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 Astronomy Colloquia at Caltech for 2009-2010 

Colloquia are held every Wednesday during the academic year at 4pm in the Cahill Hameetman auditorium. Tea and cookies are served at 3:45 pm in the Ahmanson library located on the 1st floor of Cahill.





                                                   Talk Title



Rachel Akeson


Host: Schuyler van Dyk

Infrared Interferometry and the Evolution of Circumstellar Disks


After a brief review of the current state of infrared interferometry, particularly the Keck Interferometer, I will focus on observations of circumstellar disks around young and main sequence stars. Infrared interferometry is unique in its ability to make direct, milli-arcsecond scale measurements of the physical properties of the central regions of these disks. These measurements have placed strong constraints on the inner disk regions of T Tauri and Herbig stars. More recently, this technique has also been applied to the so-called transitions disks and the debris disks around main sequence stars.



Pavel Kroupa


Host: Sterl Phinney

The satellite galaxies of the Milky Way and Andromeda


The satellite galaxies of the Milky Way, and to a less-significant amount, those of Andromeda, are distributed anisotropically about their hosts. The MW system appears to be a disk-like feature which is rotating. These and other features of the satellite galaxy population indicate that many of the satellites may be ancient tidal-dwarf galaxies. If true this would have major implications for fundamental physics.


John Carpenter


Structure and Evolution of Protoplanetary Disks


The properties and evolution of circumstellar disks around young (< 10 Myr) stars provide an indirect means to investigate the formation of planetary systems. I present recent results from the Spitzer Space Telescope that probe the evolution of disks in this time period, including the dissipation of gas-rich primordial disks and the formation of debris systems. In addition, I will present sub-arcsecond resolution CARMA images of the dust emission in a sample of primordial disks in the Taurus-Auriga and Ophiuchus molecular clouds. 



Eliot Quataert

UC Berkeley

Host: Sterl Phinney

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.


Reinhard Genzel


Host: Sterl Phinney

Spatially resolved dynamics of z~2forming galaxies


I report on two major programs of studying the kinematics, star formation and cold gas properties of z~2 massive star forming galaxies (z2SFGs) with spatially resolved spectroscopy. With the adaptive optics assisted, integral field spectrometer SINFONI on the ESO VLT we have studied about 90 z2SFGs and find compelling evidence for large, turbulent rotating disk galaxies in ~50% of the larger objects that we spatially resolve well. It appears plausible that these z2SFGs may be driven by continuous, rapid accretion of gas from their dark matter halos, and that their evolution is strongly influenced by internal, secular evolution. In a new program on the IRAM Plateau de Bure millimeter interferometer we have also detected for the first time CO 3-2 line emission in a sample of these z2SFGs (as well as in matched z~1.2 counterparts). We find that the z~1-2 SFGs are gas rich and that their star formation properties are fully compatible with a standard Kennicutt-Schmidt star formation relation. I will discuss the impact of these new observations on our understanding of galaxy evolution in the early Universe.



Andy Gould

Ohio State University

Host: Judy Cohen

Microlensing: Measuring the Galactic Distribution of Planets.


Microlensing has discovered 13 planets, including the first "cold Neptunes", the first Sun/Jupiter/Saturn analog, the least massive planet, and the heaviest planet orbiting an M dwarf.  A great strength of microlensing is that it does not depend on photons from the host star, and so probes classes of planets not accessible to other techniques.  Originally, this was also considered a great weakness: since the host cannot be seen, we generally did not expect to be able to determine its mass and distance.  I show that masses and distances have nevertheless been measured for the majority of planets discovered to date.  In particular, we can determine which are in the Galactic disk vs the Galactic bulge. I report a very surprising initial result from this observed distribution of distances. 


Mark Reid

Harvard-Smithsonian Center for Astrophysics

Host: Nick Scoville

Measuring the Cosmos


Over 2000 years ago, Hipparcus measured the parallax of the Moon from two locations across the Mediterranean Sea.  However, determining distances to stars proved much more difficult.  Many of the best scientists of the 16th through 19th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test the Heliocentric cosmology.  It was not until 1838 that Bessel measured the first stellar parallax.                                                           


Distance measurement in astronomy remained a difficult problem even into the early 20th century, when the nature of galaxies ("spiral nebulae") was still debated.  While we now know the distances of galaxies at the edge of the Universe, we have only just begun to measure distances accurately throughout the Milky Way.  I will present new results on parallaxes and motions of star forming regions with near micro-arcsecond accuracy using the VLBA.  These measurements address fundamental issues, including the spiral structure, size, and mass of the Milky Way.


Željko Ivezić

University of Washington

Host: Judy Cohen

Mapping the Milky Way: from SDSS and 2MASS to LSST and Gaia


The formation of galaxies like the Milky Way was long thought to be a steady process that created a smooth distribution of stars.  Instead, recent discoveries of complex substructure in the distribution of the Milky Way's stars have deeply shaken this standard view.  I will discuss how the unprecedentedly accurate and robust data from modern sky surveys, such as Sloan Digital Sky Survey and 2MASS, have enabled some of these discoveries, and will speculate what further  progress can be expected from the upcoming next-generation surveys,  such as Gaia and Large Synoptic Survey Telescope.


 Nov 25 –no colloquium





Wendy Freedman


Host: Judy Cohen

The Carnegie Supernova and Hubble Projects


I will discuss two ongoing projects: The Carnegie Supernovae Project (CSP), a long-term program using Type Ia supernovae to place constraints on the equation of state for dark energy; and The Carnegie Hubble Project (CHP), a new Spitzer Exploration Program  aimed at measuring the Hubble constant to an accuracy of 2%.  As part of the CSP, we have been extensively monitoring Type Ia supernovae, obtaining multi-wavelength (uBVgriYJHK) observations at low redshifts (z<0.08), and measuring the first I-band Hubble diagram out to redshifts of 0.7. The CHP is extending the entire      extragalactic distance scale calibration into the mid-infrared. Based on a geometric parallax calibration of Cepheids from the Hubble Space Telescope (and in future, from GAIA), and with negligible reddening in the mid-infrared, this program will re-measure the Cepheid distances to nearby galaxies, calibrating Type Ia supernovae and other methods well out into the Hubble flow. I will discuss how this improved accuracy in the Hubble constant, in combination with new experiments like Planck, provides strong constraints on other cosmological parameters.   






Jonathan Tan

University of Florida

Host: Jessica Lu

Massive Star Formation Through the Universe


I outline several major open questions in our understanding of massive star and star cluster formation. Starting at the highest redshifts, I describe our current view of how the first generations of Population III stars were born. I focus on our efforts to predict their initial masses. I then compare Population III star formation with present-day massive star and star cluster formation. Observational efforts to determine the initial conditions are a key step for making progress in this area. Star cluster formation is intimately connected to massive star formation: essentially all present-day massive stars are born in rich star clusters. I discuss the timescale for star cluster formation and how we are beginning to reconcile the small (~parsec) scale star cluster formation process with the global galactic scale star formation (Schmidt-Kennicutt) relations.


Nathan Smith

UC Berkeley

Host: Nick Scoville

Eta Carinae and Pre-Supernova Temper Tantrums of Massive Stars


The evolved massive stars known as luminous blue variables (LBVs) have enjoyed renewed interest in recent years for three reasons: 1) we have learned that eruptions of LBVs probably dominate the total mass lost during a star's lifetime, strongly influencing the star's death, 2) their eruptions make up many of the transient sources fainter than supernovae that will be discovered in increasing numbers in coming years, and 3) LBVs are the likely progenitors of the most luminous supernovae known, giving us a potential window to the deaths of massive stars in the early universe.  Despite astonishing mass-loss rates of as much as 1 Msun/yr and total energies of more than 1e50 ergs, the physical mechanism driving these recurring eruptions remains unexplained after decades of research.  There is hope that the new wave of transient discoveries will help improve the situation.  With that in mind, I will begin by summarizing what we have learned from detailed study of Eta Carinae, the poster-child for giant eruptions of unstable massive stars. I will then discuss how this well-studied example fits in with the range of observed LBV properties, what some outstanding mysteries are, and how this can help guide our intuition for studying luminous supernovae and eruptive transients that result from similar stars in other galaxies.


Natalie Batalha

San Jose State

Host: Schuyler van Dyk

Status of Kepler Mission and Early Discoveries


Kepler is a Discovery-class mission designed to determine the frequency of Earth-size planets in and near the habitable zone of solar-like stars. The instrument consists of a 0.95 m aperture photometer designed to obtain high precision photometric measurement of > 100,000 stars to search for patterns of transits. The focal plane of the Schmidt-type telescope contains 42 CCDs with at total of 95 megapixels that cover 115 square degrees of sky. The photometer was launched into an Earth-trailing heliocentric orbit on March 6, 2009, finished its commissioning on May 12, and is now in the science operations mode. During the commissioning, data were obtained at a 30 minute cadence for 53,000 stars for 9.7 days. During the first 33.5 days of science-mode operation, 156,000 stars have been observed.  Discoveries based on these data are presented.


Although the data have not yet been corrected for the presence of systematic errors and artifacts, the data show the presence of hundreds of eclipsing binary stars and variable stars of amazing variety.  Analysis of the commissioning data also show transits, occultations and light emitted from the known exoplanet HAT-P7b. The depth of the occultation is similar in amplitude to that expected from a transiting Earth-size planet and demonstrates that the Mission has the precision necessary to detect such planets.


Several new exoplanets discovered by Kepler are discussed and compared with known exoplanets with respect to mass, size, density, and orbital period. Detections of stellar oscillations and unusual objects are also presented.



Robert Quimby


Host: Judy Cohen

The Illuminating Deaths of Massive Stars 


Wide field optical imaging surveys such as the Palomar Transient Factory (PTF) are uncovering new classes of never before seen (or at least previously over-looked) stellar explosions. Of particular interest are a group of outbursts dwarfing the most powerful supernovae observed in the past century. With peak luminosities in excess of 10^44 erg/s and total radiative outputs greater than 10^51 erg, these events push the limits of conventional supernova explosion theory. It is possible that some of these are luminous supernovae triggered by the electron-positron pair instability, and they may thus represent local analogs of the first stellar explosions to shape the universe. Their high (restframe) ultra-violet luminosities suggest that similar events may already be detectable with existing instrumentation out to redshifts of z~4 and that they will become valued tools for selecting and studying galaxies at even larger redshifts. In this talk, I will highlight some of the key PTF discoveries in this emerging field, preliminary event rates and host galaxy constraints, and the prospects for future studies.   


Kristen Menou


Host: Sterl Phinney

Exoplanetary Atmospheres 


Comparative planetology now encompasses a large set of extrasolar planets. Recently, direct constraints on the atmospheres of a number of exoplanets have become available. I will briefly describe the observational status of this field. I will then report on various efforts to interpret these observations in terms of atmospheric responses to unusual forcing conditions, well beyond the ones found in the Solar System. The future of the field is exciting, with potentially habitable terrestrial planets on the horizon.


John Grunsfeld


Host: Tom Prince/Lynne Hillenbrand

Hubble Servicing Mission 4   (12th Annual Greenstein Lecturer)


In May 2009 a team of astronauts flew to the Hubble Space Telescope on space shuttle Atlantis. On their 13 day mission and over the course of 5 spacewalks they completed an extreme makeover of the orbiting observatory. They installed the Wide Field Camera-3, the Cosmic Origins Spectrograph, repaired the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph, as well as a number of maintenance activities. The Hubble Space Telescope story has been a fascinating study in public policy, engineering, ethics, and science. For the first time on orbit the Hubble has a full complement of instruments capable of performing state-of-the-art observations from the near infra-red to the ultraviolet end of the spectrum. The early results of the new and repaired instruments hint at a bright scientific future for Hubble and will be presented in the talk as well as a narrative of the adventures on orbit.


James Bullock

UC Irvine

Host: Jessica Lu

Dwarf Galaxies, Dark Matter, and the Threshold of Galaxy  Formation


Over the past five years, searches in Sloan Digital Sky Survey data have more than doubled the number of known satellite galaxies orbiting around the Milky Way disk, revealing a population of ultra-faint systems with total light output barely reaching ~1000 times that of the Sun.  These newly-doscovered dwarf galaxies represent galaxy formation in the extreme. They are not only the faintest galactic systems known but they are also the most dark matter dominated and most metal poor galaxies in the universe. Completeness corrections suggest that we are poised on the edge of a vast discovery space in galaxy phenomenology, with hundreds more ultra-faint galaxies to be discovered as future instruments hunt for the low-luminosity threshold of galaxy formation.  I discuss how dark matter dominated dwarfs of this kind probe the small-scale power-spectrum and offer a particularly useful target for dark matter indirect detection experiments.    




Chris Hirata


Understanding the Cosmic Recombination Epoch



Around 300,000 years after the Big Bang, the expanding Universe transitioned from an opaque ionized to a transparent neutral state.  This recombination epoch is probed directly by the cosmic microwave background, and its ionization history plays a key role in producing the observable CMB features such as acoustic peaks and polarization.  The advent of precision cosmology with the CMB and particularly tests of inflation require computations of the cosmic unprecedented accuracy.  I will explore the unusual physics that controls cosmic recombination due to the combination of high optical depth and zero metallicity.  Finally, I will discuss the empirical tests of the recombination history, and their relevance to the future of precision cosmology.   


Jason Wright

Penn State

Host: John Johnson

Exoplanets Abound


I will review the latest statistics of the orbital elements of the nearly 350 giant planets detected by radial velocity surveys around normal stars.  The distributions of orbital elements of these planets show several curious features including: the familiar "3-day pileup" among lower-mass singleton giant exoplanets; a "1 AU jump" among singleton super-Jupiters; indistinguishable eccentricity distributions between singleton planets and those in multiplanet systems; a flat log-orbital-distance distribution among planets in multiple systems; and a lack of close-in planets orbiting subgiant and giant stars. Since nearly all of the detected giant exoplanets have experienced significant migration, these features form important clues to the nature of migration, and ultimately provide tests for successful theories of planetary migration and dynamical evolution.


Rachel Somerville


Host: Jessica Lu


The formation of spheroids, black holes, and AGN: a coherent picture?


It has been shown recently that incorporating the energy feedback from growing supermassive black holes into models of galaxy formation set within the Cold Dark Matter framework can plausibly solve several of the most persistent problems that plagued these models for decades, such as  the 'overcooling' and 'star formation quenching' problems. I will discuss whether these models can rise to the challenge of correctly predicting the observed "downsizing" in stellar mass and star formation rate with cosmic time, as seen in lookback studies and in "fossil" evidence in nearby galaxies. I will then show how a revision of the classical model for spheroid formation via galaxy mergers leads to improved predictions for the fraction of early type galaxies as a function of stellar mass. Finally, I will discuss whether these "unified" models can simultaneously reproduce the evolution of galaxies and AGN over cosmic history, and what lessons we can take away about the physics of black hole growth and galaxy formation.



Gilles Chabrier

Ecole Normale Supérieure de Lyon

Host: Schuyler van Dyk

The stellar initial mass function and the early stages of star and brown dwarf evolution.


Understanding the origin of and the dominant physical processes responsible for the prestellar core mass function (CMF) and the final stellar initial mass function (IMF) remains at the heart of the problem of star formation.  In the first part of this talk, I will describe a recent analytical theory of star formation and of the IMF/CMF and highlight the specific roles played by turbulence, gravity, and the thermodynamic properties of the cloud, respectively. Comparisons with former theories,  as well as with observations and simulations, will be discussed. The second part of the talk will be devoted to the early stages of low-mass star and brown dwarf evolution, following the prestellar core formation. I will highlight the key role played by early episodic accretion and show how such accretion episodes can explain the otherwise unexplained luminosity spread in the HR diagram of young clusters.  At last, I will show how episodic accretion affects lithium-burning, precluding lithium abundance determination in young objects as a reliable age diagnostic.


Marten van Kerkwijk

University of Toronto

Host: Shri Kulkarni

White dwarf binaries, mergers, and explosions


Stars in binaries often have much more exciting lives, deaths, and afterlives than single ones. I will review the especially varied possibilities involving white dwarfs, which include revival and total annihilation. I will focus on type Ia supernova explosions, and discuss the problems with the standard picture in which unstable fusion is ignited in white dwarfs that approach or are made to exceed the Chandrasekhar mass. These problems would be resolved if instead, as I will propose, the ignition occurs more generally when two carbon-oxygen white dwarfs merge. Along the way, I hope to describe the interesting consequences of two cases, where we turned what were thought to be exciting planets and neutron stars into more mundane white dwarfs.     


Craig Walker


Host: Sterl Phinney

Probing the Jet Collimation Region in M87 with VLBA and TeV Observations


Yuri Levin


Host: Sterl Phinney

Magnetar Oscillations  


Quasi-Periodic Oscillations (QPOs) have been measured in the tails of 2 out of 3 SGR giant flares. An attractive explanation for these QPOs is that they are due to torsional oscillations of the magnetar driving the flare.  This opens up a possibility to perform asteroseismology of neutron stars.  I will present a theoretical overview of magnetar oscillations, and will concentrate on the non-trivial dynamics due to a strong hydro-magnetic coupling between the elastic crust and the (multi)fluid core of the neutron star.       



Ned Wright


Host: Schulyer van Dyk

Exploring the Infrared Universe


The Wide-field Infrared Survey Explorer (WISE) is a medium class Explorer that was launched on 14 Dec 2009.  WISE should detect hundreds of millions of stars and galaxies, including millions of ULIRGS and QSOs; hundreds of thousands of asteroids; and hundreds old cold brown dwarfs. The telescope cover was ejected on 29 Dec 2009, and the all-sky survey started on 14 Jan 2010.  WISE takes more the 7000 framesets per day, with each frameset covering 0.6 square degrees in four bands centered at 3.4, 4.6, 12 and 22 microns. WISE scans semi-circles on the sky about +95 and -90 degrees in ecliptic longitude from the Sun, and covers about 0.6 percent of the sky each day to a depth of 8 or more exposures, and will cover the whole sky in 6 months of surveying. WISE observations of solar-system objects are reported to the Minor Planet Center within a few days of the data being taken, leading to the discovery of comets, Near Earth Objects, and many main belt asteroids.  The first half of WISE data on celestially fixed objects will be released to the community 6 months after the end of the cryogenic survey, or about April 2011.  The final data release will be 11 months later, about March 2012.                  


Jacqueline van Gorkom

Columbia University

Host: Nick Scoville

Gas and Galaxy Evolution in the Local Universe                                      


Galaxies grow by merging with other galaxies and/or by accreting gas.  In this talk I will present results on the role of gas in galaxy evolution. In low density environments galaxies continue to accrete gas, in the higher density environments accretion stops and in even higher density environments gas gets removed, bringing star formation to a halt. We can identify the physical mechanisms that drive this evolution. I will argue that in dense clusters of galaxies it is the assembly of clusters that drives the evolution of galaxies.       


Garth Illingworth

Lick Observatory

Host: Richard Ellis



Galaxies in the Epoch of Reionization: Galaxy Buildup in the First Gyr                                        


The extraordinarily-deep HST WFC3/IR data taken between Aug 2009 and Feb 2010 as part of the HUDF09 program has dramatically expanded our insight into the galaxy population at z~7-8-9, and given us constraints on galaxies at z~10. Over 100 z~7-8 galaxies have now been detected from the deep HUDF09 data and the wider-field ERS data. These samples have enabled us to undertake a thorough analysis of the luminosity functions to much lower luminosities.  We have used the very deep field data (the HUDF, HUDF09 and the HUDF05 datasets) to derive the contribution to the luminosity density and the star formation rate from lower luminosity galaxies to as faint as ~0.05L* from redshift 4-7.  We have incorporated recent results on the contribution of ULIRGS and sub-mm star-forming galaxies to indicate that in the first 1-2 Gyr the dominant contributors to the star formation rate density in the universe are the lower luminosity, lower mass objects that are fully represented in the Lyman Break population at z~4-7.  Evidence from the Hz~7-8 galaxies include earlier populations that reach back to z>10. I will discuss the remarkable advances that have resulted from combining recent HST and the older deep Spitzer observations in establishing the star formation rate density and the mass density buildup in the first 1-2 Gyr.                             


Anna Frebel

CfA Harvard

Host: Judy Cohen

Stellar Archaeology: New Science with Old stars


The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena.  Since the most metal-poor Galactic stars are relics from the high-redshift Universe, they probe the chemical and dynamical conditions as the Milky Way began to form, the origin and evolution of the elements, and the physics of nucleosynthesis. They also provide constraints on the nature of the first stars, their associated supernovae and initial mass function, and early star and galaxy formation.  I will discuss examples of the most metal-poor Galactic stars with extreme and unusual abundance patterns that can help elucidate the supernovae responsible for their chemical signatures. Furthermore, stars displaying a strong overabundance of the heaviest elements, in particular uranium and thorium, can be radioactively dated, giving formation times ~13 Gyr ago, similar to the ~13.7 Gyr age of the Universe. I then transition to a description of recent discoveries of extremely metal-poor stars in dwarf satellites of the Milky Way. Their stellar chemical signatures support the concept that small systems analogous to the surviving dwarf galaxies were the building blocks of the Milky Way's low-metallicity halo. This opens a new window for studying galaxy formation through stellar chemistry.   




Jamie Bock


Host: Schuyler van Dyk

First Results from Extragalactic Surveys with Herschel


The Herschel space-borne observatory, with a 3.5 m telescope and a suite of 3 instruments for imaging and spectroscopy, is opening a new window on the far-infrared universe.  Launched in May 2009 by ESA with NASA participation, Herschel has completed the first science demonstration phase of large coordinated extragalactic survey programs ranging from deep confusion-limited images of lensing clusters to fields covering many hundreds of square degrees.  The far-infrared capabilities of Herschel are key to understanding the processes of galaxy formation and evolution, the development of structure, the reprocessing of stellar radiation, and the growth of supermassive black holes.  I describe Herschel's instrumental performance and the first scientific results from extragalactic surveys with the SPIRE instrument.         

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