Contributed Talk - Splinter HiRes

Wednesday, 20 September 2017, 17:00   (Auditorium MPS)

The potential of many-line inversions of photospheric spectropolarimetric data in the visible and near UV

T. L. Riethmüller
Max-Planck-Institut für Sonnensystemforschung (MPS), Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany

Our knowledge of the lower solar atmosphere is mainly obtained from spectropolarimetric observations, which are often carried out in the red or infrared spectral range and almost always cover only a single or a few spectral lines. In preparation for the development of a slit spectropolarimeter for the third science flight of the balloon-borne observatory \textscSunrise we investigate the feasibility of spectropolarimetry in the short-wavelength range, 3000 \rm\AA - 4300 \rm\AA, where the line density but also the photon noise are considerably higher than in the red. For an ensemble of state-of-the-art magneto-hydrodynamical atmospheres we synthesize exemplarily spectral regions around 3140 \AA (containing 352 lines), around 4080 \AA (265 lines), and, for comparison reasons, around 6302 \AA (80 lines). The spectral coverage is chosen such that at a spectral resolving power of 150000 the spectra can be recorded by a 2K detector. The synthetic Stokes profiles are degraded with a typical photon noise and afterwards inverted. The atmospheric parameters of the inversion are compared with the original MHD quantities. We find that from many-line inversions significantly more information can be obtained than from the traditional approach at identical wavelengths. A comparison of the three considered wavelength regions shows that the many-line approach at 4080 \AA provides equally good results than at 6302 \AA, the determination of the line-of-sight (LOS) velocity is even more precise by a factor of two. Compared with the red, the many-line approach at 3140 \AA provides indeed larger uncertainties for the magnetic field strength, but similarly good temperatures, and LOS velocities that are more precise by roughly a factor of two. We conclude from our results that many-line spectropolarimetry at short wavelengths offers high potential in solar physics.