The quest for the solar g modes

Abstract

A ce compte, toutes les sciences ne seraient que des applications inconscientes du calcul des probabilités ; condamner ce calcul, ce serait condamner la science tout entière." "From this point of view all the sciences would only be unconscious applications of the calculus of probabilities. And if this calculus be condemned, then the whole of the sciences must also be condemned."Henri Poincaré, 1914, La Science et l'hypothèseAbstract Solar gravity modes (or g modes) -oscillations of the solar interior for which buoyancy acts as the restoring force -have the potential to provide unprecedented inference on the structure and dynamics of the solar core, inference that is not possible with the well observed acoustic modes (or p modes). The high amplitude of the g-mode eigenfunctions in the core and the evanesence of the modes in the convection zone make the modes particularly sensitive to the physical and dynamical conditions in the core.Owing to the existence of the convection zone, the g modes have very low amplitudes at photospheric levels, which makes the modes extremely hard to detect. In this paper, we review the current state of play regarding attempts to detect g modes. We review the theory of g modes, including theoretical estimation of the g-mode frequencies, amplitudes and damping rates. Then we go on to discuss the techniques that have been used to try to detect g modes. We review results in the literature, and finish by looking to the future, and the potential advances that can be made -from both data and data-analysis perspectives -to give unambiguous detections of individual g modes. The review ends by concluding that, at the time of writing, there is indeed a consensus amongst the authors that there is currently no undisputed detection of solar g modes.

Asymptotic g modes: Evidence for a rapid rotation of the solar core

“…1), falling below the increasing background noise level before reaching the frequency range around the fundamental p-mode oscillation, where a few mixed modes (driven by both compressibility and buoyancy) are thought to exist. In this range, roughly speaking between 0.25 and 0.30 mHz, the lowest frequency p modes and highest frequency g modes are expected to exist with similar amplitudes at the solar surface, an amplitude of the order of 1 mm s −1 with a large uncertainty on any prediction (see again Appourchaux et al (2010) for a comprehensive review), and they have not been detected so far. The amplitude uncertainty remains very high in the g-mode domain, especially at lower frequencies, where the background noise increases.…”

2D dynamics of the radiative core of low mass stars

“…Moreover, we do not compute it at r = 1 since it would tend toward zero for small b and consequently the ratio δΩ C θ / δΩ S θ would diverge. The averaged core rotation rate δΩ C θ is computed at the radius r = 0.15R c because g-modes, that would allow to probe central regions, are hardly identifiable closer to the center ( [2], [21]). …”

Observational techniques to measure solar and stellar oscillations

“…Chaplin et al 1999a;Couvidat et al 2003;Eff-Darwich et al 2008;Eff-Darwich & Korzennik 2013;Elsworth et al 1995;García et al 2004García et al , 2008c or the conditions and properties of the solar core (e.g. Appourchaux et al 2010;Basu et al 1997Basu et al , 2009García et al 2007García et al , 2008aTurck-Chièze et al 2001, 2004 are some wellknown examples. Moreover, thanks to the detailed study of these variables, the position of the base of the convection zone (e.g.…”