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Astrophysics Seminars From 2011 - 2012


Fall 2011

September 12, 2011

NOTE: Special Astro Seminar -- 12-1PM SERF 329 (in lieu of Journal Club)
 "QUIET, POLARBEAR and LiteBIRD - The First 4 Years of CMB Activities in Japan"
Prof. Masashi Hazumi

National Laboratory for High Energy Physics (KEK) Institute of Particle & Nuclear Studies (IPNS), Tsukuba, Japan
Host: Brian Keating

 Abstract: The first experimental cosmology group in Japan for precision measurements of cosmic microwave background (CMB) polarization was formed at High Energy Accelerator Research Organization (KEK) in 2007. The group is currently involved in three projects for CMB polarization measurements, QUIET, POLARBEAR and LiteBIRD. This talk will mainly cover two topics, recent results from QUIET and LiteBIRD mission concept studies. QUIET is a telescope designed to detect the CMB B-mode with very sensitive polarimeters based on monolithic microwave integrated circuit (MMIC) technology. QUIET is located on the Chajnantor plateau in the Atacama desert in northern Chile at an altitude of 5,080m, which is one of the best sites in the world for CMB observations. The initial results from QUIET were accepted for publication in the Astrophysical Journal. Even though only the data from the first season (over 3000 hours) were used, the results provide some of the most precise measurements to date. The E-mode signals are in good agreement with the expectation from the standard cosmological model ( CDM model). B-mode signals were not detected, but we have succeeded in obtaining the smallest systematic uncertainties to date in the CMB polarization measurements. LiteBIRD is a space mission under consideration with JAXA's launch vehicle. With a cryogen-free cooling system, multicrhoic focal plane and small reflective optics, LiteBIRD is light enough to be launched with an epsilon rocket. The target year for launch is 2019.

September 28, 2011

 "Understanding the Progenitor Systems of the Milky Way Halo"
David Lai

Assistant Research Scientist

 Abstract: The prevailing formation theory of large disk galaxies like the Milky Way is the hierarchical assembly of smaller systems. If this is the case then the imprints of these accreted systems will be present in the chemical abundance ratios of the stars that now form the Milky Way, and may show variations depending on the location of the stars in the halo. To understand the type of systems that may have formed the Milky Way halo I will present observations comparing stellar chemical abundance ratios measured in the outer halo with the inner halo of the Galaxy, two regions that should show these chemical abundance variations. I will also present a study measuring the chemical abundance ratios in the recently discovered Bootes I dwarf spheroidal galaxy. This galaxy is likely to be similar to some of the progenitor systems that contributed stars to the Galactic halo, and our observations show that this may be the case for at least the more distant, metal-poor stellar population of the halo.

October 5, 2011

 "New Light on Type Ia Supernovae"
Daniel Kasen

Assistant Professor
UC Berkeley and Faculty Scientist, Lawrence Berkeley National Laboratory

 Abstract: Despite intense observational and theoretical study, the explosion physics and progenitor systems of Type Ia supernovae remain uncertain. I will review the various channels potentially leading to the disruption of a carbon/oxygen white dwarf, and describe what we have learned from numerical simulations concerning the ignition and propagation of a thermonuclear runaway. The aim is to discriminate between theoretical models using detailed observations of supernova spectra, light curves, and polarization. Observations of the recently discovered Type Ia event PTF11kly (aka SN2011fe) in the Pinwheel galaxy - which was caught just hours after explosion - have already shed new light on the origin of these stellar eruptions.

October 12, 2011

 "Galaxy Cluster Observations with APEX-SZ and the South Pole Telescope"
Nils Halverson

Associate Professor
University of Colorado at Boulder
Host: George Fuller

 Abstract: As the largest gravitationally bound objects in the universe, galaxy clusters yield information about large scale structure formation and cosmology. Millimeter wavelength observations of clusters using the Sunyaev-Zel'dovich (SZ) effect offer a unique observational probe of clusters at all redshifts at which they occur. I will describe targeted SZ observations of clusters with the APEX-SZ instrument and a large blind cluster survey currently being conducted with the South Pole Telescope (SPT), as well as recent results from these two projects. I will also preview our deployment of a new polarimeter on SPT for studying polarization in the Cosmic Microwave Background.

October 19, 2011

 "The Puzzle of LINERs and the Warm Ionized Gas in Early-type Galaxies"
Renbin Yan

Research Scientist
Host: Allison Coil

 Abstract: Ever since their discovery, the nature of low ionization nuclear emission-line regions (LINERs) has been hotly debated. Some authors treat them as AGNs, others argue they are not AGNs but powered by shocks or hot old stars. No universal agreement has been reached. On the other hand, early-type galaxies frequently contain spatially extended warm ionized gas and have spectra similar to LINERs. How is this large-scale emission related to the nuclear LINERs? Because LINER-like spectrum is the most common spectral type found in early-type galaxies in both nuclear and integrated spectra, understanding its nature is important to numerous topics in astrophysics.

In this talk, you will hear a story of how I converted from a supporter for AGN-powering of LINER line emission to an opponent, and what kind of convincing evidence I find made me convert. I will also discuss what we can learn about the warm ionized gas in early-type galaxies from this line emission, given that it is not an AGN indicator.

October 26, 2011

 "Galaxy Evolution in 3D: Mass, Dissipation, and Truncation"
Genevieve Graves

Miller Postdoctoral Fellow
UC Berkeley
Host: Aleks Diamond-Stanic

 Abstract: To zeroth order, early type galaxies form a one-dimensional family in which their observed properties— color, metallicity, environment, central black hole masses—all scale with their mass. This makes it difficult to disentangle the critical properties that determine their evolutionary history because everything correlates with everything else. Examining where this 1D sequence breaks down can provide essential clues to galaxy evolution. I present observational evidence that galaxy star formation histories form a multi-dimensional family, such that galaxies of the same mass today start out with similar star formation histories but shut down star formation ("quench") at different times. A parallel study using semi-analytic models of galaxy evolution suggests that these differences are due to their underlying halo mass assembly histories. Indeed, the observed family of galaxy star formation histories seems to be a generic result of a mass-threshold for quenching, given a standard ΛCDM paradigm that includes mass-dependent evolution and stochastic hierarchical assembly. At the end, I will switch gears and talk briefly about galaxies as probes of cosmology, using a new method for weak lensing analysis.

November 2, 2011

 "Deep Keck and HST Measurements of the Lyman Continuum Emissivity of High Redshift Galaxies"
Brian Siana

Assistant Professor
UC Riverside
Host: Adam Burgasser

 Abstract: Star-forming galaxies are thought to be responsible for reionizing the hydrogen in the intergalactic medium in the first billion years. However, it is not at all clear how the ionizing photons escape from the galaxies into the intergalactic medium. I will show results from the deepest far and near-UV imaging campaigns at both Keck and Hubble to directly measure the escape fraction of ionizing photons from high redshift galaxies. The results are confounding and have important implications for high redshift galaxy formation.

November 7, 2011

NOTE: Special Astro Seminar -- Monday 12-1pm in SERF 329
 "Nova Populations"
A. W. Shafter

Department of Astronomy
San Diego State University
Host: Bernie Jackson

 Abstract: Classical Novae are among the most violent explosions in the Universe, second only to supernovae and GRBs in the energetics of their eruptions. In this talk I will discuss how observations of extragalactic novae have impacted our understanding of nova populations. I'll begin with a brief introduction of classical novae as compact binary stars, followed by a discussion of nova rates and properties in nearby galaxies, particularly M31. Next, I'll present preliminary results of an ongoing spectroscopic survey of M31 novae, and conclude with a speculative discussion of the recurrent nova population in M31, and what role these systems may play as progenitors of SNeIa.

November 9, 2011

 "Searching for Planets Orbiting Low-mass Stars"
Cullen Blake

NSF Postdoctoral Fellow
Princeton University
Host: Adam Burgasser

 Abstract: The majority of stars in the solar neighborhood are low-mass M dwarfs. However, these small stars have largely been excluded from the Doppler surveys that so far have identified more than 500 extrasolar planets. Today, the precision of Doppler measurements at optical wavelengths is approaching 1 m/s, but comparable precision has not yet been demonstrated at the near infrared (NIR) wavelengths where low-mass stars are brightest. Low-mass stars are attractive targets for planet searches, particularly when searching for rocky, Earth-like planets orbiting in the so-called Habitable Zones of their hosts. I will present a new technique for measuring the velocities of low-mass stars in the NIR. This method relies on absorption features in Earth's atmosphere (telluric lines) as a velocity reference. I will discuss the results of a five-year Doppler survey of L dwarfs with the Keck telescope and describe ongoing efforts using other facilities to significantly improve Doppler precision. Finally, I will demonstrate how a Global Positioning System receiver can be used to precisely measure water vapor absorption, enabling the generation of the telluric absorption templates that are crucial for NIR Doppler measurements.

November 18, 2011

NOTE: Special Astro Seminar -- Friday 12-1pm in SERF 329
(in lieu of Journal Club)
 "Early-type galaxies: the last 8 billion years"
Sugata Kaviraj

Senior Research Fellow, Worchester College
Oxford University
Host: James Aird

 Abstract: I review our current understanding of the evolution of early-type galaxies (ETGs), in the context of recent studies of their rest-frame ultraviolet (UV) properties. Contrary to the longstanding classical notion of ETGs being old, passively-evolving objects, new restframe UV data (from GALEX at low redshift and deep, optical surveys at intermediate redshift) reveal widespread recent star formation in these galaxies since z~1. Luminous [-23 < M(V) < -21] ETGs form up to ~15% of their stellar mass over the last 8 billion years, with their less massive counterparts forming 30-60% of their stars over the same timescale. A strong correspondence between blue UV colours and the presence of morphological disturbances indicates that the star formation is merger-driven. However, the major-merger rate is several factors too low to satisfy the numbers of morphologically-disturbed ETGs, suggesting that minor mergers are likely to drive the evolution of ETGs (and massive galaxies in general) after z~1. Using early-release data from the Wide Field Camera 3 (WFC3), we demonstrate how spatially-resolved UV-optical imaging of individual galaxies can offer a comprehensive picture of their recent stellar assembly that is far more detailed than what is possible using integrated photometry. We introduce a new Cycle 19 HST-WFC3 programme, which will use UV-optical observations of a representative sample of ETGs to study local star formation and its drivers in unprecedented detail and provide empirical constraints on the (very poorly understood) minor-merger process in the local Universe.

November 29, 2011

NOTE: Special Astro Seminar -- Tuesday 12-1pm in SERF 329
 "Exciting new constraints on the reionization history of the universe"
Oliver Zahn

Postdoctoral Scholar
UC Berkeley
Host: Brian Keating

November 30, 2011

NOTE: Special Astro Seminar -- Wednesday 12-1pm in SERF 329
 "Gravitational lensing reconstruction with the SPT"
Oliver Zahn

Postdoctoral Scholar
UC Berkeley
Host: Brian Keating

 Abstract: We present the first three-frequency South Pole Telescope (SPT) cosmic microwave background (CMB) power spectra. The band powers presented here cover angular scales 2000 < ell < 9400 in frequency bands centered at 95, 150, and 220 GHz. At these frequencies and angular scales, a combination of the primary CMB anisotropy, thermal and kinetic Sunyaev-Zel'dovich (SZ) effects, radio galaxies, and cosmic infrared background (CIB) contributes to the signal. We combine Planck and SPT data at 220 GHz to constrain the amplitude and shape of the CIB power spectrum and find strong evidence for non-linear clustering. We explore the SZ results using a variety of cosmological models for the CMB and CIB anisotropies and find them to be robust with one exception: allowing for spatial correlations between the thermal SZ effect and CIB significantly degrades the SZ constraints. Neglecting this potential correlation, we find the thermal SZ power at 150 GHz and ell = 3000 to be 3.65 +/- 0.69 muK^2, and set an upper limit on the kinetic SZ power to be less than 2.8 muK^2 at 95% confidence. When a correlation between the thermal SZ and CIB is allowed, we constrain a linear combination of thermal and kinetic SZ power: D_{3000}^{tSZ} + 0.5 D_{3000}^{kSZ} = 4.60 +/- 0.63 muK^2, consistent with earlier measurements. We use the measured thermal SZ power and an analytic, thermal SZ model calibrated with simulations to determine sigma8 = 0.807 +/- 0.016. Modeling uncertainties involving the astrophysics of the intracluster medium rather than the statistical uncertainty in the measured band powers are the dominant source of uncertainty on sigma8 . We also place an upper limit on the kinetic SZ power produced by patchy reionization; a companion paper uses these limits to constrain the reionization history of the Universe.

November 30, 2011

 "From Flare Stars to Brown Dwarfs and Exoplanets: The Evolution of Magnetic Activity at the End of the Main Sequence and Beyond"
Gregg Hallinan

Jansky Postdoctoral Fellow
UC Berkeley
Host: Adam Burgasser

 Abstract: At the lower end of the main sequence, near the boundary between stars and brown dwarfs, a major transition is observed in magnetic activity. The high temperature, X-ray emitting coronae surrounding solar-type stars fade rapidly and have virtually disappeared for the coolest spectral classes, L and T. Magnetic field topologies undergo a dramatic transformation to large-scale, stable configurations and rotation rates increase by an order of magnitude, indicating stellar wind assisted magnetic braking is severely reduced or absent. Therefore, in terms of magnetospheric phenomena, brown dwarfs bear more resemblance to Jovian-type planets possessing large-scale magnetospheres and neutral atmospheres than solar-type stars exhibiting coronal activity. Perhaps the most startling manifestation of planet-like behavior has been observed in the radio. A number of ultracool dwarfs have been found to produce periodic radio pulses, with the resulting light curves very similar to those of pulsars. This radio emission is thought to be produced in the same fashion at the radio emission originating in the auroral regions of the magnetized planets in our solar system. More recently, we have conducted multi-frequency observations of one such pulsing brown dwarf that reveal further auroral emissions in the optical regime, similar to those detected at Jupiter, albeit 10^7 times more powerful. I will discuss these results, as well as ongoing studies of magnetic activity in flare stars and our search for similar auroral emissions from exoplanets, the core goal of this research being a coherent contiguous picture of magnetospheric phenomena from stars to planets.

December 7, 2011

 "Molecular Gas, AGN Feedback and the Unusual Case of NGC 1266"
Katherine (Katey) Alatalo

PhD Student
UC Berkeley
Host: Aleks Diamond-Stanic

 Abstract: NGC 1266 is an S0 galaxy that was observed in multiple wavelengths as part of the Atlas3d effort which remarkably hosts 10^9 solar masses of molecular gas and has a spectrum that exhibits extended wings of up to +/-400 km/s. High resolution CARMA observations have shed further light on this galaxy and revealed that the bulk of the gas is concentrated within 100pc of the nucleus, leading to surface densities consistent with ULIRGs, yet NGC1266 exhibits no evidence of having undergone an interaction. The star formation rate (SFR) in the dense nuclear disk appears to fall on the Kennicutt-Schmidt (K-S) relation. The presence of an AGN combined with molecular gas outflowing faster than vesc hints that this galaxy might be a local candidate for AGN feedback. The fact that the SFR is unable to support such a high energy outflow strengthens this claim. Empirical estimates of the radio jet power from the 1.4GHz flux confirms that only a 2% coupling is required for the jet to drive the outflow. NGC1266 is the first example of molecular feedback into the IGM from a relatively normal, non-interacting galaxy. How the gas fell so deeply into the potential well, and the exact nature of the driving mechanism behind the expulsion of the gas remain mysteries. Funding for the operation of CARMA comes from the National Science Foundation and the consortium universities.

December 12, 2011

NOTE: Special Astro Seminar -- Monday 12-1pm in SERF 329
 "Physical mechanism triggering CMEs"
Brigitte Schmieder

Research Scientist
Observatoire de Paris, LESIA, Meudon, France
Host: Bernie Jackson

 Abstract: CMEs are due to physical phenomena that drive both, eruptions and flares in active regions. Eruptions/CMEs must be driven from initially force-free current-carrying magnetic field. Twisted flux ropes, sigmoids, current lanes and pattern in photospheric current maps show a clear evidence of currents parallel to the magnetic field. Eruptions occur starting from equilibria which have reached some instability threshold (introduction of Aulanier et al 2010). Revisiting several data sets of CME observations we identified different mechanisms leading to this unstable state from a force free field. Boundary motions related to magnetic flux emergence and shearing favor the increase of coronal currents leading to the large flares of November 2003 (Chandra et al 2010, 2011). On the other hand, we demonstrated by numerical simulations that magnetic flux emergence is not a sufficient condition for eruptions (Torok et al 2010). Filament eruptions are interpreted either by a torus instability for an event occurring during the minimum of solar activity either by the diffusion of the magnetic flux reducing the tension of the restraining arcade (Schmieder et al 2008). We concluded that CME models (tether cutting, break out, loss of equilibrium models) are based on these basic mechanisms for the onset of CMEs.

Winter 2012

January 4, 2012

 "CMB perspectives on an evolving Universe from the South Pole Telescope"
Christian Reichardt

Postdoctoral Scholar
UC Berkeley
Host: Brian Keating

 Abstract: The polarization and fine-scale temperature anisotropy of the cosmic microwave background (CMB) is a powerful tool for cosmology, encoding the history of the Universe from inflation to structure formation. Order of magnitude improvements in sensitivity are finally opening up this rich new field, as evidenced by recent 'firsts' from the South Pole Telescope (SPT). These include the first galaxy cluster catalog selected by the Sunyaev-Zel'dovich (SZ) effect, the first detection of the background of SZ power from large-scale structure, and the first constraints on the cosmic ionization history at all redshift. I will discuss what we are learning from the SPT survey with attention to the status and prospects for galaxy cluster cosmology. I will also preview future results from the new polarization sensitive camera mounted on the SPT this winter.

January 11, 2012

 "Eccentric Ellipsoidal Red Giant Binaries"
Christine Nicholls

Postdoctoral Scholar
Host: Adam Burgasser

 Abstract: Ellipsoidal variables are binaries in which the primary star is distorted by the influence of its small, close companion. We study a sample of red giant ellipsoidal variables, some of which describe significantly eccentric orbits.

Stars lying on sequence E of Wood et al. 1999's red giant period-luminosity sequences were long suspected to be ellipsoidal variables, due to the alternating depths of the minima in their light curves. In 2010 we presented the first radial velocity curves confirming that sequence E stars are ellipsoidal variables. Roughly 10% of these ellipsoidal red giants have light curves with non-sinusoidal shapes, suggestive of eccentric orbits. We present here the first radial velocity curves confirming the eccentricity of these variables.

Because the stars in our sample are in the LMC, at known distance, we are able to model their light and velocity curves using the Wilson-Devinney code to obtain absolute orbital solutions, including masses. We also find evidence that the shape of the red giant changes throughout the orbit due to the high eccentricity and the varying influence of the companion. Defining the parameters of these systems paves the way for modelling to determine by what mechanism eccentricity is maintained in evolved binaries.

January 18, 2012

 "Watching Galaxy Evolution in High Definition"
Jane Rigby

Deputy Operations Project Scientist for JWST
NASA Goddard
Host: Adam Burgasser

 Abstract: As Einstein predicted, mass deflects light. In hundreds of known cases, "gravitational lenses" have deflected, distorted, and amplified images of galaxies or quasars behind them. As such, gravitational lensing is a way to "cheat" at studying how galaxies evolve, because lensing can magnify galaxies by factors of 10--100 times, transforming them from objects we can barely detect to bright objects we can study in detail. I'll summarize new results from a comprehensive program, using multi-wavelength, high-quality spectroscopy, to study how galaxies formed stars at redshifts of 1--3, the epoch when most of the Universe's stars were formed.

January 25, 2012

 "Unraveling the diffuse gamma-ray background using anisotropy"
Jennifer Siegal-Gaskins

Einstein Postdoctoral Fellow
Host: TBA

 Abstract: The detailed origin of the diffuse gamma-ray background is still unknown. However, the contribution of unresolved sources is expected to induce small-scale anisotropies in this emission, which may provide a means of identifying and constraining the properties of its contributors. Recent studies have predicted the anisotropy signatures of various astrophysical gamma-ray source populations, including blazars, star-forming galaxies, and millisecond pulsars, as well as those of possible exotic sources, such as extragalactic and Galactic dark matter annihilation and decay. I will present the results of an angular power spectrum analysis of the high-latitude diffuse gamma-ray emission measured by the Fermi Large Area Telescope, and discuss the implications of the measured anisotropy for gamma-ray source populations that may provide a contribution to the diffuse background.

January 31, 2012

NOTE: Special Astro Seminar -- Tuesday 12-1pm in SERF 329
(Pizza will be served)
 "Heavy Element Nucleosynthesis in the Brightest Asymptotic Giant
Branch Stars"
Amanda Karakas

Stromlo Fellow
Mt. Stromlo Observatory
Host: Christine Nicholls

 Abstract: Observations have revealed that several bright Galactic OH/IR AGB stars are enriched in the neutron-capture element rubidium (Rb). This indicates that hot bottom burning and heavy element nucleosynthesis has been occurring in these stars. Using stellar evolutionary models with masses between 5 and 9 solar masses, we show that is is possible to match the composition of the bulk of the Rb-enriched population by modifying the mass-loss rate such that the superwind starts at a later time. We finish with a discussion of one of the possible implications for this study: The origin of heavy elements in galactic globular clusters.

February 1, 2012

 "How does Environment affect Galaxy Evolution?"
Gillian Wilson

UC Riverside
Host: Alison Coil

 Abstract: The SpARCS survey is one of the largest surveys designed to detect clusters of galaxies at z > 1. It has discovered hundreds of new IR-selected clusters in the 50 square degree Spitzer SWIRE Legacy Fields. The SpARCS team has been putting huge effort into obtaining spectroscopic and multi-wavelength (X-ray/optical/IR/Herschel) follow up of the most interesting systems. I will show examples of recently confirmed high redshift clusters, and discuss what we are learning about galaxy evolution in the densest of environments from this unique wide-field IR survey.

February 8, 2012

 "Cosmic Gas as a Probe of Structure Formation and Evolution"
Taotao Fang

Postdoctoral Researcher
UC Irvine
Host: TBD - Alison Coil

 Abstract: As the main repository of baryons in the universe, cosmic gas provide important clues to the formation and evolution of the large scale structure. I will discuss three separate projects, two of which are related to the two "missing baryons" problems and one related to the numerical simulation of galaxy clusters, with a focus on understanding the cosmic structure formation and evolution through its gaseous content. At large scale, the "missing baryons" problem refers to the discovery that the observed baryonic matter in the local universe accounts for less than 50% of the total baryons. At small scale, the second ”missing baryons” problem refers to the fact that the cold baryon fraction in Milky-Way size galaxies is well-below the mean cosmic baryon fraction. I will discuss our recent progresses toward solving both puzzles. Finally, I will talk about some problems with the current, most advanced cosmological simulations of galaxy clusters, and how we can use observations to constrain gas feedback processes and determine the accuracy of the cluster mass measurement.

February 17, 2012

NOTE: Special Astro Seminar -- Friday 12-1pm in SERF 280
(in lieu of Journal Club)
 "From Millikelvin to Megakelvin: Using cold detectors to study the hot X-ray universe"
Enectali Figueroa-Feliciano

Assistant Professor of Physics
Host: Adam Burgasser

 Abstract: Supernovae are the violent (and bright) deaths of massive stars and white dwarfs. These energetic events can briefly outshine their host galaxy, and are central players in galactic structure formation and the creation and dispersal of the heavy elements. Supernova Remnants (SNRs) are the remains left behind after each stellar demise, and carry the imprints of the explosion and of the interactions between the ejected stellar material and its surroundings. These interactions produce shocks which often heat the material into million-degree plasmas emitting at X-ray energies. Through high-resolution, precision X-ray spectroscopy of this extended, diffuse plasma, we can obtain precise measurements of the kinematics, temperatures, and abundances in SNRs, and thereby probe the complex physics of these astronomical objects in novel ways. We have developed a new sounding rocket experiment called Micro-X that uses a 128-pixel transition-edge sensor microcalorimeter array coupled to a grazing-incidence X-ray optic to obtain imaging spectra at a resolution between 2-4 eV in the 0.2 to 3 KeV band. The first flight is scheduled for later this year, and will be the first space implementation of this technology. In this talk I will describe the science and technology behind Micro-X, its first planned mission to study the Puppis A SNR, and briefly touch on other applications of transition-edge sensors for dark matter detection and neutrino physics.

February 22, 2012

 "Molecule formation in the turbulent ISM: Insights from numerical models"
Simon Glover

Postdoctoral Research Fellow
Institut fur Theoretische Astrophysik
Host: Alexei Kritsuk

 Abstract: Within the past few years, it has become possible to perform high-resolution three-dimensional simulations of molecular cloud formation and evolution that trace the thermal and chemical history of the gas in addition to its dynamical history. In this talk, I will discuss some of the insights that these simulations provide into the behaviour of real molecular clouds. In particular, I will discuss what we can learn about the physical processes responsible for determining the so-called "X-factor", the conversion factor relating the CO luminosity of a Galactic giant molecular cloud (GMC) to its H2 mass. I will also present some results from recent work exploring the role that molecular cooling plays in determining the star formation rate within GMCs.

February 29, 2012

 "Star Formation in the Extreme Environments of the Massive Clusters and Supermassive Black Holes"
Jessica Lu

NSF Postdoctoral Fellow
U. Hawaii
Host: Adam Burgasser

 Abstract: The formation of stars is a fundamental astrophysical process; and yet we still debate whether it varies with environment. Milky Way young star clusters range in mass over four orders of magnitude; but, the best-studied star forming regions, such as Taurus and Orion, represent only a small range of initial conditions at the low mass end. Young star clusters with masses greater than 10,000 solar masses are promising targets for determining whether the initial mass function (IMF) that results from the star formation process is universal or depends on environment. Such clusters are challenging observational targets as they require high spatial resolution at infrared wavelengths and are heavily contaminated by field stars. I present results from a Keck adaptive optics and HST study of several massive young star clusters in the Milky Way, including around the supermassive black hole at the Galactic Center. Precise IMFs are constructed by using high-precision astrometry and spectroscopy to distinguish individual cluster stars. I will discuss whether the measured IMFs differ for massive clusters at a range of Galactocentric radii and how they compare to the "universal" IMF established locally.

March 2, 2012

NOTE: *REMOTELY VIA SKYPE* Friday 1:30-2:30pm in SERF 329
 "Formation and Dynamics of Planets"
Ruth Murray-Clay

Research Scientist
Host: Coil or Burgasser?

 Abstract: Though more than 500 confirmed and 2000 likely planets are now known, discoveries at observational frontiers continue to yield new classes of planets. Several giants have now been directly imaged, offering the first view of extrasolar planets at wide separations from their host stars. Formation of these objects, either by core accretion or by gravitational instability, presents substantial theoretical difficulties. In this talk, I will discuss the challenges and opportunities posed by wide-separation planets for theories of planet formation and orbital evolution. I will emphasize (1) a new theory of planetary core growth in the presence of gas that extends the reach of core accretion to large stellocentric distances and (2) new constraints on the dynamical history of the outer solar system.

March 7, 2012

 "The Black-Hole Mass Scaling Relations of Active Galaxies: From the Local Universe out to a Lookback Time of 10 Gyrs"
Vardha Bennert

Asst. Professor
CalPoly San Luis Obispo
Host: TBD

 Abstract: Supermassive Black Holes (BHs) seem to be ubiquitous in the center of spheroids - elliptical galaxies and bulges of spirals. The tight empirical relations between the mass of the BH and the properties of the host-galaxy spheroid (stellar velocity dispersion sigma, luminosity L, and stellar mass M) discovered in the local Universe indicate a close connection between the growth of BHs and the formation and evolution of galaxies. To understand the origin of these scaling relations, I will present results from a unique three-fold approach. (i) From a sample of ~100 Active Galactic Nuclei (AGNs) in the local Universe, we build a robust baseline of the BH mass scaling relations (MBH-sigma, MBH-L, MBH-M), combining spatially-resolved Keck spectroscopy with SDSS imaging. (ii) We study the evolution of the MBH-sigma and MBH-L relations out to a look-back time of 4-6 Gyrs using Keck spectra and HST images. Our results indicate that black hole growth precedes bulge assembly. (iii) We extend this study out to the pivotal cosmic time between the peak of AGN activity and the establishment of the present-day Hubble sequence, a look-back time of 8-10 Gyrs. We measure spheroid stellar masses using deep multi-color HST images and determine the MBH-M relation. Combining results from (i-iii) allows us to test the hypothesis that evolution is driven by disks being transformed into bulges.

March 14, 2012

 "Resonant Shattering of Neutron Star Crusts"
Dave Tsang

Sherman Fairchild Fellow
Host: Adam Burgasser?

 Abstract: The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (SGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ∼10^46–10^47  erg of energy seconds before the merger of a NS-NS or NS-black-hole binary. Such properties are consistent with Swift/BAT detections of SGRB precursors, and we use the timing of the observed precursors to place weak constraints on the crust equation of state. We describe how a larger sample of precursor detections could be used alongside coincident gravitational wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure. These two types of observations nicely complement one another, since the former constrains the equation of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state.

March 16, 2012

NOTE: Special Astro Seminar -- Friday 12-1pm in SERF 329
(in lieu of Journal Club)
 "Kepler and the RR Lyrae stars"
Katrien Kolenberg

Postdoctoral Researcher
Harvard-Smithsonian CfA & KU Leuven, Belgium
Host: Adam Burgasser

 Abstract: The spectacular data delivered by NASA's Kepler mission not only boost the discoveries of planets orbiting other stars, but they also open a window on the inner workings of the stars themselves. Kepler has been a breakthrough for the study of RR Lyrae stars and the still mysterious Blazhko effect. I will present some of the most interesting results obtained so far. To date, over 40 RR Lyrae stars have been found in the Kepler field. The outstandingly high-precision data of these stars are investigated within the RR Lyrae working group as part of the Kepler Asteroseismic Science Consortium (KASC).

March 21, 2012

 "The chemistry of galaxy formation"
Andrey Kravtsov

Assoc. Professor of Physics
U. Chicago
Host: Art Wolfe

 Abstract: I will present a novel model of star formation based on non-equilibrium treatment ofmolecular hydrogen in self-consistent cosmological simulations of galaxy formation, including effects of self-shielding and shielding by dust. The model predicts strong dependence of the global Kennicutt-Schmidt star formation relation on the metallicity ofthe interstellar medium of galaxies (and a weaker dependence on the interstellar UV field) and can explain recent results indicating inefficient star formation in high-redshift Damped Lyman alpha galaxies at z~3. General considerations and some preliminary simulation results indicate that low efficiency of star formation at high redshifts can have significant implications for galaxy formation and may help resolve many of the main problems and puzzles of galaxy formation within hierarchical CDM scenario. I will also briefly review the current status and challenges facing galaxy formation simulations. I will argue that recent modeling results indicate that correct modeling of galaxy formation requires the right "chemistry" - a non-trivial mix of nonlinear processes - to be treated correctly.

March 22, 2012

NOTE: Special Astro Seminar -- Thursday 3:30-4:30pm in SERF 280
 "Outbursts from Supermassive Black Holes seen in the Hot Atmospheres of Early-type Galaxies, Galaxy Groups, and RIch Clusters"
Bill Forman

Director of High-Energy Astrophysics Division
Harvard-Smithsonian CfA

 Abstract: We discuss the effects of supermassive black hole (SMBH) outbursts on the hot atmospheres of early type galaxies, galaxy groups, and galaxy clusters whose atmospheres are only seen through X-ray observations. We show the detailed effects of the outbursts from the supermassive black hole in M87 at the center of the Virgo cluster using Chandra and XMM-Newton observations including buoyant bubbles of relativistic plasma produced by the central SMBH, uplifted filaments of X-ray emitting gas, and the Mach 1.2 shock. We present the results from a large survey of more than 100 early type galaxies observed with Chandra. From the X-ray images, we identify the sample of hot coronae that show gas cavities, estimate cavity ages, and compute the mechanical power needed to inflate the cavities. From the X-ray luminosities, we derive Eddington ratios and briefly discuss the accretion mode for these low-luminosity actice galactic nuclei. We discuss the curious case of NGC4342 whose black hole is unusually large for its stellar mass and whose X-ray corona is similarly unusually bright. We compare the early-type galaxy AGN to their more powerful counterparts in rich clusters. Finally, we show the dramatic effects that SMBH outbursts can have on galaxy-scale hot coronae.

March 23, 2012

NOTE: Special Astro Seminar -- Friday 3-4pm in Garren Auditorium,
Basic Science Building
 "Hot Intergalactic Gas in Clusters of Galaxies, Cosmic Microwave Background and Cosmology"
Rashid Sunyaev

2011 Kyoto Prize Laureate

 Abstract: Clusters of galaxies are the most massive objects in our Universe. Each of them contains dark matter, thousands of galaxies and is filled with hot intergalactic gas radiating in X-rays. Huge gravitational potential converts clusters of galaxies into excellent gravitational lenses able to amplify the light from very distant galaxies behind them. Unusual method to detect clusters of galaxies is possible due to presence of extremely isotropic Cosmic Microwave Background Radiation (CMB) filling our Universe. Interaction of hot electrons with CMB photons changes the CMB spectrum in the directions toward clusters of galaxies. As a result clusters become negative sources of radiation in cm and mm spectral bands. The brightness and spectrum of these sources does not depend on distance or redshift. This property opens the way to detect all the reach clusters of galaxies (more than 100 000 !!!) in the observable Universe. Planck Surveyor spacecraft and specially designed ground based Atacama Cosmology Telescope, South Pole Telescope, SZ-Array and other telescopes discovered recently more than two thousands of extremely massive clusters of galaxies at different redshifts looking for such negative sources on microwave sky. The detailed observations of distant clusters of galaxies permit to measure their peculiar velocities relative to the unique reference system where CMB is isotropic. They should open a possibility to measure directly the bulk velocities and turbulence in the gas. Even more,the Planck Surveyor spacecraft has good chances to measure the temperature of the hot gas inside a cluster using only observations of CMB. Observations of clusters in X-ray and microwave spectral bands allow to measure the distance to any rich cluster of galaxies and open new way to measure the Hubble constant. It is a dream to construct the detailed history of formation of massive clusters of galaxies in the Universe, i.e. to measure their space density as a function of redshift or age of the Universe. The shape of this curve provides an important information about key parameters of our Universe and its constituents including dark energy and its equation of state. Observational cosmology is able to provide us with unique data about properties of our Universe as a whole, about its past and even future. It gives us clues about the physics working under the conditions and scales which we cannot test in the ground based laboratories.

Spring 2012

April 4, 2012

 "Exploring the Dark Side of the Universe"
Chris Fassnacht

Assoc. Professor
UC Davis
Host: Adam Burgasser

 Abstract: In this talk I will show how the powerful combination of sensitive, high-resolution imaging with gravitational lensing can provide direct observational tests of galaxy formation scenarios under the cold dark matter paradigm as well as interesting constraints on cosmology. In particular, I will discuss the following two subjects. (1) Placing observational constraints on the subhalo mass function by, for the first time, directly measuring masses of galaxy satellites outside of the Local Group. These measurements can be made even if the satellites are composed purely of dark matter. (2) Placing constraints on the Hubble Constant, curvature, and the dark energy equation of state parameter that are independent of and complementary to those obtained by other observational probes. Even with a single gravitational lens system it is possible to obtain precisions on these measurements that are comparable to those obtained by the other methods. The imaging used for these projects comes from Keck adaptive optics (AO) and Hubble Space Telescope (HST) observations. In some cases the AO imaging is clearly sharper than that obtained with HST.

April 6, 2012

NOTE: Special Astro Seminar -- Friday 12-1pm in SERF 329
(in lieu of Journal Club)
 "A Kerr Doppler Derivation: Is there Dark Matter in the Metric?"
Sophia Inzunza-Cisneros

Dr. Martin Luther King Jr. Postdoctoral Fellow
MIT Lab for Nuclear Science
Host: Adam Burgasser

 Abstract: We derive a Kerr Doppler formula to look for contributions from the luminous matter in curving the space-time in a highly symmetric case of a spiral galaxy. Previous treatments have relied upon linearizing the Kerr metric to check for contributions to the observed Doppler shifts from the frame dragging effects. We instead use the simplifying assumptions of weak fields and a highly symmetric system to solve the Kerr wave equation exactly. The results are, as expected, on the order of those predicted by the linearized theory, albeit somewhat bigger. However, a curious secondary effect arises in the wave speed of light. This preliminary result will be presented in the context of a possible contribution to the Dark Matter problem.

April 11, 2012

 "New Methods for Characterizing AGN Variability"
Brandon Kelly

CGE Postdoctoral Fellow
Host: Aleks Diamond-Stanic

 Abstract: Current and future time-domain surveys will provide new insights into the physics of many astronomical objects, providing complementary and orthogonal information to spectroscopy. For quasars, variability provides a probe of the structure and physics of the accretion disk onto the supermassive black hole. In particular, the scaling of variability properties with black hole mass constrains accretion flow solutions, and provides insight into the similarities and differences between supermassive and stellar-mass black holes. In addition, variability provides an important criteria for selecting samples of quasars, facilitating studies of quasar demographics and the quasar-host galaxy connection. Unfortunately, time series of quasar flux measurements (i.e., the quasar lightcurve) often suffer from a number of problems, including irregular and sparse sampling as well as additional variability due to measurement noise. These issues significantly complicate the analysis and quantification of quasar variability. In this talk I will discuss statistical methods that I have recently developed for modeling quasar variability in the time domain which provide reliable and powerful ways of quantifying quasar variability. In addition, I will present recent results obtained from applying my methods to optical and X-ray lightcurves of quasars, including scaling relationships between quasar variability properties and black hole mass.

April 18, 2012

 "Cosmological Information in the Cosmic Microwave Background Polarization"
Amit Yadav

Postdoctoral Scholar
Institute for Advanced Study (IAS), Princeton
Host: Brian Keating

 Abstract: In first part of my talk I will discuss what we can expect to learn about the dynamics of the universe at the very earliest moments, focusing on two complementary probes, primordial non-Gaussianity and gravitational waves (CMB B-modes). I will discuss theoretical predictions from inflationary models and their observational consequences in the CMB. In second part of my talk I will discuss the current state of CMB polarization measurements and the challenges involved in the measurement. I will also discuss how various CMB polarization based correlators can be used to extract interesting physics such as patchy reionization, parity violating physics, and primordial magnetism.

April 25, 2012

 "SZ Cluster Surveys as Probes of Neutrino Masses"
Meir Shimon

Research Associate
Tel Aviv University
Host: Brian Keating

 Abstract: Statistical measures of galaxy clusters are sensitive to neutrino masses in the sub-eV range. We explore the possibility of using cluster number counts from the ongoing PLANCK/SZ and future cosmic-variance-limited surveys, as well as the future ground-based POLARBEAR-II telescope, to constrain neutrino masses from CMB data alone.

We find that projected results from the PLANCK/SZ survey can be used to determine the total neutrino mass with an uncertainty of 0.11-0.22 eV, assuming fiducial neutrino mass in the range 0.1-0.3 eV. With a cosmic-variance-limited SZ survey we obtain an uncertainty of 0.05-0.07 eV, a level compatible with forecasted constraints from the lensed cosmic microwave background (CMB). A telescope such as POLARBEAR-II will be able to constrain a fiducial neutrino mass of 0.1 eV at the 0.08 eV level with a sample of 1700 galaxy clusters assuming this telescope observes 20 percent of the whole sky.

Our analysis shows that if the (total) neutrino mass is close to the lower limits deduced from neutrino oscillation experiments, cluster number counts should provide a viable complimentary cosmological probe to CMB lensing constraints on M_nu.

May 1, 2012

NOTE: Special Joint Plasma Physics/Astrophysics Seminar 4:00-5:00pm
in SERF 280
 "Climate Change and High-Throughput Biofuels"
Frank H. Shu

Emeritus Professor of Physics
UCSD (& Academia Sinica)
Host: Pat Diamond

 Abstract: Deficiencies in the energy technologies commercially available today relative to economic cost or environmental impact prevent a consensus from being reached on how best to address the challenges posed by climate change and global warming. To break the impasse we must have better choices in the future. In a related talk to be given in the MAE Department, we discuss the game changer possible in nuclear energy if we transition from today's uranium-235/plutonium-239 fuel cycle using light-water reactors to a thorium-232/uranium-233 fuel cycle using molten-salt reactors. In this talk we focus on high-throughput biofuels produced by the thermal-chemical processing of biomass by heated molten salts. The latter strategy takes advantage of the extensive infrastructure and distribution systems built up for fossil fuels. At the scale of a demonstration project in Taiwan being pursued by our group, the production of high-throughput biofuels can compete with fossil fuels without government subsidies. Pursued in an environmentally sensitive manner that uses biochar as a soil amendment, the technology can not only be carbon-neutral, but can actually be carbon-negative. It would then be possible to rollback the concentration of atmospheric carbon dioxide while reclaiming lands damaged by unsustainable practices.

May 2, 2012


May 8, 2012

NOTE: (In lieu of regular Astrophysics Seminar on 5/9). Special Joint MAE/CER/CASS/Plasma Physics Seminar @ 4:00PM - EBU II, Room 479
 "Molten Salt Breeder Reactors"
Frank H. Shu

Emeritus Professor of Physics
UCSD (& Academia Sinica)
Host: George Tynan & Pat Diamond

 Abstract: We outline why Generation IV nuclear reactors, especially the Molten Salt Breeder Reactor (MSBR), represent more than a simple evolution of Generation III+ light water reactors (LWRs), but are a game changer in nuclear fission. In particular, we explain why the MSBR is safe with respect to possible accidents leading to the large-scale release of radioactivity, superior in terms of cost performance if used for process heat rather then turbine electricity generation, secure relative to nuclear proliferation, and sustainable with respect to nuclear waste disposal and the ability to provide the bulk of the clean energy needed for the millennium. Wediscuss the thermal, chemical, and mechanical challenges particular to developing this technology, and we explore a proposed approach using novel materials to build two-fluid MSBRs on a rapid enough schedule to make the world free of plutonium and net CO2 emission by roughly mid-century. We then summarize the laboratory experience of our group that suggests there are probably no technical showstoppers to the practical realization of such MSBRs. Finally, we project the feasibility of coupling the capacity of these facilities to the production of high-throughput biofuels that can rollback atmospheric greenhouse gases on a time scale of about two centuries to levels that would prevent the most catastrophic consequences of global warming.

May 16, 2012

 "Cryogenic Sensors for Astrophysics and Terrestrial Materials Analysis"
Joel Ullom

National Institute of Standards and Technology (NIST), Boulder, CO
Host: Brian Keating

 Abstract: Sensors operating at temperatures near 100 mK bring exquisite sensitivity to a startlingly broad range of applications. These sensors often consist of thin superconducting films that are electrically biased in the superconducting-to-normal transition where their resistance is a strong function of temperature and hence deposited energy or power. Devices designed for gamma-ray and alpha-particle spectroscopy are able to measure the energy of single 5 MeV events with resolving powers greater than 5,000, perhaps the highest resolving power ever achieved in an energy-dispersive measurement. These devices provide new capabilities in the arena of nuclear forensics, treaty verification, and nuclear materials accounting. Kilopixel arrays of transition-edge sensors are also being used in contemporary probes of the cosmic microwave background such as ACTPol and SPTPol. Despite significant differences between these applications, the sensing elements are remarkably similar. I will review transition-edge sensor development at NIST and discuss a range of applications including submillimeter and millimeter-wave astronomy, as well as emerging applications that include nuclear materials analysis, time-resolved X-ray spectroscopy, and synchrotron science.

May 23, 2012

 "The Kepler Search for Circumbinary Planets"
William Welsh

Astronomy Professor
Host: Adam Burgasser

 Abstract: While long anticipated in both science and science fiction, the existence of a circumbinary planet orbiting a pair of normal stars was not definitively established until the discovery of Kepler-16 b, announced by the Kepler Team last September. Yet many questions remained about the nature of circumbinary planets: What kinds of orbits, masses, radii, temperatures, etc., could they have? What kinds of binary stars can host planets? And most of all, was Kepler-16 just a fluke? To address these questions we needed more cases of circumbinary planet systems, and we initially searched for non-transiting planets: transits require an extremely favorable orientation in the sky and are thus expected to be rare. Non-transiting planets do not require a fortuitous configuration and should be roughly 10x more common. By carefully measuring the eclipse times of the binary stars, we have discovered that a sizable number of systems possess significant eclipse timing variations, indicating the presence of (at least) a third body that is perturbing the binary orbit. The amplitude and period of the timing variations allow us to constrain the mass of the unseen third body: a small amplitude and a short period implies a nearby, low-mass object, perhaps substellar. While the goal was to find non-transiting planets, this search quickly revealed two more transiting circumbinary planets, Kepler-34 and Kepler-35. With three systems, we can now compare their characteristics and estimate how common such objects are in the galaxy. In this talk I will briefly showcase some highlights of the Kepler Mission, then discuss the search method, discovery, and characteristics of the three Kepler transiting circumbinary planets, and conclude with some interesting trends we have seen.

May 30, 2012

 "Phase Transitions in Rotating Neutron Stars"
Fridolin Weber

Host: George Fuller

 Abstract: Isolated rotating neutron stars are gradually spinning down to lower frequencies because of the emission of magnetic dipole radiation and a wind of electron-positron pairs. This spin-down compresses the matter inside of such neutron stars monotonically to higher densities, leading to changes in the global properties and the hadronic core compositions of such objects. In particular, spin-down may drive rotation-driven phase transitions in the cores of rotating neutron stars, which is the key topic of this talk. First, the structure and stability of rotating neutron stars will be discussed. This is followed by an overview of the different types of phase transitions that may be triggered by stellar spin-down. Finally, astrophysical signatures by means of which such phase transitions may register themselves observationally will be discussed.

Summer 2012

June 19, 2012

NOTE: Special Astro Seminar -- Tuesday 1:30-2:30pm in SERF 329
 "CfAIR2: Infrared Observations of ~100 Type Ia Supernovae with PAIRITEL"
Andrew Friedman

NSF Postdoctoral Fellow
Host: Brian Keating

 Abstract: While the discovery of dark energy and most subsequent supernova cosmology has been performed using optical wavelength observations of Type Ia Supernovae (SN Ia), a growing body of evidence suggests that Near-Infrared (NIR) SN Ia observations will be crucial for future cosmological studies. Whereas SN Ia observed at optical wavelengths have been shown to be excellent standardizeable candles, using empirical correlations between luminosity, light curve shape, and color, the CfAIR2 data set strengthens the evidence that SN Ia at NIR wavelengths are essentially standard candles, even without correction for light-curve shape or for reddening. CfAIR2 includes ~7000 near-Infrared (NIR) JHKs-band measurements of ~100 SN Ia observed from 2005-2011 using PAIRITEL, the 1.3-m Peters Automated InfraRed Imaging TELescope at the Fred Lawrence Whipple Observatory (FLWO) on Mount Hopkins, Arizona. CfAIR2 was obtained as part of the CfA Supernova Program, an ongoing multi-wavelength follow-up effort at FLWO designed to observe high-quality, densely sampled light curves and spectra of hundreds of low-redshift SN Ia. CfAIR2 is the largest homogeneously observed and processed NIR data set of its kind to date, more than tripling the number of individual observations, nearly doubling the set of well-sampled NIR SN Ia light curves, and matched only by the recently published Carnegie Supernova Project sample. CfAIR2 complements the large and growing set of low-redshift optical and NIR SN Ia observations obtained by the CfA and other programs, making this data set a unique and particularly valuable local universe anchor for future supernova cosmology.

July 27, 2012

NOTE: Special Astro Seminar -- Friday 12:00-1:00pm in SERF 329
(in lieu of Journal Club)
 "Cosmology with 21-cm Intensity Mapping"
Peter Timbie

Professor of Physics
University of Wisconsin, Madison
Host: Brian Keating

 Abstract: Future surveys of the redshifted 21 cm line from neutral hydrogen gas promise to revolutionize the field of cosmology. These surveys may ultimately encompass much larger volumes than galaxy surveys can study. They will measure the power spectrum of matter with high precision, leading to tight constraints on dark energy, neutrino mass, and other cosmological parameters. I will review recent results of 21-cm 'intensity mapping' at redshift 0.8 and then describe a planned dark energy survey called Tianlai that is underway in China and will summarize the challenges that must be overcome.

August 6, 2012

NOTE: Special Astro Seminar -- Monday 12:00-1:00pm in SERF 329
 "Alpha. Does it vary?"
John Webb

School of Physics
University of New South Wales
Host: Art Wolfe

 Abstract: We previously reported Keck telescope observations suggesting a smaller value of the fine structure constant, alpha, at high redshift. New VLT data, probing a different direction in the universe, shows an inverse evolution; alpha increases at high redshift. If interpreted as a spatial variation, the combined dataset fits a simple dipole model, significant at the 4.2-sigma level. If the effect is a not real it will require a combination of systematic effects to emulate it. I will discuss our attempts to quantify those systematics and make this result go away. So far, we have failed.