Radiative transfer effects on Doppler measurements as sources of surface effects in sunspot seismology

Abstract

We show that the use of Doppler shifts of Zeeman sensitive spectral lines to observe wavesn in sunspots is subject to measurement specific phase shifts arising from, (i) altered height range of spectral line formation and the propagating character of p mode waves in penumbrae, and (ii) Zeeman broadening and splitting. We also show that these phase shifts depend on wave frequencies, strengths and line of sight inclination of magnetic field, and the polarization state used for Doppler measurements. We discuss how these phase shifts could contribute to local helioseismic measurements of 'surface effects' in sunspot seismology.

12 pages, 4 figures, Accepted for publication in the Astrophysical Journal Letters

References in corpus (2)

• Spectral Line Selection for HMI: A Comparison of Fe I 6173 and Ni I 6768
• Surface Magnetism Effects in Time-Distance Helioseismology

Cited by in corpus (10)

• Surface-focused Seismic Holography of Sunspots: I. Observations
• Physical Properties of Wave Motion in Inclined Magnetic Fields Within Sunspot Penumbrae
• Flows around Averaged Solar Active Regions
• Local helioseismic and spectroscopic analyses of interactions between acoustic waves and a sunspot
• Enhanced p-Mode Absorption seen near the Sunspot Umbral-Penumbral Boundary
• Understanding the Fe I Line Measurements Returned by the Helioseismic and Magnetic Imager
• Statistical analysis of acoustic wave parameters near active regions
• Non-zero phase-shifts of acoustic waves in the lower solar atmosphere measured from realistic simulations and their role in local helioseismology
• Deep-Focus Diagnostics of Sunspot Structure
• Seeing-Induced Errors in Solar Doppler Velocity Measurements