Thunch schedule for Spring 2018 (12:15 - 1:15)


  • Feb 8
    • Yuan-Sen Ting
    • Postdoc, Princeton University
    • Title: The new era of Galactic Archaeology
    • Abstract: Understanding physical processes responsible for the formation and evolution of galaxies like the Milky Way is a fundamental problem. However, a key challenge is that the properties and orbits of the stars can only be observed at present: to understand what happened in the Milky Way at earlier epochs, one must explore “archaeological” techniques. I will discuss the opportunities associated with Galactic archaeology with the on-going large scale multiplexing spectroscopic surveys, including a first quantitative constraint on the radial migration of stars and on the disrupted cluster mass function in the Milky Way. I will also describe a new set of tools for efficient measuring > 20 elemental abundances from low-resolution R=2000 spectra, for discovering spectroscopically unresolved binaries, and for inferring asteroseismic parameters directly from single-epoch spectra.

  • Feb 15
    • Steve Choi
    • Grad student, Princeton University
    • Title: Precision Cosmology with Advanced ACTPol
    • Abstract: The Advanced ACTPol upgrade on the Atacama Cosmology Telescope aims to improve the measurement of the cosmic microwave background anisotropies and polarization, using four new dichroic detector arrays fabricated on 150-mm silicon wafers. In 2016, the Atacama Cosmology Telescope began mapping approximately half the sky with increased sensitivity using these new detector arrays. I will discuss the performance of the Advanced ACTPol upgrade and the improved constraints on cosmology.

  • Feb 22
    • Cole Holcomb
    • Grad student, Princeton University
    • Title: Gyroresonant Streaming Instability and Implications for Nonlinear Cosmic Ray Transport
    • Abstract: Cosmic rays (CRs) are known to be an often energetically significant component of interstellar and intracluster media. The interplay between CRs and the ambient magnetic field can produce observational signatures (e.g. CR isotropy, radio halos of galaxy clusters, etc..) and even impact galactic evolution on large scales (e.g. galactic winds). Modeling these effects has relied on ill-understood and generally unvalidated linear/quasilinear analytical models for the gyroresonant interaction between CRs and magnetic fields. We perform microphysical simulations of the gyroresonant CR streaming instability and discuss implications for modeling the associated large scale physics.


  • Mar 1
    • Edo Berger
    • Professor, Harvard
    • host: Jia Liu
    • Title: Rattle and Shine: Joint Detection of Gravitational Waves and Light from the Binary Neutron Star Merger GW170817
    • Abstract: The much-anticipated joint detection of gravitational waves and electromagnetic radiation was achieved for the first time on August 17, 2017, for the binary neutron star merger GW170817. This event was detected by Advanced LIGO/Virgo, gamma-ray satellites, and dozens of telescopes on the ground and in space spanning from radio to X-rays. In this talk I will describe the exciting discovery of the optical counterpart, which in turn led to several detailed studies across the electromagnetic spectrum. The results of the observations carried out by our team include the first detailed study of a "kilonova", an optical/infrared counterpart powered by the radioactive decay of r-process nuclei synthesized in the merger, as well as the detection of an off-axis jet powering radio and X-ray emission. These results provide the first direct evidence that neutron star mergers are the dominant site for the r-process and are the progenitors of short GRBs. I will also describe how studies of the host galaxy shed light on the merger timescale, and describe initial constraints on the Hubble Constant from the combined GW and EM detection.

  • Mar 8
    • John Hoffman [CANCELED]
    • Grad student, Princeton University
    • Title: Variable stars in the HATSouth dataset
    • Abstract: Variable star astronomy continues to be fueled by a growing number of large astronomical sky surveys like HAT, Gaia, OGLE, Pan-STARRS, and LSST. I will present some preliminary results regarding variability in the HATSouth survey. I will also discuss ongoing work to integrate detection and classification of variable stars in a single Bayesian framework in order to effectively marginalize over measurement uncertainties and model parameters.



  • Mar 15
    • John Hoffman [RESCHEDULED]
    • Grad student, Princeton University
    • Title: Variable stars in the HATSouth dataset
    • Abstract: Variable star astronomy continues to be fueled by a growing number of large astronomical sky surveys like HAT, Gaia, OGLE, Pan-STARRS, and LSST. I will present some preliminary results regarding variability in the HATSouth survey. I will also discuss ongoing work to integrate detection and classification of variable stars in a single Bayesian framework in order to effectively marginalize over measurement uncertainties and model parameters.

  • Mar 29
    • Joshua Wallace
    • Grad student, Princeton University
    • Title: Planets and Variables in Globular Clusters
    • Abstract: How common are planets in globular clusters? The answer to this question will provide important constraints on planet formation and evolution processes. I will present results from our analysis of the K2 survey of M4, the closest globular cluster to Earth. We have several promising transiting exoplanet candidates. If any of these are confirmed as exoplanets, it would represent the first non pulsar planet known in a globular cluster. I will also present some results from other variable objects present in the data, including RR Lyrae and eclipsing binaries (both detached and contact).

  • Apr 5
    • [your name here]
    • [your affiliation here]
    • host: [your host here]

  • Apr 12
    • Kris Pardo
    • Grad student, Princeton University
    • Title: Testing Modified Gravity with Dwarf Galaxies and Gravitational Waves
    • Abstract: Many modified gravity theories attempt to explain dark matter or dark energy by modifying general relativity; however, these theories can be powerfully constrained by existing astrophysical data. I will discuss how isolated dwarf galaxies can be used to test Verlinde's Emergent Gravity, a theory that attempts to account for dark matter. In addition, I will discuss how higher-dimensional theories that attempt to explain dark energy can be constrained by the recent binary neutron star merger GW170817.





  • Apr 19
    • [your name here]
    • [your affiliation here]
    • host: [your host here]

  • Apr 26
    • Spitzer lecturer
  • May 3
    • Spitzer lecturer

  • May 10
    • [your name here]
    • [your affiliation here]
    • host: [your host here]

  • May 17
    • Fei Dai
    • Grad student, MIT/Princeton
    • Title: Ultra-short-period planets: formation, evolution and unique scientific opportunities
    • Abstract: In order to understand a process as complex as planet formation, the most extreme cases are often the most revealing. At one extreme are the ultra-short-period planets (USP, orbital period <1 day), orbiting their host stars just a few stellar radii away. Thanks to their proximity to the host stars, USPs may represent our best chance of understanding the composition of small, Earth-like planets in the near future. Moreover, these highly irradiated worlds are great for studying the reflectivity/thermal emission from the rocky planets, the effect of photoevaporation, and possible planet-star magnetic interaction etc. In this talk, I will describe our recent works on the composition and orbital architecture of USP planets and the implication for their origin.

  • May 24
    • Frans Pretorius
    • Professor, Princeton University
    • Title: Black Hole Superradiance
    • Abstract: Black hole superradiance is the process by which a bosonicfield interacting with a rotating black hole gains energy
      at the expense of the rotational energy of the black
      hole. Although well studied at the perturbative level
      for decades, only within the last few years have self-consistent
      non-linear (numerical) studies explored the phenomenon. I will describe
      two such examples : large amplitude gravitational wave scattering, and
      growth to saturation of Proca-field "hair". The latter scenario is of
      relevance to the so-called "axiverse", where hypothetical
      ultralight particles could spin down black holes, possibly emitting
      detectable gravitational waves in the process.
      I will also describe the background error subtraction technique (BEST)
      that allowed a significant reduction in the computational cost of the
      simulations. This technique is applicable in any situation where
      at least some part of the computational domain is well represented by
      a known, analytic solution.



  • May 31
    • John Stocke
    • host: Michael Strauss
    • Title: The Baryon Content of Star Forming and Passive Galaxies