The Sun Asphericities: Astrophysical Relevance

Of all the fundamental parameters of the Sun (diameter, mass, temperature...), the gravitational multipole moments (of degree l and order m) that determine the solar moments of inertia, are still poorly known. However, at the first order (l=2), the quadrupole moment is relevant to many astrophysical applications. It indeed contributes to the relativistic perihelion advance of planets, together with the post-Newtonian (PN) parameters; or to the precession of the orbital plane about the Sun polar axis, the latter being unaffected by the purely relativistic PN contribution. Hence, a precise knowledge of the quadrupole moment is necessary for accurate orbit determination, and alternatively, to obtain constraints on the PN parameters. Moreover, the successive gravitational multipole moments have a physical meaning: they describe deviations from a purely spherical mass distribution. Thus, their precise determination gives indications on the solar internal structure. Here, we explain why it is difficult to compute these parameters, how to derive the best values, and how they will be determined in a near future by means of space experiments.Comment: 14 pages, 9 figures (see published version for a better resolution), submited to Proceedings of the Royal Society: Mathematical, Physical and Engineering Science

The Rotation Of The Deep Solar Layers

From the analysis of low-order GOLF+MDI sectoral modes and LOWL data (l > 3), we derive the solar radial rotation profile assuming no latitudinal dependance in the solar core. These low-order acoustic modes contain the most statistically significant information about rotation of the deepest solar layers and should be least influenced by internal variability associated with the solar dynamo. After correction of the sectoral splittings for their contamination by the rotation of the higher latitudes, we obtain a flat rotation profile down to 0.2 solar radius.Comment: accepted in ApJ Letters 5 pages, 2 figure

Inferring the equatorial solar tachocline from frequency splittings

Helioseismic inversions, carried out for several years on various ground-based and spatial observations, have shown that the solar rotation rate presents two principal regimes: a quasi-rigid rotation in the radiative interior and a latitude-dependent rotation in the whole convection zone. The thin layer, named solar tachocline, between these two regimes is difficult to infer through inverse techniques because of the ill-posed nature of the problem that requires regularization techniques which, in their global form, tend to smooth out any high gradient in the solution. Thus, most of the previous attempts to study the rotation profile of the solar tachocline have been carried out through forward modeling. In this work we show that some appropriate inverse techniques can also be used and we compare the ability of three 1D inverse techniques combined with two automatic strategies for the choice of the regularization parameter, to infer the solar tachocline profile in the equatorial plane. Our work, applied on LOWL (LOWL is an abbreviation for low degree denoted by L) two years dataset, argue in favor of a very sharp (0.05+/-0.03R_sun) transition zone located at 0.695+/-0.005R_sun which is in good agreement with the previous forward analysis carried out on Global Oscillations Network Group (GONG), Big Bear Solar Observatory (BBSO) and LOWL datasets