Asteroseismology of Red Giants: The Detailed Modeling of Red Giants in Eclipsing Binary Systems
Jean McKeever, NMSU
Asteroseismology is an invaluable tool that allows one to peer into the inside of a star and know its fundamental stellar properties with relative ease. There has been much exploration of solar-like oscillations within red giants with recent advances in technology, leading to new innovations in observing. The Kepler mission, with its 4-year observations of a single patch of sky, has opened the floodgates on asteroseismic studies. Binary star systems are also an invaluable tool for their ability to provide independent constraints on fundamental stellar parameters such as mass and radius. The asteroseismic scaling laws link observables in the light curves of stars to the physical parameters in the star, providing a unique tool to study large populations of stars quite easily. In this work we present our 4-year radial velocity observing program to provide accurate dynamical masses for 16 red giants in eclipsing binary systems. From this we find that asteroseismology overestimates the mass and radius of red giants by 15% and 5% respectively. We further attempt to model the pulsations of a few of these stars using stellar evolution and oscillation codes. The goal is to determine which masses are correct and if there is a physical cause for the discrepancy in asteroseismic masses. We find there are many challenges to modeling evolved stars such as red giants and we address a few of the major concerns. These systems are some of the best studied systems to date and further exploration of their asteroseismic mysteries is inevitable.
Surprising Impacts of Gravity Waves
Jim Fuller, Caltech
Clues to Globular Cluster Formation
David Nataf, Johns Hopkins University
Globular clusters are now well-established to host “Second-generation” stars, which show anomalous abundances in some or all of He, C, N, O, Na, Al, Mg, etc. The simplest explanations for these phenomena typically require the globular clusters to have been ~20x more massive at birth, and to have been enriched by processes which are not consistent with the theoretical predictions of massive star chemical synthesis models. The library of observations is now a vast one, yet there has been comparatively little progress in understanding how globular clusters could have formed and evolved. In this talk I discuss two new insights into the matter. First, I report on a meta-analysis of globular cluster abundances that combined APOGEE and literature data for 28 globular clusters, new trends with globular cluster mass are identified. I discuss the chemical properties of former globular cluster stars that are now part of the field population, and what can be learned.
Using every photon to learn about the physics of solar plasmas
Phil Judge, High Altitude Observatory, Boulder CO.
Role of solar Rossby waves in causing space weather on intermediate time-scales
Mausumi Dikpati, HAO
Forecasting our weather was built on the recognition that global Rossby waves, interacting with mean east-west flow on the Earth’s atmosphere, produce jet streams, which are responsible for causing winter storms, and cold outbreaks that we experience in midlatitudes. Rossby waves arise in thin layers within fluid regions of stars and planets. These global wave‐like patterns occur due to the variation in Coriolis forces with latitude. It has recently been discovered that the Sun has Rossby waves too. Therefore, the Sun’s global magnetic fields and flows are also influenced by these global‐scale waves. But unlike the Earth’s Rossby waves, due to the presence of strong magnetic fields solar Rossby waves are magnetically modified. In this talk, I will demonstrate through model-simulations how solar Rossby waves, nonlinearly interacting with differential rotation and spot-producing magnetic fields, can cause the seasonal/sub-seasonal (6-18 months) variability in solar activity, which is, in turn, the origin of space weather on intermediate time-scales. Space weather occurring on a very short time-scale (hours-to-days) and on much longer time-scale (decadal-to-millennial) have been studied extensively, but there exists a gap, namely the occurrence of space weather on intermediate time-scale of a few weeks to several months. I will also demonstrate that combining observations with our model by data-assimilation procedure it is possible to forecast an upcoming space-weather season several months ahead of time.