Solar Physics

, Volume 227, Issue 2, pp 265–281 | Cite as

Diffuse Component Spectra of Solar Active Regions at Submillimeter Wavelengths

  • Adriana V. R. Silva
  • Tatiana F. Laganá
  • C. Guillermo Gimenez De Castro
  • Pierre Kaufmann
  • Joaquim E. R. Costa
  • Hugo Levato
  • Marta Rovira


Solar maps at 212 and 405 GHz obtained by the Solar Submillimetric Telescope (SST) show regions of enhanced brightness temperature, which coincide with the location of active regions. A statistical study of the radio emission from these active regions was performed for the first time at such high frequencies during 23 days on June and July 2002, when the atmospheric opacity was low. The brightest regions on the maps were chosen for this study, where the brightness excess observed varies from 3 to 20% above quiet Sun levels (i.e., 200–1000 K) at both wavelengths. Sizes of the regions of enhanced emission calculated at half the maximum value were estimated to be between 2′ and 7′. These sizes agree with observed sizes of active regions at other wavelengths such as Hα and ultraviolet. An important result is that the flux density spectra of all sources increase toward submillimeter frequencies, yielding flux density spectral index with an average value of 2.0. The flux density of the active region sources were complemented with that from maps at 17 and 34 GHz from the Nobeyama Radio Heliograph. The resulting spectra at all four frequencies were fit considering the flux density to be due to thermal bremsstrahlung from the active region. In the calculations, the source radius was assumed to be the mean of the measured values at 212 and 405 K. The effective temperatures of the radio emitting source, assumed homogeneous, obtained from this fit were 0.6–2.9 × 104 K, for source diameters of 2′–7′.


Active Region Flux Density Brightness Temperature Radio Emission Solar Active Region 
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Copyright information

© Springer Science + Business Media, Inc. 2005

Authors and Affiliations

  • Adriana V. R. Silva
    • 1
  • Tatiana F. Laganá
    • 1
    • 2
  • C. Guillermo Gimenez De Castro
    • 1
  • Pierre Kaufmann
    • 1
    • 3
  • Joaquim E. R. Costa
    • 1
    • 4
  • Hugo Levato
    • 5
  • Marta Rovira
    • 6
  1. 1.CRAAMUniversidade Presbiteriana MackenzieSão PauloBrazil
  2. 2.Instituto de FísicaUniversidade de São PauloSão PauloBrazil
  3. 3.CCSUNICAMPCampinas, São PauloBrazil
  4. 4.Instituto Nacional de Pesquisas EspaciasINPESão José dos CamposBrazil
  5. 5.Complejo Astronómico El LeoncitoSan JuanArgentina
  6. 6.Instituto de Astronomia y Física del EspacioBuenos AiresArgentina

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