Abstract
Various observations indicate that coronal holes generally appear as low brightness temperature regions (LTRs) in the centimeter and millimeter wavelength ranges. However, within their borders local enhancements of radiation, that is, high brightness temperature regions (HTRs), often occur. The theory behind the described behavior is not fully understood and therefore we analyze full-disk solar images obtained at a wavelength of 8 mm at Metsähovi Radio Observatory and compare them with data simultaneously taken in other wavelength ranges. The observational finding that the average brightness temperature of coronal holes is not much different from the quiet-Sun level (with localized deviations toward higher and lower intensities on the order of a few percent) is compared with theoretical models of the thermal bremsstrahlung radiation originating in the solar chromosphere, transition region, and corona. Special attention is devoted to the interpretation of the localized enhancements of radiation observed inside coronal holes at millimeter wavelengths. The main conclusion is that the most important contribution to the brightness temperature comes from an increased density in the transition region and low corona (i.e., at the heights where the temperature is below 106 K). This can explain both the LTRs and HTRs associated with coronal holes.
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Aschwanden, M.: 2004, Physics of the Solar Corona, Springer, Berlin; Praxis, Chichester.
Avrett, E.: 2000, In: Cox, A.N. (ed.) Allen’s Astrophysical Quantities, AIP Press, Springer, New York, 348.
Bastian, T.S., Dulk, G.A., Leblanc, Y.: 1996, Astrophys. J. 473, 539.
Benz, A.O.: 2002, Plasma Astrophysics, 2nd edn., Kluwer Academic, Dordrecht.
Benz, A.O., Krucker, S., Acton, L.W., Bastian, T.S.: 1997, Astron. Astrophys. 320, 993.
Borovik, V.N., Kurbanov, M.S.: 1990, Astron. Nachr. 311, 371.
Brajša, R.: 1993, Solar Phys. 144, 199.
Brajša, R., Ruždjak, V., Vršnak, B., Pohjolainen, S., Urpo, S., Wöhl, H.: 1994, Hvar Obs. Bull. 18, 9.
Brajša, R., Pohjolainen, S., Ruždjak, V., Sakurai, T., Urpo, S., Vršnak, B., Wöhl, H.: 1996, Solar Phys. 163, 79.
Brajša, R., Jurdana-Šepić, R., Šaina, B., Wöhl, H.: 2007a, Solar Phys. submitted
Brajša, R., Benz, A.O., Temmer, M., Jurdana-Šepić, R., Šaina, B., Wöhl, H., Ruždjak, V.: 2007b, Proc. VIIIth Hvar Astrophys. Colloq. Cent. Eur. Astrophys. Bull. 31, 219.
Chiuderi, C., Chiuderi Drago, F.: 2004, Astron. Astrophys. 422, 331.
Doschek, G.A., Warren, H.P., Laming, J.M., Mariska, J.T., Wilhelm, K., Lamaire, P., Schühle, U., Moran, T.G.: 1997, Astrophys. J. 482, L109.
Fontenla, J.M., Avrett, E.H., Loeser, R.: 1993, Astrophys. J. 406, 319.
Fürst, E., Hirth, W.: 1975, Solar Phys. 42, 157.
Gabriel, A.H.: 1992, In: Schmelz, J.T., Brown, J.C. (eds.) The Sun: A Laboratory for Astrophysics, NATO ASI Ser. 373, Kluwer Academic, Dordrecht, 277.
Gallagher, P.T., Mathioudakis, M., Keenan, F.P., Phillips, K.J.H., Tsinganos, K.: 1999, Astrophys. J. 524, L133.
Golub, L., Pasachoff, J.M.: 1997, The Solar Corona, Cambridge University Press, Cambridge.
Gopalswamy, N., Shibasaki, K., Thompson, B.J., Gurman, J., DeForest, C.: 1999, J. Geophys. Res. 104, 9767.
Habbal, S.R., Gonzalez, R.D.: 1991, Astrophys. J. 376, L25.
Hara, H., Tsuneta, S., Acton, L.W., Bruner, M.E., Lemen, J.R., Ogawara, Y.: 1994, Publ. Astron. Soc. Japan 46, 493.
Hirth, W., Fürst, E.: 1976, Mitt. Astron. Ges. 38, 208.
Hurford, G.J.: 1992, In: Schmelz, J.T., Brown, J.C. (eds.) The Sun: A Laboratory for Astrophysics, NATO ASI Ser. 373, Kluwer Academic, Dordrecht, 297.
Kosugi, T., Ishiguro, M., Shibasaki, K.: 1986, Publ. Astron. Soc. Japan 38, 1.
Koutchmy, S.: 2000, In: Cox, A.N. (ed.) Allen’s Astrophysical Quantities, AIP Press, Springer, New York, 357.
Kundu, M.R., Liu, S.-Y.: 1976, Solar Phys. 49, 267.
Lang, K.R.: 2000, The Sun from Space, Springer, Berlin.
Marqué, Ch., Lantos, P., Delaboudiniere, J.P.: 2002, Astron. Astrophys. 387, 317.
Moran, T., Gopalswamy, N., Dammasch, I.E., Wilhelm, K.: 2001, Astron. Astrophys. 378, 1037.
Pohjolainen, S.: 2000, Astron. Astrophys. 361, 349.
Pohjolainen, S., Portier-Fozzani, F., Ragaigne, D.: 2000, Astron. Astrophys. Suppl. Ser. 143, 227.
Riehokainen, A., Urpo, S., Valtaoja, E.: 1998, Astron. Astrophys. 333, 741.
Rohlfs, K., Wilson, T.L.: 2004, Tools of Radio Astronomy, Springer, Berlin.
Schleicher, H.: 1976, Ph.D. thesis, University of Göttingen, 208.
Selhorst, C.L., Silva, A.V.R., Costa, J.E.R.: 2005, Astron. Astrophys. 440, 367.
Stix, M.: 1989, The Sun, Springer, Berlin.
Urpo, S., Pohjolainen, S., Teräsranta, H.: 1994, Solar Observations at Metsähovi in 1993, Helsinki University of Technology, Metsähovi Radio Research Station, Series A, Report 16.
Vocks, C., Mann, G.: 2003, Astrophys. J. 593, 1134.
Vršnak, B., Pohjolainen, S., Urpo, S., Teräsranta, H., Brajša, R., Ruždjak, V., Mouradian, Z., Jurač, S.: 1992, Solar Phys. 137, 67.
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Brajša, R., Benz, A.O., Temmer, M. et al. An Interpretation of the Coronal Holes’ Visibility in the Millimeter Wavelength Range. Sol Phys 245, 167–176 (2007). https://doi.org/10.1007/s11207-007-9008-4
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DOI: https://doi.org/10.1007/s11207-007-9008-4