Astrophysics Seminar

Astrophysics Seminar: "Outflows from galaxies: shocks and surprises"

Location: 
Kaplun building, Room No. 200
Thu, 07/04/2016 - 12:30 to 13:30

Lecturer: Dr. Biman Nath Affiliation: Raman Research Institute Abstract: Outflows from galaxies enrich the intergalactic medium and play a crucial role in the evolution of galaxies. The standard scenario of outflows from galaxies has been that of gas driven by thermal pressure of the interstellar medium which is heated by multiple supernovae. Recent observations of galactic outflows have shown that other mechanisms such as radiation pressure and cosmic rays may also be important. I will discuss some new results on the interplay between these processes, as well as the

"Astrophysics Seminar: Explaining Infrared Excesses Around Newborn White Dwarfs with Evaporated Exocomets"

Location: 
Kaplun building, Room No. 200
Tue, 10/11/2015 - 12:30 to 13:30

Lecturer: Dr. Nicholas Stone Affiliation: Columbia University Abstract: Several lines of observational evidence suggest that white dwarfs receive small birth kicks due to anisotropic mass loss. If other stars possess extrasolar analogues to the Solar Oort cloud, the orbits of comets in such clouds will be scrambled by white dwarf natal kicks. Although most comets will be unbound, some will be placed on low angular momentum orbits vulnerable to sublimation or tidal disruption. The dusty debris from these comets will manifest itself as an IR excess temporarily

"Special Astrophysics Seminar: A New Class of Rapidly Rising Luminous Transients"

Location: 
Danciger B building, Seminar room
Sun, 22/03/2015 - 14:00 to 15:30

Lecturer: Dr. Iair Arcavi Affiliation: Las Cumbres Observatory Global Telescope, and Kavli Institute for Theoretical Physics, University of California, Santa Barbara Abstract: We recently identified several rapidly rising (~ 10 day rise-time) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (~ -20 absolute magnitude). The rapid rise to such a luminous peak places these events in a unique part of SN phase space, challenging standard SN emission mechanisms. Spectra formally classify one of the events as a

"Astrophysics Seminar: The Era of Time Domain Radio Astronomy"

Location: 
Kaplun building, Room No. 200
Tue, 25/11/2014 - 12:30 to 13:30

Lecturer: Dr. Assaf Horesh Affiliation: Caltech Abstract: A renaissance is taking place in optical and radio astronomy due to application of rapidly evolving commercial technology. Moreover, by all accounts (including Astro2010, The Astronomy and Astrophysics Decadal Survey), this decade is regarded as the decade of time domain astronomy. The dynamic radio sky is seen as a frontier area in astrophysics, ripe for discovery. The synergy between optical and radio astronomy, such as the joint VLA-PTF collaboration, have proofed to be fruitful. This

Astrophysics Seminar: "Lighting up magnetic jets 3D instabilities and energy dissipation in relativistic MHD jets"

Location: 
Kaplun building, Room No. 200
Tue, 02/02/2016 - 12:30 to 13:30

Lecturer: Dr. Omer Bromberg Affiliation: Racah Institute of Physics, The Hebrew University of Physics Abstract: It is commonly accepted that the relativistic jets observed in extragalactic sources like GRBs and AGNs are launched magnetically and are powered by the rotational energy of a central object. Such jets carry most of their energy in the form of electromagnetic Poynting flux. However by the time the ejecta reach the emission zone most of that energy is transferred to relativistic motions of the jet material with a large fraction given

"Astrophysics Seminar: Evolution of Galaxy Shape Through Compaction and Quenching"

Location: 
Kaplun building, Room No. 200
Tue, 26/05/2015 - 12:30 to 13:30

Lecturer: Dr. Matteo Tomassetti Affiliation: Racah Institute of Physics, The Hebrew University of Jerusalem Abstract: In this talk I will show results on the analysis of the VELA suite of zoom-in cosmological simulations. Previous studies have shown that a significant fraction of high-redshift galaxies evolve from a diffuse phase into a compaction phase followed by a quenching event. Part of my research work focuses on determining the shape of the dark matter component as well as the stellar and gaseous disk during these three phases. In the first

"Astrophysics Seminar: Supernova: not what you thought - The majority of type Ia SNe may be the result of WD-WD direct collision, and core collapse SNe may be thermonuclear"

Location: 
Kaplun building, Room No. 200
Tue, 23/12/2014 - 12:30 to 13:30

Lecturer: Dr. Doron Kushnir Affiliation: Institute for Advanced Study Abstract: Type Ia: I will show that the majority of type Ia SNe may be the result of direct collisions of typical field CO-WDs in triple systems. The supporting evidences are: 1. the rate of such collisions may be comparable to the SNe Ia rate, 2. in this case the nuclear detonation is due to a well understood shock ignition, devoid of commonly introduced free parameters such as the deflagration velocity or transition to detonation criteria, 3. the observed range of Ni56 among different explosions, including the

Astrophysics Seminar: "Tidal capture formation of Low Mass X-Ray Binaries from wide binaries in the field"

Location: 
Kaplun building, Room No. 200
Tue, 22/03/2016 - 12:30 to 13:30

Lecturer: Mr. Erez Michaely Affiliation: Technion - Israel Institute of Technology Abstract: We present a dynamical formation scenario for Low Mass X-ray Binaries (LMXBs) in the field, focusing on black-hole (BH) LMXBs. In this formation channel LMXBs are formed from wide binaries ( >1000 [font rm [char A mathalpha][char U mathalpha]] ) with a BH component and a stellar companion. The wide binary is perturbed by fly-by's of field stars, its orbit random walks, until driven into a sufficiently eccentric orbit such that the binary components tidally interact and the binary

"Astrophysics Seminar: A two-zone model for GRB prompt emission in strongly magnetized outflows"

Location: 
Kaplun building, Room No. 200
Tue, 27/10/2015 - 12:30 to 13:30

Lecturer: Dr. Gill Ramandeep Affiliation: Open University of Israel Abstract: The magnetization and composition of relativistic outflows that give rise to gamma- ray bursts (GRBs) remain open questions. Studies thus far have largely focused on baryon dominated (weakly magnetized) jets that produce non-thermal gamma-rays at internal shocks by synchrotron and inverse Compton emission. However, there are many problems with this model and it's becoming more and more clear that GRB jets should have high magnetization. Poynting flux dominated jet models make

"Astrophysics Seminar: How common are snowline-region planets? First results from a second generation microlensing survey"

Location: 
Kaplun building, Room No. 200
Thu, 19/03/2015 - 12:30 to 13:30

Lecturer: Dr. Yossi Shvartzvald Affiliation: Tel Aviv University Abstract: The discovery of thousands of extrasolar planets ranks among the most exciting scientific developments of the past decade. Among the techniques currently used to discover extrasolar planets, microlensing has some unique capabilities. It is the most sensitive technique to detect planets beyond the "snowline", where gas and ice giants are likely to form. Over the past four years, we have carried out a "second generation" microlensing survey, combining OGLE, MOA, and the Wise observatory. I will present a

Astrophysics Seminar: "Signals and Interlopers: Exhausting Cosmological Information from the Depths of the Observable Universe"

Location: 
Kaplun buildilng, Room No. 200
Tue, 12/01/2016 - 12:30 to 13:30

Lecturer: Dr. Ely Kovetz Affiliation: Johns Hopkins University Abstract: The standard model of cosmology, encapsulated by a handful of parameters to describe the energy content of the universe, its rate of expansion, and the amplitude and scale- dependence of primordial perturbations, has been immensely successful when confronted with cosmological observations hitherto. However, this simple picture masks the extent of our ignorance regarding several fundamental questions in cosmology, such as what are the properties of inflation, what is the nature of

"Astrophysics Seminar: High-energy emission from Gamma-Ray Bursts: advancing our knowledge on GRBs and relativistic shocks through modeling of afterglow radiation"

Location: 
Kaplun building, Room No. 200
Tue, 05/05/2015 - 12:30 to 13:30

Lecturer: Dr. Lara Nava Affiliation: Racah Institute of Physics, The Hebrew University of Jerusalem Abstract: The physical origin of the temporally extended (~10^2 sec) high-energy emission (0.1-100 GeV) detected from Gamma-Ray Bursts by the Fermi/LAT instrument has not yet been completely understood. I present the evidences in favor of the external shock scenario, where the LAT emission is interpreted as radiation from electrons accelerated at the relativistic shock developed in interactions with the external medium. I show that the modelling of LAT

"Special Astrophysics Seminar: Probing general relativity, alternative theories of gravity, and relativistic geodesy with atomic clocks"

Location: 
Kaplun building, Room No. 200
Sun, 28/12/2014 - 14:15 to 15:15

Lecturer: Dr. Ruxandra Bondarescu Affiliation: University of Zurich Abstract: I will discuss the applicability of atomic clocks to test general relativity and alternative theories of gravity for planned missions such as the Gravitational Redshift Explorer (GRESE). We assume that the spacecraft that orbits the Earth is tracked using the observed tick rate of its clock, which is then compared to the tick rate of a local clock on the ground. The spacecraft's reconstructed 4-D trajectory can reveal the nature of gravitational perturbations

Astrophysics Seminar: "Long-Term Evolution of Binaries Toward SNIa"

Location: 
Kaplun building, Room No. 200
Tue, 08/03/2016 - 12:30 to 13:30

Lecturer: Mrs. Yael Hillman Affiliation: Tel-Aviv University Abstract: Can a white dwarf (WD) in a semi-detached binary system, accreting mass from its secondary, secularly grow, eventually reaching the Chandrasekhar mass and explode as a Type Ia supernovae (SNIa)? Via simulations of long term evolution over tens of thousands of nova cycles, we have determined the parameter space, defined by the WD mass, central temperature, and accretion rate, that may allow such growth. We have accounted for limits on the secondary mass as well as the time frame.

"Astrophysics Seminar: Exposing cohesion forces in asteroids using fast rotating bodies"

Location: 
Kaplun building, Room No. 200
Tue, 20/10/2015 - 12:30 to 13:30

Lecturer: Dr. David Polishook, Affiliation: Massachusetts Institute of Technology Abstract: Asteroids are considered to be collections of rocks separated by voids with no tensile strength to hold their components. When an asteroid is spinning-up, its gravity supposed to be the only force resisting the centrifugal acceleration before the body breaks apart. This notion is argumented by the observation that asteroids larger than ~300 m do not rotate faster than 2.2 hours per cycle. Smaller asteroids (<300 m) that reach faster rotations are therefore strong monolithic bodies