共查询到20条相似文献，搜索用时 140 毫秒
1.
B. I. Ryabov V. P. Maksimov S. V. Lesovoi K. Shibasaki A. Nindos A. Pevtsov 《Solar physics》2005,226(2):223-237
Microwave maps of solar active region NOAA 8365 are used to derive the coronal magnetograms of this region. The technique is based on the fact that the circular polarization of a radio source is modified when microwaves pass through the coronal magnetic field transverse to the line of sight. The observations were taken with the Siberian Solar Radio Telescope (SSRT) on October 21 – 23 and with the Nobeyama Radio Heliograph (NoRH) on October 22 – 24, 1998. The known theory of wave mode coupling in quasi-transverse (QT) region is employed to evaluate the coronal magnetograms in the range of 10 – 30 G at the wavelength 5.2 cm and 50 – 110 G at 1.76 cm, taking the product of electron density and the scale of coronal field divergence to be constant of 1018 cm–2. The height of the QT-region is estimated from the force-free field extrapolations as 6.2 × 109 cm for the 20 G and 2.3 × 109 cm for 85 G levels. We find that on large spatial scale, the coronal magnetograms derived from the radio observations show similarity with the magnetic fields extrapolated from the photosphere. 相似文献
2.
T. Villela J. Braga F. D'Amico U. B. Jayanthi J. A. Neri 《Astrophysics and Space Science》1994,214(1-2):161-170
We describe an imaging telescope for observations of celestial sources in the energy range between 30 keV and 1.8 MeV onboard stratospheric balloons. The detector is a 41 cm diameter, 5 cm thick NaI(Tl) crystal coupled to 19 photomultipliers in an Anger camera configuration. It is surrounded by a plastic scintillator 15 cm thick on the sides, 0.2 cm thick at the top and 20 cm thick at the bottom. The imaging device is based upon a 19 × 19 element square MURA (Modified Uniformly Redundant Array) coded mask mounted in an one-piece mask-antimask configuration. The detector's spatial resolution is about 10 mm at 100 keV. This is the first experiment to use such a mask pattern and configuration for astrophysical purposes. The expected 3 sensitivity for an on-axis source observed for 104 s at a residual atmosphere of 3.5 g cm–2 is 1.44 × 10–5 photons cm–2 s–1 keV–1 at 100 keV and 1.00 × 10–6 photons cm–2 s–1 keV–1 at 1 MeV. The angular resolution is approximately 14 arcminutes over a 13°field of view. The instrument is mounted in an automatic platform with a capability for pointing and stabilization in both azimuth and elevation axis with 2 arcmin accuracy.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9-13 November, 1992. 相似文献
3.
T. Kitamura M. Matsuoka S. Miyamoto M. Nakagawa M. Oda Y. Ogawa K. Takagishi U. R. Rao E. V. Chitnis U. B. Jayanthi A. S. Prakasa-Rao S. M. Bhandari 《Astrophysics and Space Science》1971,12(2):378-393
Results of rocket observations of SCO X-1 over the spectral range of 220 keV are presented. The observations have been performed partly in India and partly in Japan under the collaboration of the three groups. The present results are compared with results of similar observations carried out by the LRL (Lawrence Radiation Laboratory) group. Some of these X-ray observations were accompanied by simultaneous optical observations. Relationships between the hardness of the X-ray spectrum and the X-ray intensity and between the hardness and the optical luminosity are compiled. The relationships among the parameters (temperature, density and size) which characterize the postulated isothermal cloud model of SCO X-1 are given. They indicate that SCO X-1 is characterized by a temperature of about 107–108K, a density of about 1016–1017 cm–3 and a radius of about 108–109 cm respectively. We further show that the temperature is inversely correlated with the size of the source; an increase in temperature corresponds to a decrease in the radius and an increase in density. 相似文献
4.
Yvette Cuny 《Solar physics》1971,16(2):293-313
An interpretation is given of the observations of the continuous solar radiation in the spectral range 600–1700 Å. The model allows for deviations from LTE of H, C, Si and S, and is in hydrostatic equilibrium. The predicted intensity from 1680 to 1520 Å has virtually no dependence on the electron temperature variation in the optical depth range 10–3–4 × 10–5, at 5000 Å; the brightness temperature is compatible with a low electronic temperature minimum near the optical depth 10–4. The model of the low chromosphere is characterized by a steep temperature gradient. The model satisfies observations at millimeter wavelengths. 相似文献
5.
We present here the results of emission tomography studies, based on a new differential deconvolution method (DDM) of Laplace transform inversion, which we use for reconstruction of the coronal emission measure distributions in the quiet Sun, coronal holes and plage areas. Two methods are explored. The first method is based on the deconvolution of radioemission brightness spectra in a wide wavelength range (1 mm–100 cm) for temperature profile reconstructions from the corona to the deeper chromosphere. The second method uses radio brightness measurements in the cm–dm range to give a coronal column emission measure (EM).Our results are based on RATAN-600 observations in the range 2.0–32 cm supplemented by the data of other observatories during the period near minimum solar activity. This study gives results that agree with known estimates of the coronal EM values, but reveals the absence of any measurable quantities of EM in the transition temperature region 3 × 104 –105 K for all studied large-scale structures. The chromospheric temperature structure (T
e = 20,000–5800 K) is quite similar for all objects with extremely low-temperature gradients at deep layers.Some refraction effects were detected in the decimeter range for all Types of large-scale structures, which suggests the presence of dense and compact loops (up to N
e =(1–3)× 109 cm-3 number density) for the quiet-Sun coronal regions with temperature T
e > 5× 10-5 K. 相似文献
6.
Gamma-ray observations are discussed to determine the density of protons of about 1 MeV precipitating to the photosphere. It is shown that Coulomb collisions will produce a positive slope in the proton distribution for energies less than 0.1 MeV for traversed column depths greater than 1018 cm –2. This could lead to plasma wave emission and radiation near the plasma frequency for densities 3.1 × 1010 cm–3 and temperatures 4.0 × 104 K where collisional and collisionless damping of the plasma waves is sufficiently weak. It is expected that these conditions will only be satisfied sporadically which leads to stationary radio emission limited in frequency and time. Recent radio observations of impulsive phase non-drifting patches in the 1–3 GHz range with duration 2–4 s are presented which could be produced by this mechanism. 相似文献
7.
G. Pascoli 《Astrophysics and Space Science》1995,234(2):281-301
Axisymmetrical models for protoplanetary nebulae are produced. We discuss the mechanism for mass loss from evolved cool stars and the characteristics of the gas outflow. By using two-dimensional magnetohydrodynamics, we find that the gas is preferentially ejected in a so-called equatorial plane. For a grid of models, the expansion velocities are found to be of the order ofv
escape/2 and the mass loss rates tilde 10–5-10–4
M
/year which appear consistent with the available observational data. Magnetic fields intensities in the 10–4 to 10–3 gauss range are obtained in circumstellar envelopes, in good agreement with observations (Nedoluha and Bowers, 1992). 相似文献
8.
We set up diffusion equations for the nuclear component of cosmic rays and solve these to find the ratio of light to medium nuclei in the cosmic rays as well as the gamma-ray distribution in our Galaxy. From a comparison of our calculated quantities with observational data we determine the values of various parameters appearing in the model. We find that best agreement between theory and observations is obtained if the cosmic-ray confinement region consists of a narrow disk of total height 160 pc and radius 16 kpc, where the cosmic-ray sources are located, and an extensive halo of height 20 kpc. The diffusion coefficient near the Sun must be between 1026 and 1027 cm2 s–1 while it equals 1028 to 1029 cm2 s–1 in the halo. Finally, we find that the diffusion coefficient in the Galaxy must depend on the gas density as a power law with an index of the order of –1. 相似文献
9.
Grains ejected from stars at velocities of 107 cm s–1 and/or grains accelerated by the pressure of starlight in the intercloud medium to velocities in the range 2×106–107 cm s–1 are slowed to velocities of about 2×105 cm s–1 in a typical interstellar cloud. The interaction of fast grains with gas atoms as they are slowed in clouds could provide (a) the dominant heat source for interstellar clouds; (b) sites for molecule formation; and (c) a mechanism of providing a pressure balance between clouds and the intercloud medium.Paper presented at the Symposium on Solid State Astrophysics, held at the University College, Cardiff, Wales, between 9–12 July, 1974. 相似文献
10.
J. P. Vallée 《Astrophysics and Space Science》1987,139(1):129-137
Methylidyne (CH) line observations were obtained at Algonquin from the diffuse molecular cloud envelope at G180.9+4.1, sandwiched between the optical H II region S241 and the molecular cloud core at G180.8+4.0. An analysis of these observations yields several of the envelope parameters, notably a CH column density of 2×1013 cm–2, a microturbulent velocity of 2.6 km s–1, and a total space density of 40 cm–3. 相似文献
11.
The possibility of measuring magnetic fields of solar active regions at coronal heights up to 1010 cm by observing the inversion of circular polarization of local sources at microwaves is demonstrated. The observations by the radiotelescope RATAN-600 were accomplished with the angular resolution 17–34 in the wavelength range 2–4 cm. It is found that the inversion of polarization occured within a core of local source situated above the largest sunspot of Mc Math 14822. The inversion was followed during the period of June 30–July 3, 1977. The measured coronal magnetic field of 16 G is found to be at the height 12 × 109 cm. This measured field proves to agree with a simulated potential structure of Mc Math 14822 coronal magnetic field. Our analysis of the inversion has been based on the theory of interaction (coupling) of the ordinary and extraordinary wave modes in the region of quasi-transverse propagation. 相似文献
12.
The estimates of quiescent and flare time temperatures of soft X-ray emitting regions on the Sun are obtained for flares observed during March–August 1967 from X-ray observations in two soft X-ray bands, 2–12 Å (Explorer-33 data) and 8–12 Å (OSO-3 data). It is concluded that hot coronal condensation, originally at 2–3 × 106 K, is raised to the temperature of about 4–5 × 106 K and is responsible for soft X-ray enhancement.On leave from Physics Department, College of Engineering, Aurangabad, India. 相似文献
13.
The ratios of radio to optical diameter of the solar disc at 10.7 and 3 cm wavelengths are examined. The radio observations are daily east–west scans of the solar disc, made over the period 1975–1992, which includes almost two complete solar cycles. We find that the apparent disc diameter is slightly greater at solar minimum than it is at solar maximum, suggesting that the radio diameter varies over the cycle. Moreover, the ratio is smaller at 3 cm wavelength than it is at 10.7 cm, at both solar maximum and minimum. 相似文献
14.
Power spectra based on Pioneer 6 interplanetary magnetic field data in early 1966 exhibit a frequency dependence of f
–2 in the range 2.8 × 10–4 to 1.6 × 10–2 cps for periods of both quiet and disturbed field conditions. Both the shape and power levels of these spectra are found to be due to the presence of directional discontinuities in the microstructure (< 0.01 AU) of the interplanetary magnetic field. Power spectra at lower frequencies, in the range of 2.3 × 10–6 to 1.4 × 10–4 cps, reflect the field macrostructure (> 0.1 AU) and exhibit a frequency dependence roughly between f
–1 and f
–3/2. The results are related to theories of galactic cosmic-ray modulation and are found to be consistent with recent observations of the modulation. 相似文献
15.
The development of three intense active centers during their appearance on the solar disk is examined using high resolution observations at 2.8 cm. Each region shows a very bright component with brightness temperature > 106 K and size smaller than 20.The development of the bright components have been investigated on different time scales. Intensity fluctuations on a time scale of minutes are within the instrumental accuracy while the evolution over periods of days shows a variation of the flux density up to 30–40% per day.The problem of the bright cores height is discussed. Heights within 10 × 103 and 40 × 103 km are found using their apparent displacement on the disk. 相似文献
16.
K. P. Singh R. K. Manchanda S. Naranan B. V. Sreekantan 《Astrophysics and Space Science》1981,77(1):215-220
Soft X-rays (0.2–1.0 keV) have been detected from the high galactic latitude source MX 2140-60 in a rocket experiment. The measured flux of 10–10 erg cm–2 s–1 combined with OSO-7 measurements in 2–40 keV X-rays, are best fit by a power law photon spectrum with spectral index 2.3 and a neutral hydrogen column densityN
H=(3–7) 1020 atoms cm–2. The observations support the source identification with the cluster of galaxies SC 2146-594, as suggested by Lugger. 相似文献
17.
We have previously studied large-scale motions using high-resolution magnetograms taken from 1978 to 1990 with the NSO Vacuum Telescope on Kitt Peak. Latitudinal and longitudinal motions were determined by a two-dimensional crosscorrelation analysis of pairs of consecutive daily observations using small magnetic features as tracers. Here we examine the shape and amplitude of the crosscorrelation functions. We find a characteristic length scale as indicated by the FWHM of the crosscorrelation functions of 16.6 ± 0.2 Mm. The length scale is constant within ±45° latitude and decreases by about 5% at 52.5° latitude; i.e., the characteristic size is almost latitude independent. The characteristic scale is within 3% of the average value during most times of the solar cycle, but it increases during cycle maximum at latitudes where active regions are present. For the time period 1978–1981 (solar cycle maximum), the length scale increases up to 1.7 Mm or 10% at 30° latitude. In addition, we derive the average amplitude of the crosscorrelation functions, which reflects the diffusion of magnetic elements and their evolutionary changes (including formation and decay). We find an average value of 0.091 ± 0.003 for the crosscorrelation amplitude at a time lag of one day, which we interpret as being caused by the combined effect of the lifetime of magnetic features and a diffusion process. Assuming a lifetime of one day, we find a value of 120 km2 s–1 for the diffusion constant, while a lifetime of two days leads to 230 km2 s–1.Operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation. 相似文献
18.
Based on spectral observations of active region NOAA 8545 on 19 May 1999, we describe the processes responsible for non-thermal long-lasting radio emission and for narrow-band non-drifting bursts observed at the same time. Non-thermal long-lasting radio emission consisted of two components: short-duration (1–2 s) microbursts with fluxes about 0.001 s.f.u. and continuum emission with growing spectrum in the range of 1000–2000 MHz. Energetic electrons continuously existed in the active region for more than 2.2 hours. The nature and parameters of microbursts were discussed by Bogod, Mercier, and Yasnov (2001). Here we consider the continuum source nature. It is shown that the model, taking into account the cyclotron loss-cone instability of hot electrons and the generation of plasma waves at the upper hybrid frequency, may explain the observed continuum source parameters. For the narrow-band non-drifting bursts we consider two models: the first taking into account an excitation of weak shock waves across the magnetic field and the second with an excitation of the upper hybrid waves under the double plasma resonance. Continuum source parameters are close to the last model. Our estimations for the magnetic field strength are as follows: H=120–126 G, which is valid for the region where the electron density of background plasmas n=(1.4–1.9) ×109 cm–3; H=180–190 G for the region where n=(3.0–4.3) ×109 cm–3; H=290 G for the region where n
e=2.5×1010 cm–3; and H=350 G for the region where n
e=3.5×1010 cm–3. The speed of the fast electrons is about 0.10–0.14 c. 相似文献
19.
Jin Wang 《Astrophysics and Space Science》1991,184(1):31-36
We study the astrophysical bounds on the change of the gravitational constant with time. We found that |/G|<10–12yr–1 is the condition that has to be satisfied in order not to cause a conflict with the observations. We find the condition to be in accord with the lower limits, the superstring theory predicts. 相似文献
20.
Recent atomic data have been used to analyze a solar flare spectrum obtained with the Goddard Space Flight Center's grating spectrometer on the OSO-5 satellite. There exist in the wavelength region 90–200 Å strong lines from each of the ions Fe xviii-Fe xxiv. The Fe xxi lines can be used as an electron density diagnostic for the 107 K plasma. From our analysis of a particular flare, we find a steep positive slope in the emission measure between 106.5 and 107.2 K and an electron density of 4 × 1011 cm–3 at 107 K. We emphasise the need for high spectral and spatial resolution observations of solar flares in this wavelength region, which has to date been largely neglected. 相似文献