Asteroseismic measurement of surface-to-core rotation in a main-sequence star

Donald W Kurtz,Simon J Murphy,Takashi Sekii,Hiromoto Shibahashi,Hideyuki Saio,Masao Takata,R.A García,J Ballot

doi:10.1051/epjconf/201510101007

Abstract

We have discovered rotationally split core g-mode triplets and surface p-mode triplets and quintuplets in a terminal age main-sequence A star, KIC 11145123, that shows both δ Sct p-mode pulsations and γ Dor g-mode pulsations. This gives the first robust determination of the rotation of the deep core and surface of a main-sequence star, essentially model-independently. We find its rotation to be nearly uniform with a period near 100 d, but we show with high confidence that the surface rotates slightly faster than the core. A strong angular momentum transfer mechanism must be operating to produce the nearly rigid rotation, and a mechanism other than viscosity must be operating to produce a more rapidly rotating surface than core. Our asteroseismic result, along with previous asteroseismic constraints on internal rotation in some B stars, and measurements of internal rotation in some subgiant, giant and white dwarf stars, has made angular momentum transport in stars throughout their lifetimes an observational science.

Highlights

For four hundred years, since Galileo, we have known that the Sun rotates
The 100-d rotation period of Kepler Input Catalogue (KIC) 11145123 is abnormally long for any nonmagnetic A star
Amongst the magnetic Ap stars rotation periods of years are known; the longest is over a century for γ Equ

Summary

Introduction

Since Galileo, we have known that the Sun rotates. As the Sun and stars evolve, their cores shrink while their outer envelopes expand and are eventually ejected, carrying away angular momentum. Little is known of the internal rotation and angular momentum transport of stars. In asteroseismology of main-sequence stars, pressure modes probe the outer layers of a star, and gravity modes probe the deep interior [5] [6]. For the β Cep star HD 129929 Dupret et al [11] found indications of internal differential rotation (see [12]), and for another β Cep star, θ Oph, Briquet et al [13] found indications of solid-body rotation. Our aim is to find main-sequence stars that show both the pressure modes (p modes) and gravity, or buoyancy, modes (g modes) using the exquisitely precise Kepler Mission photometric data for the purpose of observing their interior rotation from the surface right to the core.

Observations and frequency analysis

Nearly model-independent inferences

Discussion and conclusions