TY - JOUR

T1 - Analysis of unresolved photospheric magnetic field structure using Fe I 6301 and 6302 lines

AU - Gordovskyy, Mykola

AU - Shelyag, S

AU - Browning, Philippa

AU - Lozitsky, V.G.

N1 - Funding Information:
Acknowledgements. MG and PKB are funded by Science and Technology Facilities Council (UK), grant ST/P000428/1. Simulations have been performed using the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility.
Publisher Copyright:
© ESO 2018.

PY - 2018

Y1 - 2018

N2 - Early magnetographic observations indicated that magnetic field in the solar photosphere has unresolved small-scale structure. Near-infrared and optical data with extremely high spatial resolution show that these structures have scales of few tens of kilometres, which are not resolved in the majority of solar observations. The goal of this study is to establish the effect of unresolved photospheric magnetic field structure on Stokes profiles observed with relatively low spatial resolution. Ultimately, we aim to develop methods for fast estimation of the photospheric magnetic filling factor and line-of-sight gradient of the photospheric magnetic field, which can be applied to large observational data sets. We exploit 3D MHD models of magneto-convection developed using MURAM code. Corresponding profiles of Fe I 6301.5 and 6302.5 $\mathrm{\AA}$ spectral lines are calculated using NICOLE radiative transfer code. The resulting I and V Stokes [x,y,$\lambda$] cubes with reduced spatial resolution of 150 km are used to calculate magnetic field values as they would be obtained in observations with Hinode/SOT or SDO/HMI. Three different methods of the magnetic filling factor estimation are considered: the magnetic line ratio method, Stokes V width method and a simple statistical method. We find that the statistical method and the Stokes V width method are sufficiently reliable for fast filling factor estimations. Furthermore, we find that Stokes $I\pm V$ bisector splitting gradient can be used for fast estimation of line-of-sight gradient of the photospheric magnetic field.

AB - Early magnetographic observations indicated that magnetic field in the solar photosphere has unresolved small-scale structure. Near-infrared and optical data with extremely high spatial resolution show that these structures have scales of few tens of kilometres, which are not resolved in the majority of solar observations. The goal of this study is to establish the effect of unresolved photospheric magnetic field structure on Stokes profiles observed with relatively low spatial resolution. Ultimately, we aim to develop methods for fast estimation of the photospheric magnetic filling factor and line-of-sight gradient of the photospheric magnetic field, which can be applied to large observational data sets. We exploit 3D MHD models of magneto-convection developed using MURAM code. Corresponding profiles of Fe I 6301.5 and 6302.5 $\mathrm{\AA}$ spectral lines are calculated using NICOLE radiative transfer code. The resulting I and V Stokes [x,y,$\lambda$] cubes with reduced spatial resolution of 150 km are used to calculate magnetic field values as they would be obtained in observations with Hinode/SOT or SDO/HMI. Three different methods of the magnetic filling factor estimation are considered: the magnetic line ratio method, Stokes V width method and a simple statistical method. We find that the statistical method and the Stokes V width method are sufficiently reliable for fast filling factor estimations. Furthermore, we find that Stokes $I\pm V$ bisector splitting gradient can be used for fast estimation of line-of-sight gradient of the photospheric magnetic field.

KW - Sun: magnetic fields

KW - Sun: photosphere

KW - Techniques: imaging spectroscopy

UR - http://www.scopus.com/inward/record.url?scp=85057344601&partnerID=8YFLogxK

UR - http://arxiv.org/abs/1808.06862
http://dx.doi.org/10.1051/0004-6361/201833421

UR - http://www.mendeley.com/research/analysis-unresolved-photospheric-magnetic-field-structure-using-fe-i-6301-6302-lines

U2 - 10.1051/0004-6361/201833421

DO - 10.1051/0004-6361/201833421

M3 - Article

SN - 0004-6361

VL - 619

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A164

ER -