THE HANLE EFFECT OF THE HYDROGEN Lyα LINE FOR PROBING THE MAGNETISM OF THE SOLAR TRANSITION REGION

We present some theoretical predictions concerning the amplitude and magnetic sensitivity of the linear-polarization signals produced by scattering processes in the hydrogen Lyα line of the solar transition region. To this end, we have calculated the atomic-level polarization (population imbalances and quantum coherences) induced by anisotropic radiation pumping in semiempirical and hydrodynamical models of the solar atmosphere, taking into account radiative transfer and the Hanle effect caused by the presence of organized and random magnetic fields. The line-center amplitudes of the emergent linear-polarization signals are found to vary typically between 0.1% and 1%, depending on the scattering geometry and the strength and orientation of the magnetic field. The results shown here encourage the development of UV polarimeters for sounding rockets and space telescopes with the aim of opening up a diagnostic window for magnetic field measurements in the upper chromosphere and transition region of the Sun.

[1]  E. Landi Degl'Innocenti,et al.  ON THE SENSITIVITY OF PARTIAL REDISTRIBUTION SCATTERING POLARIZATION PROFILES TO VARIOUS ATMOSPHERIC PARAMETERS , 2010, 1008.2585.

[2]  M. Sigwarth.  Advanced Solar Polarimetry—Theory, Observation, and Instrumentation: The 20th NSO/Sacramento Peak Summer Workshop , 2001 .

[3]  Jiri Stepan,et al.  SCATTERING POLARIZATION OF HYDROGEN LINES IN WEAKLY MAGNETIZED STELLAR ATMOSPHERES. I. FORMULATION AND APPLICATION TO ISOTHERMAL MODELS , 2011, 1102.4012.

[4]  D. Roussel-Dupre,et al.  Skylab observations of H I Lyman-alpha , 1982 .

[5]  Harry P. Warren,et al.  High-Resolution Observations of the Solar Hydrogen Lyman Lines in the Quiet Sun with the SUMER Instrument on SOHO , 1998 .

[6]  B. Battrick,et al.  39TH ESLAB Symposium on Trends in Space Science and Cosmic Vision 2020 , 2005 .

[7]  Roberto Casini,et al.  Solar Polarization 4 , 2006 .

[8]  S. Sahal-Bréchot,et al.  The Hanle effect of the coronal Lα line of hydrogen: Theoretical investigation , 1982 .

[9]  Juan M. Fontenla,et al.  Energy balance in the solar transition region. III - Helium emission in hydrostatic, constant-abundance models with diffusion , 1993 .

[10]  R. M. Sainz,et al.  Iterative Methods for the Non-LTE Transfer of Polarized Radiation: Resonance Line Polarization in One-dimensional Atmospheres , 1999 .

[11]  I. Nestoras,et al.  The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations , 2009, 0912.2272.

[12]  E. Landi Degl'Innocenti,et al.  Polarization in spectral lines , 2004 .

[13]  Jiri Stepan,et al.  ON THE PROBABLE EXISTENCE OF AN ABRUPT MAGNETIZATION IN THE UPPER CHROMOSPHERE OF THE QUIET SUN , 2010, 1002.1574.

[14]  M. Carlsson,et al.  Formation of Solar Calcium H and K Bright Grains , 1997 .

[15]  D. Dravins,et al.  Search for spectral line polarization in the solar vacuum ultraviolet , 1980 .

[16]  R Manso Sainz,et al.  Zero-field dichroism in the solar chromosphere. , 2003, Physical review letters.