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Estimating internal rotation rates of red giants in the presence of interacting mixed modes For slower rotating and less evolved red giants, linear rotational inversions remain applicable. For faster rotating and more evolved red giants, rotation induced near-degeneracy effects surpass observational uncertainties. (1)Heidelberger Institut für Theoretische Studien (2)University of Hawai’i (3)Hubble Fellow (4)Yale University (5)Heidelberg University f[email protected]g Download poster F. Ahlborn1, J. M. Joel Ong2,3, J. van Beeck1, E. P. Bellinger4, S. Hekker1,5, S. Basu4 Asteroseismic observations of internal stellar rotation have indicated a substantial lack of angular momentum transport in theoretical models of subgiant and red-giant stars. Accurate core and surface rotation rate measurements are therefore needed to constrain internal transport processes included in the models. In the presence of rotation, mixed modes with similar frequencies interact, an effect also known as near degeneracy. This leads to an asymmetry of the rotational splittings. We compute synthetic rotational splittings taking these near-degeneracy effects into account (Fig. 1). Subsequently, we invert these rotational splittings to estimate internal rotation rates using linear eMOLA inversions (Ahlborn+2022,2025) and assess the systematic errors introduced by the interaction of the mixed modes. Fig. 1: Asymmetry of synthetic rotational splittings of a 1 M☉ red-giant model as a function of frequency. The asymmetry is largest for p-dominated modes and increases with increasing core rotation rate. Fig. 2: Systematic error of estimated core and envelope rotation rates (ΔΩ) in terms of the observational uncertainties (σΩ) as a function of the large frequency separation (Δν). The rotation rates were estimated using eMOLA and the asymmetric rotational splittings described above. Different shades of blue and red refer to the core and envelope, respectively. The different symbols indicate different values of the input core rotation rates. Fig. 3: Systematic error of envelope rotation rates estimated from eMOLA inversions and the asymmetric rotational splittings as a function of core and envelope rotation rate. The systematic error of the envelope rotation rate (ΔΩ) in terms of observational uncertainties (σΩ) is colour coded. evolution
