Impact Polarization of the Hα Line during Solar Flares

  • E. Vogt
  • J.-C. Hénoux
  • S. Sahal-Bréchot
Part of the Astrophysics and Space Science Library book series (ASSL, volume 243)


The chromospheric Hα line of hydrogen shows linear polarization in solar flares. This phenomenon was discovered at Meudon Observatory with a monochromatic polarimeter. The observed polarization is interpreted as impact polarization, resulting from the excitation of hydrogen by directed beams of protons with an energy of a few hundreds keV at their origin in the corona.

To support this interpretation, it has been necessary to evaluate the role and the importance of collisions between hydrogen atoms and thermal background particles — electrons and protons — as these collisions lead to population exchange between the sublevels of the hydrogen atom that may reduce significantly the resulting polarization. Therefore, we have computed the statistical equilibrium of the hydrogen atom taking into account all the different excitation and deexcitation processes.

A more sophisticated analysis of existing observations has also been performed in order to clearly separate the solar polarization signal from the artifacts caused by atmospheric turbulence and to get a better evaluation of the degree of polarization. We have done this extended data processing on two flares observed at Meudon Observatory on July 17, 1982 and June 20, 1989.

Also, a more powerful polarimeter has been developped, using a CCD camera, to provide better data during the next maximum of solar activity. This instrument is briefly described.

Key words

Impact Polarization Solar Flares Polarimeters 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Balança, C.: 1997, Ph.D. thesis, Paris XI UniversityGoogle Scholar
  2. Balança, C. and Feautrier, N.: 1998, Astron. Astrophys., 334, 1136ADSGoogle Scholar
  3. Balança, C. and Feautrier, N.: 1999, in K.N. Nagendra, J.O. Stenflo (eds.), Solar Polarization, Proc. 2nd SPW, Kluwer, Dordrecht, (in this Volume)Google Scholar
  4. Emslie, A.G., Miller, J., Vogt, E. and Hénoux, J.-C.: 1999, Astrophys. J., (in preparation)Google Scholar
  5. Firstova, N., Hénoux, J.-C., Kazantsev, S. and Bulatov, A.: 1997, Solar Physics 171, 123ADSCrossRefGoogle Scholar
  6. Hénoux, J.-C.: 1991, in L. November (ed.), Solar Polarimetry, 11th NSO/Sac Peak workshopGoogle Scholar
  7. Hénoux, J.-C. and Chambe, G.: 1990, J. Quant. Spectrosc. Radiat. Transfer 44, 193ADSCrossRefGoogle Scholar
  8. Hénoux, J.-C. and Karlicky, M.: 1999, Astron. Astrophys., (in press)Google Scholar
  9. Hénoux, J.-C. and Semel, M.: 1981, in V. Obridko and E. Ivanov (eds.), Proceedings of the Crimea Solar Maximum Year Workshop, pp 207–210Google Scholar
  10. Hénoux, J.-C., Chambe, G., Semel, M., Sahal, S., Woodgate, B., Shine, D., Beckers, J. and Machado, M.: 1983a, Astrophys. J. 265, 1066ADSCrossRefGoogle Scholar
  11. Hénoux, J.-C., Heristchi, D., Chambe, G., Machado, M., Woodgate, B., Shine, R. and Beckers, J.: 1983b, Astron. Astrophys. 119, 233ADSzbMATHGoogle Scholar
  12. Hénoux, J.-C., Chambe, G., Smith, D., Tamres, D., Feautrier, N., Rovira, M. and SahalBréchot, S.: 1990, Astrophys. J.S 73, 303ADSCrossRefGoogle Scholar
  13. Machado, M., Avrett, E., Vernazza, J. and Noyes, R.: 1980, Astrophys. J. 242, 336ADSCrossRefGoogle Scholar
  14. Vernazza, J., Avrett, E. and Loeser, R.: 1981, Astrophys. J. Suppl. Ser. 45, 635ADSCrossRefGoogle Scholar
  15. Vogt, E.: 1997, Ph.D. thesis, Paris VII UniversityGoogle Scholar
  16. Vogt, E. and Hénoux, J.-C.: 1996, in J.O. Stenflo, K.N. Nagendra (eds.), Solar Polarization, Proc. 1st SPW, Kluwer, Dordrecht, p. 345 (also Solar Phys. 164, 345)Google Scholar
  17. Vogt, E. and Hénoux, J.-C.: 1999, Astron. Astrophys., (submitted)Google Scholar
  18. Vogt, E., Sahal-Bréchot, S. and Hénoux, J.-C.: 1997, Astron. Astrophys. 324, 1211ADSGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 1999

Authors and Affiliations

  • E. Vogt
    • 1
  • J.-C. Hénoux
    • 1
  • S. Sahal-Bréchot
    • 2
  1. 1.DASOP CNRS URA 2080Observatoire de Paris-MeudonMeudon CedexFrance
  2. 2.DAMAp CNRS URA 812Observatoire de Paris-MeudonMeudon CedexFrance

Personalised recommendations