Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986a%26a...163..340u&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 163, no. 1-2, July 1986, p. 340-342.
Astronomy and Astrophysics
Astrophysics
10
Millimeter Waves, Solar Flares, Solar Radio Emission, Bremsstrahlung, Optical Thickness, Solar Limb
Scientific paper
Solar maps at millimeter waves reveal the existence of rare sporadic off-limb sources with source heights significantly different from those of the S-component. A sample of 25 observations was extracted from more than 1500 solar maps of the Metsahovi/Finland and Hiraiso/Japan stations of the years 1979-1983 at 37, 32, and 22 GHz which display source heights ranging between 50,000 and 120,000 km above the photosphere and brightness temperatures of the order of 10,000 K. These off-limb sources appear to be related to preexisting flare events. However, similar to the long duration events in soft X-rays (LDEs), the mm-sources last essentially longer than the main phase of impulse and complex radio bursts. It is concluded that the mm-sources represent optically thick Coulomb bremsstrahlung from a cool dense plasma which is also seen in H-alpha-loops. The radiation is expected to be mixed with a substantially smaller part of optically thin mm-radiation originating in the overlying hot thin plasma which is observed in LDEs. A possible connection with coronal mass ejections needs further investigation.
Hildebrandt Joachim
Krueger Andre
Urpo Seppo
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