Frequency shifts of resonant modes of the Sun due to near-surface convective scattering

J. Bhattacharya, Shravan Hanasoge, H. M. Antia

Research output: Contribution to journalArticle

Abstract

Measurements of oscillation frequencies of the Sun and stars can provide important independent constraints on their internal structure and dynamics. Seismic models of these oscillations are used to connect structure and rotation of the star to its resonant frequencies, which are then compared with observations, the goal being that of minimizing the difference between the two. Even in the case of the Sun, for which structure models are highly tuned, observed frequencies show systematic deviations from modeled frequencies, a phenomenon referred to as the surface term. The dominant source of this systematic effect is thought to be vigorous near-surface convection, which is not well accounted for in both stellar modeling and mode-oscillation physics. Here we bring to bear the method of homogenization, applicable in the asymptotic limit of large wavelengths (in comparison to the correlation scale of convection), to characterize the effect of small-scale surface convection on resonant-mode frequencies in the Sun. We show that the full oscillation equations, in the presence of temporally stationary 3D flows, can be reduced to an effective quiet-Sun wave equation with altered sound speed, Brünt-Väisäla frequency, and Lamb frequency. We derive the modified equation and relations for the appropriate averaging of 3D flows and thermal quantities to obtain the properties of this effective medium. Using flows obtained from 3D numerical simulations of near-surface convection, we quantify their effect on solar oscillation frequencies and find that they are shifted systematically and substantially. We argue therefore that consistent interpretations of resonant frequencies must include modifications to the wave equation that effectively capture the impact of vigorous hydrodynamic convection.

Original languageEnglish (US)
Pages (from-to)614-619
Number of pages6
JournalProceedings of the International Astronomical Union
Volume11
Issue numberA29B
DOIs
StatePublished - Jan 1 2015

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frequency shift
sun
convection
oscillation
scattering
wave equation
oscillations
wave equations
resonant frequencies
solar oscillations
stars
physics
hydrodynamics
homogenizing
bears
wavelength
deviation
modeling
simulation
effect

ASJC Scopus subject areas

  • Astronomy and Astrophysics

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Frequency shifts of resonant modes of the Sun due to near-surface convective scattering. / Bhattacharya, J.; Hanasoge, Shravan; Antia, H. M.

In: Proceedings of the International Astronomical Union, Vol. 11, No. A29B, 01.01.2015, p. 614-619.

Research output: Contribution to journalArticle

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