Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 62, Number 17
Friday–Saturday, October 20–21, 2017; Fort Collins, CO
Session K1: Astronomy and Astrophysics |
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Chair: Stacey Palen, Weber State University Room: Lory Student Center 304 |
Saturday, October 21, 2017 9:25AM - 9:49AM |
K1.00001: Gone with the (solar) wind: Escape to Space of the Ancient Martian Atmosphere Invited Speaker: Dave Brain The Martian atmosphere today is too cold and thin for liquid water to be stable on the surface of the planet, yet the Martian surface contains abundant evidence that long-lived liquid water has played a prominent role in shaping the surface. We infer that the atmosphere has changed considerably over time, from a more substantial atmosphere billions of years ago to the tenuous atmosphere that exists today. What happened to the ancient atmosphere? Some portion could have been incorporated into the surface and subsurface over time, and some could have been removed to space via several distinct physical processes. Due to the small size of Mars relative to Earth and the lack of a global magnetic field to shield the atmosphere from the impinging solar wind, it is thought that escape to space could have been considerable over Martian history. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been in Mars orbit since late 2014, making measurements relevant to the removal of atmospheric particles to space. We will discuss the rationale for the important of atmospheric escape at Mars, the physical processes involved (Ohm's Law! Thermal Escape! Photochemistry! Collisions!), and the MAVEN observations that have allowed us to evaluate the importance of atmospheric escape in altering the Martian climate. Finally, we will discuss the implications of MAVEN's observations for atmospheric evolution at planets everywhere. [Preview Abstract] |
Saturday, October 21, 2017 9:49AM - 10:01AM |
K1.00002: Equilibrium models of relativistic stars with differential rotation and toroidal magnetic fields Logan Carpenter, Eric Hirschmann We construct equilibrium models of strongly magnetized neutron stars in general relativity under the assumptions of axisymmetry and stationarity. ~The matter is represented by a magnetized fluid in the ideal MHD approximation and incorporates differential rotation and a toroidal magnetic field. ~We solve for these equilibrium states using a numerical scheme similar to the self-consistent field method. ~We construct as an initial guess a TOV star, add differential rotation and subsequently include the magnetic field. ~ We then explore the parameter space of these equilibrium solutions looking for maximum mass, magnetic field strength, and energy distribution in the star.~ [Preview Abstract] |
Saturday, October 21, 2017 10:01AM - 10:13AM |
K1.00003: Understanding the role of a stars surface gravity on its spectrum Jessica Galbraith-Frew, Inese Ivans In order to properly model the stellar atmosphere of a star, you must first have an understanding of its effective temperature, surface gravity (gravitational acceleration at the surface of the star), chemical composition and atomic parameters. Having a correct model of the stellar atmosphere is important in determining accurate chemical abundances for different elements. Traditionally, astronomers use a set of spectroscopic constraints to hone in on the effective temperature, surface gravity, and chemical composition, while using laboratory results to understand the atomic parameters that define the transition. However, for solar-type unevolved stars in the infrared, the transitions used in spectroscopic constraints are difficult to measure in the data taken by the Apache Point Galactic Evolution Experiment (APOGEE). The APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP) focuses on evolved stars but the solar-type stars in the sample can also provide information about the Milky-way Galaxy's chemical history. Dwarf stars however, have much higher surface gravities and other mechanisms that mimic surface gravity making there a need for better surface gravity determination. For this reason, we have explored new techniques to determine the properties of the stellar atmosphere. I will discuss the role of surface gravity on the spectrum of a solar-type star, and its impact on the abundances derived using spectroscopic techniques. . [Preview Abstract] |
Saturday, October 21, 2017 10:13AM - 10:25AM |
K1.00004: Polarization behavior of stellar wind bow shocks Manisha Shrestha, Jennifer L. Hoffman, Hilding R. Neilson, Richard Ignace Stellar wind bow shocks are structures created by stellar wind traveling at supersonic velocity relative to interstellar medium (ISM). They can be studied to understand the properties of evolved stars as well as the ISM. Since bow shocks are asymmetric, the light scattered in the dense shock material becomes polarized. We use a Monte Carlo radiative transfer code to simulate the polarization signatures produced by both resolved and unresolved bow shocks with analytically derived shapes and density structures. When electron scattering is the polarizing mechanism, we find that optical depth plays an important role in the polarization signatures. While results for low optical depths reproduce theoretical predictions, higher optical depths produce higher polarization and position angle rotations at specific viewing angles. This is due to the geometrical properties of the bow shock along with the multiple scattering effect. For dust scattering, we find that the polarization signature is strongly affected by wavelength, dust model and viewing angle. Depending on the viewing angle, the total polarization may increase or decrease as a function of wavelength. We will present results from these simulations and preliminary comparisons with observational data. [Preview Abstract] |
Saturday, October 21, 2017 10:25AM - 10:37AM |
K1.00005: Surveillance of Ionized Hydrogen Near Supermassive Black Holes Samuel Montgomery Central regions of several nearby spiral galaxies appear completely void of atomic hydrogen, the most abundant element in the Universe. Using a telescope at the Etscorn Observatory fitted with a charge coupled device with several different filters, direct observations of spiral galaxies have been made. The detection of ionized hydrogen is expected to take the place of the absent atomic hydrogen. Ionized hydrogen is observed as a byproduct of the recombination of protons with freed electrons in an ionized soup of hydrogen atoms. This recombining of particles triggers the emission of a specific wavelength photon in a process known as H-alpha emission. The galaxies M81 and NGC 2903 show the presence of ionized hydrogen, glowing strongly in the images produced using an H-alpha filter. Ionized hydrogen resides in galactic environments with energy sources high enough to strip electrons from their host protons. The primary sources of this ionization energy are the supermassive black hole located at the centers of M81 and NGC 2903. When matter forms an accretion disk around a supermassive black hole it forms a quasar. Quasars emit a powerful amount of radiation, which is hypothesized as the source for the energy needed to ionize the surrounding atomic hydrogen. [Preview Abstract] |
Saturday, October 21, 2017 10:37AM - 10:49AM |
K1.00006: Spectropolarimetry with SALT: New Observations of Wolf-Rayet Binaries Andrew G. Fullard, Jennifer L. Hoffman, Kenneth H. Nordsieck Mass loss from massive stars is an important yet poorly understood factor in shaping their evolution. Wolf-Rayet (WR) stars are of particular interest due to their stellar winds, which create large regions of circumstellar material (CSM). They are also supernova progenitors and possible gamma-ray burst (GRB) progenitors. Like other massive stars, WR stars often occur in binaries, where interaction can affect the mass loss rate and provide the rapid rotation thought to be required for GRBs. The diagnostic tool of spectropolarimetry, along with the potentially eclipsing nature of a binary system, help us to better characterize the CSM created by the stars’ colliding winds. Thus, we can determine mass loss rates and identify rapid rotation. We present early spectropolarimetric results for the WR+O binary systems WR 30 and WR 47, from the Robert Stobie Spectrograph at the South African Large Telescope (SALT), between April and August 2017. The data allows us to map both continuum and emission line polarization variations with phase, which constrains where different CSM components scatter light. We discuss our initial findings and interpretations of the polarimetric variability. [Preview Abstract] |
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