Dear Dr. Berlinsky, Please consider our application for a 1 week visit following the KITP program “Galactic Archaeology and Precision Stellar Astrophysics”. The proposing team wants to meet again to continue some very exciting work that was started at KITP and led to groundbreaking results in the field of stellar physics and asteroseismology. Please find below a brief description of the results that the team achieved during/after the KITP program and the follow up work we intend to perform while together at KITP. A team justification closes this application. We would like to meet at KITP either on 15-22 NOVEMBER (strong preference for this week) or 6-13 December. INTRODUCTION The team members enjoyed a very productive period of collaboration during the Galactic Archaeology and Precision Stellar Astrophysics program at KITP in 2015. That collaboration led to two papers on red giant asteroseismology, recently submitted to Science and Nature. The first paper discussed the ability to measure internal magnetic fields in red giant stars using asteroseismology, and the second used this technique to constrain/measure magnetic fields in the core of thousands of red giant stars. We believe this work has paved the way to a new sub-field of stellar astrophysics that is ripe for additional study. Consequently, there are several research topics which we wish to pursue during a follow-up visit to KITP. PROJECT OVERVIEW The first research topic we intend to investigate is the EXISTENCE OF STRONG MAGNETIC FIELDS WITHIN STARS ON THE RED CLUMP. The previous works only analyzed stars ascending the red giant branch, but similar physics will occur for red clump stars burning helium in their cores. However, identifying the asteroseismic signature of strong magnetic fields in clump stars is slightly more difficult because they are difficult to distinguish from ascending red giants. Collaboration between the team members will allow us to work out the details of this process from the observational end, and what can be learned from these observations on the theoretical end. A second topic of investigation are “DROOPY-LIKE” STARS that show a particular asteroseismic signature that allows for a more precise measurement of their internal magnetic fields. Thus far, only one star KIC 8561221 (“Droopy”) that shows this signature has been analyzed in detail (Garcia et al. 2014). However, more Droopy-like stars likely exist. We intend to identify these stars in the data, measure their internal magnetic field strengths, and use them to trace the evolution of internal magnetic field strengths in red giant stars. Third, we hope to use additional time at KITP to examine the OCCURRENCE OF MAGNETIC FIELDS IN CLUSTER STARS. These stars have nearly identical ages and compositions and provide the perfect testbed to understand evolution of magnetic fields in a uniform population of stars. Red giant cluster stars exist in both Kepler data and recent and upcoming K2 fields, with substantial data already secured by the team. These red giants are found in several clusters (of differing ages and metallicities) and can be used to understand the development of magnetic fields in different populations of stars. As a fourth research topic (time permitting) we will try to CONSTRAIN THE GEOMETRY OF INTERNAL MAGNETIC FIELDS in red giants with suppressed dipoles, using the scattering properties of dipolar gravity waves on the magnetic fields. Proposing Team and Team Justification 1. Lars Bildsten (KITP resident) 2. Matteo Cantiello (KITP resident) 3. Jim Fuller (Caltech) 4. Rafael A. Garcia (CEA, Paris) 5. Stéphane Mathis (CEA, Paris) 6. Dennis Stello (Sydney University) Five of the six team members outlined above are the main authors in the two papers submitted to Science (Theory) and Nature (Observations). Thanks to their complementary expertises, this group of scientists found a remarkable synergy while at KITP. Thanks to the presence of both theorists and observers, we were able to quickly identify an observational puzzle, find a theoretical explanation and test it on brand new data. In the process this led to the discovery of a novel, powerful way to look for magnetic fields in stellar interiors. The team has remained in touch and active after meeting at KITP, but it’s clear that only re-creating a full-immersion atmosphere can lead to rapid progress on the follow-up research program.

Despite its importance for the evolution and final end states of stars, the physics of stellar angular momentum transport remains poorly understood. Recent advances in ensemble asteroseismology has yielded measurements of core rotation in many ascending red giant branch stars (RGB) . The main result (Fig [period]) is that the cores of these stars are rotating at least 10 times slower than what is predicted by state-of-the art models . Moreover, detailed asteroseismic modeling shows that the bulk of radial differential rotation is localized in the radiative region between the H-burning shell and the bottom of the convective envelope . The magnetorotational instability (MRI) has been extensively studied in the context of angular momentum transport in accretion disks. However, it is not clear what role–if any–it might play in the radiative regions of differentially rotating stars. The existing literature is limited , and attempts to simulate this mechanism in stellar interiors have not yielded complete results appropriate for inclusion in stellar evolution codes. We propose to investigate the role of the MRI in stars using simulations that account for the important physical ingredients of stellar radiative regions: stable radial stratification, mean molecular weight gradients, differential rotation, and magnetic fields. These effects are parameterized by the Brunt-Väisälä frequency N, background gradient ∇μ, shear parameter q = dlogΩ/dlogR, and plasma β. emphasized the importance _double-diffusive_ effects in the stellar MRI. These effects occur when there is an imbalance between the microphysical dissipation of momentum ν, magnetic field η, and heat χ. In their analysis, they note that double diffusive effects can both stabilize and destabilize depending on the relative ratio of these coefficients. Here, we will carefully consider the effects of double-diffusive effects by a series of fast, linear solutions to characterize the parameter space most relevant to stellar parameters. Using the Dedalus framework, we will simulate the MRI in a simplified geometry to extract effective torques over a range of parameters. We will then implement these results in a 1D implementation in the MESA code to test against the full set of observations available: the core rotation of red giants, the solar core rotation profile, and the final spin rate of compact remnants. This project is extremely ambitious owing to the many length scales that must be resolved simultaneously and the very large parameter space to be spanned. However, we have at our disposal the ideal tools to make significant progress: the spectral magnetohydrodynamic simulation framework Dedalus and the extremely flexible stellar evolution code MESA. Dedalus provides an excellent platform to study the MRI in stellar interiors: it can be adapted to include the new terms and its spectral accuracy ensures that the widest possible dynamic range for a given resolution (Fig. [Dedalus]). Thanks to the extraordinary results from Kepler asteroseismology and the versatility of the open stellar evolution code MESA, we will be able to immediately test our results against the observations. This project could lead to a novel theory for internal angular momentum transport in stellar interiors, and, among other results, to updated predictions for SN and GRB progenitors. Both the Dedalus and MESA codes are fully open, so our results will be fully testable and reproducible by the astrophysics community. We will publish not only our results, but also our input files and configuration for both codes.

A variety of research demonstrates that humans learn and communicate best when more than one processing system (e.g. visual, auditory, touch) is used . And, related research also shows that, no matter how technical the material, most humans also retain and process information best when they can put a narrative "story" to it. So, when considering the future of scholarly communication, we should be careful not to do blithely away with the linear narrative format that articles and books have followed for centuries: instead, we should enrich it.