共查询到20条相似文献，搜索用时 31 毫秒
1.
We present new results of heliographic observations of quiet‐Sun radio emission fulfilled by the UTR‐2 radio telescope. The solar corona investigations have been made close to the last solar minimum (Cycle 23) in the late August and early September of 2010 by means of the two‐dimensional heliograph within 16.5–33 MHz. Moreover, the UTR‐2 radio telescope was used also as an 1‐D heliograph for one‐dimensional scanning of the Sun at the beginning of September 2010 as well as in short‐time observational campaigns in April and August of 2012. The average values of integral flux density of the undisturbed Sun continuum emission at different frequencies have been found. Using the data, we have determined the spectral index of quiet‐Sun radio emission in the range 16.5–200 MHz. It is equal to –2.1±0.1. The brightness distribution maps of outer solar corona at frequencies 20.0 MHz and 26.0 MHz have been obtained. The angular sizes of radio Sun were estimated. It is found that the solar corona at these frequencies is stretched‐out along equatorial direction. The coefficient of corona ellipticity varies slightly during above period. Its mean magnitudes are equal to ≈ 0.75 and ≈ 0.73 at 20.0 MHz and 26.0 MHz, respectively. The presented results for continuum emission of solar corona conform with being ones at higher frequencies. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
K. R. Subramanian R. Ramesh M. S. Sundara Rajan Ch. V. Sastry 《Astrophysics and Space Science》1996,243(1):259-262
Observations of the Sun at two frequencies (51 and 77 MHz) using the East-West arm of the Gauribidanur Radio heliograph are presented. 相似文献
3.
L. Győri 《Solar physics》2010,267(2):445-461
Accurate heliographic coordinates of objects on the Sun have to be known in several fields of solar physics. One of the factors
that affect the accuracy of the measurements of the heliographic coordinates is the accuracy of the orientation of a solar
image. In this paper the well-known drift method for determining the orientation of the solar image is applied to data taken
with a solar telescope equipped with a CCD camera. The factors that influence the accuracy of the method are systematically
discussed, and the necessary corrections are determined. These factors are as follows: the trajectory of the center of the
solar disk on the CCD with the telescope drive turned off, the astronomical refraction, the change of the declination of the
Sun, and the optical distortion of the telescope. The method can be used on any solar telescope that is equipped with a CCD
camera and is capable of taking solar full-disk images. As an example to illustrate the method and its application, the orientation
of solar images taken with the Gyula heliograph is determined. As a byproduct, a new method to determine the optical distortion
of a solar telescope is proposed. 相似文献
4.
Samuel C. Vila 《Earth, Moon, and Planets》1984,31(3):313-315
The question of the survival of the planet Earth as the Sun becomes a red giant and possibly a planetary nebula depends on the maximum extent of the Sun's envelope. This study shows that if the Earth is reached by this envelope, it will be destroyed; but if it is not, it will survive. Present stellar evolution calculations imply that the Earth will be destroyed. 相似文献
5.
Kenneth H. Schatten 《Astrophysics and Space Science》1975,34(2):467-480
If the Sun loses angular momentum from its core, due to core contraction, into the solar wind at the observed rate, then an 0.7 day rotational period for the core of the Sun is required for temporal equilibrium. The rotational power released in the core contraction process can equal the observed magnetic energy released in the solar activity cycle if the Sun's core rotates with a period near 1.4 to 4 days. The rotational power released from a rotating object is , where is the torque on the object and is its angular velocity. Fitting this to the solar wind torque and core rotation rate provides an 0.5 to 5 day rotation period for the Sun's core. A gravitational Pannekoek-Rosseland electric field in the Sun makes the Ferraro theorem inapplicable in such a way that rather than a constant angular velocity with radius, an inverse square radial dependence occurs. This results in a two day rotational period for the region in the Sun where most of the angular momentum resides. The consistency of the above four methods suggests that the Sun's observed oblateness is due to a rapidly rotating solar core. The oblateness of the photosphere is estimated to be near 3.4×10–5. 相似文献
6.
OSIPOV S. N. GANDZHA S. I. ANDRIYENKO O. V. KARPOV M. V. KOSTIK R. I. 《Solar physics》1997,172(1-2):361-370
The primary shortcomings of existing methods for spectrophotometry of the Sun as a star are discussed. A new observational method is proposed. This method is based on a repeated scanning of the Sun's image while summing the signal of each step across the solar disk. A device for precise spectrophotometry of the Sun as a star has been developed around a double-pass spectrograph. This device and its operation algorithm are described. Errors caused by scanning irregularities and seeing are estimated. Several Sun-as-a-star spectrum line profiles and their bisectors are presented and compared with the same ones from the Kitt Peak FTS solar flux atlas. 相似文献
7.
Saturn’s diffuse E ring consists of many tiny (micron and sub-micron) grains of water ice distributed between the orbits of Mimas and Titan. Various gravitational and non-gravitational forces perturb these particles’ orbits, causing the ring’s local particle density to vary noticeably with distance from the planet, height above the ring-plane, hour angle and time. Using remote-sensing data obtained by the Cassini spacecraft in 2005 and 2006, we investigate the E-ring’s three-dimensional structure during a time when the Sun illuminated the rings from the south at high elevation angles (>15°). These observations show that the ring’s vertical thickness grows with distance from Enceladus’ orbit and its peak brightness density shifts from south to north of Saturn’s equator plane with increasing distance from the planet. These data also reveal a localized depletion in particle density near Saturn’s equatorial plane around Enceladus’ semi-major axis. Finally, variations are detected in the radial brightness profile and the vertical thickness of the ring as a function of longitude relative to the Sun. Possible physical mechanisms and processes that may be responsible for some of these structures include solar radiation pressure, variations in the ambient plasma, and electromagnetic perturbations associated with Saturn’s shadow. 相似文献
8.
G. A. Gontcharov 《Astronomy Letters》2009,35(11):780-790
A new analytical 3D model of interstellar extinction within 500 pc of the Sun as a function of the Galactic spherical coordinates
is suggested. This model is physically more justified than the widely used Arenou model, since it takes into account the presence
of absorbing matter both in the layer along the equatorial Galactic plane and in the Gould Belt. The extinction in the equatorial
layer varies as the sine of the Galactic longitude and in the Gould Belt as the sine of twice the longitude in the Belt plane.
The extinction across the layers varies according to a barometric law. It has been found that the absorbing layers intersect
at an angle of 17° and that the Sun is located near the axial plane of the absorbing layer of the Gould Belt and is probably
several parsecs below the axial plane of the equatorial absorbing layer but above the Galactic plane. The model has been tested
using the extinction of real stars from three catalogs. 相似文献
9.
The Ulysses spacecraft orbits the Sun on a highly inclined orbit, and the impact ionization dust detector on board continuously measures interstellar dust grains with masses up to , penetrating deep into the Solar System. The flow direction is close to the mean apex of the Sun's motion through the local interstellar cloud (LIC), and the grains act as tracers of the physical conditions in the LIC. Previous analysis gave a velocity dispersion of up to 40° for the interstellar grains. We partially re-analyzed the Ulysses interstellar dust data set, taking into account the detector's inner side walls. As the side walls have a sensitivity for dust impact detection almost identical to that of the instrument's target area, wall impactors must be taken into account for estimating the intrinsic velocity dispersion of the interstellar impactors and the interstellar dust flux value. Neglect of the sensor side walls overestimates the interstellar dust stream velocity dispersion by about 30% and the interstellar dust flux by about 20%. 相似文献
10.
M. Waldmeier 《Solar physics》1981,70(1):93-96
Two sunspot groups in symmetrical positions relative to the Sun's equator were flaring almost simultaneously. The larger northern group was highly irregular: the two main spots were surrounded by one and the same penumbra, the magnetic polarities were inverted and the inclination of the axis was exceptionally large and of the wrong direction. The larger southern flare consisted of two parallel ribbons that developed into a loop prominence. The two ribbons were moving sideways and upwards, forming a cone. The speed of this motion amounted to 10 km s–1 at the beginning and decreased to 2 km s–1 in the course of one hour. The streaming along the slopes of the cone indicates the direction of the magnetic fields. 相似文献
11.
太阳耀斑爆发时,日冕中磁自由能通过磁重联在短时间内转换成其他形式的能量,并伴随等离子体的加速和加热,以及带电粒子的加速。在这些过程中,宏观电场的出现起到关键的作用。但是到目前为止,由于太阳上宏观电场的探测比较困难,对电场的研究较少。近几年来随着一系列空间探测卫星被投入使用,加深了人们对日地空间事件发生、发展的物理过程的认识。但是太阳爆发和日冕加热机制等磁活动现象没有得到本质上的认识。太阳宏观电场的探测对突破这一瓶颈具有重要作用。综述了国内外在太阳宏观电场测量上的进展,并提出中国巨型望远镜(ChineseGiant Solar Telescope)在宏观电场观测上可能的科学目标。 相似文献
12.
In selected flares that occurred in AR 7260, we have studied the geometry of the brightest soft X-ray loop by tracing it on an image. Even under the assumption that the loop is contained in a plane, it is clear that a single image does not permit us to determine the full geometry. It only provides possible loop shapes as a function of the inclination angle of the loop plane with respect to the vertical. However, all the loops that reproduce the observed appearance give the same direction of increasing height as projected on to the image plane. This direction is compared with two relevant observations. Based on 2-D reconnection models that involve a cusp configuration, it is expected that the soft X-ray loop top source moves upward with time and that a higher temperature region exists above the loop top. Several flares are found to contradict these predictions, presumably implying the inadequacy of the models. Lastly we discuss a possibility of constraining the inclination angle (and hence the loop shape) with spatially-unresolved soft X-ray line spectra which are Doppler-shifted due to plasma upflows. 相似文献
13.
14.
We use an N -body/hydrodynamic simulation to forecast the future encounter between the Milky Way and the Andromeda galaxies, given present observational constraints on their relative distance, relative velocity, and masses. Allowing for a comparable amount of diffuse mass to fill the volume of the Local Group, we find that the two galaxies are likely to collide in a few billion years – within the Sun's lifetime. During the interaction, there is a chance that the Sun will be pulled away from its present orbital radius and reside in an extended tidal tail. The likelihood for this outcome increases as the merger progresses, and there is a remote possibility that our Sun will be more tightly bound to Andromeda than to the Milky Way before the final merger. Eventually, after the merger has completed, the Sun is most likely to be scattered to the outer halo and reside at much larger radii (>30 kpc). The density profiles of the stars, gas and dark matter in the merger product resemble those of elliptical galaxies. Our Local Group model therefore provides a prototype progenitor of late-forming elliptical galaxies. 相似文献
15.
Recent observational evidence for magnetic field direction effects on helioseismic signals in sunspot penumbrae is suggestive of magnetohydrodynamic (MHD) mode conversion occurring at lower levels. This possibility is explored using wave mechanical and ray theory in a model of the Sun's surface layers permeated by uniform inclined magnetic field. It is found that fast-to-slow conversion near the equipartition depth at which the sound and Alfvén speeds coincide can indeed greatly enhance the atmospheric acoustic signal at heights observed by Solar and Heliospheric Observatory/Michelson Doppler Imager and other helioseismic instruments, but that this effect depends crucially on the wave attack angle , i.e. the angle between the wavevector and the magnetic field at the conversion/transmission depth. A major consequence of this insight is that the magnetic field acts as a filter, preferentially allowing through acoustic signal from a narrow range of incident directions. This is potentially testable by observation. 相似文献
16.
17.
Proton heating at stream interaction regions in the solar wind is investigated based on the solar wind data obtained by Suisei spacecraft between 0.68 and 1.01 AU from the Sun. The deflection angle of the solar wind flow in the ecliptic plane is used to identify the interaction region. In the solar wind flows coming from east of the Sun in low-speed streams and coming from west in high-speed streams, the radial gradient of proton temperature is flattened owing to heating in the interaction region. From comparison of the best-fitted power law dependence of proton temperature on the radial distance in the deflected flow with that in the non-deflected flow, it is suggested that heating in the interaction regions starts around 0.6–0.7 AU from the Sun. 相似文献
18.
Thanks to the recent data obtained from the NEAR space probe, we calculate in this paper, with a precision never reached so far for an asteroid, the precession and the nutation of Eros 433. In a preliminary step, we show that Eros obliquity has a remarkable value of 89.0° which tends to align its figure axis along the orbital plane. This very specific obliquity has some consequences on the motion of the axis of figure: one is the very small amplitude of the precession in longitude, for which we get the value . Moreover, we calculate Eros nutation for the figure axis due to the Sun, after developing the perturbing potential at the 4th order of the eccentricity. We show that the figure axis undergoes very large oscillations in the direction perpendicular to Eros orbital plane, due to the nutation in obliquity. Peak to peak, these oscillations reach 55″, which is far larger than the amplitudes of the nutations of the Earth due to the Sun (of the order of 2″). Moreover, we give the analytical developments of Δψ and Δε, both for the axis of angular momentum, and the axis of figure. 相似文献
19.
Faraday rotation data on 40 pulsars are used in a detailed study of the magnetic field and its fluctuations in the direction of the spiral arm of Sagittarius. These results mostly agree with standard models for the galactic magnetic field. A magnetic field on the order of 3.2 G is directed from galactic longitude l
0=55° (toward the sun). However, an asymmetry has been found in the degrees of rotation relative to a plane lying in the southern hemisphere parallel to the galactic plane and at a distance of 50-60 pc from it. All the pulsars with measures of dispersion greater than 30 pc·cm-3 and lying to the north of this plane have positive measures of rotation which increase linearly with distance, while the pulsars lying to the south of this plane have unusually absolutely low negative measures of rotation. We propose that the spiral arm of Sagittarius lies entirely to the north of this plane, while the negative measures of rotation of the pulsars below this plane are caused by the magnetic field of the halo of the southern hemisphere of the galaxy. The magnetic field in the arm of Sagittarius is regular to a great extent and its fluctuating component is roughly half the regular component. 相似文献
20.
J. P. Rozelot 《Solar physics》1998,177(1-2):321-327
The objective of this paper is to present some results deduced from the analysis of (space-based) solar irradiance observations used jointly with (ground-based) solar diameter variations. The idea which is explored consists in searching a possible influence of the variability of the Sun's whole shape on the luminosity. It is shown that such an effect, albeit small, may occur. Thus, the global geometry of the Sun – which is not a perfect static ellipsoid – would have to be taken into account when attempting to model the irradiance. Our very preliminary results may help to construct empirical models that can be used, in turn to force any model of the thermal structure of the ocean and atmosphere to deduce climate variations, if any. 相似文献