Differences between these images include the facts that:
- Disk filaments and limb darkening are strongly visible in the 10 830 Å positive image, but they are weakly visible (as lightenings) in the 304 Å negative image.
- The contrast between the chromospheric network and the network cell centers is much greater in the 10 830 Å image than in the 304 Å negative image.
2.
3.
Using near-simultaneous full disk solar X-ray images and Hei 10830 spectroheliograms from three rocket flights, we compare dark points identified on the Hei maps with X-ray bright points identified on the X-ray images. We find that for the largest and most obvious features there is a strong correlation: most Hei dark points correspond to X-ray bright points. However, about two-thirds of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced Hei absorption which, however, would not a priori have been selected as a dark point. Therefore, the Hei dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. Hei dark points do, however, identify the locations of the stronger X-ray bright points.Visitor, National Solar Observatory. National Optical Astronomy Observatories operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation. 相似文献
4.
In this letter, we bring attention to prominences which show different morphology in H and Heii 304 Å, as observed simultaneously by BBSO and EIT on board SOHO. Those two lines have been thought to represent similar chromospheric structures although they are formed at significantly different temperatures. We give two examples representing two kinds of anomaly: (1) prominences showing strong H emissions in the lower part and strong Heii emissions in the upper part, and (2) erupting prominences showing extensive Heii emission, but nothing in H. Our results indicate that a part or the whole of a prominence may be too hot to emit H radiation, possibly due to heating or thermal instability. Please note that these are not just two isolated cases, many other prominences show the similar differences in H and Heii 304 Å. 相似文献
5.
Morphological differences between coronal images on the one hand, and a Hei image on the other, are used to demonstrate the independence of Heii excitation from coronal radiation. The distribution of magnetic flux is found to be more important for Heii excitation. Collisional excitation by non-thermal electrons produced in nano-flare events is proposed as the mechanism for Heii excitation. 相似文献
6.
Full disk, He I 10 830 Å solar spectroheliograms have been generated using the Haleakala Stokes polarimeter-spectrometer. The spectroheliograms, with spatial resolution of 10 × 16 arc sec and wavelength bandpass of 0.53 Å, were developed for the detection of coronal holes, and have been compared with nearly simultaneous H and Ca K flltergrams.Areas of reduced helium absorption have been noted in the neighborhood of filaments and neutral zones in the longitudinal solar magnetic field. The existence of these helium lanes is discussed in terms of their relationship to H filament channels or to the coronal cavities which surround prominences. 相似文献
7.
Gui-Ping Wu Guang-Li Huang Yu-Hua Tang Yu Dai Department of Physics Southeast University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2007,7(1):141-147
1INTRODUCTIONEnrichment of3He and heavy ions(i.e.,Ne,Mg,Si and Fe),characteristic of impulsive?ares,have beenstudied for more than three decades.It is found that they are generally associated with nonthermal energeticelectron-rich events(Reames et al.1988;Reames1999and references therein;Ho et al.2001;Wang et al.2006)and are related to the peculiar ratio of charge to mass(Mazur et al.1996;Reames1999).Althoughthe abundance of3He ions is not correlated with the abundance of heavy ions,s… 相似文献
8.
Arbab I. Arbab 《Astrophysics and Space Science》1996,246(2):193-196
An anisotropic model with variableG and and bulk viscosity is considered. The model exhibits an inflationary behavior during which the coefficient of bulk viscosity varies lineraly with the energy density. This allows the anisotropy energy to decrease exponentially with time. Other results overlap with our earlier work with a different ansatz for . The gravitational constant was found to increase during the radiation and matter epochs. 相似文献
9.
The astrophysical S-factor of the experimental cross section data of the main reactions in the proton–proton chain, i.e. 3He(3He,2p)4He, 3He(4He,γ)7Be and 7Be(p,γ)8B, are reanalyzed by using the exact tunneling probability in nuclear reactions. Our goal is to test this treatment in finding the reaction rate per pair for non-resonant reactions. At low temperatures, the exact treatment is identical to the standard formalism but diverges at higher temperatures. 相似文献
10.
Mohsen Shadmehri 《Astrophysics and Space Science》2008,317(3-4):201-207
We present self-similar solutions for advection-dominated accretion flows with thermal conduction in the presence of outflows. Possible effects of outflows on the accretion flow are parametrized and a saturated form of thermal conduction, as is appropriate for the weakly-collisional regime of interest, is included in our model. While the cooling effect of outflows is noticeable, thermal conduction provides an extra heating source. In comparison to accretion flows without winds, we show that the disc rotates faster and becomes cooler because of the angular momentum and energy flux which are taking away by the winds. But thermal conduction opposes the effects of winds and not only decreases the rotational velocity, but increases the temperature. However, reduction of the surface density and the enhanced accretion velocity are amplified by both of the winds and the thermal conduction. We find that for stronger outflows, a higher level of saturated thermal conduction is needed to significantly modify the physical profiles of the accretion flow. 相似文献
11.
Anisotropic Bianchi-III cosmological model is investigated with variable gravitational and cosmological constants in the framework of Einstein’s general relativity. The shear scalar is considered to be proportional to the expansion scalar. The dynamics of the anisotropic universe with variable G and Λ are discussed. Without assuming any specific forms for Λ and the metric potentials, we have tried to extract the time variation of G and Λ from the anisotropic model. The extracted G and Λ are in conformity with the present day observations. Basing upon the observational limits, the behavior and range of the effective equation of state parameter are discussed. 相似文献
12.
Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i 10830 Å line.The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures. 相似文献
13.
A. A. Coley 《Astrophysics and Space Science》1987,138(2):393-401
The constraints on the present baryon density from primordial nucleosynthesis in universes with interacting radiation and matter are investigated. For illustration, a class of exact cosmological models is studied in which two separate, interacting fluids act as the source of the gravitational field, a radiative perfect fluid modelling the cosmic microwave background and a second perfect fluid modelling the observed material content of the Universe. Althought the two fluid models under consideration are found to predict primordial element abundances similar to those predicted in the standard model (and consequently in general accord with observed values), the upper limit on the present baryon density inferred from the observed abundances of the light elements is found to be greater than that in the standard model due to the different evolution of the baryon density in the models. From this result, and using the fact that the upper limit on
B
(the ratio of the present value of the baryon density to the value of the critical density) is further weakened in inhomogeneous cosmological models, it is found that unlike the situation in the standard model, cosmologies with
B
1 are permitted without violating the constraints of nucleosynthesis, thereby allowing the possibility that the Universe could be closed by baryonic matter alone. 相似文献
14.
Atmospheric models of He-peculiar stars: synthetic He I line profiles and absolute visual magnitudes
Rodolfo Vallverdú Lydia Cidale René Rohrmann Adela Ringuelet 《Astrophysics and Space Science》2014,352(1):95-102
We analyze the influence of magnetic pressure effects on the atmospheric structure of B peculiar type stars, as well as, on the emergent He?I line profiles and absolute visual magnitudes. We consider a photosphere in local thermodynamic and hydrostatic equilibrium. The hydrostatic equilibrium equation is modified to include the Lorentz force. Atomic occupational numbers are computed in LTE considering non-ideal effects in the gas equation of state. We depict the influence of a magnetic field on local He?I line profiles and discuss the effects of the helium abundance in magnetic B-type stars. The Lorentz force might explain local variations up to 7 % in the equivalent width of helium lines, while local enhancements of He chemical abundances would produce larger changes. To analyze the line variations in real stars we computed the net contribution of a bipolar magnetic field over the stellar disk. The resulting disk-averaged magnetic field predicts variations with the rotation phase up to 2–3 % in the line EWs for a dipolar magnetic field of 1000 G. 相似文献
15.
Li-Li Li Yan-Xia Zhang Yong-Heng Zhao Da-Wei Yang 《中国天文和天体物理学报》2007,7(3):448-456
We calculate photometricredshifts from the Sloan Digital Sky SurveyData Release 2 (SDSS DR2) Galaxy Sample using artificial neural networks (ANNs). Different input sets based on various parameters (e.g. magnitude, color index, flux information) are explored. Mainly, parameters from broadband photometry are utilized and their performances in red- shift prediction are compared. While any parameter may be easily incorporated in the input, our results indicate that using the dereddened magnitudes often produces more accurate pho- tometric redshifts than using the Petrosian magnitudes or model magnitudes as input, but the model magnitudes are superior to the Petrosian magnitudes. Also, better performance re- sults when more effective parameters are used in the training set. The method is tested on a sample of 79346 galaxies from the SDSS DR2. When using 19 parameters based on the dereddened magnitudes, the rms error in redshift estimation is σz = 0.020184. The ANN is highly competitive tool compared to the traditional template-fitting methods when a large and representative training set is available. 相似文献
16.
N. Ibotombi Singh S. Surendra Singh S. Romaleima Devi A. Sumati Devi 《Astrophysics and Space Science》2009,324(1):67-70
We consider cosmology with the gravitational and cosmological constants generalized as coupling scalars in Einstein’s theory.
A general method of solving the field equations is given. We study here the exact solutions for negative pressure models satisfying
G=G
0(R/R
0)
n
. 相似文献
17.
The impact of superthermal particles on nonlinear drift solitary and shock like structures are presented in an inhomogeneous electron-ion plasma with κ-distributed electrons. It is shown that the amplitude of the drift solitons and shocks is modified significantly in the presence of superthermal particles. The condition for the existence of drift solitons is found modified in the presence of higher energy particles. Furthermore, Kadomtsev–Petviashvili (KP) equation is also derived for the present plasma model. 相似文献
18.
Jay M. Pasachoff Evan D. Tingle Ingolf E. Dammasch Alphonse C. Sterling 《Solar physics》2011,268(1):151-163
Using mainly the 1600 Å continuum channel and also the 1216 Å Lyman-α channel (which includes some UV continuum and C iv emission) aboard the TRACE satellite, we observed the complete lifetime of a transient, bright chromospheric loop. Simultaneous observations with the SUMER instrument aboard the SOHO spacecraft revealed interesting material velocities through the Doppler effect existing above the chromospheric loop imaged with TRACE, possibly corresponding to extended nonvisible loops, or the base of an X-ray jet. 相似文献
19.
A combination of diamagnetic pumping and a nonlocal α-effect of the Babcock–Leighton type in a solar dynamo model is shown to reproduce observations of solar magnetic activity. The period of the solar cycle can be reproduced without reducing magnetic diffusivity in the bulk of the convection zone below the standard mixing-length value of 1013?cm2?s?1. The simulated global fields are antisymmetric about the equator, and the toroidal-to-poloidal field ratio is about one thousand. However, the time–latitude diagrams of magnetic fields in the model without meridional flow differ from observations. Only when the meridional flow is included and the α-effect profile peaking at mid-latitudes is applied, can the observed butterfly diagrams be reproduced. 相似文献
20.
Imad A. Ahmad 《Solar physics》1977,53(2):409-415
The intensity of the He+ 304 coronal line relative to the H0 1216 line, including the dominant contribution due to resonance scattering, is presented. All physical processes important in the corona are included. It is found that He+ 304 is a major contributor to the XUV corona, and that the sensitivity of the He+ 304/H0 1216 intensity ratio to coronal temperature is very weak, supporting the belief that this ratio is a good indicator of the coronal helium abundance. 相似文献