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|Thu, Apr 03|
|Eric Agol and Ethan Kruse|
University of Washington
"Discovery of a new class of eclipsing binary"
|Thu, Apr 10|
" The Galactic Center: Unveiling the Heart of our Galaxy"
Over the last two decades, we have used the world's largest telescopes and next-generation imaging technology to study the center of our galaxy with more resolving power than ever before. These observations have tracked the motions of stars to provide the best evidence to-date that supermassive black holes exist, challenging our knowledge of fundamental physics and suggesting that most, if not all, galaxies harbor such objects at their cores. This work has also shown that the environment near a central supermassive black hole looks quite different from what was expected. I will discuss our recent results on the black hole, its environment, G2 (the tidally distorted object currently undergoing periapse passage), and upcoming opportunities to carry out unique tests of Einstein?s theory of General Relativity in the extreme environment near a supermassive black hole.
|Thu, Apr 17|
Penn. State University
" Probing the outer accretion disks of quasars via their broad emission lines"
|Thu, Apr 24|
University of Hong Kong
"Synthesis of Complex Organics in the Late Stages of Stellar Evolution"
Infrared spectroscopic observations of the stretching and bending modes of aliphatic and aromatic compounds are now seen throughout the Universe, from the diffuse interstellar medium of the Milky Way Galaxy to distant galaxies. Observations of evolved stars have revealed a rapid (~103 year time scale) and continuous synthesis of organic materials from the end of the asymptotic giant branch (AGB), to proto-planetary nebulae, to planetary nebulae. These synthesized products are ejected into the interstellar medium through stellar winds and as a result enriching the Galaxy with complex organics. Over 70 gas-phase molecules, including rings, radicals, and molecular ions, as well as fullerene (C60) have been identified by millimeter-wave and infrared spectroscopic observations through their rotational and vibrational transitions. Possible chemical pathways leading to the formation of complex organics will be discussed. Analysis of the infrared spectra suggests that the chemical structure of the carrier is consistent with that of mixed aromatic and aliphatic nanoparticles (MAON). These structures are very similar to those of the insoluble organic matter found in meteorites, suggesting that the early solar system may have been enriched by stellar ejecta.
|Thu, May 01|
"Observatories in China and Photometry of Interesting Cataclysmic Variables"
Cataclysmic Variables (CVs) comprise one category of active mass transfer binaries containing a white dwarf accreting from an orbiting companion. Undoubtedly, non-magnetic CVs, intermediate polars and polars constitute a powerful probe of the structure of accretion onto white dwarfs and the theories of angular momentum loss, which elucidate the long-term evolution leading to the formation of these short period compact binaries. Combining photometric data from Chinese telescopes with well-calibrated data from the AAVSO demonstrate novel discoveries, including evidence of potential substellar objects orbiting CVs with short orbital periods, peculiar characteristics of transient events in low-state prototype polars, cycle-to-cycle variations in light curves of many subtypes of CVs and so on. Based on new statistics of the period gap and orbital period analysis for targets around the gap, the standard evolution tracks of CVs might be queried. A few objects may indicate unexpected secular orbital period increase or possible stagnation in evolution. These interesting contradictions further uncover the internal complexities of CVs.
|Thu, May 08|
Arizona State Univ
"Classical and Recurrent Nova Outbursts: Hot Flashes on Degenerate Dwarfs"
A nova outburst is one consequence of the accretion of hydrogen rich material onto a white dwarf in a close binary stellar system. The strong electron degeneracy of the massive white dwarf acts to contain the gas and allows the temperatures in the nuclear burning region to exceed 100 million degrees under virtually all circumstances. A thermonuclear runaway occurs and a major fraction of the CNONeMg nuclei in the envelope are transformed into positron-decay nuclei. The result is that the material ejected by the explosion has a distinctly non-solar composition. I will present new calculations describing the effects of improvements in the nuclear reaction library on the resulting explosion and how changes in the initial composition can change the characteristics of the explosion. I will also present new observational results, such as the discovery of VHE gamma-ray emission with the Fermi/ Large Area Telescope, that are testing our understanding of these explosions.
|Thu, May 15|
University of Texas
"Black Holes, Dark Matter, Dark Energy through the Eyes of Texas"
Both the central black hole and the dark matter profile play essential roles for understanding the dominant evolutionary processes in galaxies. I will overview recent observations which demonstrate significant differences compared to previous analysis, focusing on the most massive black holes and dark haloes in the smallest galaxies. I will also present expectations from future advances in each area, specifically coming from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX).
|Thu, May 22|
University of Wisconsin
"Shedding Light on Distant Galaxies with 200,000 Quasars"
Distant quasars backlight the Universe over most of cosmic time, revealing the evolving gas distribution of the cosmic web. Intervening metal absorption lines in quasar spectra can provide sensitive tracers of the gaseous processes regulating star formation in foreground galaxies to high redshift, but observational difficulties have traditionally limited comparisons to the stellar properties of the absorbing galaxies. The extraction and statistical analysis of absorption line systems from ~200,000 quasar spectra in the Sloan Digital Sky Survey (SDSS I-III) has recently catalyzed our understanding of the physical environments of the most prolific metal absorption species (e.g., Mg II, C IV) observed in optical quasar spectra. I will present recent stacking and clustering measurements made possible by the vast quasar absorption line samples from the SDSS, and present new, direct observations of Mg II absorber host galaxies at high redshift using the Hubble Space Telescope. Together these studies reveal compelling links between strong Mg II absorbers and large-scale star formation-driven outflows, providing insights into the role of feedback in the evolution of galaxies from z~2.
|Thu, Jun 05|
University of California, Berkeley
"Planetary Systems in Four Dimensions"