Constraining transport of angular momentum in stars Combining asteroseismic observations of core helium burning stars and white dwarfs

Context Transport of angular momentum has been a challenging topic within the stellar evolution community, even more since the recent asteroseismic surveys. All published studies on rotation using asteroseismic observations show a discrepancy between the observed and calculated rotation rates, indicating there is an undetermined process of angular momentum transport active in these stars. Aims We aim to constrain the efficiency of this process by investigating rotation rates of 2.5 M-circle dot stars. Methods First, we investigated whether the Tayler-Spruit dynamo could be responsible for the extra transport of angular momentum for stars with an initial mass of 2.5 M-circle dot. Then, by computing rotating models including a constant additional artificial viscosity, we determined the efficiency of the missing process of angular momentum transport by comparing the models to the asteroseismic observations of core helium burning stars. Parameter studies were performed to investigate the effect of the stellar evolution code used, initial mass, and evolutionary stage. We evolved our models into the white dwarf phase, and provide a comparison to white dwarf rotation rates. Results The Tayler-Spruit dynamo is unable to provide enough transport of angular momentum to reach the observed values of the core helium burning stars investigated in this paper. We find that a value for the additional artificial viscosity nu(add) around 10(7) cm(2) s(-1) provides enough transport of angular momentum. However, the rotational period of these models is too high in the white dwarf phase to match the white dwarf observations. From this comparison we infer that the efficiency of the missing process must decrease during the core helium burning phase. When excluding the nu(add) during core helium burning phase, we can match the rotational periods of both the core helium burning stars and white dwarfs

NuGrid stellar data set - III. Updated low-mass AGB models and s-process nucleosynthesis with metallicities Z = 0.01, Z = 0.02, and Z = 0.03

© 2019 Oxford University Press. All rights reserved. The production of the neutron-capture isotopes beyond iron that we observe today in the Solar system is the result of the combined contribution of the r-process, the s-process, and possibly the i-process. Low-mass asymptotic giant branch (AGB) (1.5 10 M☉) stars have been identified as the main site of the s-process. In this work we consider the evolution and nucleosynthesis of low-mass AGB stars. We provide an update of the NuGrid Set models, adopting the same general physics assumptions but using an updated convective-boundary-mixing model accounting for the contribution from internal gravity waves. The combined data set includes the initial masses MZAMS/M☉ = 2, 3 for Z = 0.03, 0.02, 0.01. These new models are computed with the MESA stellar code and the evolution is followed up to the end of the AGB phase. The nucleosynthesis was calculated for all isotopes in post-processing with the NuGrid mppnp code. The convective-boundary-mixing model leads to the formation of a 13C-pocket three times wider compared to the one obtained in the previous set of models, bringing the simulation results now in closer agreement with observations. Using these new models, we discuss the potential impact of other processes inducing mixing, like rotation, adopting parametric models compatible with theory and observations. Complete yield data tables, derived data products, and online analytic data access are provided

Suffering and dying well: on the proper aim of palliative care

In recent years a large empirical literature has appeared on suffering at the end of life. In this literature it is recognized that suffering has existential and social dimensions in addition to physical and psychological ones. The non-physical aspects of suffering, however, are still understood as pathological symptoms, to be reduced by therapeutical interventions as much as possible. But suffering itself and the negative emotional states it consists of are intentional states of mind which, as such, make cognitive claims: they are more or less appropriate responses to the actual circumstances of the patient. These circumstances often are such that it would rather be a pathological symptom not to be sad and not to suffer. Suffering, therefore, is sometimes and to some extent a condition to be respected. Although I do not dispute that the alleviation of suffering is the main aim of palliative care, in pursuing that aim we should acknowledge a constraint of realism