Abstract
The broad-band circular polarization of sunspots is discussed on the basis of the observations made in the Okayama Astrophysical Observatory. The observation with the spectrograph proves that it is the integrated polarization of spectral lines in the observed spectral range. A velocity gradient in the line-of-sight can produce this integrated polarization due to the differential saturation between Zeeman components of magnetically sensitive lines. The observed degree of polarization and its spatial distribution in sunspots is explained when we introduce a differentially twisted magnetic field in addition to the velocity gradient. The differential twist has the azimuth rotation of the magnetic field along the line-of-sight and generates the circular polarization from the linear polarization due to the magneto-optical effect. The required azimuth rotation is reasonable and amounts at most to 30°. The required velocity gradient is compatible with the line asymmetry and its spatial distribution observed in sunspots. The observed polarity rule leads to the conclusion that the sunspot magnetic field has the differential twist with the right-handed azimuth rotation relative to the direction of the main magnetic field, without regard to the magnetic polarity and to the solar cycle. The twist itself is left-handed under the photosphere, when the sunspot is assumed to be a unwinding emerging magnetic field.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Adjabshirzadeh, A. and Koutchmy, S.: 1980, Astron. Astrophys. 89, 88.
Auer, L. H. and Heasley, J. N.: 1978, Astron. Astrophys. 64, 67.
Beckers, J. M.: 1968, Solar Phys. 5, 15.
Backers, J. M.: 1969a, Solar Phys. 9, 372.
Beckers, J. M.: 1969b, A Table of Zeeman Multiplets, Physical Sciences Research Papers No. 371, Air Force Cambridge Research Laboratories.
Henson, G. D. and Kemp, J. C.: 1984, Solar Phys. 93, 289.
Illing, R. M. E., Landman, D. A., and Mickey, D. L.: 1974a, Astron. Astrophys. 35, 327.
Illing, R. M. E., Landman, D. A., and Mickey, D. L.: 1974b, Astron. Astrophys. 37, 97.
Illing, R. M. E., Landman, D. A., and Mickey, D. L.: 1975, Astron. Astrophys. 41, 183.
Kawakami, H.: 1983, Publ. Astron. Soc. Japan 35, 459.
Kemp, J. C.: 1981, Smithsonian Astrophys. Obs. Special Rep. No. 392, 1, 191.
Kemp, J. C. and Henson, G. D.: 1983, Astrophys. J. 266, L69.
Kuveler, G. and Wiehr, E.: 1985, Astron. Astrophys. 142, 205.
Landman, D. A. and Finn, G. D.: 1979, Solar Phys. 63, 221.
Leroy, J. L.: 1962, Ann. Astrophys. 25, 127.
Makita, M.: 1981, in F. Moriyama and J.-C. Henoux (eds.), Proc. Japan-France Seminar on Solar Physics, p. 99.
Makita, M.: 1986, Solar Phys. 103, 1.
Makita, M. and Kawakami, H.: 1986, Publ. Astron. Soc. Japan 38, 257.
Makita, M. and Ohki, Y.: 1986, Ann. Tokyo Astron. Obs. 21, 1.
Makita, M., Hamana, S., Kawakami, H., and Nishi, K.: 1982, Ann. Tokyo Astron. Obs. 19, 24.
Makita, M., Hamana, S., and Nishi, K.: 1985a, in M. J. Hagyard (ed.), Measurements of Solar Vector Magnetic Fields, NASA CP-2374, p. 173.
Makita, M., Hamana, S., Nishi, K., Shimizu, M., Koyano, H., Sakurai, T., and Komatsu, H.: 1985b, Publ. Astron. Soc. Japan 37, 561.
Martres, M. J., Soru-Escaut, I., and Rayrole, J.: 1973, Solar Phys. 32, 365.
Moore, Ch. E., Minnaert, M. G. J., and Houtgast, J.: 1966, The Solar Spectrum 2935 to 8770 Å, NBS Monograph 61, US Government Printing Office, Washington D.C., U.S.A.
Rachkovsky, D. N.: 1962, Izv. Krymsk. Astrofiz. Obs. 27, 148.
Severny, A. B.: 1964, Izv. Krymsk. Astrofiz. Obs. 31, 126.
West, E. A. and Hagyard, M. J.: 1983, Solar Phys. 88, 51.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Makita, M. An interpretation of the broad-band circular polarization of sunspots. Sol Phys 106, 269–286 (1986). https://doi.org/10.1007/BF00158497
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00158497