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.
Dark Sky Images
Ken, an retired engineer, is a highly technically skilled and artistic
astrophotographer. He will be sharing some of his work and elaborating on
the technical methods and processing techniques he applies to obtain his
unique and enhanced images. You can see Ken’s work at:
Breaking the Self-Similarity of Galaxy Formation: A Circumgalactic Medium Perspective
Benjamin Oppenheimer, University of Colorado Boulder
If you could see a dark matter halo directly without knowing the scale, you probably could not distinguish a Milky Way halo from a cluster-sized halo. However, if you look at the galaxies, you would likely see a dominant spiral galaxy in the former and a many quenched and quenching galaxies in the latter. The study of galaxy formation aims to understand how very different galaxies form in dark matter halos of different masses. I will argue for the importance of understanding the gaseous baryons in this context. In contrast to the hot intracluster medium detected in emission in clusters, the circumgalactic medium (CGM) has to be probed by absorption lines toward background quasars and tells a vastly different and complicated story. I will demonstrate, with the aid of hydrodynamic simulations, how the CGM is multi-phase (with cool ~10^4 K clouds embedded in a hot, ambient medium), plus how non-equilibrium ionization processes altering the heavy element ions we probe in spectra. The next frontiers in the CGM require understanding the dynamics encoded not only in absorption line spectra of the UV, but in the X-ray via emission and absorption.
Your hosts for the October Open House at the Campus Observatory are Kristian Finlator, Sten Hasselquist, Rachel Marra, and Aleczander Herczeg.
Galaxy Evolution in High Definition Via Gravitational Lensing
Dr. Jane Rigby
Deputy Project Scientist for JWST, NASA Goddard Space Flight Center
Abstract: In hundreds of known cases, “gravitational lenses” have deflected, distorted, and amplified images of galaxies or quasars behind them. As such, gravitational lensing is a way to “cheat” at studying how galaxies evolve: lensing can magnify galaxies by factors of 10–100 times, transforming them from objects we can barely detect to bright objects we can study in detail. For such rare objects, we are studying how galaxies formed stars at redshifts of 1–4, the epoch when most of the Universe’s stars were formed. For lensed galaxies, we can obtained spectral diagnostics that are currently unavailable for the distant universe, but will become routine with next-generation telescopes.
In particular, I’ll discuss MEGaSaURA, The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas, which comprises high signal-to-noise, medium spectral resolution (R~3300) spectra of 15 extremely bright gravitationally lensed galaxies at redshifts of 1.6<z<3.6. The sample, drawn from the SDSS Giant Arcs Survey, are many of the brightest lensed galaxies known. The MEGaSaURA spectra reveal a wealth of spectral diagnostics: absorption from the outflowing wind; nebular emission lines that will be key diagnostics for JWST, GMT, and TMT; and photospheric absorption lines and P Cygni profiles from the massive stars that power the outflow.