| Date |
Time
|
Location
|
Speaker
|
Affiliation
|
Title
|
Abstract
|
July 19th
|
3:00 pm |
3rd floor middle conference room |
Dong Lai |
Cornell University |
Tidal Dissipations in Binaries: From Merging White Dwarfs to and Hot Jupiter Systems |
Dynamical tides, involving the excitation and dissipation of waves and oscillation modes, play an important role in many different binary systems. I will discuss recent works on dynamical tides in three types of systems: (i) Compact white dwarf binaries undergoing orbital decay due to gravitational radiation; (ii) main-sequence star binary exhibiting tidally induced oscillations; (iii) Exoplanetary systems containing hot Jupiters and misaligned host stars. |
July 18th
|
3:00 pm |
3rd floor Lecture Theatre |
Bing Zhang |
University of Nevada, Las Vegas |
Gamma-ray burst models in the strongly magnetized regime: high-Gamma, high-sigma, resistive MHD needed |
Gamma-ray bursts are the most luminous explosions in the universe. Recent observations by the Fermi Gamma-Ray Space Telescope suggest that the relativistic jet launched from the central engine is strongly magnetized, and that at least for some GRBs, the gamma-ray emission is powered by turbulent reconnection in the strong magnetic field regime. I will review the observational and theoretical progress in this field, and point out that numerical models that invoke relativistic, magnetically dominated, resistive MHD are demanded to tackle the GRB problem. |
July 17th
|
3:00 pm |
3rd floor middle conference room |
Fayin Wang
|
Nanjing University |
Self-organized criticality in X-ray flares of gamma-ray burst afterglows |
X-ray flares detected in nearly half of gamma-ray-burst (GRB) afterglows are one of the most intriguing phenomena in high-energy astrophysics. All the observations indicate that the central engines of bursts, after the gamma-ray emission has ended, still have long periods of activity, during which energetic explosions eject relativistic materials, leading to late-time X-ray emission. It is thus expected that X-ray flares provide important clues as to the nature of the central engines of GRBs, and more importantly, unveil the physical mechanism of the flares themselves, which has so far remained mysterious. Here we report statistical results of X-ray flares of GRBs with known redshifts, and show that X-ray flares and solar flares share three statistical properties: power-law frequency distributions for energies, durations, and waiting times. All of the distributions can be well understood within the physical framework of a self-organized criticality (SOC) system. The statistical properties of X-ray flares of GRBs are similar to solar flares, and thus both can be attributed to a SOC process. Both types of flares may be driven by a magnetic reconnection process, but X-ray flares of GRBs are produced in ultra-strongly magnetized millisecond pulsars or long-term hyperaccreting disks around stellar-mass black holes. |
July 17th
|
10:30 am |
3rd floor middle conference room |
Weiwei Zhu
|
UBC, Canada |
Probing gravitation with high-precision pulsar timing |
Pulsars are excellent test grounds for fundamental physics. As precise cosmic clocks, they have been used in many experiments, especially in testing gravitational theories. We report 20-year timing of one of the most stable pulsar---J1713+0747, achieved using the world’s largest telescopes. These results set new records on pulsar timing precision, constrain alternative gravitational theories and test the constancy of gravitational constant. |
July 16th
|
3:00 pm |
3rd floor middle conference room |
Hui Li
|
Los Alamos National Lab |
Astrophysical Jets as a Plasma Laboratory |
Powerful jets from supermassive black holes have fascinated astronomers and physicists for more than half a century. As more observations become available, it is generally recognized that plasma physics holds the key to understanding the formation and propagation of jets as well as the dissipation processes within jets (sometimes with extreme parameters). We will describe the key observations that help us to determine the physical parameters and what we believe the key processes are. We will present relativistic magnetohydrodynamic (MHD) simulations of jet propagation, emphasizing the role of current-driven instabilities and energy conversion between magnetic fields and kinetic+internal energies. These studies are yielding new insights on understanding the jet stabilities and their associations with the observed variabilities in multi-wavelength observations. Progress has benefited from extensive knowledge in fusion research and collaboration with plasma physicists. Furthermore, dedicated laboratory plasma experiments to study jets have begun to offer new insights into various aspects of jet research. |
June 27th
|
3:00 pm |
3rd floor Lecture Theatre |
Andrew Cooper
|
NAOC |
Galactic accretion and galaxy structure in the cold dark matter model |
One of the major outstanding puzzles of galactic astronomy is why galaxies have the great variety of different shapes and sizes we observe. In this talk, I'll first review theories that connect the structure of galaxies (quantified by surface brightness profiles) to their evolution. Although a host of upcoming ultra-deep photometric surveys (notably LSST) are about to reveal the complex outer structure of galaxies in unprecedented detail, surprisingly few large simulations have tested even these well-known ideas as an integrated part of CDM galaxy formation. The work I'll present focuses on one of the easier parts of this problem -- the structure of massive elliptical galaxies. I'll show new predictions for the structure of ellipticals, based on a novel way of combining semi-analytic models and N-body simulations, and explain why these turn out to be remarkably consistent with observational data -- the fundamental reason is the importance of galactic accretion and merging. I'll discuss the insights our simulations give into familiar but little-understood observational phenomena, including the galaxy mass-size relation, cD galaxies and intracluster light. I'll also mention how these concepts (and our simulations) are relevant to the stellar haloes of much less massive galaxies like the Milky Way. |
June 20th
|
3:00 pm |
3rd floor Lecture Theatre |
Zachariah Etienne
|
University of Illinois at Champaign-Urbana, USA |
Can Black Hole-Neutron Star Binary Mergers Produce Gamma-Ray Bursts? |
Gravitational waves sap orbital angular momentum and energy from a black hole--neutron star (BH-NS) binary, driving it to inspiral and merge. In the violence of merger, the NS may tidally disrupt and form a hot accretion disk with the collimated magnetic fields necessary to launch jets, providing the central engine for one of the most energetic phenomena in the Universe: a gamma-ray burst (GRB). We assess the feasibility of this scenario with numerical relativity simulations of magnetized BH-NS binary mergers, seeding the NS with magnetic fields and exploring their effects on the remnant disk and the gravitational waves. We find that the gravitational waves are likely to be detectable by Advanced LIGO if the merger occurs within around 100Mpc, though the effects of magnetic fields on the waveforms are likely negligible. Further, we find that a GRB central engine may form if large-scale poloidal magnetic fields anchored in the disk are accreted onto the BH after the NS disrupts. |
June 13th
|
3:00 pm |
3rd floor Lecture Theatre |
Thomas Greve
|
UCL, UK |
ALMA sheds new light on dusty starburst galaxies in the early Universe |
The now well-known discovery of a significant population of highly dust-obscured, star forming galaxies at z > 1 - made more than a decade ago using the famous submillimeter camera, SCUBA - marked the beginning of an extremely exciting and rich area of research that continues to this day. One of the latest developments has been the finding of high-z galaxies ten times more submillimeter-bright than the SCUBA sources. The rarity of these 'new' sources (< 0.1 per sq. degree) is the reason they were missed by the relatively modest survey areas covered by SCUBA and its contemporary cameras. Their discovery had to wait for truly large-scale (>1000s of sq. degrees) millimeter and sub-millimeter surveys such as the ones recently carried out by the 10m South Pole Telescope (SPT) and the Herschel Space Observatory.
In this talk I will present the some of the results from our comprehensive multi-wavelength followup campaign of the ultra-bright sources uncovered by the SPT. In line with theoretical expectations we find that they are strongly lensed (magnification factors >10) IR-luminous dusty galaxies, powered by star formation. A large fraction (>30%) have optical/UV and/or CO line spectroscopic redshifts >4, indicating that the fraction of dusty starburst galaxies at high redshift is far greater than previously thought. |
June 6
|
3:00 pm |
3rd floor Lecture Theatre |
Yu Gao |
Purple Mountain Observatory, CAS |
The star formation law: the dense cores and star-forming galaxies connection |
We first show that the disk-averaged surface density of star formation rate (SFR) has the tightest linear correlation with that of dense molecular gas (traced by HCN), not the molecular gas (H2) or total gas (HI+H2), using a large sample of ~180 galaxies including over 60 (ultra)luminous IR galaxies [(U)LIRGs]. This is consistent with the tight FIR-HCN correlation established globally for both dense cores and star-forming galaxies near and far. The Kennicutt-Schmidt law that relates the total gas and SFR appears to have no unique power-law slope with larger scatters since the correlation slopes change from ~1 for normal spirals to ~1.5 when (U)LIRGs are included. New observations using other dense molecular gas tracers, such as multi-transition CS lines, as well as high-J CO lines from Herschel SPIRE/FTS observations, further reveal that the SFR and dense gas relationship is linear. Additionally, the locally resolved SFR-HCN correlation in M51 is also roughly consistent with the globally established linear SFR-HCN correlation. All of these suggest that dense cores are the basic units contributing to the SFR and SFR might depend linearly upon the mass of dense molecular gas (the star formation law). |
| May 23 |
3:00 pm |
3rd floor Lecture Theatre |
Jilin Zhou |
Nanjing University |
Progress on Exoplanet Detection and Formation |
Exoplanet detection has become one of the most active area in astronomy. With more than 880 exoplanet being detected by various methods, statistics of exoplanets has become more clear. In lecture, I will first review the most recent progress on exoplanet deception, then focus on the various orbital architectures of the revealed planet systems, where we proposed a tentative classification of exoplanet systems and related problems. Finally we give a brief discussion on some future exoplanet detection projects. |
| May 20 |
3:00 pm |
3rd floor Lecture Theatre |
Houjun Mo |
University of Massachusetts |
The star formation and mass assembly histories of galaxies |
The average star formation and stellar mass assembly histories in dark matter halos can be inferred from the observed stellar mass/luminosity functions at different redshifts combined with the observed stellar mass/luminosity function of cluster galaxies at low z. The inferred star formation and stellar mass assembly histories show different characteristics in three different stellar mass/halo mass scales.Dwarf galaxies on average show two stage of star formation, but their star formation/assembly histories are very diverse. Massive galaxies with form their stars early but the most massive galaxies may have assembled later. Galaxies in the intermediate mass range formed and assembled their stars late. These results have important implications for galaxy formation and evolution. |
| May 16 |
3:00 pm |
3rd floor Lecture Theatre |
Masaru Matsuoka
|
JAXA, Riken, Japan |
Highlights of transient phenomena obtained by MAXI |
MAXI is a Monitor of All-sky X-ray Image on Japanese Experimental Module of International Space Station. It has observed X-ray variability of thousands-X-ray objects since August, 2009. MAXI has discovered 10 new X-ray transients and novae, and six of them were black hole candidates. It has also detected more than 30 new soft GRBs. The six black hole candidates revealed typical or atypical light curves in considerable lower level.
MAXI discovered a flash from tidal disruption of a star in normal galaxy cooperating with Swift. It was like a long GRB, but it is still sometimes detected by Fermi gamma-ray detector. MAXI detected also a short flash from a nova with white dwarf in SMC. The detailed analysis suggested that this nova have a heavy white dwarf near Chandrasekhar limit. MAXI detected a super X-ray burst caused probably an accompanying outburst from NS-LMXB. MAXI is monitoring Be-binary X-ray pulsars, and consequently detected 42 outbursts from 14 X-ray pulsars, in which we detected aperiodic phenomena, sometimes revealing a long-time precession period. MAXI detected a lot of stellar flares with unbiased all sky observations. Consequently, we have proposed that the origin of GRXE is explained by a composite X-rays consisting of large and faint stellar flares and cataclysmic variables.
Finally, soft X-ray monitor MAXI/SSC obtained a probable hyper-nova remnant in Cygnus constellation which occurred 3 million years ago with energy of 10^{53~54} ergs. |
| May 9 |
3:00 pm |
3rd floor Lecture Theatre |
Gerhard Hensler
|
University of Vienna, Institute of Astrophysics |
The Evolution of Tidal-tail Dwarf Galaxies and their survival |
Within the hierarchical structure formation scenario in Cosmology today’s massive galaxies are assumed to form by the accumulation of smaller, gas-rich cosmological “building blocks”. When massive galaxies merge, angular momentum and energy conservation lead to the expulsion of long, thin, and gas-rich tidal arms. These fragment into multiple self-gravitating and star-forming units, by this, resembling a new type of dwarf galaxies (DGs) denoted as Tidal DGs (TDGs). From the merger rate and the observable bright TDGs, it can be speculated that their production may provide an important contribution to the faint-end of the galaxy luminosity function. As the result of merger and due to their location these low-mass objects can merely be gravitationally supported by Cold Dark Matter halo, but show active star formation, so that the question arises, whether and which fraction of TDGs survive the re-accretion to the parent merger, its tidal action, and, most importantly, the stellar energy feedback. In order to understand their survival and to uncover observable features that help distinguishing TDGs from “normal” CDM-dominated DGs, we perform self-consistent chemo-dynamical numerical 3D models. I will present the early stages of TDG evolutionary models under the aspect how and which processes affect their evolution and discuss structural and chemical signatures to distinguish tidally formed DM-free DGs from 'classical' ones. |
| May 2 |
3:00 pm |
3rd floor Lecture Theatre |
Rudy Wijnands
|
University of Amsterdam |
Sub-luminous accreting neutron stars and black holes |
Sub-luminous accreting black holes and neutron stars in Galactic X-ray transients have atypical low X-ray luminosities of 1e34-1e36 erg/s (compared to the 1e37 to 1e39 erg/s observed for ordinary transients), which corresponds to <<1% of the Eddington luminosity. The last decade a large amount of observational information on the behaviour of those systems at such low accretion rates has been obtained, both for brighter transients which on their way to their quiescent state go through this accretion rate regime (often displaying enigmatic behaviour), as well as for those transients which never become brighter than 1e35-1e36 erg/s. I will present a short overview of our knowledge of those systems and what we can learn from them with respect to the theories explaining accretion flows (including outflows) near black holes and neutron stars and how we can make progress in this field. |
| Apr. 25 |
3:00 pm |
3rd floor Lecture Theatre |
Xia Xiaoyang
|
Tianjin Normal University |
The Infrared Ultraluminous QSOs |
In my talk I will introduce the multi-wavelength properties of infrared ultraluminous QSOs, discussing the growth of the central black hole and spheroid of the QSO host based on low and high redshift samples of infrared ultraluminous QSOs with CO detections.
The gas reservoir of infrared ultraluminous QSOs ranges from several times 10^9 M_sun to a few times 10^10 M_sun, suggesting that sufficient cold molecular gas exists to sustain massive starbursts for these QSOs. There also exists tight correlations between L_FIR and L_CO and between L_FIR and 6.2mum PAH luminosity, implying that the FIR emissions of all QSOs are mainly from star formation. The correlation between AGN-associated bolometric luminosities and L_CO indicates a possible link between the cold molecular gas on kpc scales (disk/ring) and the central black hole accretion process. Furthermore, the Mdot/SFR values for local infrared ultraluminous QSOs and a few high-redshift, relatively faint QSOs are comparable to the local M_BH/M_sph value. These QSOs might be in the transition stage from gas-rich galaxy mergers to QSOs then to elliptical galaxies, exhibiting both high SFR and high accretion rates. However, the local M_ BH/M_sph relation could not be established in this short transition phase. If the black hole continues to grow vigorously after this transition period, then the M_BH/M_sph relation might be established afterwards. On the other hand, for both local and very bright high-redshift QSOs, the black hole appears to grow much faster than the spheroids. |
| Apr. 18 |
3:00 pm |
3rd floor Lecture Theatre |
Chao Liu
|
NAOC |
The dynamics of the Galactic disk and the LAMOST survey |
The rotation curve is an important tool to detect the dark matter halo and the mass distributions of other components (e.g., the bulge and the disk) of a galaxy. The Milky Way's rotation curve, which usually measured from the radio sources, e.g., HI, CO etc., is still very uncertain due to the large systematic errors in the distance estimations for the radio sources in the outer disk. In order to map the underlying gravitational potential of the Milky Way, we measured so far the most accurate rotation curve of the Milky Way using more than 4000 red clump stars in the 2nd quadrant of the Galactic disk. It is likely that there is a mass substructure in the outskirt of the Galaxy as well as the disk and the halo components. Except the rotation of the disk stars, their net streaming is also of interest because it reflects the rotating asymmetric components of the potential of the Milky Way, such as the bar and the spiral arms. I will show some new discovered moving groups and patterns in the velocity distributions of the stars either in the solar neighborhood observed by the LAMOST pilot survey or in the outer disk observed by the MMT Hectospec. They may be associated with the resonance of the rotating bar. We expect that, after 5-year survey of the LAMOST, there will be more than 500,000 spectra of the K giants in the disk and around a million of the nearby F/G dwarf stars. These data will constrain the Galactic rotation curve, with which the mass profile of our Galaxy will be accurately mapped from 5 to 20 kpc in Galactocentric radius. Moreover, they will reveal more details of the complicated motions of the disk stars and help to better understand the role that the rotating bar and the spiral arms play in the dynamical evolution of the Galactic disk. |
| Apr. 11 |
3:00 pm |
3rd floor Lecture Theatre |
Jiasheng Huang |
Harvard-CfA & NAOC |
Studies of ULIRGs and Massive Galaxy Formation at z~2 with Space Telescopes |
In this talk, I will present studies of ULIRGs at z~2 with Spitzer, Herschel and Hubble. Dusty galaxies at high redshifts were first observed with submm/mm telescopes. Spectrosocpy for these submm galaxies to identify their redshifts became difficult because of faint optical counterparts. The Spitzer telescope observed large amount of 24micron selected IR galaxies at z~2, and the mid-IR spectroscopy with IRS directly identifies their redshifts. The mid-IR spectroscopy also shows rich spectral features, including PAH emission and silicate absorption features. Recently the Herschel Space Telescope detected those galaxies in FIR bands. The dust temperatures for the MIPS 24 sources are unbiased comparing with submm galaxies biased towards cold dust emission. More recently the HST largest multi cycle program, CANDELS, took deep NIR imaging of 5 fields, permitting studies of the rest-frame optical morphologies of these galaxies. |
| Mar. 22 |
3:00 pm |
3rd floor Lecture Theatre |
Douglas N. C. Lin |
University of California Santa Cruz, USA |
Ubiquity of planets and diversity of planetary systems: Origin and Destiny of Hot Jupiters and Super-Earths |
Planetary astrophysics is the most rapidly advancing field in the world-wide astronomical community today. Advancement in observational facilities over the past two decays has led to the discoveries of more than 700 extra solar planets and nearly 3000 candidates including some with masses and sizes ranging from those of the Earth to Jupiter. The dynamical structure of multiple planetary systems are surprisingly diverse and intriguing. This game-changing influx of data has stimulated intense theoretical efforts to understand the formation and evolution of extra solar planets. I will discuss some paradigm shifts in theoretical planetary astrophysics and their compatibility with the latest observations. The topics to be discussed include the role of migration, planets' interaction with their host stars, and the internal structure of exoplanets. |
| Mar. 21 |
3:00 pm |
3rd floor Lecture Theatre |
Michael Blanton |
New York University, USA |
The Future of the Sloan Digital Sky Survey |
I describe plans for the next-generation Sloan Digital Sky Survey, to begin in July 2014, and which consists of three programs, APOGEE-2, MaNGA and eBOSS. APOGEE-2 will use both the Sloan Foundation Telescope at Apache Point and the du Pont Telescope at Las Campanas to study Galactic archaeology with high-resolution near-infrared spectroscopy. MaNGA will develop fiber bundle technology for the BOSS spectrograph to perform multiplexed spatially resolved spectroscopy with an unprecedented combination of wavelength coverage and resolution for 10,000 nearby galaxies. eBOSS will study the Universe’s expansion using a massive survey of galaxies and quasars. eBOSS will also perform follow-up spectroscopy on X-ray and variable sources, making it both the largest and most broadly selected quasar survey. I will show how this innovative set of programs will lead to a better understanding of cosmology and galaxy formation, as well as stellar and exoplanetary astronomy. |
| Mar. 14 |
2:30 pm |
3rd floor Lecture Theatre |
Shude Mao |
NAOC, China |
Dynamical modelling of the Milky Way and Nearby Galaxies |
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