共查询到20条相似文献，搜索用时 15 毫秒
1.
The method of computer controlled photoelectric drift scans has been improved by virtue of a new timing technique, allowing for an accuracy of 4 ms or equivalently 50 km on the Sun. With this technique, our previous result for the solar semidiameter has been confirmed: R = 960.277″. The extreme solar limb intensity profile at 5012 Å has been derived from drift scans. A comparison with the computed profile has been made, and parameters for the base of the chromosphere have been derived.
相似文献2.
The existence of limb brightening at the equator of the quiet Sun at 3.1 cm is derived from a statistical analysis of scans of the solar disk taken during 1968.A ratio of 0.7% is found between the flux emitted by the equatorial limb enhancements and that of a disk of uniform brightness temperature. 相似文献
3.
Arthur E. Covington 《Solar physics》1977,54(2):393-402
Radio cool regions observed on strip scans of the Sun made at 2800 MHz with a 1.5 min arc fan beam are associated with X-ray coronal holes and are used to derive lower envelopes which are similar to spotless Sun drift curves. Fluxes are evaluated from the Ottawa-ARO solar patrol;. e.g. that of Coronal Hole 1 observed during the Skylab Mission with central meridian passage on July 25, 1973 is 66.5 s.f.u. ± 0.6%. This level is identified as that observed during sunspot minimum by comparison with the flux of 67.2 observed in July, 1964, and with the low daily values of 67.5 and 67.1 observed in April, 1975 and January, 1976. The enhancement of the quiet Sun of 3.0 s.f.u. for the optically inactive hemisphere of May 20, 1974 suggests that the radio quiet Sun may vary during the sunspot cycle. 相似文献
4.
The radio azimuths for many kilometric type III bursts that originate near or behind the limb of the Sun are observed to drift far to the east or far to the west of the spacecraft-Sun line. It is shown that the behavior of the observed burst parameters for these events corresponds to the response of a spinning dipole antenna to halo-like sources of radiation around the Sun. Our results provide evidence for a previous suggestion that behind-the-limb type III events should appear as halo-like sources of radiation to an observer on the opposite side of the Sun, due to scattering of the radiation from the primary source back around the Sun. 相似文献
5.
John P. Hagen Paul N. Swanson Robert W. Haas Fred L. Wefer Raymond W. Vogt 《Solar physics》1971,21(2):286-296
The 7 March, 1970 total solar eclipse was observed at wavelengths of 3.2 and 8.3 mm; the object being to use the knife edge of the Moon as it passed across the Sun to improve angular resolution on the Sun. This in turn would provide a radial brightness distribution of the Sun with an angular resolution of a few seconds of arc.Excellent eclipse curves were obtained at 3 mm; however, some external interference marred the 8 mm record near totality.The 8 mm brightness distribution is subject to some uncertainty, but tends to show limb brightening. The 3 mm brightness distribution shows a well defined complex limb brightening within about 1 arc min of the optical limb. The maximum brightening is approximately 30% above the average disc temperature. 相似文献
6.
Makarov V. I. Stoyanova M. N. Sivaraman K. R. 《Journal of Astrophysics and Astronomy》1982,3(4):379-382
Ring-like filaments have been detected on the spectroheliograms in the H-alpha line. Inside these filaments the magnetic field
flux has a predominant polarity. Some of the dark filaments are connected by filament channels which can be seen at the limb
either as (a) weak prominences or (b) dense low chromospheric features or (c) multi-channel system of matter flow between
two prominences or (d) common quiescent prominences. The filament and the filament channel together form a continuous closed
contour and outline the region of thef polarity particularly at the beginning of the solar cycle. The change in sign of the polar field of the Sun is associated
with the drift of the filament band to high latitudes. 相似文献
7.
The brightness distributions of the Sun were observed at 33 and 37 GHz. Maximum limb brightening of about 10% was observed at both frequencies. 相似文献
8.
Maps of the brightness distribution of the ‘quiet Sun’ at 80 and 160 MHz reveal the presence of features both brighter and darker than average. The ‘dark’ regions are well correlated with dark regions on UV maps; we deduce that they result from ‘coronal holes’. The ‘bright’ regions are associated with quiescent filaments and not plages or bright regions on microwave or UV maps; we deduce that they result from ‘coronal helmets’.
When coronal holes appear near the centre of the disk we can estimate the density and kinetic temperature in the holes from the radio observations. For a hole observed on 1972 July 20–21, we find T ≈ 0.8 × 106 inside the hole and T ≈ 1.0 × 106 in average regions outside the hole. Inside the hole the density is estimated to be about one-quarter of that in Newkirk's model of the spherically symmetric corona.
Variations in brightness at a fixed height above the limb are generally well correlated with scans at a similar height made with a K-coronameter. Occasional differences may result from streamers protruding beyond the limb from the back of the Sun. These can be seen by the K-coronameter but, because of refraction of the radio rays, not by the radio-heliograph.
相似文献9.
Recent solar observations at Pic du Midi are reported that yield a value of J
2=(2.57 ± 2.36) x 10–6 for the quadrupole moment of the Sun. These observations were conducted from July 1993 to July 1994 after several improvements of the scanning heliometer. This instrument operates by fast photoelectric scans of opposite limbs of the Sun quasi-simultaneously, which provides the distance between both inflection points of the limb profiles. Any number of solar diameters in any position angle can be measured within a time interval short enough to minimize the scattering of the observational parameters. Errors due to atmospheric deterioration are discussed. From our results, compared to previous values obtained by other authors, it can be concluded than an upper limit for J
2 is probably 1.0 × 10-5. 相似文献
10.
D. Utz A. Hanslmeier A. Veronig O. Kühner R. Muller J. Jurčák B. Lemmerer 《Solar physics》2013,284(2):363-378
Small-scale magnetic fields can be observed on the Sun in high-resolution G-band filtergrams as magnetic bright points (MBPs). We study Hinode/Solar Optical Telescope (SOT) longitude and latitude scans of the quiet solar surface taken in the G-band in order to characterise the centre-to-limb dependence of MBP properties (size and intensity). We find that the MBP’s sizes increase and their intensities decrease from the solar centre towards the limb. The size distribution can be fitted using a log–normal function. The natural logarithm of the mean (μ parameter) of this function follows a second-order polynomial and the generalised standard deviation (σ parameter) follows a fourth-order polynomial or equally well (within statistical errors) a sine function. The brightness decrease of the features is smaller than one would expect from the normal solar centre-to-limb variation; that is to say, the ratio of a MBP’s brightness to the mean intensity of the image increases towards the limb. The centre-to-limb variations of the intensities of the MBPs and the quiet-Sun field can be fitted by a second-order polynomial. The detailed physical process that results in an increase of a MBP’s brightness and size from Sun centre to the limb is not yet understood and has to be studied in more detail in the future. 相似文献
11.
A method is presented for the direct measurement of the heights of the radio emission of solar active regions when they are located at the limb in order to reconstruct the vertical structure of the magnetic field in solar active regions. The method involves an analysis of radio source positions in the scans based on high frequency resolution one-dimensional centimeter-wave measurements performed on the RATAN-600 radio telescope. Radio sources are difficult to identify at many frequencies when observed at the limb at zero position angle because of abrupt signal variations at the solar limb. To eliminate edge effects on the scan, special observing periods are used (near vernal and autumnal equinoxes), when the source at the limb is located far from the scan edge because of the large position angle of the Sun. As a result of these observations, the spectra of relative heights are constructed for a number of sources for the period from 2007 through 2012. Source heights are shown to generally increase with wavelength. The height difference between the 5 and 2 cm emission is equal to 5.2 ± 2.0 Mm, and the corresponding height difference between the 8 and 2 cm emission is equal to 9.6 ± 3.0 Mm. It is shown that such characteristics can be obtained for a field generated by a dipole submerged under the photosphere at a depth of 17 Mm irrespective of the possible reduction of relative altitudes to absolute altitudes. 相似文献
12.
This paper introduces a new method of describing the limb darkening phenomenon of stellar atmospheres in the 1st and 2nd order approximations. The limb darkening coefficients are given by direct measurements of relevant physical quantities or measurements of flux and a supplementary quantity, namely, the star's surface temperature. The comparison either with solar observations or with the method of numerical simulation of the atmosphere shows that the new method can very accurately describe the star's limb darkening and determine its relevant coefficients. The accuracy of the new direct method is assessed using 176 observational data points of the Sun, and the mean fractional differences is found to be 0.38% for the 1st-, and 0.26% for the 2nd-order approximations. The mean differences of the indirect method are close to, and slightly larger than these values. When compared with numerical models of the atmosphere, the differences are in the range from under 1% to under 3%. 相似文献
13.
M. Simon 《Solar physics》1971,21(2):297-304
High resolution observations of the Sun at 3.3 mm, 3.5 mm, 1.35 cm, and 1.95 cm which were obtained by tracking narrow beam width antennas on the lunar limb as it occulted the Sun are described. The observations indicate that: (1) the region emitting at these wavelengths is very irregular with typical length scales smaller than one half minute of arc, (2) the number of roughness elements responsible for the irregular structure is small within an area of one half minute of arc square, and (3) the roughness elements observed at wavelengths greater than 1 cm extend to 109 cm beyond the optical limb. 相似文献
14.
Bruce W. Lites 《Solar physics》1983,85(2):193-214
Detailed computations of synthetic solar limb curves are carried out for the purpose of estimating the effects of inhomogeneities in the solar atmosphere upon the observed limb position. Methods of determining the limb position given a solar limb curve are compared. The method of finding the locus of a fixed intensity level with respect to the average disk-center intensity at a given wavelength seems to be the most tractable definition to use on noise free data. It is found that limb fluctuations due to the solar 5-min p-mode oscillations produce a fluctuation in the limb height of about 6 km (0.008 arc sec) rms. Limb fluctuations due to granulation and chromospheric structure are much smaller. The wavelength dependence of the solar H? opacity causes the height of the limb to increase by about 35 km between 400 and 850 nm, thus leading to a ‘limb reddening’ at the extreme limb of the Sun. 相似文献
15.
Magnetic flux tubes are considered to be a possible source of observed brightness variations on the extreme limb of the Sun. A computer code to simulate the brightness fluctuations is developed. It follows from numerical modeling that a filling factor of f=4% is required to explain the observed fine structure. Such a value is typical for the boundaries of supergranules. Tubes produce a local maximum of intensity just inside the limb. 相似文献
16.
The evolution of the large-scale magnetic field of the Sun has been studied using an algorithm of tomographic inversion. By analyzing line-of-sight magnetograms, we mapped the radial and toroidal components of the Sun??s large-scale magnetic field. The evolution of the radial and toroidal magnetic field components in the 11-year solar cycle has been studied in a time?Clatitude aspect. It is shown that the toroidal magnetic field of the Sun is causally related to sunspot activity; i.e., the sunspot formation zones drift in latitude and follow the toroidal magnetic fields. The results of our analysis support the idea that the high-latitude toroidal magnetic fields can serve as precursors of sunspot activity. The toroidal fields in the current cycle are anomalously weak and also show a barely noticeable equatorward drift. This behavior of the toroidal magnetic field suggests low activity levels in the current cycle and in the foreseeable future. 相似文献
17.
Observations at 9 mm wavelength of the partial solar eclipse of February 25th 1971 were made to investigate possible limb brightening of the Sun. The results obtained show that less than 5% of the solar disc power can be contained in any such brightening. 相似文献
18.
The brightness distribution of the quiet Sun at 8.6 mm wavelength is synthesized from off-meridian observations using an eight element east-west interferometer with a maximum base line of 16.38 m (1913). The observed brightness distribution is practically flat from the disk center to the optical limb. The effective radius of the nearly uniform component is 1.01 R
. If the limb brightening is present, the brightening located between 0.95 R
and 1.01 R
, and the total flux density of the limb brightening is less than 1% of the total flux density of the Sun. In addition to the nearly uniform component there exists a coronal component just outside the optical limb. 相似文献
19.
A new method for measuring spectroscopically the rotation at the Sun's poles is described. Using solar CO lines at 4.666 µm, infrared spectra are recorded at a fixed limb distance of 4.8 arc sec while progressing along an arc ±5.7 deg from the Sun's rotational pole. Since the poles dip twice a year to about 7 arc sec from the limb, our observations can range either side of and through the vortex axis. Advantages to this technique are: (1) a low disturbing signal from supergranules owing to their superposition at the limb, (2) no ‘limb shift’ error since limb distance is constant and the CO lines have no known limb shift, (3) emphasis is on the quiet Sun since the CO molecule is confined there, (4) negligible scattered light in the IR (<1%), and (5) the improved seeing afforded by the IR. Although any definitive determination of solar rotation requires observations over an extended time span, our preliminary results suggest two features peculiar to the extreme pole: (1) the occasional apparent cessation of rotation, (2) some sort of singularity, again occasional, producing a sharp velocity signal (a vortex?) within 1 deg of the pole. 相似文献
20.
Ronald J. Kroll 《Solar physics》1994,152(1):105-110
In an effort to monitor solar limb-darkening variability, the continuum radiation intensity at 550 nm over the outermost 32 arcseconds of the limb is measured at various solar latitudes. Using the Finite Fourier Transform Definition, the edge location of the Sun is determined for a series of scan amplitudes at each of the observed positions. The differential radius is the difference between edge locations for a fixed pair of scan amplitudes, and is a quantity which characterizes the slope of the solar limb-darkening function. Utilizing the differential radius, such observations offer the possibility of revealing a latitudinal variation of the photospheric temperature gradient and could provide clues to the mechanisms and variability of energy transport out of the Sun. These observations began in 1988 with measurements at 24 separate limb positions and include observations since 1990 when 36 positions were observed. The daily differential radius measurements for each position that is free of contamination from solar active regions are weighted according to the corresponding daily variance and averaged to obtain an overall value at each position for the observing season. The results indicate that during the 1991 observing season, there were regions near 20°N latitude and 30°S latitude on the Sun where the differential radius values were significantly greater than surrounding regions. This suggests that perturbations to the temperature gradient occur in latitudinally localized regions and persist for at least several months. It is shown that this phenomenon could have the same origin as the observed latitudinal variations of surface temperature and could also speak to the question of a lag time between the cycles of irradiance and magnetic variation. 相似文献