Probing sunspots with two-skip time–distance helioseismology

¹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
e-mail: duvall@mps.mpg.de
² School of Mathematical Sciences and Monash Centre for Astrophysics, Monash University, Clayton, Victoria 3800, Australia
³ Institute für Astrophysik, Georg-August-Universtät Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

Received: 6 December 2017
Accepted: 26 January 2018

Abstract

Context. Previous helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure.

Aims. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated.

Methods. We study waves reflected almost vertically from the underside of a sunspot. Time–distance helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison.

Results. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed.

Conclusions. With sufficient modeling effort, these should lead to better understanding of sunspot structure.