ANGULAR MOMENTUM TRANSPORT WITHIN EVOLVED LOW-MASS STARS

Abstract

Asteroseismology of 1.0-2.0 Msun red giants by the Kepler satellite has\nenabled the first definitive measurements of interior rotation in both first\nascent red giant branch (RGB) stars and those on the Helium burning clump. The\ninferred rotation rates are 10-30 days for the ~0.2Msun He degenerate cores on\nthe RGB and 30-100 days for the He burning core in a clump star. Using the MESA\ncode we calculate state-of-the-art stellar evolution models of low mass\nrotating stars from the zero-age main sequence to the cooling white dwarf (WD)\nstage. We include transport of angular momentum due to rotationally induced\ninstabilities and circulations, as well as magnetic fields in radiative zones\n(generated by the Tayler-Spruit dynamo). We find that all models fail to\npredict core rotation as slow as observed on the RGB and during core He\nburning, implying that an unmodeled angular momentum transport process must be\noperating on the early RGB of low mass stars. Later evolution of the star from\nthe He burning clump to the cooling WD phase appears to be at nearly constant\ncore angular momentum. We also incorporate the adiabatic pulsation code,\nADIPLS, to explicitly highlight this shortfall when applied to a specific\nKepler asteroseismic target, KIC8366239. The MESA inlist adopted to calculate\nthe models in this paper can be found at \\url{https://authorea.com/1608/}\n(bottom of the document).\n