Department of Astronomy
Abstracts for Fall 2009 Colloquia (most recent update: November 22, 2009)
Department of Astronomy
Abstracts for Fall 2009 Colloquia (most recent update: November 22, 2009)
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| Sept. 1st, 2009 |
Ramón J. García López, Instituto de Astrofísica de Canarias "Technology in Astrophysics: The IAC's Experience" Instrumentation developments for ground-based and space observatories are in the front-end of today's technologies. I will review in this talk the experience achieved by the IAC (Instituto de Astrofísica de Canarias) in this matter and our involvement in present-day projects for the Canary Islands, Chile and space. |
| Sept. 10th, 2009 |
Sukanya Chakrabarti, University of California, Berkeley |
| Sept. 15th, 2009 |
No talk scheduled. |
| Sept. 22nd, 2009 |
Lisa Prato, Lowell Observatory "The Youngest Extrasolar Planets" The detection of planets orbiting 1 to 2 million year old T Tauri stars and the determination their properties will provide a solid basis for advancing planet formation theory. Our young planet radial velocity survey at McDonald Observatory's 2.7 m Harlan J. Smith telescope has yielded a number of promising extrasolar planet candidates orbiting young targets in the Taurus star forming region. Follow up infrared observations to date have revealed two cases in which we were misled by the presence of spots on rapidly rotating, active, young stars, and one case of what appears to be a bona fide, newly-formed planet with a mass of about 6 M_Jupiter and a period of 8.3 days. This discovery sets the lower age limit on either the formation and/or the migration of hot Jupiters around low-mass stars. |
| Sept. 29th, 2009 |
No talk scheduled. |
| Oct. 6th, 2009 |
No talk scheduled.
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| Oct. 13th, 2009 |
Mark C. Lewis, Trinity University The Cassini probe has now been in orbit around Saturn for more than five |
| Oct. 20th, 2009 |
No talk scheduled, to avoid conflict with Bashfest (October 18-20).
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| Oct. 27th, 2009 |
Kevin L. Luhman, Pennsylvania State University "The Origin of Brown Dwarfs" The origin of brown dwarfs is a mystery because standard theories of star formation cannot easily create objects at such low masses. I will review the current state of observational and theoretical work on understanding how brown dwarfs form. I will first describe the latest measurements of various properties of brown dwarfs, including their initial mass function, binarity, circumstellar environment (disks, accretion, envelopes), and spatial and velocity distributions at birth, and I will then compare these data to the predictions of theories for the formation of brown dwarfs. |
| Oct. 27th, 2009 7:00 p.m. ACES 2.302 Public Lecture |
Rashid Sunyaev, Max-Planck Institute for Astrophysics (Antoinette de Vaucouleurs Public Lecture) "The Richness and Beauty of the Physics of Cosmological Recombination" The initial temperature of radiation in our Universe was very high and hydrogen and helium were completely ionized. At redshifts z ~ 1400 the temperature dropped to 3800 K and, according to the Saha equation, the recombination of hydrogen should occur. In reality this process is strongly delayed and some frozen amount of electrons should be present till the reionization of the Universe at z ~10. Process of recombination defines the position and the width of the last scattering surface which is crucial for the formation of the observed angular fluctuations of cosmic microwave background radiation (CMB), acoustic peaks and barionic oscillations in the distribution of galaxies and clusters of galaxies. The recombination of hydrogen occurs under conditions of very low density and in the presence of black body radiation. As a result, usually insignificant atomic processes begin to play a role. They influence the shape of CMB acoustic peaks at a level which will be detectable by the "Planck Surveyor" spacecraft and we should take them into account when estimating the key parameters of the Universe from CMB data. The recombination of hydrogen and helium leads to the appearance of recombinational lines in millimeter, centimeter and decimeter spectral bands. Observations of these lines will make it possible to check the predictions of the big bang recombination theory and will open a possibility to measure directly the density of barions, the CMB monopole temperature and specific entropy of the Universe, to check the presence of any significant energy release in early Universe (for example due to decay of unknown particles).Observations of helium recombination lines originated at redshifts 6000 and 2500 will open a way to measure the prestellar abundance of helium in the Universe. |
| Oct. 27th, 2009 Wednesday 3:30 p.m. RLM 15.216B |
Rashid Sunyaev, Max-Planck Institute for Astrophysics (Antoinette de Vaucouleurs Memorial Lecture) "Cosmic Microwave Background, Clusters of Galaxies and Cosmology" Rich clusters of galaxies contain thousands of galaxies moving in a huge potential well with velocities exceeding 1000 km/s. They are filled with dark matter and extremely hot intergalactic gas. This gas diminishes the brightness of CMB in the directions towards clusters of galaxies opening new way to discover distant unknown clusters. The spectrum of the brightness change is unique and does not depend on the redshift. Similarly the surface brightness of the cluster in the microwave spectral band does not depend on the redshift. This opens a way to observe the most distant clusters in the Universe, to study the key parameters of our Universe, and even to measure the peculiar velocities of clusters of galaxies in respect to the unique coordinate frame where CMB is isotropic. Planck Surveyor Spacecraft, South Pole Telescope, Atacama Cosmology Telescope, APEX, AMI and SZ-Array observed hundreds of clusters using this method. Using the data of microwave surveys and results of the new Russian-German space project SPEKTR-X/eRosita planning to map whole sky in X-Rays we will get an opportunity to construct the "curve of growth" for clusters of galaxies and to measure the baryonic acoustic oscillations in the distribution of clusters in the relatively old Universe. The X-Ray calorimeters and hot gas observations in the lithium-like Fe57 hyperfine structure line with wavelength 3.06 mm together with broad band microwave measurements will give a unique information about about turbulence and bulk motions in the hot intercluster gas. |
| Nov. 3rd, 2009 |
Eliot Quataert, University of California, Berkeley (Tinsley Visiting Professor) "The Birth of Neutron Stars and Black Holes in Gamma-ray Bursts" Gamma-ray bursts (GRBs) have long been among the most enigmatic of astrophysical transients. Observations during the past decade have led to a revolution in our understanding of long-duration GRBs, associating these events with the core-collapse of massive stars. However, only in the past few years have the host galaxies of short-duration GRBs been established, confirming that these arise from a separate progenitor population; the leading model for such events is the merger of two compact objects (e.g., a neutron star and a black hole) although alternative possibilities remain viable (e.g., the accretion induced collapse of a white dwarf to a neutron star). In this talk, I will describe theoretical models for both long and short-duration bursts, emphasizing several outstanding problems. Short GRBs are particularly interesting since compact object mergers are the primary target for km-scale gravitational wave observatories such as Advanced LIGO. I will describe possible electromagnetic counterparts to these gravitational wave sources. |
| Nov. 10th, 2009 |
Benjamin Weiner, Steward Observatory, University of Arizona "Infrared-luminous galaxies and their evolution: what, where and maybe some of how" Infrared-luminous galaxies are powered by star formation or active galactic nuclei, but emit much of their light as radiation reprocessed by dust into the far infrared. The most massive starbursts in both the local and high redshift universe manifest themselves as ultraluminous infrared galaxies. This class of galaxies was discovered by IRAS; observations with Spitzer have revealed many IR-luminous galaxies from z=0 to z=1 and yielded measurements of the evolution in global IR luminosity density. However, it remains controversial what IR-luminous galaxies at z=1 are, and what they will evolve into. Are IR-luminous galaxies at high redshift mostly galaxy mergers, as they are at low redshift? Are ultraluminous IR galaxies strongly clustered, and can we infer whether they must evolve into cluster galaxies today? I will discuss these questions on IR-luminous galaxy properties and clustering using data from Spitzer/MIPS, HST, and the DEEP2 redshift survey. |
| Nov. 17th, 2009 |
Christian Marois, NRC Herzberg Institute of Astrophysics, Montreal, Canada "Imaging Planets Orbiting Other Stars: the HR8799 Multi-Planet System" Almost 15 years ago the first unambiguous direct detection of a substellar object around a star (Gl229B) was made. Several teams have since then pursued ambitious adaptive optics surveys on large telescopes, but only several brown dwarfs and a few possible candidate planets have been detected so far at generally wide >100 AU separations - it is unlikely that these have formed in a disk like the planets of our solar system and are probably the result of the binary star formation process. The essentially null result of these surveys, in contrast with the very successful radial velocity searches <5 AU, is suggesting that massive Jupiter-like planets are rare >20 AU around stars. The year 2008 marks then end of this long drought with the direct detection of planets around A-type stars. One of these discoveries, the HR8799 planetary system made at the Gemini North and Keck telescopes, is the first multi-planet system portrait and also the first direct detection of thermal emission of confirmed planets in orbit around a star. This system also shows convincing evidences that the three planets formed in a disk. The HR8799 system discovery marks an important step forward in the direct characterization of Jovians to Earth-like planets with future instrumentations and large ELTs. I will describe the HR8799 system discovery, new 2009 results and what we can expect in the near future with new generation adaptive optics systems and 30-m class telescopes. |
| Nov. 24th, 2009 |
Daisuke Nagai, Yale University "Cosmology and Astrophysics with Galaxy Clusters" Clusters of galaxies are unique and powerful probes of cosmology and astrophysics, promising to provide new insights into the nature of dark energy and dark matter to the physics of galaxy formation. The study of galaxy clusters combines the richness of plasma physics with the predictive power of modern cosmological models to explain remarkable new observational results. In this talk, I will describe recent advances in theoretical and intensive numerical modeling of galaxy cluster formation to interpret recent X-ray and Sunyaev- Zel'dovich Effect cluster surveys. Finally, I will discuss outstanding issues and future directions in this area. |
| Dec. 1st, 2009 |
Juna Kollmeier, Carnegie Observatories "Probing the Inner and Outer Milky Way" The Milky Way provides an opportunity for a close-up investigation of the complex processes of galaxy and star formation. I will discuss recent efforts to do this by using rare, but important, probes of these phenomena. In the first portion of the talk I will present results on hypervelocity stars primarily from the Sloan Digital Sky Survey. The distribution of these stars, in physical properties and in space, allows us to place interesting limits on star formation and dynamics at the Galactic Center as well as the possibility to constrain the shape of the Milky Way's dark matter halo. I will discuss progress we have made toward these goals. In the second portion of the talk, I will discuss how one can use RR Lyrae stars to probe the outer halo of the Milky Way and find new and distant substructures which are difficult to probe by other means. Our recent confirmation of a distant structure in RR Lyrae stars highlights the power of this approach to unraveling the outer halo and showcases exciting possibilities for future all-sky time-domain surveys. |
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Department of Astronomy Abstracts for Spring 2010 Colloquia |
| Jan. 19th, 2010 |
Edo Berger, Harvard University "Title: TBA" |
| Jan. 26th, 2010 |
Andrew Blain, California Institute of Technology "Title: TBA" |
| Feb. 2nd, 2010 |
Jane Rigby, Carnegie Observatories "Title: TBA" |
| Feb. 9th, 2010 |
Ravit Helled, University of California, Los Angeles "title: TBA" |
| Feb. 16th, 2010 |
Angela Speck, University of Missouri, Columbia "Title: TBA" |
| Feb. 23rd, 2010 |
John Johnson, California Institute of Technology "title: TBA" |
| Mar. 2nd, 2010 |
Evgenya Shkolnik, Carnegie Institution Department of Terrestrial Magnetism "Title: TBA" |
| Mar. 9th, 2010 |
No talk scheduled, to avoid conflict with the following Conference: "The First Stars and Galaxies: Challenges for the Next Decade" (March 8-11). |
| Mar. 15-19, 2010 |
No talk scheduled, to avoid conflict with Spring Break (March 15-19). |
| Mar. 16th, 2010 |
Dara Norman, National Optical Astronomy Observatory (NOAO) "title: TBA" (attempting to reschedule) |
| Mar. 23rd, 2010 |
Suvi Gezari, Johns Hopkins University "title: TBA" |
| Mar. 30th, 2010 |
Genevieve Graves, University of California, Berkeley "title: TBA" |
| Apr. 6th, 2010 |
Anders Johansen, Leiden University "title: TBA" |
| Apr. 13th, 2010 |
Adam Burrows, Princeton University (Tinsley Visiting Professor) "title: TBA" |
| Apr. 20th, 2010 |
No talk scheduled yet. |
| Apr. 27th, 2010 |
No talk scheduled yet. |
| May. 4th, 2010 |
Emily Freeland, Texas A&M University "title: TBA" |