Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session S11: From Planets to Galaxy Clusters |
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Sponsoring Units: DAP Chair: Michelle Hui, NASA/MSFC Room: 250C |
Monday, April 18, 2016 1:30PM - 1:42PM |
S11.00001: Detecting Extrasolar Asteroid Belts Through Their Microlensing Signatures Ethan Lake, Zheng Zheng, Subo Dong We propose that extrasolar asteroid belts can be detected through their gravitational microlensing signatures and present a simple theoretical understanding of how asteroid belts behave as gravitational lenses. Asteroid belt + star lens systems create so-called “pseudo-caustics”, which are regions in the source plane where the magnification of the source exhibits a discontinuous jump. Such a magnification change can be associated with either a change in image multiplicity or with a sudden change in the size of an image. The existence of pseudo-caustics and the complex interplay between them and the formal caustics (which possess formally infinite magnification) lead to several interesting consequences, such as the presence of open caustics and the violation of Burke’s theorem. These features allow such systems to generate very distinctive microlensing light curves across a wide region of asteroid belt parameter space and possess remarkably large lensing cross-sections. By constructing simulated light curves for a range of asteroid belt parameters, we demonstrate that upcoming space-based microlensing surveys like WFIRST are well-poised to discover extrasolar asteroid belts with masses on the order of $0.1M_{\oplus}$. [Preview Abstract] |
Monday, April 18, 2016 1:42PM - 1:54PM |
S11.00002: Long-term Stability Of Earth-like Planets Niyousha Davachi Different regions of phase space where Earth-like planets can persist for long time near a binary system is the target of our studies. Study of different mass ratios and eccentricities in different scenarios yields to more specific regions where Earth-like planets are stable. By using multiple body integrators and taking planets to be test particles in different initial conditions we obtain minimum and maximum orbits in which the planet is stable. This helps us determine in what regions expect seeing stable Earth-like planets. [Preview Abstract] |
Monday, April 18, 2016 1:54PM - 2:06PM |
S11.00003: Studying the nature of runaway stars using Andromeda's massive stellar population. Jordan Bulkley, Anil Seth, Cliff Johnson, Julianne Dalcanton, Raja Guhathakurta, Claire Dorman, Katie Hamren, Nelson Caldwell, Ben Williams Theory of the formation of massive stars remains incomplete, the question of the environments required have yet to be answered. An agreement on whether all massive stars must form in cluster type environments, or if isolated formation is viable has yet to be reached. This is further complicated by the presence of runaway stars, stellar objects which have been ejected from their host cluster. Studying the nature of these isolated runaway stars becomes paramount in the larger goal of developing a more comprehensive massive star formation theory. Creating a survey of runaway star candidates is possible thanks to Panchromatic Hubble Andromeda Treasury's UV and optical photometry, and the identified clusters from the Andromeda Project. A first glimpse into the data suggests large body of massive stars are 50 parsecs or more from the closest cluster and roughly half of the entire massive stellar population is found outside of defined cluster boundaries. Additional analysts shows a stark difference between the velocity dispersion of massive stars and appropriately young clusters, the stars exhibiting a inflated dispersion. Using this result in conjunction with artificial clusters and star populations, constrains on the percentage of expected runaway objects can be made. [Preview Abstract] |
Monday, April 18, 2016 2:06PM - 2:18PM |
S11.00004: Lattice Structure in Astrophysics: A reconsideration of White Dwarfs, Variables, and Wolf-Rayet Stars. Pierre-Marie Robitaille Stars of the main sequence display a mass-luminosity relation which indicates that they share a common building block (hydrogen) and lattice structure (hexagonal planar) with the solar photosphere. White dwarfs however display very low luminosity in spite of their elevated color temperature. Rather than postulate that these stars represent degenerate matter, as Eddington and Chandrasekhar were forced to assume given their gaseous models, within the context of a Liquid Metallic Hydrogen Solar Model white dwarfs might simply be thought as possessing a different lattice structure (e.g. body centered cubic) and hence a lowered emissivity. They do not need to possess exceeding densities, reduced radii, and degeneracy in order to account for their lowered emissivity. Similarly, variable stars might well be oscillating between lattices types wherein the energy differences involved in the transformations are small. Other stars, such as Wolf-Rayet stars, which lack photospheric emission, might be too hot to enable a discrete lattice to form. Though condensed, the photosphere in that case would have a lattice which is so poorly organized that its emissivity is trivial. Nonetheless, the broad emission lines of Wolf-Rayet stars indicates that these objects are not breaking apart but rather, are important sites of condensation. [Preview Abstract] |
Monday, April 18, 2016 2:18PM - 2:30PM |
S11.00005: Large-scale Inference Problems in Astronomy: Building a 3D Galactic Dust Map Douglas Finkbeiner The term "Big Data" has become trite, as modern technology has made data sets of terabytes or even petabytes easy to store. Such data sets provide a sandbox in which to develop new statistical inference techniques that can extract interesting results from increasingly rich (and large) databases. I will give an example from my work on mapping the interstellar dust of the Milky Way. 2D emission-based maps have been used for decades to estimate the reddening and emission from interstellar dust, with applications from CMB foregrounds to surveys of large-scale structure. For studies within the Milky Way, however, the third dimension is required. I will present our work on a 3D dust map based on Pan-STARRS1 and 2MASS over 3/4 of the sky (http://arxiv.org/abs/1507.01005), assess its usefulness relative to other dust maps, and discuss future work. [Preview Abstract] |
Monday, April 18, 2016 2:30PM - 2:42PM |
S11.00006: The Luminous Convolution Model for Galaxy Rotation Curves Shanon Rubin, Maria Mucci The LCM takes as input only the observed luminous matter profile from galaxies, and allows us to confirm these observed data by considering frame-dependent effects from the luminous mass profile of the Milky Way. The LCM is useful when looking at galaxies that have similar total enclosed mass, but varying distributions. For example, variations in luminous matter profiles from a diffuse galaxy correlate to the LCM’s five different Milky Way models equally well, but LCM fits for a centrally condensed galaxy distinguish between Milky Way models. In this presentation, we show how the rotation curve data of such galaxies can be used to constrain the Milky Way luminous mass modeling, by the physical characteristics of each galaxy used to interpret the fitting. Current Investigations will be presented showing how the convolved parameters of Keplerian predictions with rotation curve observations can be extracted with respect to the crossing location of the relative curvature versus the assumption of the luminous mass profiles from photometry. Since there currently exists no direct constraint to photometric estimates of the luminous mass in these systems, the LCM gives the first constraint based on the orthogonal measurement of Doppler shifted spectra from characteristic emitters. [Preview Abstract] |
Monday, April 18, 2016 2:42PM - 2:54PM |
S11.00007: Equation for the Origin of Rotation of Two Armed Spiral Galaxies Stewart Brekke Pre-formed galactic arms were created in sets of two or more before galaxies were formed. These pre-formed galactic arms were orbiting each other. Over time, due to gravitational attraction, the orbits of the arms decayed with the set of two arms tangentially colliding in their fore sections and attaching there forming two armed spiral galaxies which began to rotate. The rotation of the two armed spiral galaxies was due to the conversion of the angular momenta of each of the arms adding together to form the total angular momentum of the newly formed two armed spiral galaxy. If $(I\omega)_{arm}$ is the angular momentum of each of the pre-formed galactic arms, and $(I\omega)_{galaxy}$ is the angular momentum of the newly formed two armed spiral galaxy, the equation for the origin of rotation of the galaxy is $ (I\omega)_{arm1} + (I\omega)_{arm2}= (I\omega)_{newly formed galaxy}$. [Preview Abstract] |
Monday, April 18, 2016 2:54PM - 3:06PM |
S11.00008: The Best Constraints on the Transport Processes in the Intracluster Medium Yuanyuan Su, Ralph Kraft, Paul Nulsen, Elke Roediger, Christine Jones, William Forman, Eugene Churazov, Scott Randall, Marie Machacek The intracluster medium, as a magnetized and highly ionized fluid, provides an ideal laboratory to study plasma physics. NGC 1404 is a bright elliptical galaxy falling through the ICM of the Fornax Cluster. The hot, gaseous corona surrounding NGC 1404 is characterized by a sharp upstream edge and a downstream gaseous tail. We resolve the scales of contact discontinuities down to an unprecedented level due to the combination of the proximity of NGC 1404, the superb spatial resolution of Chandra, and a very deep (670 ksec) exposure. For the first time, we observed Kelvin-Helmholtz instability rolls and put limits on the viscosity of hot cluster plasma. We also observed a mixing between the hot cluster gas and the cold galaxy gas in the downstream stripped tail, providing further support of a low viscosity plasma. Across the upstream front, we measured a discontinuity smaller than the mean free path. The magnetic field is strong enough to suppress electron diffusions but weak enough to allow KHI rolls unsuppressed. Our simulation, tailored to the specific scenario, will provide further insight into the details of the merger process. [Preview Abstract] |
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