// Enter speaker information here. The format is:
//
// ["Date","Name","Affiliation","Title","Abstract","Day","Time"]
//
// In the Abstract field you must escape double quotes (\"). Some HTML
// is possible (like
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// ** Edited to add color change for special day/time.
// ** If Day or Time field is not empty, special day/time
// ** is/are added in date column in red.
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// Template:
// January[0] =["day","name","association","title","abstract","",""];
January[0] =["14","Coral Wheeler",
"University of California, Irvine",
"Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites",
"If LCDM is correct, then all dark matter halos hosting galaxies, from those hosting dwarfs to those hosting giant clusters, are filled with abundant substructure down to very low mass scales (<< 10^9 Msun). Specifically, even the dark matter halos of Local Group field dwarfs should be filled with subhalos, many of which should be fairly massive (~ 10^8 Msun), and thus are potential targets for hosting small (ultrafaint) galaxies. Here we make predictions for the existence of ultrafaint satellites of dwarf galaxies using the highest resolution cosmological dwarf simulations yet run (mgas~ 250 Msun). We simulate four halos — two each at the mass of classical dwarf galaxies (Mvir ~10^10 Msun) and ultrafaint galaxies (Mvir ~ 10^9 Msun) — down to z=0 using the GIZMO (Hopkins 2014) code. This code relies on state-of-the-art MFM hydrodynamics and implements the FIRE (Feedback in Realistic Environments) recipes (Hopkins et al. 2014) for converting gas into stars and capturing the energy fed back from those stars into the surrounding medium. We predict that ultrafaint galaxies (M* ~ 3,000 Msun) should exist as satellites around more massive dwarf galaxies (M*~ 10^6 Msun) in the Local Group. These tiny satellites, as well as the two isolated ultrafaints, have uniformly ancient stellar population (>10 Gyr) owing to reionization-related quenching. The more massive systems, in contrast, all have late-time star formation. Our results suggest that Mhalo ~ 5 x10^9 Msun is a probable dividing line between halos hosting reionization 'fossils' and those hosting dwarfs that can continue to form stars in isolation after reionization. Importantly, we show that the extended ~50 kpc regions around Local Group “field” dwarfs may provide efficient search locations for discovering new ultrafaint dwarf galaxies, and discuss the prospects for their discovery in light of the new generation of large surveys and giant telescopes. If these tiny satellites are observed, this would provide evidence that dark matter substructure is truly hierarchical, as predicted in the standard paradigm.","",""];
January[1] =["19",
"Adrian Hamers",
"Leiden University",
"The Long-term Evolution of Hierarchical Systems",
"Secular dynamics in hierarchical systems have important implications for short-period binaries, hot Jupiters and multiplanet systems. We present a new efficient method for studying the long-term dynamics of hierarchical systems composed of nested binary orbits, with any hierarchical structure and any number of bodies. We apply this method to explain the current observed lack of circumbinary planets around short-period binaries. In particular, we relate this observation to the origin of short-period binaries in stellar triples. Furthermore, we consider the formation of hot Jupiters though high-eccentricity migration with secular chaos in multiplanet systems with at least three planets, and present preliminary results. Finally, we discuss future directions of studying the long-term evolution of multiplanet systems.","Tuesday","11am"];
February[0] =["04",
"Subo Dong",
"Kavli Institute for Astronomy and Astrophysics, Peking University",
"Observational Tests of SN Ia Explosion Models in a Paradigm Shift",
"The field of type Ia supernova (SN Ia) explosion physics is in a crisis. Decades of theoretical researches fail to demonstrate that successful explosions can be convincingly achieved from the popular single degenerate and double degenerate merger models. A growing number of observational evidences contradict these two popular scenarios to explain the SN Ia population. We argue that the direct white dwarf-white dwarf collisions in the field multiple stellar systems is the most promising mechanism to explain the SN Ia population. Not only do collisions explain several robust features across the entire SN Ia population, but also their predictions of the bi-modal Ni56 distributions in the ejecta are recently discovered observationally. I will discuss key observational tests on the collision models enabled by the All Sky Automatic Survey for SuperNovae (ASAS-SN)-- the most successful bright supernova survey at present.",
"",""];
February[1] =["11",
"Kimberly Boddy",
"University of Hawai'i at Manoa",
"Dark Hydrogen with Hyperfine Interactions",
"",
"Thursday","2pm"];
February[2] =["18",
"Ben Bar-Or",
"IAS, Princeton",
"Stellar Dynamics around a Massive Black Hole",
"Galactic nuclei and the Massive black holes (MBHs) in their centers are rich environments, where the complex stellar dynamics plays an important role in many physical phenomena. We show that the standard description of the two-body relaxation, around an MBH, as a diffusion process, is incomplete. We derived a non-perturbative solution for energy relaxation as an anomalous diffusion process, and a robust estimation technique to measure it in N-body simulations. We also show how the dynamics of a nearly-Keplerian N-body system, where the angular momentum evolution is accelerated by resonant relaxation, can be described and studied in a formal statistical mechanics framework. In this framework the background potential is described as a correlated Gaussian noise. We obtained the leading order, phase-averaged stochastic equations of motion and derived an effective Fokker-Plank equation for a general correlated Gaussian noise. We combine the Fokker-Plank description of two-body relaxation and resonant relaxation to study the loss-cone dynamics in Galactic nuclei.",
"",""];
February[3] =["25",
"Masataka Fukugita",
"University of Tokyo",
"Circumgalactic cosmology",
"",
"",""];
March[0] =["3",
"Ilse Cleeves",
"Harvard, CfA",
"The role of energetic processes in the cold chemistry of protoplanetary disks",
"Planets form from the coldest and densest parts of circumstellar disks around young stars. During this phase, the active nature of the star subjects the disk to relatively high fluxes of UV and X-ray photons and energetic particles. Simultaneously, the local star-forming environment may provide additional external UV and/or radioactive pollutants from recent massive stellar populations. These energetic agents play a vital role in 1) setting protoplanetary disks' turbulent and thermal physics, and 2) regulating the important gas and grain surface chemical reactions, impacting the overall disk molecular composition. Consequently, chemistry can used to 'map out' the important ionizing processes in disks using molecular emission. Using data from the Submillimeter Array and Atacama Large Millimeter/Submillimeter Array, we have put strong constraints on the ionization levels in the deep disk of TW Hya, constraining the cosmic ray rate to a value two orders of magnitude below the dense interstellar value. This result has major consequences for the active disk chemistry and, in particular, the chemistry of water. Finally, I will discuss future directions aiming to resolve ionization structure and time variability.",
"",""];
March[1] =["10",
"",
"",
"",
"",
"No seminar",""];
March[2] =["17",
"Erika Nesvold",
"Carnegie Institution for Science",
"Warm Circumstellar Debris Disks: Diagnosing the Unseen Perturber",
"Observations of circumstellar debris disks have revealed that a subset of this population harbor a warm dust component. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the planetesimals in the belt and produce dust via collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the planetesimals’ eccentricities and inclinations via the Kozai-Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai-Lidov excited disk can generate a dust disk via collisions and compare the results of the Kozai-Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we discuss possible observational tests of a warm disk that can distinguish whether the disk was produced by an exterior brown dwarf or stellar companion or an interior planet.",
"",""];
March[3] =["24",
"Erin Kara",
"University of Maryland",
"Probing the Inner Accretion Flow of Supermassive Black Holes with X-ray Reverberation Mapping",
"In recent years, X-ray reverberation mapping has opened a new way to investigate the inner accretion flow around black holes. XMM-Newton and NuSTAR observations of the rapid variability in Active Galactic Nuclei have shown that the soft excess, broad iron K line and Compton hump lag behind the continuum emission, suggesting light travel distances of a few gravitational radii. Beyond simply detecting reverberation, we are beginning to use X-ray reverberation to map out the geometry of the inner accretion flow, testing the compactness of the X-ray emitting source, the structure of the disc and the origin of the variability. In this talk, I will give an overview of the observational results discovered thus far, and will present new results of X-ray reverberation in a tidal disruption event.",
"",""];
March[4] =["31",
"Nir Shaviv",
"Hebrew University of Jerusalem",
"Evidence for excess dark matter at the galactic plane",
"Paleoclimatological evidence suggests that the total gravitating mass density at the galactic plane is about twice the baryonic density. I will discuss this measurement and show that it is consistent with the different determinations of the local and column densities of both the baryonic and total mass, including the seemingly inconsistent kinematically determined local mass density, which due to spiral arm passages has a systematic offset. When all the data is combined we find evidence for dark matter having a local density of about 0.1 Msun/pc^3, and a column density of about 10 to 20 Msun/pc^2. I will also show that a cooling dark matter component is theoretically predicted to be able to cool to roughly this local density but not any denser.",
"",""];
April[0] =["7",
"",
"",
"",
"",
"","No seminar"];
April[1] =["14",
"Jens Chluba",
"University of Manchester, UK",
"CMB spectral distortions within LCDM",
"Spectral distortions of the CMB provide a powerful new probe of early Universe processes. Even if so far no average spectral distortion has been seen, LCDM does predict several signals that are within reach of current technology. In this talk, I will give a broad brush overview of our most recent understanding of the formation and evolution of distortions in the early Universe, highlighting guaranteed LCDM signals and what we hope to learn from them about the Universe we live in.",
"",""];
April[2] =["21",
"Eric Mamajek",
"University of Rochester",
"Transiting Circumplanetary Disks",
"",
"",""];
May[0] =["12",
"Aaron Zimmerman",
"CITA, Toronto",
"Quasinormal modes beyond Kerr black holes",
"The historic first detection of a gravitational waves from merging black holes came with an unexpected windfall: the first observation of a black hole ringdown. The ringdown of a black hole through damped ''quasinormal'' oscillation modes provides us with a unique measurement of the properties of a black hole. Deviations from General Relativity are imprinted on the spectrum of modes, and there is an unexpected richness in ringdown phenomena even in the case of standard Kerr black holes. In this talk, I will discuss past work on the spectrum of rapidly rotating black holes and their unique ringdown signature. I will also discuss a method for computing the spectrum of black hole spacetimes which are perturbed from Kerr. The application of this method reveals the possibility of a parametric instability in rapidly rotating black holes, and allows for the calculation of quasinormal mode frequencies in weakly charged Kerr-Newman black holes.",
"Thursday","2pm"];
May[1] =["19",
"Liang Dai",
"IAS, Princeton",
"Gravitational lensing of transient events",
"",
"Thursday","2pm"];
June[0] = ["2",
"Jordi Miralda Escudé",
"University of Barcelona",
"The Lyman-alpha forest and DLAs: probes to large-scale structure and galaxy formation",
"",
"",""];