A Faint Flux-Limited LAE Sample at z = 0.3
Isak Wold, UT Austin
Observational surveys of Lya emitters (LAEs) have proven to be an efficient method to identify and study large numbers of galaxies over a wide redshift range. To understand what types of galaxies are selected in LAE surveys – and how this evolves with redshift – it is important to establish a low-redshift reference sample that can be directly compared to high-redshift samples. The lowest redshift where a direct Lya survey is currently possible is at a redshift of z~0.3 via the Galaxy Evolution Explorer (GALEX ) FUV grism data. Using the z~0.3 GALEX sample as an anchor point, it has been suggested that at low redshifts high equivalent width (EW) LAEs become less prevalent and that the amount of escaping Lya emission declines rapidly. A number of explanations for these trends have been suggested including increasing dust content, increasing neutral column density, and/or increasing metallicity of star-forming galaxies at lower redshifts. However, the published z~0.3 GALEX sample is pre-selected from bright NUV objects. Thus, objects with strong Lya emission but faint continuum (high-EW LAEs) could be missed. In this talk, I will present my efforts to re-reduce the deepest archival GALEX FUV grism data and obtain a sample that is not biased against high-EW LAEs. I will discuss the implications of this new sample on the evolutionary trends listed above.
The Magnetic Mid-life Crisis of the Sun
Dr. Travis Metcalfe, Space Sciences Institute
After decades of effort, the solar activity cycle is exceptionally well characterized but it remains poorly understood. Pioneering work at the Mount Wilson Observatory demonstrated that other sun-like stars also show regular activity cycles, and suggested two possible relationships between the rotation rate and the length of the cycle. Neither of these relationships correctly describe the properties of the Sun, a peculiarity that demands explanation. Recent discoveries have started to shed light on this issue, suggesting that the Sun’s rotation rate and magnetic field are currently in a transitional phase that occurs in all middle-aged stars. We have recently identified the manifestation of this magnetic transition in the best available data on stellar cycles. The results suggest that the solar cycle may be growing longer on stellar evolutionary timescales, and that the cycle might disappear sometime in the next 0.8-2.4 Gyr. Future tests of this hypothesis will come from ground-based activity monitoring of Kepler targets that span the magnetic transition, and from asteroseismology with the TESS mission to determine precise masses and ages for bright stars with known cycles.
Long duration solar gamma ray flares
Lisa Winter, LANL
Long duration solar gamma ray flares (LDGRFs) present a challenge to models of solar flares. While the gamma ray emission initially was thought to be the high energy extension of emission produced at the footprints of flare loops, LDGRFs are more energetic than expectations and last hours after the X-ray emission subsides. Evidence of gamma ray emission from flares on the backside of the Sun prompted the idea that LDGRFs instead are created from acceleration of particles in the shock waves of coronal mass ejections (CMEs). To determine which of these scenarios is more likely, we conducted a study of the flare and CME properties for LDGRFs detected by the Fermi Gamma-Ray Observatory. We also performed a reverse association analysis to determine which flares and CMEs do not produce gamma-ray emission. In this talk, these results are presented, showing that LDGRFs are most likely associated with CME acceleration.
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.
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.
Science with the James Webb Space Telescope
Jane Rigby, NASA/GSFC
NASA’s James Webb Space Telescope (JWST) will have revolutionary capabilities and sensitivity for imaging and spectroscopy from 0.7 to 28 micron. JWST should make major scientific advances across astrophysics, including the physics of reionization, galaxy formation and assembly, planetary science, and extrasolar planets. In anticipation of a scheduled launch in 2019, JWST Cycle 1 Guest Observer proposals will be due in spring of 2018. I will review the scientific capabilities of the telescope, the integration and test program, and how observers will plan observations and analyze JWST data.
The statistical study of solar dimmings and their eruptive counterparts
Larisza Krista, Cu/CIRES, NOAA/NCEI
Results are presented from analyzing the physical and morphological properties of 154 dimmings (transient coronal holes) and the associated flares and coronal mass ejections (CMEs). Each dimming in the catalog was processed with the semi-automated Coronal Dimming Tracker (CoDiT) using Solar Dynamics Observatory AIA 193 Å observations and HMI magnetograms. Instead of the typically used difference images, the transient dark regions were detected “directly” in extreme ultraviolet (EUV) images. This allowed us to study dimmings as the footpoints of CMEs—in contrast with the larger, diffuse dimmings seen in difference images that represent the projected view of the rising, expanding plasma. Studying the footpoint-dimming morphology allowed us to better understand the CME structure in the low corona. While comparing the physical properties of dimmings, flares, and CMEs, the relationships between the different parts of this complex eruptive phenomenon were identified: larger dimmings were found to be longer-lived, which suggests that it takes longer to “close down” large open magnetic regions. During their growth phase, smaller dimmings were found to acquire a higher magnetic flux imbalance (i. e., become more unipolar) than larger dimmings. Furthermore, the EUV intensity of dimmings (indicative of local electron density) was found to correlate with how much plasma was removed and how energetic the eruption was. Studying the morphology of dimmings (single, double, fragmented) also helped identify different configurations of the quasi-open magnetic field.
Dr Larisza Krista received an MSc degree in astrophysics in 2007 from Eotvos Lorand University, in Budapest, Hungary. She did her PhD at Trinity College Dublin (Ireland) as a Government of Ireland Scholar, on “The Evolution and Space Weather Effects of Solar Coronal Holes”. She moved to Boulder in 2011 to accept a research scientist position at CU/CIRES in residence at NOAA/SWPC. She has also been a long-term scientific visitor at the High Altitude Observatory, where she collaborates with Dr Scott McIntosh. Her main interests involve the evolution of open solar magnetic field regions over the solar cycle as well as the related heliospheric structures and geomagnetic effects.