List of Past Astronomy Colloquia : 01-Jan-2015 to 01-Jun-2015

Date:   Wednesday 04-Feb-2015
Speaker:   Dr. Aki Roberge (GSFC)
Title:  "Gas and Dust in Debris Disks: Clues to the Late Stages of Planet Formation"

The basic character of debris disks was established soon after their discovery in the mid-1980's. These disks around nearby main sequence stars are composed of material (mostly dust) produced by collisions and/or evaporation of extrasolar asteroids and comets. However, fundamental observational questions about debris disks remain unanswered. How much material do debris disks typically contain and how does it evolve with time? What is the composition of their dust and gas? Are planets present or forming in the disks? Answers to these questions will provide insights into the late stages of planetary system formation and the origins of terrestrial planet atmospheres.

In this talk, I will explain our current understanding of the place of debris disks in the planet formation process. Progress toward addressing the questions given above will be discussed, with emphasis on recent studies of the small but important gas component. Finally, I will outline the implications of debris dust for future efforts to directly image and characterize extrasolar terrestrial planets.

Date:   Wednesday 011-Feb-2015
Speaker:   Dr. John Grant (Smithsonian)
Title:  The Mars Exploration and Mars Science Laboratory Rovers: More than a Decade of Exploration on the Red Planet

The twin Mars Exploration Rovers began their exploration of Gusev crater and Meridiani Planum, Mars, more than 11 years ago. The Spirit rover ceased operation more than six years after landing, but the Opportunity rover continues to operate with relatively recent investigations focused along the rim of the 22 km-diameter Endeavour crater. The larger Mars Science Laboratory Curiosity joined in the exploration of Mars when it landed in Gale crater just over two and a half years ago. Although these two missions had differing objectives, each of the rovers has revealed new information about the evolution of Mars and confirmed the occurrence of potentially habitable settings on the planet.

Date:   Wednesday 18-Feb-2015
Speaker:   Dr. Steve Lubow (STSci)
Title:  Dynamics of Misaligned Disks in Binary Systems

Disks in binary systems can sometimes be misaligned or even counter-rotating with respect to the orbit of the binary. Under certain conditions, the orbit of a ballistic object in a binary system can undergo strong oscillations of tilt and eccentricity. This effect, known as the Kozai-Lidov (KL) effect, occurs when the orbit is sufficiently inclined with respect to the binary orbit plane. I will review the history of the discovery of this effect and its applications to several astronomical systems. We have recently investigated the dynamical effects of inclined and counter-rotating disks in binary systems. I will discuss how tidal effects operate on such disks and our recent finding that disks can undergo KL oscillations. Such effects may have important implications to disk evolution and planet-disk interactions.

Date:   Wednesday 25-Feb-2015
Speaker:   Dr. Steinn Sigurdsson (PSU)
Title:  Diagnostics of a Black Hole in a Globular Cluster

Black holes in globular clusters are potentially very interesting laboratories for a range of astrophysics, and may be an important class of gravitational radiation sources. The dynamical evolution of globular clusters provides for an interesting range of possible fates for the black holes formed in them. Recent observations have provided some very interesting candidate black holes in globular clusters. I discuss some of the theoretical considerations of the recent findings, in particular the candidate in NGC 1399.

Date:   Wednesday 04-Mar-2015
Speaker:   Dr. Eliot Quataert (Berkeley)
Title:  The Surprisingly Dynamic Last Years in the Lives of Massive Stars

In the last few years of the lives of massive stars, fusion in the core of the star produces a nuclear power that greatly exceeds the Eddington luminosity. This drives vigorous convection in numerous core and shell burning phases. I describe the surprising effect that waves excited by such convection can have on the properties of massive stars in the years leading up to core collapse. Wave transport of energy into the stellar envelope can power prodigious mass loss in the last year of stellar evolution. And angular momentum transport by waves excited during shell burning phases may well determine the angular momentum of the pre-supernova core, setting the birth spins of compact objects.

Date:   Wednesday 11-Mar-2015
Speaker:   Dr. Vicky Kaspi (McGill)
Title:  The Hunt for Millisecond Pulsars

The continued search for more of nature's most perfect clocks -- millisecond radio pulsars -- has recently taken a more urgent turn given the potential of these objects to detect and study gravitational waves from a variety of potential sources, most likely merging supermassive black holes. Additionally, their discovery has inevitably led to surprising and interesting astrophysical results as novel binary MSPs are revealed and studied. Such bonuses include constraints on the equation-of-state of dense matter, tests of theories of gravity, as well as surprises in binary evolution. Most recently, the hunt for millisecond pulsars has led to a new, serendipitous discovery, the so-called `Fast Radio Bursts,' few-ms single pulses of unknown origin, from apparently cosmological distances. Here I describe ongoing millisecond pulsar searches and their recent bounty, as well as plans for future study of these objects, as well as of single-burst sources.

Date:   Wednesday 18-Mar-2015
Speaker:   UMD-CLOSED

Date:   Wednesday 25-Mar-2015
Speaker:   Dr. Beth Willman (Haverford College)
Title:  Triumphs and tribulations of near-field cosmology with wide-field surveys: a biased perspective

Over the last decade, wide-field surveys have revolutionized our view of the Milky Way’s stellar halo and dwarf galaxy population. Much of this observational progress has been motivated by a series of apparent “crises” for our cosmological model: the missing satellites problem, too big to fail, and the apparent planar distribution of dwarf satellite galaxies. These challenges have effectively functioned as flashlights pointing us to interesting galaxy formation physics. I will highlight related observational progress in our understanding of galaxy formation using near-field observations. I will then focus on the limiting impacts of observational bias and ways that current and future surveys will be used to tackle these biases. In particular, I will present new predictions for the number of Milky Way dwarf galaxies expected to be discovered in DES and LSST, RR Lyrae stars as a tool to discover dwarf galaxies in previously unexplored territory, and the use of M giant stars to map the Milky Way’s halo beyond its virial radius.

Date:   Wednesday 01-Apr-2015
Speaker:   Dr. Eric Ford (PSU)
Title:  Characterizing the Distribution of Planetary Architectures with Kepler

For centuries, planet formation theories were fine tuned to explain the details of solar system. The diversity of planetary systems uncovered by Doppler surveys challenged previous theories and led to insights into planet formation, orbital migration and the excitation of orbital eccentricities and inclinations. NASA's Kepler mission has identified 450 systems with multiple transiting planet candidates, including nearly 1200 planet candidates and many potentially rocky planets. I will discuss how Kepler data can be used to characterize the distribution of planetary orbital properties and the architectures of planetary systems, including small and rocky planets. Architectures refers to planet masses, orbits and their relationships among planets with a common host star which can serve as probes of the planet formation process. I will discuss early efforts to translate these observations into constraints on the formation and orbital evolution of planetary systems.

Date:   Wednesday 08-Apr-2015
Speaker:   Dr. Tom Megeath (University of Toledo)
Title:  Orion as a Laboratory of Protostellar Evolution: Results from the Herschel Orion Protostar Survey

The Orion molecular clouds are a remarkable laboratory for studying star formation across the mass spectrum and across the full range of environments in which stars form, from crowded clusters containing massive stars to relatively isolated low mass star formation. I will present results from the Herschel Orion Protostar Survey, or HOPS, a study of over 300 protostar in the Orion clouds with the Herschel, Spitzer, Hubble and APEX telescopes. The goal of this study is to study low to intermediate mass protostars in the Orion molecular clouds (but outside the Orion Nebula) from the earliest phases through the termination of mass infall. By performing extensive multi-wavelength observation of a large sample of protostars and the dense gas from which they form, we can study the evolution of protostars and how environment influences the formation of stars. I will overview results from analyses of protostellar envelopes using 1.6-870 micron SEDs, of protostellar outflows with 57-196 micron far-IR spectroscopy, and the study of binaries and disks with high resolution imaging at 1.6 micron.

Date:   Wednesday 15-Apr-2015
Speaker:   Dr. Dusan Keres (UCSD)
Title:  "Galaxies on FIRE: stellar feedback and galaxy evolution"

"Galaxies grow through accretion of gas and mergers in their complex cosmological environment. However, this growth needs to be regulated. Without additional "feedback” processes modeled galaxies end up too massive when compared to observed galaxies. I will present cosmological simulations from Feedback in Realistic Environments (FIRE) project. In FIRE we have implemented physical feedback model from massive stars in the form of radiation pressure, stellar winds, supernovae momentum and energy and photo-ionization, on local (~5-50pc) scales within the resolved interstellar medium. Unlike many of the previous stellar feedback implementations we account for relevant hydrodynamical interactions and cooling processes at all times. Non-linear interactions of feedback mechanisms regulate the structure of the inter-stellar medium and galactic star formation and drive large scale galactic outflows that eject large amounts of galactic gas. With the energy and momentum input from the standard population synthesis models our simulations produce galaxies with realistic stellar masses, star formation histories and metallicities. Our model galaxies undergo episodic star formation and blow powerful galactic winds that interact with the circum-galactic medium and lower the central concentrations of cold dark matter. I will connect these findings to the observed universe and discuss current limitations and future improvements in models of galaxy formation."

Date:   Wednesday 22-Apr-2015
Speaker:   Dr. Nikole Lewis (StSci)
Title:  Probing Weather on Distant Worlds

The number of planets detected outside of our solar system has increased at an almost exponential rate over the past 10 years with currently more than 1800 confirmed exoplanets. Slowly, we are beginning to characterize the physical properties of these planets including their atmospheric composition, thermal structure, and global circulation patterns. Here I discuss the combination of sophisticated three-dimensional atmospheric models with space-based observations to probe weather patterns in exoplanet atmospheres. I will focus on recent phase-curve and eclipse-mapping observations with the Spitzer, Hubble, and Kepler Space Telescopes aimed at characterizing the global circulation patterns of extrasolar planets. I will also touch on efforts to extend these three-dimensional models to brown dwarf atmospheres and future prospects with the James Webb Space Telescope. The combination of high-precision observations with three-dimensional atmospheric models will hopefully shed new light on the radiative, dynamic, and chemical process that are at work in these atmospheres beyond our solar system.

Date:   Wednesday 29-Apr-2015
Speaker:   Dr. Alyssa Rhoden (JHU APL)
Title:  Reading Between the Lines: Using Fractures to Understand Icy Satellite Evolution

The satellites of the outer solar system record diverse and complex geologic histories. Gravitational interactions between the satellites and their host planets provide energy that maintains present-day liquid water oceans, causes pervasive tectonism, and powers active plumes. Tidal heating and tidal stress, governed by the orbits and rotation states of these satellites, offer an entirely different way of maintaining geologic activity, and creating potentially habitable worlds, than we observe in the inner solar system. I will discuss the geologic processes operating on Europa, the secrets revealed by its tectonic record, and the implications of a recent detection of a water vapor plume. I will then provide an overview of the next big science questions that can be addressed with the tidal-teconic approach, including the formation of the Saturnian satellites and the evolution of the Pluto-Charon system.

Date:   Wednesday 06-May-2015
Speaker:   Dr. Mark Vogelsberger (MIT)
Title:  The era of large-scale cosmological simulations

Progress in our understanding of galaxy formation, improved numerical algorithms, and increased computing power have recently lead to a number of impressive large-scale hydrodynamical simulations, which are able to reproduce key observables of the local and higher redshift Universe. These simulations allow us, for the first time, to study the interplay between large-scale structure and galaxy formation in detail. I will give an overview of these efforts and focus on the successes and failures of some of them.

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