New IRIS constraints on the solar core rotation
Аннотация
Abstract. Four time series of IRIS data (4 to 6 months) havebeen used to obtain improved measurements of the low degree(` =1,2,3) rotational splitting frequencies. Assuming that therotation law is known in the outer layers of the Sun, we investi-gate the implications of IRIS splittings for the central regions.Bothaone-shellandatwo-shellrotationmodelhavebeencon-sidered in the solar core. A core rotating slightly faster than theouter radiative envelope provides the best fit to the data. Someevidence for the reliability of the observations is shown by thevisibility of differential rotation in the ` = 3 multiplets.Key words: Sun: rotation – Sun: oscillations – Sun: interior1. IntroductionSincerotationliftstheazimuthaldegeneracyofglobalmodesofoscillation, helioseismology gives access to the Sun’s internalangular velocity. Spatially resolved observations of moderateand high degree modes have already provided estimates of theangular velocity outwards from R /3, but the inference of therotationinthecoreitselfreliesentirelyonaknowledgeofrota-tionalsplittingfrequenciesof p-modeswithverylowharmonicdegree `. Thanks to very stable full-disk seismometers, longobservations with high duty-cycles can reveal the fine structureof the ` =1,2,3 multiplets. However, spectral line fitting isrendered very delicate by mode mixing, the presence of noise,and the χ