Bibcode
Felipe, T.; Braun, D. C.; Crouch, A. D.; Birch, A. C.
Referencia bibliográfica
The Astrophysical Journal, Volume 829, Issue 2, article id. 67, 10 pp. (2016).
Fecha de publicación:
10
2016
Revista
Número de citas
12
Número de citas referidas
12
Descripción
Wave propagation through sunspots involves conversion between waves of
acoustic and magnetic character. In addition, the thermal structure of
sunspots is very different than that of the quiet Sun. As a consequence,
the interpretation of local helioseismic measurements of sunspots has
long been a challenge. With the aim of understanding these measurements,
we carry out numerical simulations of wave propagation through sunspots.
Helioseismic holography measurements made from the resulting simulated
wavefields show qualitative agreement with observations of real
sunspots. We use additional numerical experiments to determine,
separately, the influence of the thermal structure of the sunspot and
the direct effect of the sunspot magnetic field. We use the ray
approximation to show that the travel-time shifts in the thermal
(non-magnetic) sunspot model are primarily produced by changes in the
wave path due to the Wilson depression rather than variations in the
wave speed. This shows that inversions for the subsurface structure of
sunspots must account for local changes in the density. In some ranges
of horizontal phase speed and frequency there is agreement (within the
noise level in the simulations) between the travel times measured in the
full magnetic sunspot model and the thermal model. If this conclusion
proves to be robust for a wide range of models, it would suggest a path
toward inversions for sunspot structure.