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1.
Profiles of weak Fraunhofer lines have been recorded photoelectrically in both the faculae and the undisturbed photosphere. The entrance slit of the double-pass spectrograph corresponded to 1 × 20 on the solar disk. Turbulent velocities were found by comparing half-widths of the observed profiles with those of model calculations. These latter were carried out with aid of an electronic computer for the Bilderberg Continuum Atmosphere (BCA) under the assumption of true absorption and depth independent turbulent velocities. Line-formation levels were derived from the contribution curves computed by the method of weighting functions. For the undisturbed photosphere a turbulent velocity of about 2.6 km/s was found with no appreciable increase with the depth. In facular filaments all lines formed above = 0.1 showed smaller turbulence velocities, the velocity differences being in the range between 0.2 and 0.6 km/s (see Table II). 相似文献
2.
R. S. Bogart S. H. Ferguson P. H. Scherrer T. D. Tarbell A. M. Title 《Solar physics》1988,116(2):205-214
The SOUP experiment demonstrated that photospheric surface flows can be measured by correlation tracking of white-light intensity features at high resolution (November et al., 1987). In order to assess the feasibility of this technique with observations made at lower resolution, we have applied it to the same SOUP data artificially degraded, but still free of seeing distortion. Comparison with the velocity structures inferred from the original data shows generally good agreement when the resolution is better than about 2. The radial outflow from a sunspot penumbra, however, can only be seen with resolution of better than 1. With resolution of worse than 2, the inferred velocity fields rapidly lose coherence, while resolution of better than 1 yields little improvement. We conclude that apertures as small as 10–14 cm on a space-based platform will be useful for the measurement of large-scale horizontal motions. 相似文献
3.
J. Kovalevsky 《Celestial Mechanics and Dynamical Astronomy》1980,22(2):153-163
The European Space Agency project of an astrometric satellite-HIPPARCOS-is shortly described. It will measure the angles between stars situated in fields separated by about 70°. The precision of the elementary measurements is expected to be of the order of 0.005. A similar accuracy is found to apply to the basic reduction giving the abcissae of stars referred to great circles on the sky. The final overall reduction should yield accuracies better than 0.002 in position and parallaxes and 0.002 per year in proper motions.The main features of the final catalogue are described and some possible consequences for fundamental astronomy are given.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978. 相似文献
4.
Correlations between continuum intensity, velocity, and equivalent widths of two Mn i lines as observed with two different entrance apertures tend to deteriorate with improvement in spatial resolution. The KPNO multichannel magnetograph was used to make area scans at the center of the disk with entrance apertures 3.5×2.5 arc and 1×1 arc. A coherence analysis shows that this effect is caused by marked differences of fluctuations in temperature and temperature gradients as well as in the velocity structure of photospheric elements of various sizes. 相似文献
5.
A prime objective of this experiment was to determine whether type I or IV sources at 333 MHz contain features of small (arc sec) scale. With the VLA, our resolution was better than 4. However, we never observed any structure of size smaller than about 30, with the typical source sizes being between about 40 and 90.Many observations were simultaneous with the Trieste Astronomical Observatory records at 327 MHz. The observations were made on two days in November 1988. On 8 November the observations were of a type I storm about two hours after a major flare. On 14 November they were mostly of the main phase of a type IV event, including pulsations of a kind rarely seen, strongly circularly polarized, and having a well-defined period of about 12 s. The size of the pulsating source was about 40 by 60, and the brightness temperature was about 109 K. We compare these pulsations with those observed earlier. 相似文献
6.
Y. Fukada S. Hayakawa I. Kasahara F. Makino Y. Tanaka H. Akiyama M. Matsuoka J. Nishimura M. Oda M. Nakagawa H. Sakurai V. S. Iyenger P. K. Kunte R. K. Manchanda B. V. Sreekantan 《Astrophysics and Space Science》1976,42(1):245-248
The size of the hard X-ray source in the Crab Nebula was observed with scintillation counters on board two balloons at a lunar occulatation on 24 January, 1975. The Gaussian width of the source is 34 (+17, –14) and the center thereof is offset from the pulsar by 6±4 at position angle 102°. The observed time profile can also be fitted to an alternative model of two line sources whose intensities are 48% at 11 and 25.5% at 7 on both sides of the pulsar.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
7.
Some properties of the photospheric granulation near the centre of the quiet sun have been investigated on the basis of two high-definition Stratoscope photographs. We obtain (1) a number density of 54 granules per 10 × 10, (2) a total number of granules on the whole surface of 6.3 × 106, (3) a mean cell diameter of 1.5 or 1100 km and a mean granule diameter of 1.2 or 850 km, the difference of 250 km being ascribed to the mean width of the dark intergranular lanes, (4) frequency distributions of cell diameters and granule diameters (Figures 1 and 2), and (5) an isophotal map in relative intensity (Figure 3). In general, larger granules are brighter than smaller granules (Figure 4). Cross-section profiles are shown for some granules and intergranular lanes (Figures 5 and 6). These quantities have not yet been corrected for the finite resolution of the telescope. 相似文献
8.
CASPIR is a near-infrared spectrometer/imager being built for the Mount Stromlo and Siding Spring Observatories' 2.3 m telescope. The instrument is based on a SBRC 256×256 InSb detector array and uses AR-coated Sapphire, MgO, CaF2, and BaF2 optics to produce two imaging focal plane scales with 0.5/pixel and 0.25/pixel. Spectral resolving powers of 500 will be achieved through a 1×128 slit with three grisms designed for the J, H, and K bands. IJ, JH, and HK cross-dispersed échelle grisms will achieve resolving powers of 1100 through a 1×15 slit. Coronograph and imaging polarimetry modes will also be available. The various observing configurations are selected via five remotely controlled wheels. The instrument design and system architecture are discussed, and preliminary detector performance figures reported. 相似文献
9.
R. Muller 《Solar physics》1977,52(2):249-262
From time series of high resolution photographs, morphological properties of the photospheric facular granules were derived. The facular granules are cells of the common granular pattern, brighter than the normal granules when seen between cos = 0.6 and the limb. Their apparent diameter, which decreases towards the limb, is smaller than that of the normal granules: 0.65 and 1.25 respectively at cos = 0.55; their lifetime is 25 min but their bright stage lifetime is only 15 min; they are visible closer to the limb than the normal granules: 1.2 compared to 2–5; the brightening of the facular granules occurs at a faster rate than their fading. From the great similitude of both morphological properties and temperature models of facular and normal granules, it appears possible that the photospheric facular granules are convective cells modified by the presence of a magnetic field of some hundreds Gauss. 相似文献
10.
A. T. Fomenko 《Celestial Mechanics and Dynamical Astronomy》1981,25(1):33-40
We present some results of new calculations ofD(t)-the second derivative of the Moon's elongation as a function of time. The paper contains an explanation of the well-known R. Newton's effecthe rapid decline inD(t) from about 700 yr to about 1300 yr. The new graph ofD is based on the revised dates of the ancient eclipses and has a qualitatively different character; in particular, the decline inD(t) vanishes completely andD(t) oscillates at a roughly constant value, which coincides with the modern one. This fact agrees with the independent chronological results in the author's [7] paper. 相似文献
11.
The temporal and spatial variations of EUV emission from a small growing active region were investigated. Frequent localized short term ( few minutes) fluctuations in EUV emission were observed throughout the 7.2 hr interval when the most continuous observations were acquired. Approximately 20% of the 5 x 5 pixels had intensity variations exceeding a factor of 1.3 for the chromospheric L line, a factor of 1.5 for lines formed in the chromospheric-coronal transition region and a factor of 1.4 for the coronal Mg x line. A subflare in the region produced the largest intensity enhancements, ranging from a factor of 2.3 for the chromospheric L line to 8 for the transition region and coronal lines. The EUV fluctuations in this small active region are similar to those observed in coronal bright points, suggesting that impulsive heating is an important, perhaps dominant form of heating the upper chromospheric and lower coronal plasmas in small magnetic bipolar regions. The responsible mechanism most likely involves the rapid release of magnetic energy, possibly associated with the emergence of magnetic flux from lower levels into the chromosphere and corona. 相似文献
12.
The two available methods for determining the rms amplitude of the granular convective velocity field, namely the interpretation of line profiles, and direct measurements of velocity fluctuations in highly resolved spectra, give values ( 2 km/sec, and 0.4 km/sec, resp.) which are apparently inconsistent both in magnitude and in their dependence upon optical depth. We give both theoretical and observational evidence for the working hypothesis, that the best resolved spectra mainly show velocity fluctuations due to the oscillation of the solar atmosphere, whereas the contribution of the granular velocity field is greatly reduced because of atmospheric seeing and can be found only as a weak superposition to the oscillatory velocity field. Realistic assumptions for the typical size of the granulation (2.5) and for the seeing parameter (1), together with a simplified model of the granular velocity field, lead to correction factors of 30 to 40 between the true and observed amplitudes of the granular velocities.Mitteilungen aus dem Fraunhofer Institut, Nr. 95. 相似文献
13.
J. P. Mehltretter 《Solar physics》1971,16(2):253-271
Continuum brightness and Doppler velocity fluctuations in the lines 6301.5 and 6302.5 Å of Fei, measured in two selected spectrograms, are analysed by standard statistical (power- and coherence spectrum) methods. It is shown qualitatively that the oscillatory component of the velocity fluctuations (at spatial wavelengths > 4) decreases, while the supposedly granular component (at spatial wavelengths < 4) as well as the coherence between brightness and velocity fluctuations increases with optical depth.The spatial resolution of the spectrograms is estimated by comparing the observed power spectrum of brightness fluctuations with spectra found in the literature, assuming the combined instrumental and seeing spread function to be Gaussian. The resolution thus determined is = 1.24 ± 0.07. If the measured values are corrected accordingly, we obtain a true brightness rms of 10 to 14%, depending upon the shape of the power spectrum chosen for comparison, and a velocity rms at continuum optical depth of 1.3 km/sec. It is shown, however, that using the same correction function for the velocity power spectrum as for the brightness possibly gives rise to misestimating the velocity rms.Mitteilungen aus dem Fraunhofer Institut Nr. 100. 相似文献
14.
As a consequence of an astrometry program, conducted since 1975 on a solar astrolabe at the Calern Observatory (Observatoire de la Côte d'Azur), we have obtained a data set of apparent solar diameters which encompasses periods greater than one solar cycle. From a set of more than 5000 visual observations, made by the same observer between 1975 and 1994, the mean value of the semidiameter was measured at 959.42 ± 0.01. Also, a set of CCD measurements made with the same instrument between 1989 and 1994 yields the mean value 959.40 ± 0.01. Both results obtained by raw measurements are consistent but significantly differ from values obtained by other methods and on other instruments. We discuss some systematic effects that can affect our visual measurements and their precision. Taking account of a zenith distance effect provides for the semi-diameter a mean value closer to the value of the ephemeris. Our observations also reveal deviations around the mean diameter in the royal zones and for high heliographic latitudes; their amplitudes reaching as much as 0.08. Finally, semi-diameter variations appear in our series; their origin is unknown but they may possibly be related to observed variations of magnetic activity or other solar parameters. 相似文献
15.
J. Chapront 《Celestial Mechanics and Dynamical Astronomy》2000,78(1-4):75-82
Taking advantage of the JPL Long Ephemeris DE406 and of the semi-analytical solution for the planetary motions VSOP87, we make an approximation of the differences JPL–VSOP. The form of the approximation (arguments and Poisson expansions) is analogous to the time series of the theory. We improve the planetary solution VSOP87 in two directions: a better fit of the integration constants via the highly precise observations used in DE406 and an extension of the length of validity covering the 6000 years of the source ephemeris. Over an interval of 2000 years, we achieve on the mean longitudes (test variables) a precision better than 0.005 for inner planets and 0.015 for outer ones. On the longest time interval covering 6000 years the precision is better than 0.03 for inner planets and 1.2 for outer ones. 相似文献
16.
The Gauribidanur Radioheliograph 总被引：1，自引：0，他引：1
A new radio heliograph for obtaining two-dimensional images of the solar corona sequentially at many frequencies in the range 40–150 MHz has been built by the Indian Institute of Astrophysics at the Gauribidanur Radio Observatory (lat. 13°3612 N and long. 77°2707 E) about 100 km north of Bangalore, India. This paper describes various aspects of the antenna system, receiver front end, digital hardware, the data acquisition and the calibration procedure. The performance of the instrument is illustrated with maps of the continuum emission from the undisturbed corona at different frequencies. 相似文献
17.
We have used the ESO 10 m camera, TIMMI, to image with a very high angular resolution (PFoV: 0.3; FWHM:0.9) several main-sequence star disk candidates. Information on the -Pictoris dust disk has been obtained in a region largely inaccessible to previous observations: 0–80 AU, with a resolution of about 5 AU after deconvolution. Another promising target for 10 m imaging, 51 Ophiuchi, appears point-like.based on data collected at the European Southern Observatory (ESO), La Silla, Chile 相似文献
18.
We have studied running penumbral waves, umbral oscillations, umbral flashes and their interrelations from H observations of a large isolated sunspot. Using a subtraction image processing technique we removed the sharp intensity gradient between the umbra and the penumbra and enhanced the low contrast, fine features. We observed running penumbral waves which started in umbral elements with a size of a few arcseconds, covered the umbra and subsequently propagated through the penumbra. The period of the waves was 190 s and the mean propagation velocity was about 15 km s–1. We detected intense brightenings, located between umbral elements from where waves started, which had the characteristics of umbral flashes. There are indications that umbral flashes are related to the propagation of the waves through the umbra and their coupling. The subtraction images also show considerable fine structure in the chromospheric umbra, with size between 0.3 and 0.8. 相似文献
19.
3D, the next-generation near-IR spectrometer developed at the MPE, produces in a single integration, a datacube of a 8×8 field characterised by 0.5 resolution in image space and a resolving power of R=1000 over the entire K-band in wavelength space.A detailed account of this work, including results of the first test measurements, will be presented elsewhere (Weitzel et al., in preparation). 相似文献
20.
The velocity field has been mapped for 42 min in an area 80 by 85 containing a unipolar sunspot. Apparent shifts of Fe i
5233 were measured photoelectrically using a rectangular scanning aperture 1.6 × 4.0. The sunspot did not exert a marked influence on the generally random pattern of oscillations at a period of 300 s. Discrete periods of oscillation both longer and shorter than 300 s were excited within the enhanced magnetic field boundaries of this spot. Umbral oscillations at periods near 180 s were detected in agreement with independent observations of the same spot during the previous solar rotation.NRC Postdoctoral Fellow, 1969–71. 相似文献