Microwave, ultraviolet, and soft X-ray observations of Hale region 16898

• Published in: Solar physics 1983-12, Vol.89 (2), p.307-321
• Main Authors: SHIBASAKI, K, CHIUDERI-DRAGO, F, MELOZZI, M, SLOTTJE, C, ANTONUCCI, E
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Other topics on the solar system; Solar system
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/BF00217253

Hale region 16898 was observed by the Westerbork synthesis radio telescope at 6 cm and by the UV spectrometer and polarimeter and the X-ray spectrometer on the Solar Maximum Mission satellite. Optical pictures of the same active region were taken at Sacramento Peak, Big Bear, and Meudon observatories. The radio emission mechanisms are identified by comparing radio data with UV and soft X-ray data. The height of the radio sources and the magnetic field strength at that height are deduced. A radio source above a large sun spot shows a crescent-shaped depression of circular polarization and a high brightness temperature. The emission mechanism is identified as gyroresonance at the second and the third harmonic layers, and it is found that the second harmonic layer, where the magnetic field strength is 900 G, must be in the corona. An extended looplike source connecting the leading and the following part of the active region and the sources associated with small spots are due mainly to thermal free-free emission by hot and dense plasma that is also observed in UV and soft X-ray radiation. The calculated radio brightness temperature, using the physical parameters deduced from the UV and soft X-ray line intensities, agrees with the observed brightness temperature. The height of the low brightness temperature sources above the small spots is 6000 plus or minus 3000 km, and that above the large spot is