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  • 1
    Digitale Medien
    Digitale Medien
    Stellar flares (1994)
    Springer
    Space science reviews 68 (1994), S. 261-274 
    Details
    ISSN: 1572-9672
    Schlagwort(e): Stars: Activity ; Stars: Flare ; Radio Continuum: Stars ; X-Rays: Stars
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Radio and X-ray observations of stellar flares provide the most direct probes of energy relaase particle acceleration, and energy transport on stars other than the Sun. In this review, the observational basis for our understanding of the flare phenomenon on other stars is briefly described and outstanding interpretive and theoretical issues are discussed. I shall confine my attention to objects which are “solar-like”, to the extent that they possess deep convective envelopes and display activity which is presumed to be magnetic in origin. These include pre-main sequence objects, classical flare stars, and close binaries. Future directions are briefly discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00749152
    Standort Signatur Erwartet Verfügbarkeit
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    Artikel (Nationallizenzen)
    Volltext
  • 2
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    Unbekannt
    3D reconstruction methods of coronal structures by radio observations (1992)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The ability to carry out the three dimensional (3D) reconstruction of structures in the solar corona would represent a major advance in the study of the physical properties in active regions and in flares. Methods which allow a geometric reconstruction of quasistationary coronal structures (for example active region loops) or dynamic structures (for example flaring loops) are described: stereoscopy of multi-day imaging observations by the VLA (Very Large Array); tomography of optically thin emission (in radio or soft x-rays); multifrequency band imaging by the VLA; and tracing of magnetic field lines by propagating electron beams.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: ESA, Proceedings of the First SOHO Workshop: Coronal Streamers, Coronal Loops, and Coronal and Solar Wind Composition; p 217-220
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 3
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    Dual frequency observations of flares with the VLA (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Observations are presented of two subflares near the limb on 21 and 22 November 1981 and an M7.7 flare on 8 May 1981 made at 5 and 15 GHz using the VLA. One of the November flares produced no 5 GHz radiation, while the 15 GHz radiation in the other flare emanated from a source which was smaller, lower, and displaced from the 5 GHz source. The flare occurring on 8 May was intense and complex, and contained two or more sources at both 5 and 15 GHz. Prior to the peak of the flare, the sources were found to grow in size, after which time only weak subsources were visible to the VLA. These subsources were found to be located between or at the edge of the H-alpha ribbons and the two hard X-ray sources imaged by the Hinotori satellite. Highly polarized, bursty radiation was observed at 1 and 2 GHz, which indicated that an electron-cyclotron maser operated during the flare. The maximum field strength in flaring loops is estimated to be 360-600 gauss.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: (ISSN 0038-0938)
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 4
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    Multiple wavelength observations of an off-limb eruptive solar flare (1993)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The eruptive prominence and limb flare which occurred at 1454 UT on June 20, 1989 is described and analyzed. This event was observed by many different instruments providing an unusual amount and variety of data: images at 1.4 GHz, 37 GHz, and H-alpha, and spectra in hard X-ray, soft X-ray, and radio frequencies. This array of data makes it possible to explore the relationships between flare and eruptive prominence emissions at different wavelengths. VLA images at 1.4 GHz show changing sources in a set of high (about 10 exp 10 cm) coronal loops associated with the erupting prominence. We use a full gyrosynchrotron code to model a 1.4 GHz source early in the flare as a large coronal loop. The model results lead us to conclude that the initial acceleration occurs in smaller, denser loops which also produce the flare's hard X-ray emission. We also present evidence that a source at 1.4 GHz later in the event is due to second-harmonic plasma emission. This source is adjacent to a leg of the prominence and comes from a dense column of material in the magnetic structure supporting the prominence.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 412; 2; p. 853-864.
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 5
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    Unbekannt
    A multisource limb flare observed at multiple radio wavelengths (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-27
    Beschreibung: A flare with several radio sources occurred on the solar limb at 2155 UT on 1989 June 20. It was observed by the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO). The VLA data consisted of images at 1.4 GHz, while OVRO provided spectral and spatial information over the range 1-15 GHz. We develop a new gyrosynchrotron model to analyze the sources observed at flare peak. This model differs from many previous ones in that it contains spatial variations of both the magnetic field and accelerated particle density. It uses a new gyrosynchrotron approximation which is valid at very low harmonics of the gyrofrequency. For the first time we find that the cause of the change of microwave source size with frequency in the event studied was due primarily to the spatial variation of the accelerated electron density. This is contrary to the common assumption that the variation in size is due to a nonuniform magnetic field. We also investigate a polarized source which brightened later in the flare, finding that it could have been due to plasma radiation or gyrosynchrotron emission.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 433; 2; p. 575-585
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 6
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    Two-frequency imaging of microwave impulsive flares near the solar limb (1986)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: VLA observations of two impulsive microwave and hard X-ray flares close to the solar limb on November 21 and 22, 1981 are presently interpreted in terms of an inhomogeneous flare volume, with the magnetic field strength and orientation varying with position both transverse to, and along, the line-of-sight. The 15 GHz radiation of the flares on both days may be due to electrons of E = 300 keV in weak nonthermal tail; the absence of 4.9 GHz radiation from these sources is attributed to absorption along the ray path from the flare to the earth, on the basis of the fact that thermal bremsstrahlung and gyrosynchrotron radiation mechanisms generate more low than high frequency radiation.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 300; 438-441
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 7
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    Variation of the quiet sun at 21 cm - 1981-1987 (1988)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The sun was imaged at a wavelength of about 21 cm during 1981-1987 using the VLA, the Green Bank 91-m telescope, the Arecibo 305 m telescope, and powerful maximum entropy image reconstruction techniques. There was a systematic decrease in the quiet sun's brightness temperature at 21 cm as the sun declined from sunspot maximum to sunspot minimum; this was accompanied by a systematic decrease in the sun's radius. The two-fold decrease in the electron number density in the solar transition region and low corona could have been the cause of these variations.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Sacramento Peak Summer Symposium on Solar and Stellar Coronal Structure and Dynamics; Aug 17, 1987 - Aug 21, 1987; Sunspot, NM; United States
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 8
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    Decimetric solar type U bursts - VLA and Phoenix observations (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-27
    Beschreibung: Observations of type U bursts, simultaneously detected by the VLA at 1.446 GHz and by the broadband spectrometer Phoenix in the 1.1-1.7 GHz frequency band on August 13, 1989 are reported. Extrapolations of the coronal magnetic field, assuming a potential configuration, indicate that the VLA 20 cm source demarcates an isodensity level. The source covers a wide angle of diverging magnetic field lines whose footpoints originate close to a magnetic intrusion of negative polarity into the main sunspot group of the active region with dominant positive polarity. The centroid of the 20-cm U-burst emission, which corresponds to the turnover frequency of the type U bursts and remains stationary during all U bursts, coincides with the apex of extrapolated potential field lines at a height of about 130,000 km. It is demonstrated that the combination of radio imaging and broadband dynamic spectra, combined with the magnetic field reconstruction from magnetograms, can constrain all physical parameters of a magnetic loop system.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 391; 1 Ma
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
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