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Northwestern University

Weekly Astrophysics Seminars 2013-2014

Seminars are held at 4:00 PM on Tuesdays in Room F160
on the first floor of the Technological Institute (2145 Sheridan Road) unless otherwise noted


Spring Quarter 2014

  Date      Speaker / Seminar Host
  April 1

Anil Seth
    University of Utah
    Finding and Forming Star Clusters in Andromeda

The Panchromatic Hubble Andromeda Treasury (PHAT) survey has taken deep gigapixel images at six wavelengths that cover 1/3rd of the galaxy. These images resolve about 100 million individual stars and also reveal the most extensive star cluster system catalogued in any galaxy. I will discuss the "Andromeda Project", our crowd sourcing project to identify star clusters in the PHAT data. We are using these clusters to study the formation of stars, including the stellar and cluster initial mass functions, and the efficiency of star cluster formation.

Aaron Geller
  April 8

John Ruhl
    Case Western Reserve University
    Chasing Inflation

The Cosmic Microwave Background (CMB) has provided one of our most robust and powerful tools for learning about the contents and history of the universe. Temperature anisotropies mapped over a wide range of angular scales have given strong support to the basic 6-parameter “Inflationary Lambda Cold Dark Matter” cosmological model, and allowed us to measure those parameters exquisitely. For the past decade, several teams have been building instruments to search for a potential new signal from Inflation in the polarization of the CMB, of which the Bicep2 collaboration recently reported a detection. In this talk I will describe that signal, provide an overview of the SPIDER and SPTpol programs, and look to the future of CMB cosmology.

Giles Novak

  April 29

Daniel Holz
    University of Chicago
    Gravitational-Wave Astrophysics with Gamma-Ray Bursts

The next few years should see the birth of gravitational wave astrophysics, a revolutionary new way to learn about our Universe. Construction of advanced gravitational wave observatories, such as LIGO and Virgo, is actively underway. We focus on the most likely sources for these detectors, which is the inspiral and merger of a stellar mass binary system, such as a pair of neutron stars and/or black holes. In addition to being extraordinarily loud in gravitational waves, these systems may be associated with short gamma-ray bursts, and thus are also very bright in the electromagnetic spectrum. This offers the promise of multi-messenger astronomy: the combination of gravitational wave and electromagnetic observations to elucidate the physics and astrophysics of these sources. We present estimates for the event rate of these systems, showing that we can expect the first detections within months of operation. These measurements will teach us about the systems themselves (e.g., elucidating the central engine, constraining the beaming), as well as informing us about broad astrophysical and cosmological questions (e.g., the ratio of neutron stars to black holes, precision measurements of the Hubble constant). Of particular interest are the loudest events; we discuss the important role these have to play in gravitational wave astrophysics.

Vicky Kalogera
  May 6

Michael Line
    UC-Santa Cruz
    Characterizing Substellar Object Atmospheres: Bridging the Gap Between Stars
    and Planets

Understanding the compositional differences between stars and planets opens a window into their formation environments. Planets form in proto-stellar discs which are subject to enhanced metallicities and compositional gradients within that disk, where as stars form in molecular clouds. We would expect to observe differences in their atmospheric compositions due to their uniquely different formation environments. Given the spectroscopic characterization of dozens of transiting exoplanets and many more brown dwarfs we can begin to address big-picture questions about their formation. I will first discuss the inverse modeling machinery used to extract atmospheric temperature and abundance information from a spectrum. Second, I will show temperature and abundance results for a small set of exoplanets observed in secondary eclipse, their derived carbon to oxygen ratios, and then discuss the robustness of molecular detections in their atmospheres. Third, I will present some preliminary inverse modeling results from a well studied brown dwarf Gl 570D. Finally, I will discuss what we can learn from comparing the compositions of brown dwarfs and exoplanets.

Nick Cowan
  May 13

Alison Sills
    McMaster University
    Multiple Populations in Globular Clusters

Globular clusters are some of the simplest objects in the universe. For this reason, they are fundamental test beds to understand star formation and evolution in much more complex systems like galaxies. Globular clusters are spherical clusters of hundreds of thousands of stars, all of which were formed at the same time, in the same place and from the same material. They are old, and have been passively evolving for almost the age of the universe. They are quite beautiful, and also rather boring. Or so generations of astronomy students were taught until a few years ago.
I will summarize the evidence that these ancient objects contain more than one stellar generation, and outline the emerging paradigm to explain the observations. I will discuss some of the implications of, and problems with, this new scenario, and present some alternatives.

Fred Rasio

  May 20

Laura Lopez
    Dissecting the Explosions and Environments of Nearby Supernovae

Evidence has mounted that Type Ia and core-collapse (CC) supernovae (SNe) can have substantial deviations from spherical symmetry; one such piece of evidence is the complex morphologies of supernova remnants (SNRs). In this talk, I will highlight techniques we have developed to ascertain the role of explosion geometry and environment in shaping these SNRs. I will discuss application of these methods to extensive multiwavelength data of Milky Way and Magellanic Cloud SNRs, and I will explore the implications regarding the nature of the progenitors and the dynamical evolution of these sources.

Daryl Haggard

Past Astrophysics Seminars