April 2, 2014 | 3:00 PM | BSLC 115 | Wednesday colloquium A Tale of Two Collaborations: A New Precise Measurement of Cosmological Parameters Using Type Ia Supernovae Rick Kessler, The University of Chicago
April 9, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium The GMT Project: Science and Status Rebecca Bernstein, Carnegie Observatories
PDF In this talk, I will give an overview of the GMT project and the science cases and goals that are driving its design. I will also describe the current status of the project and the first generation instruments that are now under development.
April 23, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium Asteroseismology and Exoplanets: A Kepler Success Story Daniel Huber, NASA
PDF Asteroseismology - the study of stellar oscillations - is a powerful observational tool to probe the structure and evolution of stars. In addition to the large number of newly discovered exoplanets, the Kepler space telescope has revolutionized asteroseismology by detecting oscillations in thousands of stars from the main-sequence to the red-giant branch. In this talk I will highlight recent asteroseismic discoveries by Kepler, focusing in particular on studies of exoplanet host stars and the application of asteroseismology to measure stellar spin-orbit inclinations. I will furthermore discuss current efforts to improve fundamental properties (such as temperatures, masses, and radii) of Kepler targets, and their importance for deriving accurate planet occurrence rates using the Kepler sample. Finally, I will give a brief overview on first results by Kepler's ecliptic plane follow-up mission, K2.
April 30, 2014 | 3:00 PM | BSLC 115 | Wednesday colloquium Searches for Particle Dark Matter Tim M.P. Tait, UC Irvine
PDF Dark Matter is all around us, a clear sign of physics beyond the Standard Model, and yet we will have not understood what it is and how it fits into the larger picture. In this talk, I will discuss what we know about dark matter and how different kinds of searches, including searches for its collision with heavy nuclei, production at accelerators, and signs of its annihilation in our galaxy, combine together to give us information about how it (doesn't) interact with ordinary matter. The picture that will emerge is one where different searches complement each other, offering rich opportunities to understand the nature of dark matter in the near future.
May 7, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium Turbulence and dynamo action in accretion flows Fausto Cattaneo, University of Chicago
The most remarkable thing about accretion discs is that they accrete. The rate at which material can be accreted from a disc onto a central compact object is controlled by the rate at which angular momentum can be transported out of the disc. Thus efficient accretion requires efficient angular momentum transport, typically many orders of magnitude larger than what could be accounted by viscous processes alone. Consequently, it has long been assumed that astrophysical discs must be turbulent, and that the turbulence is what causes the enhanced transport. Yet, basic considerations indicate that discs with near-Keplerian velocity profiles should be hydrodynamically stable. Thus the accretion disc conundrum: how can a stable system be turbulent? One possible resolution is that, in an electrically conducting disc, the presence of a weak magnetic field drastically alters the stability property of the disc. A powerful, rapidly growing instability—the magneto-rotational-instability (MRI), can develop, lead to turbulence and efficiently transport angular momentum outwards. Better still, there is evidence that turbulence driven by the MRI can, through dynamo action, regenerate the very magnetic field necessary for the instability to develop in the first place. In this talk I shall introduce the basic physics underpinning the MRI, present some numerical models of MRI-driven turbulence and show how it can lead to the self-driven magnetization of a disc. Image: MRI driven turbulence in a full disc simulation (G. Bodo, F. Cattaneo, A. Mignone, P.Rossi).
May 14, 2014 | 3:00 PM | BSLC 115 | Wednesday colloquium The GeV Excess in the Inner Galaxy: Pulsars or Dark Matter? Douglas P Finkbeiner, Harvard University
May 21, 2014 | 3:00 PM | BSLC 109 | Wednesday colloquium Lessons from two success stories Gabriele Veneziano, College de France
PDF Our present understanding of Nature is based on the Concordance Model of gravity and cosmology and on the Standard Model for the constituents of matter and their non-gravitational interactions. Their amazing successes --and puzzles-- may carry some important lessons for our quest of a truly unified theory of space, time, and matter.
May 28, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium The Dynamic Universe: Palomar Transient Factory Shri Kulkarni, California Institute of Technology
PDF That occasionally new sources ("Stella Nova") would pop up in the heavens was noted more than a thousand years ago. The earnest study of cosmic explosions began in earnests less than a hundred years ago. Over time, astronomers have come to appreciate the central role of supernovae in synthesizing new elements (and making life as we know possible). The Palomar Transient Factory (PTF), an innovative 2-telescope system, was designed to explicitly chart the transient sky with a particular focus on events which lie in the nova-supernova gap. PTF can find an extragalactic transient every 20 minutes and a galactic (strong) variable every 10 minutes. The results so far: classification of 2000 supernovae; identification of an emerging class of ultra-luminous supernovae; the earliest discovery of a la supernovae; discovery of luminous red novae; the most comprehensive UV spectroscopy of la supernovae; discovery of low energy budget supernovae; clarification of sub-classes of core collapse and thermo-nuclear explosions; mapping of the systematics of core collapse supernovae; identification of a trove of eclipsing binaries and the curious AM CVns.
June 4, 2014 | 3:00 PM | BSLC 115 | Astronomy Colloquium From Hot Jupiters to Habitable Worlds: A Survey of Exoplanet Atmospheres Heather Knutson, California Institute of Technology
Although the space-based Kepler survey has dominated discussions of exoplanet statistics in recent years, ground-based surveys have been undergoing a quiet renaissance of their own. This has resulted in an ever-growing sample of lower-mass and longer-period planets transiting bright, nearby stars. Such systems provide a unique opportunity to extend the current statistical studies of hot Jupiter atmospheres down to smaller and cooler planets (so-called "super-Earths") that are still favorable for detailed characterization. The best-studied planets in this regime have puzzling properties that have yet to be adequately explained; in my talk I will present new measurements from Hubble and Spitzer that aim to place these planets in a larger statistical context and to illuminate their formation and migration histories. These studies also serve to illustrate the crucial role of space-based infrared telescopes (both present and future) in addressing some of the most exciting and pressing questions related to low-mass exoplanets.
April 4, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Excess of Diffuse Gamma-ray Emission from the Inner Galaxy: Bubbles, Jets, and Dark Matter Meng Su, MIT
Our analysis of data from the Fermi Gamma-ray Space Telescope revealed a pair of large gamma-ray bubble structures, named the Fermi bubbles, each extending ~10 kpc above and below the Galactic center. I will present new results using five years Fermi-LAT data and multi-wavelength observations of the Fermi bubbles in X-ray, microwave, and radio, including updates from dedicated observations. New observations help us to distinguish hadronic from leptonic origin of the cosmic-ray electrons emitting gamma-ray/radio emission, and constrain the magnetic field within the Fermi bubbles. I will also show our numerical simulations which demonstrate that the bubble structure could be evidence for past accretion events and outflow from the central supermassive black hole. Furthermore, we recently found gamma-ray evidence for large-scale collimated jet-like structure penetrating through the bubbles from the Galactic center, which might provide further evidence of a past activity in the Galactic center. We have proposed to change the survey strategy of Fermi to increase the exposure at the inner Galaxy by more than a factor of 2. This new survey strategy has been initiated since December 2013 and will last for at least one year. I will end up with a discussion of future gamma-ray space missions.
April 11, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Science with CMB Spectral Distortions: a New Window to Early-Universe Physics Jens Chluba, JHU
Since COBE/FIRAS we know that the CMB spectrum is extremely close to a perfect blackbody. There are, however, a number of processes in the early Universe that should create spectral distortions at a level that is within reach of present day technology. I will give an overview of recent theoretical and experimental developments, explaining why future measurements of the CMB spectrum will open up an unexplored window to early-universe and particle physics, with possible non-standard surprises but also guaranteed signals awaiting us.
April 18, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Measuring the Power Spectrum of Dark Matter Substructure with Gravitational Lensing Yashar Hezaveh, Stanford University
The abundance of substructure within dark matter halos surrounding galaxies has been an area of intensive study for over a decade.
Quantifying the small-scale structure of dark matter halos, which is influenced by the spectrum of primordial density fluctuations and the micro-physics of dark matter, can allow us to probe multiple areas of fundamental physics. Observationally, however, very little is known about the true abundance and the structure of dark matter sub-halos.
In this talk, I will discuss the promising prospects of using ALMA and the recently discovered populations of strong gravitational lenses in mm/submm-wave surveys (SPT, Herschel, ACT, Planck) for mapping the small-scale structure of galaxy halos. In particular, I will show that we can measure the power spectrum of dark matter substructure by analyzing the correlations in perturbations of strongly lensed images.
I will show that the large number of discovered lenses and the spectacular power of ALMA paint a bright future for a robust characterization of the small-scale structure of dark matter halos.
May 2, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar The Weak Lensing Signal and Clustering of SDSS-III CMASS Galaxies Hironao Miyatake, Princeton University
Weak gravitational lensing is a powerful tool to understand how galaxies populate dark matter halos. In this talk, I report a weak lensing measurement of SDSS-III/CMASS galaxies, which is a luminous, high redshift (z~0.5), spectroscopic galaxy sample. For this analysis, I use the publicly-available CFHTLenS galaxy catalog for shapes and photometric redshifts of source galaxies. After performing systematic tests carefully, I find a highly significant detection of the CMASS weak lensing signal with signal-to-noise ratio of 28. Combining with clustering signals, I fit a halo model to the measurements. Based on this result, I will discuss details of matter properties of the CMASS galaxies such as stellar mass and halo concentration. In addition, I will introduce preliminary results of cosmological constraints obtained by combining the lensing and clustering measurements.
May 9, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar The first three years of AMS-02 experiment on the International Space Station Veronica Bindi, University of Hawaii
The Alpha Magnetic Spectrometer (AMS-02) is a precision large-acceptance high energy particle detector which was successfully deployed in 2011 on the International Space Station (ISS) where it will operate for the next decades. To date, the detector has collected over 40-billion cosmic ray events. Among the physics objectives of AMS are a search for the understanding of Dark Matter, Antimatter, the origin of cosmic rays and the exploration of new physics phenomena. An overview of the operations and performance of the AMS-02 detector as well as the results based on data collected during the first three years of operations in space will be presented.
May 16, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Seeking Gravity and Light from Binary Supermassive Black Holes Sarah Burke Spolaor, California Institute of Technology
In a major merger, two supermassive black holes will meet at the center of the merger remnant. Before their eventual coalescence, the giant black hole pair endures prolonged interaction with its environment, which may produce electromagnetic emissions. If observed, these would represent direct probes of late-stage merger dynamics, and could provide a smoking gun for gravitational wave emitters detectable by "Pulsar Timing Arrays". No small-orbit binary systems have yet been conclusively confirmed. We are investigating the use of both electromagnetic observations and Pulsar Timing Arrays to constrain, support, or disprove the binary SMBH hypothesis in current candidate binary systems. We will present results from ongoing searches for binary supermassive black holes, and will consider the prospects of Pulsar Timing Arrays to place physically interesting gravitational wave limits on target systems.
May 23, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Towards a first measurement of pp neutrinos in real time Pablo Mosteiro, Princeton University
The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. Neutrinos produced by these nuclear reactions exit the Sun and reach Earth within minutes, providing us with key information about what goes on at the core of our star. This talk presents progress towards the rst measurement of pp neutrinos in the Borexino detector, which would be the rst direct real-time measurement of pp neutrinos independent of other experiments. This would be, furthermore, another validation of the LMA-MSW model of neutrino oscillations. In addition, it would complete the spectroscopy of pp chain neutrinos in Borexino, thus validating the experiment itself and its previous results.
May 30, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Supernova neutrinos at present and future underground detectors Cecilia Lunardini, Arizona State University
A core collapse supernova is a very powerful source of ~ 10-20 MeV neutrinos. In the extreme environment of the collapsing star, the phenomenology of these neutrinos is very rich, and, in many respects, unique. I will first review the theory of neutrino emission and propagation inside a supernova, with focus on the physics of neutrino oscillations. In the second part of the talk, I will discuss what fundamental properties might be learned from future detections of supernova neutrinos. I will emphasize the potential of studying the diffuse flux of neutrinos from all the supernovae in the universe. This flux is constant in time and therefore it is a guaranteed signal at a detector of mass 0.1 Mt or higher. It also offers a unique possibility to study the whole population of supernovae, including those with failed or very dim explosions.
June 6, 2014 | 12:00 PM | LASR Conference Room | Friday noon seminar Planck Data Reconsidered Renee Hlozek, Princeton University
We re-analyse the Planck data and find that the 217GHz x 217GHz detector set spectrum used in the Planck analysis is responsible for some of the tension between the Planck parameters and other astronomical measurements. We will describe our map-based foreground cleaning procedure, which relies on a combination of 353 GHz and 545 GHz maps to reduce residual foregrounds in the intermediate frequency maps used for cosmological inference. While in broad agreement with the results reported by the Planck team, the parameters we obtain using our foreground cleaning imply a universe with a lower matter density of Omega_m=0.302 +- 0.015, and parameter values generally more consistent with pre-Planck CMB analyses and astronomical observations. We compare our cleaning procedure with the foreground modelling used by the Planck team and find good agreement. The difference in parameters between our analysis and that of the Planck team is mostly due to our use of cross-spectra from the publicly available survey maps instead of their use of the detector set cross-spectra which include pixels only observed in one of the surveys. We show evidence suggesting residual systematics in the detector set spectra used in the Planck likelihood code, which is substantially reduced for our spectra.
May 23, 2014 | 1:30 PM | LASR Conference Room | Special seminar Constraining fundamental physics with Planck Silvia Galli, IAP (Paris)
One of the major challenges of modern cosmology is to understand the nature of dark matter and dark energy. Our poor understanding of these components might even be indicating that physics as we know it today is not sufficient to describe the universe at large scales. In this talk, I will propose two ways to try to answer few of the questions of standard model of cosmology with Planck data. First, I will show how the CMB is a very powerful tool to constrain the characteristics of dark matter particles, as it strongly constrains dark matter annihilation. I will review the general ideas behind searches of dark matter annihilation with the CMB and present current and forecasted results from the Planck satellite. Second (time permitting), I will show how the detection of hundreds of new galaxy clusters through the Sunyaev-Zel'dovich effect by Planck and other ongoing experiments is a potentially powerful new probe of fundamental physics. In particular, the x-ray and SZ observations of these objects can be used to test the value of fundamental constants, i.e. to test the validity of currently known physics, at redshifts z< 1. I will show that current data can constrain the value of the fine structure constant at the level of 0.8%, comparable to CMB constraints.
June 16, 2014 | 1:00 PM | KPTC 120 | Special seminar Toward an Understanding of Foreground Emission in the BICEP2 Region David Spergel, Princeton University
BICEP2 has reported the detection of a degree-scale B-mode polarization pattern in the Cosmic Microwave Background (CMB) and has interpreted the measurement as evidence for primordial gravitational waves. Motivated by the profound importance of the discovery of gravitational waves from the early Universe, we examine to what extent a combination of Galactic foregrounds and lensed E-modes could be responsible for the signal. We reanalyze the BICEP2 results and show that the 100x150 GHz and 150x150 GHz data are consistent with a cosmology with r=0.2 and negligible foregrounds, but also with a cosmology with r=0 and a significant dust polarization signal. We give independent estimates of the dust polarization signal in the BICEP2 region using four different approaches. While these approaches are consistent with each other, the expected amplitude of the dust polarization power spectrum remains uncertain by about a factor of three. The lower end of the prediction leaves room for a primordial contribution, but at the higher end the dust in combination with the standard CMB lensing signal could account for the BICEP2 observations, without requiring the existence of primordial gravitational waves. By measuring the cross-correlations between the pre-Planck templates used in the BICEP2 analysis and between different versions of a data-based template, we emphasize that cross-correlations between models are very sensitive to noise in the polarization angles and that measured cross-correlations are likely underestimates of the contribution of foregrounds to the map. These results suggest that BICEP1 and BICEP2 data alone cannot distinguish between foregrounds and a primordial gravitational wave signal, and that future Keck Array observations at 100 GHz and Planck observations at higher frequencies will be crucial to determine whether the signal is of primordial origin.
April 3, 2014 | 2:00 PM | LASR Conference Room | Open Group seminar Searching for the highest energy emission from pulsars with Fermi and HAWC Pablo Saz Parkinson, UC Santa Cruz
June 11, 2014 | 3:00 PM | LASR Conference Room | Open Group seminar Shaped Antenna measurement of the background RAdio Spectrum Nipanjana Patra, Raman Research Institute
The measurement of the absolute spectrum of the cosmic radio background (CRB) at low radio frequencies and detection of spectral features that are predicted to arise from events in cosmological evolution of the primordial gas is an important goal of present day observational cosmology. Precision measurements of the CRB, which may be decomposed into Galactic components and an isotropic extragalactic background, is essential for constraining the cosmological population of radio sources as well as components of the radio emission of the Milky Way. The energy exchange in the 21-cm transition as the CMB photons propagate through the primordial neutral Hydrogen results in absorption and emission features in the CMB spectrum; due to cosmological expansion such spectral features of cosmic origin are now redshifted to long radio wavelengths. Although the amplitude of these signatures are smaller by orders of magnitude than the total Galactic and Extragalactic contributions at these frequencies, the later are expected to have relatively smooth spectral shapes over the scales of several hundred MHz and hence the cosmological signatures are separable. Detection of such spectral signatures constrains the thermal history of the gas and the nature of the sources of first light in the Universe. SARAS (Shaped Antenna measurement of the background RAdio Spectrum) is a correlation spectrometer purpose designed for precision measurements of CRB at meter wavelengths (Patra et al. 2013). The strategic system design takes a complex correlation approach to solving for total power spectra, which enables characterizing the system non-idealitites. We present the system configuration and results of background spectrum measurements by SARAS.
March 27, 2014 | 3:00 PM | TAAC 41 | Special Seminar Zonal Flows and Vortices in Circumstellar Disks: The Formation of Planetesimals in Starving Mode Hubert Klahr, MPIA, Heidelberg
PDF The formation of kilometer-sized planetary building blocks, called planetesimals, is still a hotly debated problem. A pure "hit and stick" model of dust grains faces several difficulties: from drift barrier, to bouncing and fragmentation barrier, to finally the 10km barrier. Thus, models have been invoked that lead swiftly to 100km-sized planetesimals from cm-sized objects via turbulent concentration and gravitational collapse. In this talk I will highlight the role of zonal flows in magnetohydrodynamical (MHD) active regions of circumstellar disks and of vortices in the MHD-dead zones. In the latter, radial and vertical stratification is the key to understanding the hydrodynamical stability of these disks. The fact that these features are able to concentrate the tiniest amount of small dust in an amount sufficient to trigger a streaming and gravitational instability enables us to work out a size distribution for initial planetesimals that resembles observational findings in the asteroid and Kuiper belts.