Background and urgency: photons emitted from stellar surfaces and neutrinos released from stellar interiors may not directly reveal all that we want to know about the internal constitution of the…

This is a $476,501 grant awarded by the National Aeronautics and Space Administration (NASA) to Arizona State University (ASU) for a research program focusing on probing the interior composition of white dwarf stars. The research will leverage precision pulsation data from NASA's Kepler and TESS missions, along with stellar evolution models and machine learning techniques, to provide new constraints on the nuclear reaction rates and interior structure of white dwarfs. This grant does not have a set-aside designation. ASU, as the prime contractor, will be conducting this work as part of its broader capabilities in space science, astronomy, and advanced scientific research for federal agencies. The outcomes of this program are expected to include new insights into white dwarf interiors, open-source software tools for white dwarf seismology analysis, and increased diversity among white dwarf seismology researchers.

Background and urgency: photons emitted from stellar surfaces and neutrinos released from stellar interiors may not directly reveal all that we want to know about the internal constitution of the STARS. For example, a direct view of the chemical stratification from the core to the surface is hidden. These interior abundance profiles matter: they impact a star's opacity, thermodynamics, nuclear energy generation, and pulsation properties. The stellar models, in turn, are used to interpret the integrated light of stellar clusters and galaxies, decipher the origin of the elements, predict the frequency of merging neutron STARS and black holes, and decipher the population(s) of exploding white dwarfs that underlay type IA supernova cosmology. Fit and relevance: the interiors of white dwarfs encapsulate their stellar evolution history, especially the nuclear reactions and rotational mixing that take place during the helium-burning stage. The pulsation properties of variable white dwarfs are sensitive to their mechanical, thermal, and composition structures, and hence white dwarf seismology offers the potential to probe the interior composition of white dwarfs, and by extension, the nuclear reaction rates responsible for the chemical stratification. The proposed research program has three interwoven focus efforts that will leverage the 6-7 digits of precision in the observed pulsation periods of variable white dwarfs from NASA's kepler and tess missions to open a new frontier on constraining their interior abundance profiles. A vision of the future and a road map: the goal of this proposal is to reveal the interior mass fraction profiles of pulsating white dwarfs. To reach this goal, we will bind the following into a tightly coupled, BI-directional closed loop: seismology data of variable white dwarfs from NASA's kepler and tess missions, nuclear data from the facility for rare isotope beams and other laboratories, stellar evolution models from mesa, stellar pulsation calculations from gyre, and a machine learning technique aimed at connecting the observed white dwarf pulsation data with the stellar models. Specifically, the nuclear physics experiments and astronomy observations will provide essential input for the dynamic stellar models. The stellar pulsation models, coupled with a random forest regressor machine learning technique, will then provide guidance to the nuclear physics experiments (e.g., which reaction rates to measure or refine) and enable predictions of new features for white dwarf seismology observations to close the loop. Outcomes: the major outcomes of this research program will be (1) potentially groundbreaking new constraints on the interior composition of white dwarfs (2) an open-source random forest regressor software instrument for extracting reaction rate and rotational parameters of the stellar models that produce white dwarfs from the observed g-mode pulsation periods and other properties of white dwarfs (3) increasing the diversity of white dwarf seismology researchers. The resulting products of the research will be freely shared in support of NASA science activities.