Volume 630, October 2019
|Number of page(s)||11|
|Published online||04 October 2019|
Using the infrared iron lines to probe solar subsurface convection
Max Planck Institute for Solar System Research, Justus-von-Liebig Weg 3, 37077 Göttingen, Germany
2 Department of Physics, University of Colorado, Boulder, CO 80309, USA
3 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
4 National Solar Observatory, Boulder, CO 80303, USA
Accepted: 9 April 2019
Context. Studying the properties of solar convection using high-resolution spectropolarimetry began in the early 1990s with the focus on observations in the visible wavelength regions. Its extension to the infrared (IR) remains largely unexplored.
Aims. The IR iron lines around 15 600 Å, most commonly known for their high magnetic sensitivity, also have a non-zero response to line-of-sight (LOS) velocity below log(τ) = 0.0. In this paper we explore the possibility of using these lines to measure subsurface convective velocities.
Methods. By assuming a snapshot of a three-dimensional magnetohydrodynamic simulation to represent the quiet Sun, we investigate how well the iron IR lines can reproduce the LOS velocity in the cube and to what depth. We use the recently developed spectropolarimetric inversion code SNAPI and discuss the optimal node placements for the retrieval of reliable results from these spectral lines.
Results. We find that the IR iron lines can measure the convective velocities down to log(τ) = 0.5, below the photosphere, not only at the original resolution of the cube, but also when degraded with a reasonable spectral and spatial PSF and stray light. Instead, the commonly used Fe I 6300 Å line pair performs significantly worse.
Conclusions. Our investigation reveals that the IR iron lines can probe the subsurface convection in the solar photosphere. This paper is a first step towards exploiting this diagnostic potential.
Key words: methods: data analysis / line: profiles / Sun: infrared
© I. Milić et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open Access funding provided by Max Planck Society.
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