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  • 1
    Electronic Resource
    Electronic Resource
    Observations at 6 cm of the solar active region (1975)
    [s.l.] : Nature Publishing Group
    Nature 257 (1975), S. 465-467 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The WSRT consists of twelve 25 m paraboloids along an east-west baseline, combined to form 20 interferometers. For our observations the minimum spacing was 90 m, the maximum 1,458m, the separation between successive baselines was 72 m and the integration time was 30 s. At the wavelength of 6 cm and ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/257465a0
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  • 2
    Electronic Resource
    Electronic Resource
    Microwave emission above steady and moving sunspots (1987)
    Springer
    Solar physics 112 (1987), S. 89-105 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two-dimensional maps of radio brightness temperature and polarization, computed assuming thermal emission with free-free and gyroresonance absorption, are compared with observations of active region 2502, performed at Westerbork at λ = 6.16 cm during a period of 3 days in June 1980. The computation is done assuming a homogeneous model in the whole field of view (5′ × 5′) and a force-free extrapolation of the photospheric magnetic field observed at MSFC with a resolution of 2″.34. The mean results are the following: (a) A very good agreement is found above the large leading sunspot of the group, assuming a potential extrapolation of the magnetic field and a constant conductive flux in the transition region ranging from 2 × 106 to 107 erg cm−2s−1. (b) A strong radio source, associated with a new-born moving sunspot, cannot be ascribed to thermal emission. It is suggested that this source may be due to synchrotron radiation by mildly relativistic electrons accelerated by resistive instabilities occurring in the evolving magnetic configuration. An order-of-magnitude computation of the expected number of accelerated particles seems to confirm this hypothesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148490
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  • 3
    Electronic Resource
    Electronic Resource
    Lifetime of the dark and bright mottles of the solar chromosphere (1970)
    Springer
    Solar physics 11 (1970), S. 59-60 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00156550
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  • 4
    Electronic Resource
    Electronic Resource
    Velocity pattern of small scale magnetic fields (1990)
    Springer
    Solar physics 126 (1990), S. 403-406 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High resolution observations of horizontal proper motions, as well as vertical Doppler velocities measured over two selected regions of small scale magnetic elements show a coherent behaviour. In a region with two opposite polarities, approching with a velocity of 0.4 km s-1, the material in between moves downwards with a velocity of 0.10 to 0.45 km s-1; while in a region with two peaks of the same polarity, moving apart with a velocity of 0.3 km s-1, the material in between moves predominantly upwards, with a velocity of up to 0.3 km s-1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153059
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  • 5
    Electronic Resource
    Electronic Resource
    Coronal magnetic fields from microwave polarization observations (1996)
    Springer
    Solar physics 167 (1996), S. 167-179 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The solar active region (AR) 7530 was observed at 6 cm on July 3 and 4, 1993 with the Westerbork Synthesis Radio Telescope, using a multi-channel receiver with very narrow bandwidth. We compare the radio data with Yohkoh SXT observations and with the magnetic field extrapolated from the Marshall vector magnetograms in the force-free and current-free approximations. The comparison with soft X-rays shows that, although a general agreement exists between the shape of the radio intensity map and the X-ray loops, the brightness temperature, T b, obtained using the parameters derived from the SXT is much lower than that observed. The comparison with the extrapolated photospheric fields shows instead that they account very well for the observed T b above the main sunspots, if gyroresonance emission is assumed. In the observation of July 4 an inversion and strong suppression of the circular polarization was clearly present above different portions of the AR, which indicates that particular relationships exist between the electron density and the magnetic field in the region where the corresponding lines of sight cross the field quasi-perpendicularly. The extrapolated magnetic field at a much higher level (∼ 1010 cm), satisfies the constraints required by the wave propagation theory all over the AR. However, a rather low electron density is derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146335
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  • 6
    Electronic Resource
    Electronic Resource
    ARTEMIS Mark-IV, THE NEW GREEK–FRENCH DIGITAL RADIO SPECTROGRAPH AT THERMOPYLES, GREECE (1997)
    Springer
    Solar physics 172 (1997), S. 353-360 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the new digital solar radio spectrograph located at the Thermopyles station, Greece, operated by the University of Athens. Observations cover the range from 110 to 600 MHz, using a 7-m parabolic antenna. The reception system uses two techniques in parallel: sweep frequency and multi-channel, the latter being based on the Acousto-Optical technique. The data acquisition system is based on two subsystems, a Sun Sparc-5 workstation and a front end based on a VME Motorola system. The two subsystems are connected through the Ethernet and are operated using the VxWorks real-time package. The daily operation is completely automated: pointing of the antenna to the sun, starting and stopping the observations at pre-set times, acquiring data, compressing data by silence suppression in real time, and archiving the data on a routine manner on DAT tapes. Apart from its usual function, this instrument will be used in conjunction with other instruments, including the Nançay decameter array and the low frequency radio receivers on the Wind spacecraft.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004941710308
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  • 7
    Electronic Resource
    Electronic Resource
    Coronal sources at meter and optical wavelengths during the declining phase of the solar cycle (1996)
    Springer
    Solar physics 165 (1996), S. 83-98 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present observations of the corona at 169 MHz with the Nançay Radioheliograph during the summer of 1984. We compare synoptic maps of the metric radio emission on the solar disk with synoptic charts of the K-corona as well as of the green and the red lines. Local sources of radio emission are not located near regions of enhanced green or red line emission which, in turn, are in general above chromospheric faculae. Thus the radio emissions located in the surroundings of faculae are apparently related to different loop systems, with lower density. The comparison of the radio data with the K-corona showed one radio source associated with enhanced emission both at 1.3 and at 1.7 R ⊙, apparently a streamer. Other radio sources did not show any clear associations, but were nevertheless located within the coronal plasma sheet, delineated by the large-scale K-corona emission. Moreover the large-scale structure of the corona at 169 MHz was quite similar to the coronal plasma sheet observed at 1.3 R ⊙ above the limb. The extent of the radio emission in latitude is very similar to that of the K-corona, while the coronal line emission is more concentrated near the solar equator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149091
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  • 8
    Electronic Resource
    Electronic Resource
    Fine Structure of the solar atmosphere from near-limb observations in three wavelengths (1997)
    Springer
    Solar physics 172 (1997), S. 133-138 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We analyze a time series of high-resolution observations near the limb, in the continuum, in the Mg b 1 line (-0.4 Å off line center), and in the wings of Hα (+0.75 Å). The observations were obtained with a CCD camera at the Vacuum Tower telescope of the Sacramento Peak Observatory. We study the association of facular points, as they appear at different heights of the solar atmosphere (continuum, b 1 - 0.4 Å, Hα + 0.75 Å) with the feet of fine dark mottles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004912030626
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  • 9
    Electronic Resource
    Electronic Resource
    Coronal structures observed at metric wavelengths with the Nançay radioheliograph (1985)
    Springer
    Solar physics 97 (1985), S. 267-282 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present and discuss two-dimensional maps of the Sun at 169 MHz, obtained with the Nançay radioheliograph used as an Earth rotation aperture synthesis instrument. The maps have been computed on the basis of about 6 hr of one-dimensional observations by the east-west and the north-south arrays of the radioheliograph and have a resolution of 1.5′ by 4.2′ for a solar declination near 23°. In addition to a broad background component, the maps show several features both brighter and darker than the background. Some of the bright features are sources of noise storm continua, as evidenced by their positions relative to active regions and by the occurrence of type I bursts. Weaker emission regions are apparently associated with neutral lines of the photospheric magnetic field. We found no sources associated with extended quiescent filaments. Some of the depressions on the maps correspond to coronal holes both in the equatorial region and near the poles, while the more shallow ones may be arch regions with low electron temperature and/or emission measure. The distribution of brightness temperature at a height of 0.15 solar radii above the photospheric limb shows a gross similarity with coronal green line observations. The present results indicate that the notion of the slowly varying component at metric wavelengths may have to be reexamined, since sources of different nature may have been grouped in this component in the past.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00165990
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  • 10
    Electronic Resource
    Electronic Resource
    Two-dimensional solar mapping at 5.2 cm with the Siberian Solar Radio Telescope (1992)
    Springer
    Solar physics 142 (1992), S. 341-358 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present two-dimensional solar maps at 5.2 cm computed from one-dimensinal observations with the Siberian Solar Radio Telescope (SSRT), using Earth rotation aperture synthesis techniques. The resolution attained with the E-W branch of the instrument is 15 by 45″ for a solar declination of about 23°. Maps during the period of June 8 to 13, 1988 clearly show the quiet-Sun background, sunspot and plage associated emission as well as compact sources above the neutral line in some active regions. We found that the latter disappear as the gradient of the longitudinal magnetic field decreases. We also detected emission associated with active regions behind the limb, apparently from unresolved loops, extending up to ∼40″. The prospects of the SSRT, as a dedicated solar instrument, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151458
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