Date: Monday 24-Jan-2011
Speaker: Mia, Edmund, and Rob
Title: Highlights of the AAS Meeting (Jan 9-13)
http://aas.org/meetings/aas217
Date: Monday 07-Feb-2011
Speaker: Soko Matsumura (UMD)
Title: Highlights of the latest Kepler findings
Analysis of the first 4 months of data: http://arxiv.org/abs/1102.0541 Multiple Transiting Planet Systems: http://arxiv.org/abs/1102.0543 Kepler-10b, Kepler's first rocky planet: http://arxiv.org/abs/1102.0605 Kepler-11, six transiting planets: http://arxiv.org/abs/1102.0291
Date: Monday 14-Feb-2011
Speaker: Peter, Tamara, and Richard
Title: Astroph Discussion
Baryons at the Edge of the X-ray Brightest Galaxy Cluster Simionescu, Allen, and Mantz et al. arXiv:1102.2429 http://arxiv.org/abs/1102.2429
Date: Monday 28-Feb-2011
Speaker: Cole Miller (UMD) & Stratos Boutloukos (University of Tuebingen)
Title: Radius of a binary pulsar
Date: Monday 07-Mar-2011
Speaker: Ranjan Vasudevan (UMD)
Title: New Perspectives on the Luminous Power Output of AGN
Date: Monday 14-Mar-2011
Speaker: Styliani (Stella) Kafka (Carnegie Institution of Washington)
Title: CANCELLED Magnetic Activity on the Donor stars of Cataclysmic Variables: Nature or Nurture?
Chromspheric Activity on the mass-losing secondary star in cataclysmic variables (CVs) is commonly invoked to explain sustained mass transfer caused by system angular momentum loss via a magnetized stellar wind. Such activity may also be responsible for the CV period gap, and for the widely differing mass transfer rates among CVs at the same orbital period. Until recently, there was a substantial lack of observational support for these scenarios, because conventional activity indicators (such as X-rays, H-alpha emission, and flares) can also be produced by accretion. I present an extended spectroscopic monitoring campaign of a few magnetic CVs at times of reduced accretion, when the stellar components are exposed. Observed structures in emission lines, reveal magnetically confined gas in the system. A comparison with similar detached systems, reveal similarities that link the two categories to a uniform paradigm for mass transfer, providing new aspects of CV evolution.
Date: Monday 28-Mar-2011
Speaker: Styliani (Stella) Kafka (Carnegie Institution of Washington)
Title: Magnetic Activity on the Donor stars of Cataclysmic Variables: Nature or Nurture?
Chromspheric Activity on the mass-losing secondary star in cataclysmic variables (CVs) is commonly invoked to explain sustained mass transfer caused by system angular momentum loss via a magnetized stellar wind. Such activity may also be responsible for the CV period gap, and for the widely differing mass transfer rates among CVs at the same orbital period. Until recently, there was a substantial lack of observational support for these scenarios, because conventional activity indicators (such as X-rays, H-alpha emission, and flares) can also be produced by accretion. I present an extended spectroscopic monitoring campaign of a few magnetic CVs at times of reduced accretion, when the stellar components are exposed. Observed structures in emission lines, reveal magnetically confined gas in the system. A comparison with similar detached systems, reveal similarities that link the two categories to a uniform paradigm for mass transfer, providing new aspects of CV evolution.
Date: Monday 04-April-2011
Speaker: Constantinos Kalapotharakos (GSFC/NASA)
Title: Force Free Electrodynamics and the 3D Pulsar Magnetosphere
We will see a brief of the Pulsars' magnetosphere problem. We will present the Force-Free Finite Difference Time Domain (FDTD) code that helped us to produce time evolving simulations that reveal the 3D structure of the Pulsar magnetosphere. We will show the 3D structure of the Pulsar magnetosphere for the whole spectrum of the inclination angles between the magnetic and the rotation axis. We will see how this structure helped us to produce pulses that are in well agreement with the observations. Finally we will discuss the prospects for the future.
Date: Monday 18-April-2011
Speaker: Mia Bovill (UMD)
Title: The Fossils of the First Galaxies in the Local Universe
We use a new set of cold dark matter simulations of the local universe to investigate the distribution of fossils of primordial dwarf galaxies around the Milky Way. We build upon previous results showing agreement between observed stellar properties of a subset of the ultra-faint dwarfs and our simulated fossils. However, we find an overabundance of bright (L_V > 10^4 L_solar) satellites with respect to observations where they are nearly complete. This "bright satellite problem" is most evident in the outer parts of the Milky Way, but is present at radii as small as 50 kpc. We estimate the bright satellites' primordial stellar populations may be extremely diffuse, producing ghost halos with surface brightnesses below surveys' detection limits and easily stripped by tidal forces. Although we cannot yet present unmistakable evidence for the existence of the primordial fossils in the Local Group, the detection of "ghost halos" of primordial stars around isolated dwarfs would prove that stars formed in minihalos before reionization, and strongly suggest that a fraction of the ultra-faint dwarfs are fossils of the first galaxies.
Date: Friday 29-April-2011
Speaker: Eric Linder (UC Berkeley/LBNL/IEU)
Title: Testing Dark Energy and Gravity
In the 13 years since discovery of the acceleration of the universe, great developments have been made in cosmological observations and great numbers of theories have proliferated to explain the dark energy causing the speed-up. I discuss the most recent data and what we might expect in the future. For the present, the observed behavior near to Einstein's cosmological constant can result from a wide variety of different physics - from quantum fields to new gravity. For the future, I explore how mapping the three-dimensional galaxy distribution will allow us to test cosmology and gravity.
Date: Monday 2-May-2011
Speaker: Richard Greenberg (University of Arizona)
Title: Characterizing Multi-planet Systems with Classical Secular Theory
Classical secular theory can be a powerful tool to describe the qualitative character of multi-planet systems and offers insight into their histories. For example, major axes currently locked in alignment may indicate substantial tidal damping. Current near-separatrix behavior may suggest an early mutual scattering event. Also, eigenmodes help assess dynamical coupling. For 55 Cancri, using the orbital solution by Fischer et al. (2008), the current alignment of major axes is fortuitous as these planets are all controlled by dierent eigenmodes. Also, there are two dynamical groups: the inner three planets and the outer two. With the orbit solution from Dawson and Fabrycky (2010), again the alignment of major axes is fortuitous. Also, the group structure changes: the innermost planet is now fairly decoupled from the other inner planets. This decoupling allows the eccentricity of the inner planet to stay fairly low independent of planetary interactions. For 61 Virginis, the libration of the outer planets' major axes is not due to eccentricity damping (contrary to speculation by Vogt et al.). Instead the outer planets are in a dynamical group and libration results from initial conditions and a propensity due to the system's basic architecture (i.e. masses and semi-major axes). Classical secular theory reproduces the behavior of the hypothetical system discussed by Mardling 2007 despite the eccentricities being large. other systems, including Gliese 581, will also be discussed.
Date: Thursday 12-May-2011
Speaker: Ilya Mandel (MIT/University of Birmingham)
Title: GW astrophysics with compact binaries
The ground-based gravitational-wave telescopes LIGO and Virgo approach the era of first detections. In this talk, I will review the current knowledge of the coalescence rates and parameter distributions of merging neutron-star and black-hole binaries. I emphasize the bi-directional connection between gravitational-wave astronomy and conventional astrophysics. Astrophysical input will make possible informed decisions about optimal detector configurations and search techniques. Meanwhile, rate upper limits, detected merger rates, and the distribution of masses and spins measured by gravitational-wave searches will constrain astrophysical parameters through comparisons with astrophysical models. I report on ongoing efforts to develop a framework for converting gravitational-wave observations into improved constraints on astrophysical parameters and discuss future developments necessary to the success of gravitational-wave astronomy.
Date: Monday 16-May-2011
Speaker: Alberto Bolatto (UMD)
Title: The State of the Gas and the Relation Between Gas and Star Formation at Low Metallicity: the Small Magellanic Cloud
*** Paper by Bolatto, Leroy, Jameson, Ostriker, et al.
We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from Halpha in the Small Magellanic Cloud (SMC). By using infrared dust emission and local dust-to-gas ratios, we construct a map of molecular gas that is independent of CO emission. This allows us to disentangle conversion factor effects from the impact of metallicity on the formation and star formation efficiency of molecular gas. On scales of 200 pc to 1 kpc (where the distributions of H2 and star formation match well) we find a characteristic molecular gas depletion time of tau_dep ~ 1.6 Gyr, similar to that observed in the molecule-rich parts of large spiral galaxies on similar spatial scales. This depletion time shortens on much larger scales to ~0.6 Gyr because of the presence of a diffuse Halpha component, and lengthens on much smaller scales to ~7.5 Gyr because the Halpha and H2 distributions differ in detail. We estimate the systematic uncertainties in our dust-based tau_dep measurement to be a factor of ~2-3. We suggest that the impact of metallicity on the physics of star formation in molecular gas has at most this magnitude, rather than the factor of ~40 suggested by the ratio of SFR to CO emission. The relation between SFR and neutral (H2+HI) gas surface density is steep, with a power-law index ~2.2+/-0.1, similar to that observed in the outer disks of large spiral galaxies. At a fixed total gas surface density the SMC has a 5-10 times lower molecular gas fraction (and star formation rate) than large spiral galaxies. We explore the ability of the recent models by Krumholz et al. (2009) and Ostriker et al. (2010) to reproduce our observations. We find that to explain our data at all spatial scales requires a low fraction of cold, gravitationally-bound gas in the SMC. We explore a combined model that incorporates both large scale thermal and dynamical equilibrium and cloud-scale photodissociation region structure and find that it reproduces our data well, as well as predicting a fraction of cold atomic gas very similar to that observed in the SMC.
Date: Monday 23-May-2011
Speaker: Julio Chaname (Carnegie Institution of Washington)
Title: The Non-Violent End of the Binary Semi-Major Axis Distribution
While stars in binary systems of all types have been always recognized to be of fundamental importance in astronomy, only in recent years has the population of binaries at the wide end of the distribution of orbital separations (semi-major axis of 100 AU and larger) been properly exploited. I will review the status of research on wide binaries and highlight the potential inherent to these objects for the study of the Galaxy, including their unique usefulness as probes of inhomogeneities of the gravitational potential.
Date: Friday 10-June-2011
Speaker: Camilla Colombo (University of Strathclyde - Glasgow)
Title: Orbital dynamics of high area-to-mass spacecraft and future applications
Future missions for the exploration of the solar system require maximising scientific return while being affordable in cost. This can be enabled by deploying a number "smart dust" devices that can be injected directly into orbit from a primary spacecraft. Recent advances in miniaturisation allow the fabrication of operational spacecraft down to the dimensions of a single chip, with sensing, computing and communication capabilities. These are satellites-on-a-chip or SpaceChips.
Due to their high area-to-mass ratio, the orbital dynamic of SpaceChips presents many similarities to dust dynamics in planetary systems. Surface perturbations, such as solar radiation pressure and atmospheric drag can be exploited to generate new families of highly perturbed non-Keplerian orbits. The long-term evolution of a swarm of SpaceChips is expressed in the phase space in term of the secular variation of the orbital elements due to the effect of solar radiation pressure, drag and the Earth's oblateness.
Different families of orbits in this highly perturbed dynamics can be exploited for novel future science missions (planetary magnetic tail, atmosphere, solar radiation through the atmosphere exploration), efficient observation of the day side of a planet for imaging, self-organising swarms of spacecraft for communications, geo-engineering applications, passive end-of-life de-orbit and active orbit control through electrochromic coating of the spacecraft.
This seminar will introduce the fascinating dynamics of high-area-to-mass ratio spacecraft and will present the concepts and potentialities for future engineering applications.
