Research Events
For the Public
Northwestern University

CIERA Special Seminars 2015-2016

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

Fall Quarter 2015

  Date/Time      Visitor Host
  Sept. 15
  Tech F160

Adrian Hamers
    Leiden Observatory
    Secular dynamics of high-order multiple systems
     applications to circumbinary planets and Hot Jupiters

We present a new efficient method to study the long-term dynamics of hierarchical multiple systems such as high-multiplicity stellar systems and multiplanet systems, without restrictions on the number of bodies nor on the hierarchical configuration. We apply this method to hierarchical quadruple systems consisting of a hierarchical triple orbited by a fourth body, in different contexts. First, we consider the general dynamics, and we characterise the behavior of the system in terms of a ratio of Kozai-Lidov (KL) time-scales applied to different binary pairs. Second, we apply the method to explain the currently observed lack of transiting circumbinary planets around short-period binaries. Finally, we present preliminary integrations of multiplanet systems, in which secular chaos gives rise to high eccentricities and tidal shrinkage in the innermost planet's orbit, giving a pathway for producing Hot Jupiters. Our new method allows for much faster and longer integrations compared to previous direct N-body integrations, making it an excellent tool for better understanding the conditions for producing Hot Jupiters in multiplanet systems through secular chaos.

Fabio Antonini
  Oct. 8
  Tech F160

Andrew W. Smith
    University of Maryland, College Park and NASA/GSFC
    Revealing The Violent Universe: Current Results and The Future of Gamma-ray Astronomy

The last 10 years have seen a dramatic explosion of important science results from space based instruments (~0.3-300 GeV) such as Fermi-LAT and AGILE, as well as ground based instruments (~100-5000 GeV) such as VERITAS, HESS, and MAGIC. These instruments have provided an in-depth exploration of particle acceleration in the the most energetic known cosmic sources (supernova remnants, gamma-ray bursts, pulsars, AGN, and the center of our own Galaxy), as well as providing important clues to the mystery of high energy cosmic ray origins. In this talk I will review the most important recent results from these instruments as well as providing a preview of the next generation of both ground and space based gamma-ray observatories. The future for ground based instruments is already being cemented with the completion of the HAWC array in Mexico, as well as the upcoming CTA array planned for both the Northern and Southern Hemispheres. The successor to Fermi-LAT is also in the works, with several mature mission concepts progressing forward already. I will review some of these concepts and provide an outlook for the future of this exciting and dynamic field.

Farhad Yusef-Zadeh
  Nov. 11
  Tech F160

Tuguldur Sukhbold
   University of California Santa Cruz
    Core-Collapse Supernovae from Neutrino-driven Explosions

Nucleosynthesis, light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive stars with solar metallicity and masses between 9-120 solar masses. The full evolution is followed using an adaptive reaction network of up to 2000 nuclei. A novel aspect of the survey is the use of a one-dimensional neutrino transport model for the explosion. This explosion model has been calibrated to give the observed energy for SN 1987A and Crab supernova. As a result of using a calibrated central engine, the final kinetic energy of the supernova is variable and sensitive to the structure of the presupernova star. Many progenitors with extended core structures do not explode, but become black holes, and the masses of exploding stars do not form a simply connected set. The resulting nucleosynthesis agrees reasonably well with the sun provided that a reasonable contribution from Type Ia supernovae is also allowed, but with a deficiency of light s-process isotopes. The resulting neutron star IMF has a mean gravitational mass near 1.4 solar masses. The average black hole mass is about 9 solar masses if only the helium core implodes, and 14 solar masses if the entire presupernova star collapses. Only ~10% of supernovae come from stars over 20 solar masses and some of these are Type Ib or Ic. Some useful systematics of Type IIp light curves are explored.

Ron Taam

  Nov. 16
  Tech F160

John Tobin
   Leiden Observatory
    Toward Understanding the Formation of Proto-planetary Disks and Multiple Star Systems

Disks and multiple star systems are thought to form early in the star formation process. Conservation of angular momentum enables the formation of protostellar disks; protostellar companions can also form if the disk is gravitationally unstable. However, theory and simulations have suggested that large, massive disk formation may be difficult due to removal of angular momentum by magnetic fields. Observations are now sensitive enough to begin testing these predictions, and Keplerian disks have been discovered around newly formed star systems. However, the numbers of Keplerian disks remain small and the frequency of companion protostars on scales < 150 AU is poorly known. To greatly expand our knowledge on the frequency of disks and multiplicity, I am leading a 264 hour VLA large program to observe all protostars in a single star forming region, the Perseus molecular cloud (d 230 pc, N 80), with a spatial resolution of 15 AU. With these data, we are identifying new protostellar disk candidates and closer multiple systems than have ever been previously identified. We have found evidence for a bimodal distribution of protostar separations, suggesting that multiple formation mechanisms are acting on different scales. Finally, we also see indications of evolution in the separation distribution for younger protostars relative to those that are more-evolved. These results open the door to expanded multiplicity and disk surveys to determine if the trends found in Perseus are applicable to other star forming regions.

Farhad Yusef-Zadeh

  Nov. 23
  Tech F160

Morgan MacLeod
    University of California, Santa Cruz
    Common Envelope and the Formation of Close Neutron Star Binaries

How do close neutron star binaries form? Many aspects of our understanding of the complex channels through which compact binaries form remain uncertain. This talk focuses on a crucial phase in the formation of close binary pairs of neutron stars: a common envelope episode. During the common envelope phase, one star evolves to engulf its companion in a shared gaseous envelope. Before this envelope is ejected, drag forces pull the two stellar cores into a tighter orbit. But the neutron star can also accrete from the surrounding gas. This talk explores the hydrodynamics of the common envelope phase in order to model the metamorphosis of the neutron star and the binary orbit.

Fabio Antonini


Winter Quarter 2016

  Date/Time      Visitor Host
  Jan. 14
  Tech F160

Ian Stephens
    Boston University

Giles Novak and Farhad Yusef-Zadeh



For more information, contact: ciera@northwestern.edu

Past CIERA Special Seminars