High resolution interferometry of the Sun at 3.7 cm wavelength
β Scribed by Kenneth R. Lang
- Publisher
- Springer
- Year
- 1974
- Tongue
- English
- Weight
- 931 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0038-0938
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β¦ Synopsis
lnterferometric observations of the Sun at a wavelength 2 -3.7 cm and an effective angular resolution of 0=7 or 15" are presented. When active regions are observed, circularly polarized radiation is found with an angular size of 0 ~ 15", an effective temperature of T~. 5 β’ 105K, and 20 to 303/o circular polarization. This S-component of solar radio radiation is interpreted in terms of the theory of gyroradiation and gyroresonant absorption. Prior to the onset of a solar flare, an additional S-component is observed with an angular size of 0 < 7", an effective temperature of T_> 106 K, and 90 β’ 10 % circular polarization. A small scale, quasi-periodic component of solar radio radiation is also observed to be coming from all over the solar disk; and this component is found to be less than 10% circularly polarized. The angular sizes, O, and periods, P, of this component lie in the ranges 7" < 0 % 37" and 180 s 5~ P< 750 s. The observed modulation in flux density, AS. lies in the range 20 f.u. <~ AS< 200 f.u. (1 f.u. = 10 -26 Wm -2 Hz -1 or 10 -23 erg s -~ cm -2 Hz -1) and the brightness temperature fluctuations, AT, lie in the range 103K < AT<~ 105K. This component of solar radio radiation is thought to be the free-free radiation (bremsstrahlung) of temperature fluctuations associated with velocity oscillations in the chromosphere-corona transition region. High resolution observations of impulsive microwave bursts show that some of the radiation is linearly or circularly polarized, has an angular size 0_<7", and a peak brightness temperature of T> 3 β’ 106K. This component of solar radio flares is interpreted in terms of the theory of gyro-synchrotron radiation, and the density of accelerated electrons is found to be greater than 100 cm -3. The size of the emitting region is, however, comparable to that of the feet of magnetic dipoles rather than the region between them. Phase shifts in the interferometer pattern observed during an impulsive burst are interpreted in terms of hydrodynamic waves travelling at a velocity of 7000 km s 1, but further observations are needed to confirm the result.
π SIMILAR VOLUMES
The two-element interferometer at Hat Creek Observatory was used at 1.3 cm wavelength to study the fine structure of the radio emissive regions on the Sun. Observations of the quiet Sun at 1.3 cm show sudden changes in the fringe amplitude and phase, lasting for typically about 5-8 min. Assuming tha
High resolution observations of the Sun at 3.3 ram, 3.5 ram, 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 typ