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Northwestern University


CIERA Special Seminars 2017-2018

*Tech = Technological Institute (2145 Sheridan Road)
**Db = Dearborn Observatory (2131 Tech Drive)

 

Fall Quarter 2017


  Date/Time      Visitor Host
  Aug. 25
   Tech F160
   2:00pm

Janet Chen
    Max Planck University
    Giant Explosions in Dwarf Hosts : “GREAT” Survey of Superluminous Supernovae

A new class of supernovae, superluminous supernovae, has been discovered in the past few years. They are 100 times brighter (with absolute mag ~ -21) than normal core-collapse supernovae. This means that the standard paradigm of iron-core collapse cannot account for the origin of superluminous supernovae. An alternative mechanism is needed to power such high luminosities, including magnetar spin down, pair-instability explosions and shell collisions. In this talk, I will present our work from discovery of superluminous supernovae with our "GREAT" (GRond-Epessto-ATlas) survey, which aim is to find superluminous supernovae at very first stage; to classification with the Public ESO Spectroscopic Survey for Transient Objects (PESSTO), and follow-up campaign with large facilities such as the Very Large Telescope. We found superluminous supernovae appear to occur exclusively in dwarf, metal-poor host galaxies, and a sub-solar metallicity seems required to produce superluminous supernovae. We also found a possible relation that if magnetar powering is the source of the extreme luminosity then the required initial spins appear to be correlated with metallicity of the host galaxy. Finally I will also focus on the diversity of superluminous supernovae and a challenge of metal rich environment has been found for SLSNe.

Giacomo Terreran
  Sep. 11
   Tech F210
   1:30pm

Om Sharan Salafia
    University of Milano-Bicocca
    Where and When: How to Combine Information from the GW Signal and EM Counterpart
    Models to Inform and Optimize the EM Follow-up Strategy

The electromagnetic follow-up of a gravitational wave event requires astronomers to scan a wide sky region for the detection and identification of a transient whose features are very uncertain a priori. A sky position posterior probability map (“skymap”) is provided by the LIGO/Virgo collaboration (containing information on "where" to search), but no timing ("when") information is available, other than conjectures based on the expected properties of the candidate EM counterparts. I will describe a novel approach to schedule observations using information from GW parameter estimation, thus allowing for an event-specific optimization of the EM follow-up strategy. I will illustrate the result of applying the approach to an example NS-NS injection with an associated SGRB oprhan afterglow and dynamical ejecta macronova, showing that the follow-up is significantly improved. I will discuss the possible application of the method to future real GW triggers, including the case when only low-latency information is available.

Wen-fai Fong
  Sep. 20
  F210
  2:00pm

Adrian Barker
    University of Leeds
    Tidal Flows in Extrasolar Planets

Tidal interactions between short-period planets and their host stars are thought to play an important role in the evolution of planetary orbits, and stellar and planetary spins. However, the mechanisms responsible for tidal dissipation are not well understood theoretically. I will present results from hydrodynamical (and magnetohydrodynamical) simulations of tidal flows in short-period gaseous planets and stars from first principles. I will discuss the outcome of two fluid instabilities that could be important for tidal dissipation (the elliptical and precessional instabilities). Finally, I will present some new results on the influence of semi-convective layers on tidally-excited waves and tidal dissipation in planets.

Yoram Lithwick
  Sep. 22
  F160
  11:00am

Suzanne Aigrain
    University of Oxford
    Taming the Stochastic: How Gaussian Processes are Transforming Exoplanet Studies

Almost all of the staggering progress in detecting and characterizing extra-solar planetary systems over the past 20 years or so has relied on time-series data. The planetary signals are typically buried in complex, correlated noise, such as stellar variability or instrumental systematics, which the "traditional" statistical toolbox of most astronomers was ill equipped to deal with. Over the past few years, Gaussian process (GP) regression has become increasingly popular as a means of modelling these "nuisance signals" explicitly, within a Bayesian framework, so that the resulting uncertainties can be propagated through to the final exoplanet parameters.

Adam Miller,
Ben Nelson
  Oct. 3
  F160
  4:00pm

Ian Christie
    Purdue University
    Modeling Stellar Wind Interactions

Interactions between stellar winds and their surrounding medium are powerful tools for investigating local properties of the medium (e.g. gas density, temperature), whose features can be revealed through thermal and non-thermal radiation mechanisms. As the stellar wind collides with the medium, the ram pressure terminates the wind by a strong shock. The non-thermal emission from these interactions is produced by relativistic electron-positron pairs accelerated at the shock front, while the thermal emission is produced from the compression and heating of the shocked stellar wind. In this talk, I will present model predictions about the observational signatures in X-rays and/or radio wavelengths of three different systems: i) the S2-star interacting with the accretion flow surrounding Sgr A*, ii) a fiducial young and bright pulsar interacting with the Galactic Center environment, and iii) the pulsar/Be binary system PSR J2032+4127.

Sasha Tchekhovskoy
  Oct. 19
  F160
  11:00am

Payaswini Saikia
    Radboud University, Netherlands
    The Optical Fundamental Plane of Black Hole Activity

Black hole accretion disc and its associated jets form a coupled system, which is thought to scale globally across the entire black hole mass range - from the stellar mass X-ray Binaries to the supermassive Active Galactic Nuclei. Using a sample of 39 low-luminosity AGN selected from the Palomar Spectroscopic Survey and the 4 best-studied stellar mass X-ray binaries in the low/hard state, we report the discovery of a fundamental plane of black hole activity in the optical band, with the nuclear [OIII] emission line luminosity as a tracer of accretion rate.

We show that the fundamental plane can be used to provide insights on the underlying distributions of relativistic jet parameters (eg. opening angles, Lorentz factor distribution) in blazars. We also study a large sample of 10149 AGN on the optical fundamental plane, obtained by cross-correlating the AGN samples in SDSS survey and 1.4 GHz VLA FIRST catalogue and show that 1.4 GHz FIRST fluxes do not trace pure AGN nuclear activities, and is rather heavily contaminated by environmental and other non-nuclear factors.

Deanne Coppejans
  Nov. 8
  F210
  2:00pm

Adrian Hamers
    IAS; Princeton
    Hot Jupiters Driven by High-eccentricity Migration in Globular Clusters

Hot Jupiters (HJs) are short-period giant planets that are observed around ~1% of solar-type field stars. One possible formation scenario for HJs is high-eccentricity (high-e) migration, in which the planet forms at much larger radii, is excited to high eccentricity by some mechanism, and migrates to its current orbit due to tidal dissipation occurring near periapsis. We consider high-e migration in dense stellar systems such as the cores of globular clusters (GCs), in which encounters with passing stars can excite planets to the high eccentricities needed to initiate migration. We study this process via Monte-Carlo simulations of encounters with a star+planet system including the effects of tidal dissipation, using an efficient regularized restricted three-body code. HJs are produced in our simulations over a significant range of the stellar number density n_*. Assuming the planet is initially on a low-eccentricity orbit with semimajor axis 1 AU, for n_* < 1e3 pc^{-3} the encounter rate is too low to induce orbital migration, whereas for n_* > 1e6 pc^{-3} HJ formation is suppressed because the planet is more likely ejected from its host star, tidally disrupted, or transferred to a perturbing star. The fraction of planets that are converted to HJs peaks at ≈2% for intermediate number densities of ≈4e4 pc^{-3}. Warm Jupiters, giant planets with periods between 10 and 100 days, are produced in our simulations with an efficiency of up to ≈0.5%. Our results suggest that HJs can form through high-e migration induced by stellar encounters in the centers of of dense GCs, but not in their outskirts where the densities are lower.

Fabio Antonini
  Nov. 21
  F160
  4:00pm

Benjamin Oppenheimer
    University of Colorado - Boulder

Alex Richings
  Nov. 30
  F160
  11:00am

Ben Ryan
    University of Illinois

Sasha Tchekhovskoy
For more information, contact: ciera@northwestern.edu


Past CIERA Special Seminars