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  • Suppressed Dipoles

    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.

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