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Activity > Colloquium

Colloquium (2012)

ASIAA Colloquium is usually held on Wednesdays at 2:20-3:20 pm in Room 1203 of the Astronomy-Mathematics Building, NTU. All scientists are welcome to attend.

The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.

Contact: Colloquium Committee (talks_replace2@_asiaa.sinica.edu.tw)

No. Time/Place Speaker Topic / Abstract
download PDF: download talk PDF file
12012-12-28 Fri
14:00~15:00
R1203
no colloquium this week
[ASIAA]
22012-12-25 Tue
14:00~15:00
R1203
Jongsuk Hong
[Seoul National University]
*Special Seminar*
N-body and Fokker-Planck simulations for rotating star clusters with 2-component models
Abstract

To understand the effects of the initial rotation on the evolution of the tidally limited clusters with mass spectrum, we have performed the N-body simulations of the clusters with different initial rotations and compared the results to those of the Fokker-Planck (FP) simulations. We confirmed that the cluster evolution is accelerated by not only the initial rotation but also the mass spectrum. For the slowly rotating models, the time evolutions of mass, energy and angular momentum show good agreements between N-body and FP simulations. On the other hand, for the rapidly rotating models, there are significant differences between these two approaches at the early stage of the evolution because of the bar instability in N-body simulations. shape of cluster for N-body simulations becomes tri-axial or even prolate, while the 2-dimensional FP simulation can treat only axisymmetric systems.

32012-12-24 Mon
14:00~15:00
R1203
Katherine Lee
[UIUC]
*Special Seminar*
Fragmentation and Kinematics of Starless Cores in Orion
Abstract

We study the structure and kinematics of nine starless cores (0.1 pc) in Orion with the IRAM 30-m telescope and CARMA. With the high angular resolution CARMA provides, fragmentation is observed in a majority of the cores. By morphologically comparing the structures between the data from IRAM, CARMA and Herschel 500 micron images, it is shown that the starless cores and their fragments are formed along the ambient filamentary structures, implying the importance of filamentary structures in the star formation process. In addition, we discovered large velocity gradients across the cores which are best interpreted as convergent flows. All together, our study suggests that turbulent fragmentation occurs at the stagnation of the convergent flows. These cores may be seeds for future massive star formation through competitive accretion. However, as the number of fragments is less than the prediction from theories, magnetic fields and radiative feedback, which have the ability to suppress fragmentation, may play a role in the core-forming process.

42012-12-21 Fri
14:00~15:00
R1203
Rainer Spurzem
[NAOC and Univ. of Heidelberg]
Supermassive Black Hole Binaries in Galactic Nuclei and Gravitational Wave Emission
Abstract

Many if not all galaxies contain supermassive black holes (SMBH). We study their growth and evolution by tidal accretion of stars and the presence of a central gas disk, and the motion of central SMBH during and after a galaxy merger. Dynamical Friction and superelastic three-body scatterings with stars will lead to the formation of a SMBH binary - two black holes of millions of solar masses orbiting each other in a distance comparable to the size of our planetary system. Relativistic corrections to Newtonian dynamics (so-called Post-Newtonian approximations) have to be taken into account at this stage, the SMBH binary orbit will have periastron shifts and ultimately lose energy by gravitational radiation emission. Spin-Spin and Spin-Orbit interactions of the SMBH's are taken into account. We show how such a binary emits gravitational radiation across a huge range of the frequency spectrum. Ground based and space based gravitational wave detection is discussed, including pulsar timing, and shows how gravitational wave astronomy will become in the future as rich as electromagnetic astronomy.

52012-12-17 Mon
15:30~16:30
R1203
Ryosuke Asano
[Nagoya University]
*Special Seminar*
Evolution of grain size distribution in galaxies
Abstract

Dust in galaxies affects the various evolutionary properties of galaxies, like star formation and spectral energy distribution (SED) of galaxies, etc. Furthermore, these effects depend strongly on the grain size distribution in galaxies as well as the amount of dust. Both the total dust mass and the grain size distribution in galaxies are affected by various processes. These processes occur in galaxies ubiquitously, and they depend strongly on the metallicity, the size distribution of grains. Hence, it is crucial to consider all dust processes in a unified framework to understand the evolution of the evolution of the total dust mass and the grain size distribution in galaxies. We construct a dust evolution model taking into account the grain size distribution and investigate the evolution of the distribution in galaxies. We consider three processes as follows: (1) dust destruction by supernova (SN) shocks, (2) metal accretion onto the grain surface in the interstellar medium (ISM) (3) grain-grain collisions in turbulence (shattering and coagulation). In this talk, I will introduce our dust evolution model, show the evolution of grain size distribution obtained by our model, and discuss what process is the dominant source of the grain size distribution at every stage of galaxy evolution.

62012-12-14 Fri
14:00~15:00
R1203
Ji Yeon Seok
[ASIAA]
download PDF Infrared supernova remnants in the Large Magellanic Cloud
Abstract

Supernova remnants (SNRs) are unique places where we can study the physical and chemical evolution of the interstellar medium by SN shocks. In particular, dust processing by shocks can be directly investigated by observing SNRs in IR wavebands. Thanks to its less IR confusion compared to the Milky Way, the Large Magellanic Cloud (LMC) has a great advantage to study IR emission from SNRs. I will present the near- to mid-IR study of SNRs using the AKARI and Spitzer data of the LMC as well as a detailed study of LMC SNR N49 with the AKARI NIR spectroscopy in terms of Unidentified Infrared bands. I will discuss the characteristics of IR SNRs, the comparison with multi-wavelength data, and the IR emission mechanisms.

72012-12-13 Thu
14:00~15:00
R1203
Sarah Sonnett
[University of Hawaii]
*Special Seminar*
Curious Surfaces of Neutral Trans-Neptunian Objects
Abstract

Trans-Neptunian Objects (TNOs) are early solar system relics that carry information about dynamical and chemical processes in the disk and small body populations of the solar system. Being cold and isolated makes TNOs some of the best observable proxies to the early solar system. TNOs are expected to be isolated and inactive over their entire lives, leading to very red optical colors compared to the Sun. However, a surprisingly large fraction of TNOs (~32%) have neutral colors characteristic of resurfaced bodies. Are collisions more common than we think, or are these bodies outgassing? Recent cometary-like outgassing can produce homogeneously neutral colors through global resurfacing while collisions cannot, so assessing the change in color with rotation helps discern between competing resurfacing mechanisms. We are conducting a survey of 10 neutral TNOs to determine their color variation with rotation. Toward that end, we first present the results of testing several photometry algorithms (tphot, DAOPHOT, DoPHOT, APT, and multiple techniques within Source Extractor and IRAF's PHOT) on data for a faint, slow-moving solar system object with a known light curve, with the intent of determining the best algorithm to use for slowly moving objects. Lastly, we report the survey results for one object, Haumea family member 2002 TX300.

82012-12-07 Fri
14:00~15:00
R1203
Julian Merten
[Caltech/JPL]
Creation of cosmic structure in clusters of galaxies
Abstract

The widely accepted current standard model of cosmology predicts a hierarchical scenario of structure formation. Driven by small initial seed overdensities, structure collapses due to gravity and decouples from the Hubble flow. Through a subsequent sequence of mergers large and massive dark matter dominated halos form. The largest structures we observe today in this bottom-up scenario are clusters of galaxies and as the youngest structures to date, clusters are rendered as ideal laboratories to test our standard picture of structure formation. While observable in many different wavelength regimes, clusters reveal their mass components to the observerÕs eye. In my talk I will present the latest results from the HST/MCT programme CLASH, which spends a significant amount of Hubble observing time on the study of a sample of 25 galaxy clusters. Properties like the dark matter density profile of halos can be determined to high precision and when used as cosmic telescopes, clusters allow a peak at the very young Universe. Furthermore, I will present the latest results from the study of merging clusters of galaxies, like the Bullet and PandoraÕs Cluster. Those most energetic events in the Universe provide the unique opportunity to observe the different matter components of the Universe under extreme conditions and allow for the direct derivation of microscopical properties of dark matter. For this reason a Cluster Merger Collaboration (MC^2) has been created to study mergers in the context of alternative dark matter models. I will end in outlining this project.

92012-11-30 Fri
14:00~15:00
R1203
Phillip Zukin
[ASIAA/UC Berkeley]
download PDF Dark Matter Dynamics
Abstract

N-body simulations have revealed a wealth of information about dark matter halos, but their results are largely empirical. Using analytic means, we attempt to shed light on simulation results by generalizing the self-similar secondary infall model to include tidal torque. Imposing self-similarity allows us to analytically calculate the structure of the the halo in different radial regimes and numerically compute the profiles of the halo without being limited by resolution effects inherent to N-body codes. I will describe this simplified halo formation model and compare our results to mass and velocity profiles from recent N-body simulations. We find that angular momentum plays an important role in determining the structure of the halo at small radii.

102012-11-27 Tue
14:00~15:00
R1203
Chien-Ting Chen
[Dartmouth]
*Special Seminar*
Probing the hidden AGN activities in star-forming galaxies
Abstract

I will present our recent studies on the co-evolution of galaxies and the super-massive black holes (SMBHs) in their centers. With the advantage of far-infrared (250 micron) data taken by the Herschel Space Observatory, the SFR can be estimated with minimal contamination from AGN. We found a global correlation between galactic SFR and the average SMBH growth in our far-IR selected sample in the Bootes survey region, which is consistent with a simple picture that the growths of SMBHs and galaxies are closely linked over galaxy evolution time scale. I will also present results on the search of Compton-thick AGN in the extremely deep Chandra Deep Field South 4Ms catalog using our STACKFAST program.

112012-11-23 Fri
14:00~15:00
R1203
Martin Kilbinger
[CEA]
download PDF Constraints on dark energy and modified gravity models from CFHTLenS weak lensing
Abstract

I present results from weak gravitational lensing by the large-scale structure from CFHTLenS (Canada-France-Hawaii Lensing Survey). Using multi-band optical data over 155 square degrees, we measure the weak lensing correlation of high-redshift galaxies from small out to very large, linear scales. We reconstruct the largest maps of dark matter ever made, and infer information on cosmological parameters for flat and curved Lambda and dark-energy CDM models, and modified gravity (the latter together with redshift-space distortions from Wiggle-Z). In addition, by comparing the lensing observations with the light distribution from galaxies, we measure the relation (bias and cross-correlation) between total and luminous matter. I will give an introduction to weak gravitational lensing and its use in cosmology. I will present an overview over the CFHTLenS lensing analysis and the likelihood and sampling methods (Population Monte Carlo, PMC). These results will be put in a larger context of large on-going and planned ground- and space-based galaxy surveys such as DES and Euclid. See www.cfhtlens.org for links to the released data and more details.

122012-11-20 Tue
14:00~15:00
R1203
Jinhua He
[Yunnan Astronomical Observatory]
*Special Seminar*
1.1-mm spectral line survey of EGOs -- similarity and randomness
Abstract

We have performed a 1.1-mm spectral line survey to a sample of 89 GLIMPSE extended green objects (EGOs) by using the SMT 10m. The survey covers molecular line tracers of dense gas, hot gas and shocks. The indications of the results will be discussed. Further combining this with our previous observation of low density tracers, isotopic CO 1-0 lines toward the same sample of EGOs, I will discuss the ubiquitous log-linear line luminosity correlations among all the tracer lines and the data scatter. I will try conclude that most of the EGO associated molecular clouds have similarity in thermal and density structures and shock properties. I will also try to demonstrate that the randomness in the cloud structure and turbulence velocity field increases over larger ranges of cloud substructure size scales or whole-cloud size scales.

132012-11-16 Fri
14:00~15:00
R1203
Luis Ho
[Carnegie Observatories]
Very Old and Very Young Galaxies
Abstract

I will discuss galaxies on two opposite ends of the age spectrum. The first project concerns the structural properties of nearby massive elliptical galaxies. I will describe new observational evidence that these objects participated in a two-phase formation scenario, consisting of a highly dissipative phase at z = 2-3 followed by a prolonged period of dissipationless accretion, most likely through minor mergers, during which "red nuggets" doubled in mass and quadrupled in size. The second project aims to detect the progenitor molecular clouds that give rise to super star clusters, the basic units of star formation in starburst systems. If time permits, I will also outline a new theory for the formation of S0 galaxies, and perhaps introduce the concept of galaxy lopsidedness.

142012-11-12 Mon
14:00~15:00
R1203
Steven Charnley
[NASA/GSFC]
*Special Seminar*
Theoretical Models of Astrochemical Processes
Abstract

Interstellar chemistry provides a natural laboratory for studying exotic species and processes at densities, temperatures, and reaction rates, that are difficult or impractical to address in the laboratory. Thus, many chemical reactions considered too slow by the standards of terrestrial chemistry, can be `observed' and modeled. Various proposals concerning the nature and chemistry of complex interstellar organic molecules will be described. Catalytic reactions on grain surfaces can, in principle, lead to a large variety of species and this has motivated many laboratory and theoretical studies. Gas phase processes may also build large species in molecular clouds. Future laboratory data and computational tools needed to construct accurate chemical models of various astronomical sources to be observed by Herschel and ALMA will be outlined.

152012-11-06 Tue
14:20~15:15
Room 104, CCMS-New Physics Building
Jean Turner
[UCLA]
*ASIAA/NTU Joint Colloquium*
Molecular Gas and Star Formation in Galaxies
Abstract

The development of millimeter-wave array telescopes has made it possible to study gas and star formation in galaxies beyond the Milky Way. Dense gas is the fuel for star formation, and it can be mapped via its emission lines of molecules such as carbon monoxide. The dynamics, excitation and chemistry of the gas can be studied in a range of galactic environments, including galactic nuclei and starbursts. What facilitates and regulates star formation in galaxies? How does star formation shape galactic structure? I discuss recent results from the Submillimeter Array, and the potential for future discoveries with the Atacama Large Millimeter-Submillimeter Array (ALMA).

162012-11-05 Mon
14:00~15:00
R1203
Renbin Yan
[University of Kentucky]
download PDF Supermassive Black Holes and the Warm Ionized Gas in Early-type Galaxies
Abstract

Almost every galaxy more massive than our Milky Way contains a central supermassive black hole. Observations suggest that the growth of these black holes is intimately connected with the evolution of their host galaxies. The feedback energy produced by accretion onto these supermassive black holes has often been invoked to solve problems in galaxy evolution, such as the quenching of star formation and the maintenance of low star formation rate in early-type galaxies. Therefore, it is important to survey their accretion rates and modes. On the other hand, almost every massive elliptical or lenticular galaxy contains significant amount of weakly ionized gas, which is often assumed to be photoionized by the radiation produced by accretion onto supermassive black holes. However, I will show in this talk that the true ionizing source for this gas cannot be the accreting black hole but is probably an elusive population of hot evolved stars distributed throughout each galaxy. This finding raises important questions about the role of supermassive black holes in galaxy evolution. More importantly, it opens new windows for studying the origin of the cold and warm gas in these massive galaxies. Time permitting, I will also talk about MaNGA, the next generation IFU survey to be conducted on the Sloan Telescope as part of the SDSS-IV project.

172012-10-26 Fri
14:00~15:00
R1203
Ryan Keenan
[ASIAA]
download PDF Investigations of Large-Scale Inhomogeneity in the Local Universe
Abstract

The size of large-scale structures in the local universe (sheets, voids, and superclusters of galaxies), and our location among them, is of critical importance to the interpretation of observational results. Cosmic variance due to large-scale structure can lead to systematic variations in observational data. Such systematics can dominate over other sources of error if a volume sufficient to average over cosmic variance has not been sampled. However, it remains unclear just what the upper limit on the size of large-scale structure is, and hence what volume constitutes a representative sample of the universe. I will summarize recent advances in theoretical and observational cosmology, including my own observational work, which suggest that large-scale inhomogeneities may yet present an obstacle in the determination of locally measured cosmological observables.

182012-10-24 Wed
14:00~15:00
R1203
Dr. Kevin C. Xu
[Caltech/IPAC]
*Special Seminar*
Close Major-Merger Pairs Since z=1: Evolution of Merger Rate & sSFR Enhancement
Abstract

I will present results on the cosmic evolution of galaxy pairs based on studies of two large samples, namely a local (z<0.1) sample (KPAIR, 170 pairs) and a sample of pairs with 0.2

192012-10-19 Fri
14:00~15:00
R1203
Stefanie Phleps
[MPE]
download PDF How do galaxies become red? - An HOD model of the dependence of SDSS DR7 galaxies on their multiscale environment
Abstract

Following the new approach of Wilman et al 2010 (MNRAS, 406, 1701) we model the dependence of red and blue central and satellite galaxies on their multiscale environment. We fit an HOD model to the multiscale measurements of a sample of ~113000 galaxies from the SDSS DR7, in order to understand the influence of the environment on the transition of blue galaxies to the red sequence. We find that a model in which the red satellite fraction grows slowly with halo mass fits the data best, pointing towards a scenario in which galaxies can already become red in small mass haloes just before they are accreted onto larger mass haloes. We plan to extend the analysis to higher redshifts using VIPERS data, in order to investigate the evolution of the red satellite and central fraction since z=1.

202012-10-12 Fri
14:00~15:00
R1203
You-Hua Chu
[University of Illinois at Urbana-Champaign]
download PDF Supernova Remnants in Distant Galaxies
Abstract

The high angular resolution of the Hubble Space Telescope opened a new window for us to study supernova remnants (SNRs) in distant galaxies. For example, a SNR with a 10 pc diameter extends 0.2 arcsec at a distance of 10 Mpc, and can still be resolved by HST images with a pixel size of ~0.05 arcsec/pixel. We have used HST images of M101 to study its SNRs. The H-alpha images were used to identify the SNR candidates that were previously identified from ground-based H-alpha and [S II] images. The continuum images were used to study the underlying stellar population, the presence or absence of a population of massive stars. It is possible to use the interstellar and stellar environments of each SNR candidate to assess its nature. We find that the largest SNR candidates are superbubbles. Among the “confirmed” SNRs, about 1/4 are likely associated with Type Ia SNe and 3/4 core-collapse SNe. This ratio is consistent with the observed ratio for spiral galaxies. Recently we are exploring the possibility of detecting Type Ia SNRs in elliptical galaxies. Using the Type Ia SNRs in the Large Magellanic Cloud as template, we find that Type Ia SNRs can be detected somewhat easily at ~5 Mpc and with difficulty at ~10 Mpc. I will use HST H-alpha images of the elliptical galaxy Maffei 1 at 3-4 Mpc to illustrate the search for Type Ia SNRs. Global statistics of SNRs in other galaxies provide an independent means to estimate SN rates.

212012-10-05 Fri
14:00~15:00
R1203
Anthony Gonzalez
[University of Florida]
download PDF Galaxy Clusters at z=1-2: An Infrared View
Abstract

While the galaxy cluster population at z<1 has long been accessible, only in recent years has it become possible to identify and study statistical cluster samples in the redshift regime z=1-2. This era is of particular interest because it is expected to be the formation epoch for the first massive galaxy clusters and also provides a direct view of the cluster galaxy population during a period of significant star formation and mass assembly. In this talk I will describe a series of surveys based upon Spitzer and WISE data that are designed to identify large samples of clusters at these redshifts, complementing the new generation of Sunyaev-Zel'dovich surveys. I will also present recent results, including a few surprises, from detailed follow-up studies of a subset of these clusters with HST, Spitzer, and ground-based facilities.

222012-09-21 Fri
14:00~15:00
R1203
Emmanuel Momjian
[NRAO]
High Redshift QSOs and SMGs: A VLBI Perspective
232012-09-14 Fri
14:00~15:00
R1203
David Jewitt
[UCLA]
Mass-Loss from Asteroids
Abstract

In the last few years, a new class of body has been identified in the asteroid belt. About a dozen (dynamical) asteroids have been found to show comet-like comae and tails. Both are surprising yet unambiguous indicators of mass-loss from objects formerly thought to be inert rocks. In this talk I will present the new evidence, discuss plausible physical interpretations and point towards possible future exploration of these bodies using both telescopes and spacecraft.

242012-09-07 Fri
14:00~15:00
R1203
Juergen Ott
[NRAO]
The Galactic Center: Feeding and Feedback
Abstract

The Galactic Center is maybe of the most violent region for star formation in our Galaxy. It contains a large fraction of molecular material in the Central Molecular Zone, dominated by shocks, tidal fields and energetic input from massive stars and possibly from the central black hole. We present high and low resolution observations of molecular tracers in the Central Molecular Zone, gathered in large observing campaigns with different radio telescopes. The gas properties reveal large differences in the physical conditions, shock, temperatures, and density. High-and low resolution ammonia act as a thermometer of the gas on all scales. The gas position may be tracked by the conditions along the way to flow along x1 orbits and eventually accrete on x2 orbits (which could be the recently found figure 8 found in HIGAL dust temperature maps). We find gas that might be streaming in and being shocked along the way. Eventually the gas will form stars and they feed back energy to the Galactic Center region in the form of stellar winds and SNe. In addition, energetic input into the ISM may be provided by (previous) episodes of activity of Sgr A*. This may establish the connection to the prominent 'Fermi Bubbles' that reach 10 kpc into the Galactic halo.

252012-09-05 Wed
14:00~15:30
R1203
Dr. Robert Wittenmyer
[University of New South Wales]
*Special Seminar*
Exoplanetary Science in Australia: Detection, Characterisation, and Destruction
Abstract

I give an update on three major exoplanetary science initiatives being pursued by Australian-based planet-search teams. In addition to the long-running Anglo-Australian Planet Search, I describe the Pan-Pacific Planet Search, a radial-velocity survey of Southern hemisphere evolved, intermediate-mass stars using the 3.9m Anglo-Australian Telescope. We currently achieve velocity precisions of 3-6 m/s, and there are several planet candidates emerging as more data are obtained. In collaboration with John Johnson's Lick and Keck survey of Northern subgiants, this all-sky survey of over 600 stars will significantly improve our knowledge of the frequency and properties of planets orbiting stars more massive than the Sun. At New Zealand's Mt John Observatory, we are undertaking an intensive observational campaign targeting the nearest Sun-like stars, Alpha Centauri A & B, to search for Earth-like planets in their habitable zones. We are observing year-round for 4 years, with the aim of gathering 50,000 precision radial velocity measurements. This project is the first ultra-deep reconnaissance of nearby Sun-like stars, which is necessary to understand the frequency and characteristics of rocky planets in potentially habitable orbits. Finally, I present results from our recent series of papers in which we have performed extensive suites of dynamical simulations to test the veracity of proposed multiple-planet systems. We show that some systems are strongly constrained by protected low-order resonances, while others are wildly unstable on short timescales. This work highlights the critical need to include dynamical stability analysis as an integral part of the discovery process for candidate multi-planet systems.

262012-08-24 Fri
14:00~15:00
R1203
Yi-Nan Chin
[TKU]
A brief history of the Chinese astronomy
272012-08-23 Thu
14:00~15:00
R1203
Kevin Walsh
[Southwest Research Institute]
*Special Seminar*
The Grand Tack: Jupiter's migration to 1.5 AU, and how it shaped the inner solar system
Abstract

A persistent difficulty in terrestrial planet formation models is creating Mars analogs with the appropriate mass: Mars is typically an order of magnitude too large in simulations. A recent work found that a small Mars can be created if the planetesimal disk from which the planets form has an outermost edge at 1.0 AU. However, this work and no previous work, can explain such a truncation of the planetesimal disk and preserve the asteroid belt. We show that gas-driven migration of Jupiter inward to 1.5 AU, before its subsequent outward migration, can truncate the disk and repopulate the asteroid belt. This dramatic migration history of Jupiter suggests that the dynamical behaviour of our giant planets was more similar to that inferred for extra-solar planets than previously thought, as both have been characterized by substantial radial migration.

282012-08-17 Fri
14:00~15:00
R1203
Jan Cami
[University of Western Ontario]
Fullerenes in circumstellar and interstellar environments
Abstract

We have recently discovered the unmistakable spectral signatures of the fullerene species C60 and C70 in Spitzer observations of a young planetary nebula; this represents the first identification of large aromatics in astrophysical environments, and these species are now the largest molecules known to exist in space. Since our discovery, fullerenes have been reported in a wide variety of astronomical objects at abundances of typically ~0.3% of the cosmic carbon. They are formed in carbon-rich evolved stars, survive in the interstellar medium and are also detected in the disks surrounding young stars. Fullerenes have many interesting properties and could play a unique role in the physics and chemistry of the interstellar medium. In this talk, I will give an overview of what we have learned so far from observational analyses, theoretical models and laboratory efforts with a special focus on the surprising aspects that have challenged our understanding of some of the physics and chemistry involved -- in particular about the formation, state and excitation of cosmic fullerenes. I will also discuss how fullerenes compare to polycyclic aromatic hydrocarbon (PAHs) in these environments.

292012-08-16 Thu
14:00~15:00
R1203
Jack Sayers, Sunil Golwala
[Caltech]
*Special Seminar*
The Caltech Submm Observatory - Instrumentation and Capabilities
Abstract

We will describe the current suite of instrumentation at the Caltech Submm Observatory, including: MUSIC: The long-wavelength photometric camera with 2304 detectors, a 14 arcmin FOV, and simultaneous operation at 0.85, 1.0, 1.3, and 2.0 mm with PSFs of 23, 26, 32, and 44 arcsec. SHARC II: The short-wavelength photometric camera with 384 detectors, a 2.59 x 0.97 arcmin FOV, and operation at 350, 450, and 850 um with PSFs of 8-9 arcsec at 350 um. Zspec: The long-wavelength moderate resolution spectrometer covering 195 - 310 GHz with resolving power of R = 250-400. ZEUS II: The short-wavelength moderate resolution spectrometer simultaneously covering the 215, 350, 450, and 625 um windows with a resolving power of R ~ 1000 with 9-10 spatial pixels. Heterodyne receivers: - 177-286 and 382-530 GHz, 4-8 GHz IF BW, T_sys = 40 K - 300-410 GHz, 4-8 GHz IF BW, T_sys = 50 K - 810-900 GHz, 1-2 GHz IF BW, T_sys ~ 400 K - 315-380 and 620-730 GHz, 1-2 GHx IF BW, T_sys = 90 and 230 K (deployment soon)

302012-08-10 Fri
14:00~15:00
R1203
Shih-Ping Lai
[NTHU]
Evolution of transition protoplanetary disks: Two paths?
Abstract

Understanding how primordial circumstellar disks of young stellar objects dissipate gas and small dust grains and evolve into debris disks is crucial for advancing our knowledge in planet formation. Recent observations suggest that multiple pathways may exist for the disk evolution. In order to clearly identify the physical conditions influencing the evolutionary paths, here we perform a statistical analysis of the spectral energy distributions (SEDs) morphologies. By comparing the theoretical SEDs from Robitaille et al. (2006) to the observed SEDs from the Spitzer's c2d Legacy project, we find supporting evidence for two evolutionary pathways.

312012-08-08 Wed
14:00~15:00
R1203
Javier Blasco Herrera
[Stockholm University]
*Special Seminar*
Halpha kinematics of star forming regions: from HII regions to starburst galaxies
Abstract

The understanding of the formation and evolution of galaxies will not be complete until we understand the physical processes that trigger and regulate star formation in them. We have studied the kinematics of star forming regions of several sizes, from HII regions to starburst galaxies. This includes the study of 157 H II regions in the spiral galaxy M83, in order to test the relation, if any, between luminosity (L) and integrated velocity dispersion, finding no direct relation but an upper envelope with a maximum luminosity for a given velocity dispersion. The bulk of our work has been in the study of 2D velocity maps of starburst galaxies, showing that they are, in general, not supported by rotation and that many of them are consistent with a recent merger which affected their morphology and kinematics.

322012-08-03 Fri
14:00~15:00
R1203
Frederick Walter
[SUNY Stony Brook]
The Stony Brook/SMARTS Atlas of (mostly) Southern Novae: New Clues to the Physics of Exploding Stars
Abstract

The Stony Brook/SMARTS Atlas of (mostly) Southern Novae now consists of spectroscopic and photometric observations of 57 novae in our galaxy and 4 in the LMC, amassed since the fall of 2003. The reason for collecting all these data, the largest specto-photometric survey of galactic novae, is to facilitate study of their evolution on both long and short terms. Novae are among the most complex phenomena in the universe: a detailed synoptic study of a large number of novae is needed to to make sense of the broad range of observed characteristics. After a brief review of the characteristics of novae (thermonuclear explosions on the surfaces of accreting white dwarfs), I will present an overview of the atlas. The bulk of the talk will concentrate on three science questions that have arisen based on examination of these data: 1). In novae that eventually develop strong supersoft X-ray emission, there is a spectral progression wherein first the N III 4640A lines grow, followed by the growth of He II 4686, which the fades as the X-rays turn on. The N III lines are pumped by the Bowen Fluorescence mechanism, which is active in planetary nebulae, cataclysmic variables, and low mass X-ray binaries. Whereas these oresent more-or-less steady state situations, in the novae these lines are formed in a dynamic expanding envelope. I will discuss some premininary thoughts about the time-dependent problem. 2). The emission line profiles of the recurrent novae and the He-N novae are unlike those of the classical (Fe II) novae, and instead resemble what one might expect from an optically-thin disk in Keplerian rotation around the white dwarf. I shall present and discuss the evolution of these line profiles, and will show that the spectral evolution is consistent with the rapid re-establishment of the accretion disk after (or survival through) the nova explosion. 3). The star V Sge has been enigmatic for decades. It shows broad eclipses, and high excitation (C IV, N V, O VI) optical lines atop a blue continuum. It has been variously explained as a nova-like variable (i.e., a hot accretion disk), a massive white dwarf undergoing steady surface nuclear burning, a Wolf-rayet system, or two non-degenerate stars in a contact configuration. After 4 years, one of our novae has taken on the appearance of a V Sge star, with broad eclipses and hot permitted line emission, while another show a similar spectrum. Knowing where they came from will give clues to the real nature of the V Sge stars.

332012-07-30 Mon
15:30~16:30
R1203
Patrice Theule
[University of Provence]
*Special Seminar*
chemistry in interstellar ices
Abstract

I would like to present my research activities and recent results on interstellar ice chemistry. I will present laboratory studies of chemical reaction in ice analogues, and will show how laboratory studies enable to build a chemical reactions network that can be transposed to interstellar grain chemistry.

342012-07-27 Fri
14:00~15:00
R1203
Shigehisa Takakuwa
[ASIAA]
download PDF Kinematics of Circumbinary Disks around the Prototypical Protostellar Binary System L1551 IRS 5 and NE
Abstract

In the present talk I will show our recent results of submillimeter continuum and molecular-line observations of prototypical protostellar binary systems L1551 IRS 5 and L1551 NE observed with the SMA. In both sources we found ~500-AU scale ``circumbinary disks'' surrounding the protostellar binary systems, elongated perpendicularly to the axis of the associated protostellar jets. The circumbinary disk around L1551 NE shows a clear Keplerian rotation with a central stellar mass ~0.8 M. On the other hand, the circumbinary disk around L1551 IRS 5 does not show a Keplerian rotation but shows vrot ~r-1 rotation. In L1551 IRS 5, the expected radius of the Keplerian rotation is ~35 AU, which is comparable to the orbital radius of the binary. This mean that in L1551 IRS 5 there is no Keplerian circumbinary disk. I will discuss the different rotational profiles of the circumbinary disks around the prototypical binary protostars in the context of binary formation and evolution.

352012-07-25 Wed
14:00~15:00
R1203
Xiaoyu Shi
[UC Davis]
*Special Seminar*
Experimental Reproduction of Oxygen Isotope Anomaly in the Solar Nebular - first laser test of "CO Self-Shielding" in dissociation of CO using photodissociation, photoionization and photoion imaging
Abstract

This talk focuses on a twofold problem regarding the origin of oxygen isotope anomaly in the solar nebula. First, is the self-shielded CO photodissociation the source of isotopically anomalous oxygen in the solar reservoir and the source of meteoritic oxygen isotopic compositions? Our vacuum ultraviolet tunable narrow-band laser dissociation and ionization experiments created an analog to the environment of the early solar nubula, and simulated the CO self-shielding effect on oxygen isotope composition. A slope-1 three oxygen isotope plot was generated experimentally, as same as observed in the solar nebula and meteorites. These results verified the dominant role of "CO self-shielding" mechanism in interpretation of the oxygen isotope anomalies. Recent solar wind measurements (Marty et al., 2011; McKeegan et al., 2011) from the Genesis mission revealed that on terrestrial planets, rare-nitrogen-isotope enrichment is more efficient than rare-oxygen-isotope enrichment. This report introduces the second fold of the problem — what causes the difference between the self-shielding effects on oxygen and nitrogen? It was suggested (Clayton, 2011) that this large difference might be due to the more reactive nature of atomic N photofragments from N2 compared to atomic O photofragments from CO. Our branching ratio measurements for CO using time-slice velocity-map ion imaging supports Clayton's idea and helps to rationalize the different rare-isotope enrichment between N and O reported by the Genesis team.

362012-07-20 Fri
14:00~15:00
R1203
Dr. T. Akahori
[KASI]
Shocks, Turbulence, and Magnetic FIelds in Galaxy Clusters and the Large-Scale Structure of the Universe
Abstract

The cosmological structure formation simulations have shown that the intracluster medium (ICM) in galaxy clusters and the warm-hot intergalactic medium (WHIM) in filaments of galaxies are mostly heated by the shock waves caused by multiple mergers and accretions of galaxies, galaxy groups, and clusters. Actually, the shocks have been observed in some merging galaxy clusters, that are useful laboratories for studying plasma astrophysics. For instance, X-ray emissions from the ICM in the electron-ion two temperature structure and the non-equilibrium ionization state and Sunyaev-Zel'dovich effects of very hot ICM have been studied. It is also predicted that the cosmological shocks could generate the intergalactic magnetic field (IGMF) in the ICM and WHIM and could amplify it through turbulence dynamo, but observational evidences for the origin and evolution are not enough yet. Theoretical estimations of RM due to the IGMF in filaments of galaxies is 1-10 rad/m2, which could be observed with the ASKAP POSSUM by using the so-called RM synthesis. The above studies could be tested with international observatories such as Astro-H, ALMA, and SKA.

372012-07-18 Wed
14:00~15:00
R1203
Prof. Sara Beck
[Tel Aviv University]
*Special Seminar*
Heavy Metal and High Resolution: Gas Kinematics of Embedded Star Clusters
Abstract

RISN, Radio-Infared Supernebulae, are excited by young, deeply embedded star clusters. They are to Extragalactic Super Star Clusters as Ultra-compact HII regions are to Galactic OB stars, and, like UC HII regions, the internal kinematics are puzzling. Ionized gas motions in RISN have until now been measured via infrared and radio hydrogen lines, and have been found to be too fast for sound, too slow for stellar winds, and inconsistent with the cluster ages. We show that hydrogen lines are inherently too broad to probe kinematics in these sources--they must be observed with metal lines. We have measured the ionized gas in the RISN of several well-known starburst galaxies with effective resolution--including thermal broadening--of ~5 km/sec and can for the first time see their gas motions in detail. We find many sources are undergoing bulk outflows, probably pressure driven. These could be analogous to the 'champagne flow' model, but for giant clusters instead of individual stars, and may explain RISN lifetimes. Other remarkable kinematic features, including sub-clusters, can be detected with these heavy metal lines. We argue that high spectral resolution requires extra observational effort, but is worth it.

382012-07-16 Mon
14:00~15:00
R1203
Dr. Eiichiro Komatsu
[MPA]
download PDF Critical Tests of Theory of the Early Universe using the Cosmic Microwave Background
Abstract

The Cosmic Microwave Background (CMB), the fossil light of the Big Bang, is the oldest light that one can ever hope to observe in our Universe. The CMB provides us with a direct image of the Universe when it was still an "infant" - 380,000 years old - and has enabled us to obtain a wealth of cosmological information, such as the composition, age, geometry, and history of the Universe. Yet, can we go further and learn about the primordial universe, when it was much younger than 380,000 years old, perhaps as young as a tiny fraction of a second? If so, this gives us a hope to test competing theories about the origin of the Universe at ultra high energies. In this talk I review the present status and future prospects on our quest to probe the physical condition of the very early Universe.

392012-06-29 Fri
14:00~15:00
R1203
Dr. Xuening Bai
[Princeton University]
Accretion in Protoplanetary Disks: Magneto-rotational Instability or Magneto-centrifugal Wind?
Abstract

Magnetic field is widely believed to play a crucial role in driving accretion in astrophysical disks, mainly via the magneto-rotational instability (MRI) or the magneto-centrifugal wind. In protoplanetary disks (PPDs), these mechanisms are strongly affected by non-ideal MHD effects (Ohmic resistivity, Hall effect and ambipolar diffusion) due to the weak ionization level in PPDs. In this talk, I first examine the effectiveness of the MRI by applying simulation results in different non-ideal MHD regimes to PPD models. It is found that in the inner region of PPDs (~1AU), the MRI itself is insufficient to account for the observed PPD accretion rates. The MRI works more efficiently in the outer disk, especially in the presence of PAHs which reduces the strength of ambipolar diffusion. In the second part of the talk, I describe our vertically stratified shearing-box simulations of PPDs that for the first time, simultaneously include the effects of both Ohmic resistivity and ambipolar diffusion in a self-consistent manner. In the presence of a weak net vertical magnetic field (beta~1e5 at midplane), the MRI is completely suppressed in the inner region of PPDs, where the gas flow is purely laminar. A a strong magneto-centrifugal wind is launched that efficiently carries away the disk angular momentum, and the resulting wind-driven accretion rate is consistent with observations. I conclude by proposing a new scenario on the accretion processes in PPDs.

402012-06-25 Mon
15:30~16:30
R1203
Djazia Ladjal
[Denver University]
*Special Seminar*
The Herschel Planetary Nebula Survey (HerPlaNS)
Abstract

HerPlaNS is a Herschel Open Time program that exploits the unprecedented spatial resolving power in the far infrared of the Herschel Space Observatory to investigate a sample of 11 planetary nebulae (PNe). The aim of the program is to study the chemistry, the energetics and the physical evolution of the nebula by tracing the cold dust component by means of imaging data with PACS and SPIRE and tracing the gas component by means of spectroscopy observations with PACS and SPIRE at different locations in the nebula. Combining both imaging and spectroscopy data will teach us about the interplay between the gas and dust as well as the interaction between the stellar material and the interstellar medium. HerPlaNS offers a novel view of Planetary Nebulae by it spatial spectral and imaging data. In this talk, l will introduce the HerPlaNS program and discuss some of our preliminary results.

412012-06-22 Fri
14:00~15:00
R1203
Dr. Frédéric Deschamps
[Institute of Earth Sciences, AS]
download PDF The role of anti-freeze compounds in maintaining subsurface oceans in icy moons' interiors
Abstract

A key parameter that controls the crystalization of primordial oceans in large icy moons is the presence of anti-freeze compounds. The phase diagram of the water-ammonia system is well documented, and several studies showed that the presence of a few wt% of ammonia in the primordial oceans of icy moons may stop the crystalization of these oceans. Another anti-freeze compound that may be present in Titan's interior is methanol. Using a thermodynamic model of the solar nebula and assuming a plausible composition of its initial gas phase, we first calculate the condensation sequence of ices in Saturn's feeding zone, and show that in Titan's building blocks methanol can have a mass fraction of ~4 wt% relative to water, i.e., methanol can be up to four times more abundant than ammonia. We then combine available data on the phase diagram of the water-methanol system and scaling laws derived from thermal convection to estimate the influence of methanol on the dynamics of the outer ice I shell and on the heat transfer through this layer. Our results indicate that a small fraction of methanol, which is consistent with the determination of Titan's building blocks composition, strongly reduces the vigor of convection in the outer ice shell. The effect of 5 wt% methanol is equivalent to that of 3 wt% ammonia. Thus, if methanol is present in the primordial ocean of Titan, the crystallization may stop, and a sub-surface ocean may be maintained between the ice I and high pressure ice layers. A preliminary estimate indicates that the presence of 4 wt% methanol and 1 wt% ammonia may result in an ocean at least 90 km thick.

422012-06-15 Fri
14:00~15:00
R1203
Dr. Jean Coupon
[ASIAA]
download PDF New insights on galaxy evolution since z ~ 1.2 from the CFHT Legacy Survey
Abstract

In the last few years, it is has become increasingly apparent that the mass of dark matter haloes in which galaxies reside is a key factor in regulating their formation and evolution. It is now evident that galaxies in low- and high-mass haloes experience very distinct fate. In this presentation, I will first explain why studying the relationship between stellar mass and halo mass brings valuable clues about physical processes involved in galaxy evolution. In the context of the halo model, the simple - but powerful - assumption that the number of galaxies only depends on halo mass, the halo occupation distribution (HOD) model, leads to an accurate analytic prediction of the galaxy distribution. Reciprocally, interpreting galaxy clustering using the HOD model allows to make a direct comparison between galaxy properties and halo mass. By using accurate galaxy clustering measurements over 133 deg2 of the “Wide” component of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS), we performed a detailed investigation of the changing relationship between galaxies and the dark matter haloes they inhabit from z ~ 1.2. I will then pursue my talk with a presentation of this unique data set combining depth, large area and high image quality, and I will finally present our results and their implications for galaxy evolution.

432012-06-08 Fri
14:00~15:00
R1203
No colloquium this week
[[outing]]
442012-06-05 Tue
14:20~15:15
R104, NTU Condensed Matter Building
Donglai Feng
[Fudan University]
*ASIAA/NTU Joint Colloquium*
A march toward the universal mechanism of iron based superconductors
Abstract

Superconducting gap is a direct consequence of electron forming Cooper pairs in a superconductor, which holds the key to its microscopic mechanism. For example, in conventional BCS superconductor, an isotropic gap distribution around the Fermi surface is a hallmark of the so-called s-wave pairing; while in cuprate high temperature superconductors, an anisotropic gap distribution with zero-gap line (or nodes) is the consequence of the so-called d-wave pairing. A new class of high temperature superconductors, the iron-based superconductor, was discovered in 2008. It is found that they have both members with nodes and members without nodes. There are also large variations of Fermi surface topology among the members. With angle-resolved photoemission spectroscopy, we have systematically studied the superconducting gap and electronic structures of iron based superconductors, and unified nodal gap into the s-wave pairing symmetry. Moreover, we point out that the inter-electron/hole-Fermi surface scattering is not the driving force of the superconductivity, and a local pairing scenario can generally account for various properties of the iron-based superconductors.

452012-05-24 Thu
14:00~15:00
R1203
Dr. Megan Schwamb
[NSF Fellow at Yale University]
Extreme Orbits in the Outer Solar System (***note special date***)
Abstract

I'll present the results of observational campaigns to study and probe two families of extreme planetesimal orbits discovered in the outer solar system: the distant Sedna population and the high inclination Centaurs. The discovery of Sedna on a highly eccentric orbit beyond Neptune challenges our understanding of the solar system and suggests the presence of a population of icy bodies residing past the Kuiper belt. With a perihelion of 76 AU, Sedna is well beyond the reach of the gas-giants and could not be scattered onto its highly eccentric orbit from interactions with Neptune alone. Sedna’s aphelion at ~1000 AU is too far from the edge of the solar system to feel the perturbing effects of passing stars or galactic tides in the present-day solar neighborhood. Some other mechanism no longer active in the solar system today is required to emplace Sedna on its orbit. Several possible scenarios have been offered to explain Sedna’s extreme orbit, including interactions with planet-sized bodies, stellar encounters, multiple stellar fly-bys in a stellar birth cluster, interstellar capture, and perturbations from a wide-binary solar companion. These planetesimals in the Sedna region are dynamically frozen and the relics of their formation process. Finding just a handful of these bodies, we can begin to read this dynamical record. I will discuss the implications for a distant Sedna-like population beyond the Kuiper belt. I will present the results from surveys designed to search for additional members of the Sedna population and discuss future prospects for detecting and studying these distant bodies, focusing in particular on the constraints we can place on the embedded stellar cluster environment the early Sun may be have been born in. The discovery of 2008 KV42 with a perihelion near Uranus and an extreme (nearly perpendicular) inclination of 104 degrees, suggests a population of bodies on similar orbits with high inclinations compared to typical KBOs and Centaurs. In the La Silla-QUEST KBO Survey, we have found the third new member of this high-inclination population, 2010 WG9 with an inclination of 70 degrees and a perihelion of 18.7 AU. These high inclination (i > 60 degrees) Centaurs are metastable gravitationally interacting and scattering off of Uranus and Neptune with lifetimes of hundreds of million years, suggesting there must be a source population feeding this unstable reservoir. I'll discuss the evidence that these objects are escapees from the Oort cloud rather than originating in the Kuiper belt and present observational constraints on the size and orbital distribution of such a population of extreme high-inclination orbits in the Kuiper belt.

462012-05-23 Wed
14:00~15:00
R1203
Dr. Michael Mumma
[Department of Astronomy, University of Maryland and NASA-Goddard Space Flight Center]
*Special Seminar*
The Chemical Composition of Comets: Emerging Taxonomies and Natal Heritage
Abstract

Viewed from a cosmic perspective, Earth is a dry planet yet its oceans are enriched in deuterium by a large factor relative to nebular hydrogen. Can comets have delivered Earth’s water? The question of exogenous delivery of water and organics to Earth and other young planets is of critical importance for understanding the origin of Earth’s water, and for assessing the possible existence of exo-planets similar to Earth. Strong gradients in temperature and chemistry in the proto-planetary disk, coupled with dynamical models, imply that comets from the Oort Cloud and Kuiper Disk reservoirs should have diverse composition. The primary volatiles in comets (ices native to the nucleus) provide the preferred metric, and taxonomies based on them are now beginning to emerge [1, 2, 3]. The measurement of cosmic parameters such as the nuclear spin temperatures for H2O, NH3, and CH4, and of enrichment factors for isotopologues (D/H in water and hydrogen cyanide, 14N/15N in CN and HCN) provide additional important tests for the origin of cometary material. I will provide an overview of these aspects, and their implications for the origin of Earth’s water and prebiotic organics.

472012-05-22 Tue
14:20~15:30
R104, CCMS-New Physics Building
Prof. Jean-François Roch
[Laboratoire Aimé Cotton]
*ASIAA/NTU Joint Colloquium*
Nanoscale optical and magnetic imaging using color centers in diamond nanoparticles
Abstract

Numerous works have been devoted to the development of efficient probes for nanoscale imaging. I will report the application of optically and magnetically active nanodiamonds to nanoscale mapping using the unique properties of the nitrogen-vacancy (NV) color center. The NV center is hosted in a diamond nanocrystal which is attached to the tip of an atomic force microscope. Combining nanometer scale spatial resolution, high sensitivity and room temperature operation, this NV-based scanning microscope opens up numerous perspectives in nanotechnology.

482012-05-18 Fri
14:00~15:00
R1203
Dr. Masahiko Kimura
[Univ. of Tokyo/ASIAA]
download PDF Instruments of the prime focus on the Subaru telescope
Abstract

The prime focus of the telescope has a small number of the focal ratio and a wide field of view, suitable for the survey observations. The Subaru Telescope is one of the two 8-meter class telescopes in the world with the ability to mount an instrument at prime focus. I talk the four instruments (Suprime-Cam, FMOS, HSC and PFS) of the prime focus with the Subaru telescope. In these instruments, I have developed the Suprime-Cam and FMOS. I participate in development of PFS by ASIAA from April. I will talk about these instrument.

492012-05-15 Tue
14:20~15:30
R104, NTU Condensed Matter Building
Prof. Pisin Chen
[NTU]
*ASIAA/NTU Joint Colloquium*
Probing the Edge of the Universe from the Edge of the Earth: Searching for Cosmic Neutrinos at South Pole
Abstract

This year (2012) marks the centenary of Victor Hess’s historical discovery of cosmic rays. Over the 100 years’ time, scientists further realized that the universe is filled with all sorts of elementary particles. By investigating these cosmic particles, we can gain knowledge about the universe that is complementary to what offered by the more traditional optical telescopes. Neutrinos is known to interact very weakly with other particles and therefore can travel across the entire universe freely. A neutrino telescope can therefore in principle help to probe into the deepest of the universe, which also corresponds to looking back to its earliest history. However since neutrino is weakly interacting, it requires a large target to intercept when it arrive to Earth. With its huge volume of pristine ice, Antarctica is an ideal place for building such neutrino telescopes. The Askaryan Radio Array (ARA) Neutrino Observatory is one of such attempts. When completed in 4-5 years, it will cover 100 km^2 in area, to become the largest neutrino telescope in the world. Taiwan has been playing a key role in the inception and the construction of the ARA project. This is Republic of China's first major scientific project at the South Pole in its 100 years of history. In this lecture, we will introduce the science and technology of ARA and share with the audience the photos and videos taken at the South Pole in December 2011.

502012-05-04 Fri
14:00~15:00
R1203
Dr. Shaw Chen Liu
[Academia Sinica]
Global warming and impacts on Taiwan
512012-04-27 Fri
14:00~15:00
R1203
Dr. Ramon Brasser
[ASIAA]
download PDF The Great Archean Bombardment
Abstract

The Late Heavy Bombardment (LHB), together with the Great Archean Bombardment on Earth, constitutes an epoch of intense cratering on the terrestrial planets and the Moon approximately 500 Myr after their formation. Here I present evidence for the LHB having occurred and demonstrate that this had to coincide with a major event in the solar system. The most likely explanation is an instability in the outer solar system with the giant planets scattering each other onto eccentric orbits. This scattering event destabilised asteroids from the now-empty E-belt asteroid belt directly outside Mars and sent them towards the terrestrial planets. The intensity, duration and latest models for the bombardment are discussed.

522012-04-13 Fri
14:00~15:00
R1203
Dr. Chin-Wei Chen
[ASIAA]
download PDF The Scaling Relation of Early Type Galaxies in Virgo Cluster
Abstract

We present photometric and structural parameters for 100 ACS Virgo Cluster Survey (ACSVCS) galaxies based on homogeneous, multi-wavelength (ugriz), wide-field SDSS (DR5) imaging. These early-type galaxies, which trace out the red sequence in the Virgo Cluster, span a factor of nearly ~103 in g-band luminosity. We describe an automated pipeline that generates background-subtracted mosaic images, masks field sources and measures mean shapes, total magnitudes, effective radii, and effective surface brightnesses using a model-independent approach. A parametric analysis of the surface brightness profiles is also carried out to obtain Sérsic-based structural parameters and mean galaxy colors. We compare the galaxy parameters to those in the literature, including those from the ACSVCS, finding good agreement in most cases, although the sizes of the brightest, and most extended, galaxies are found to be most uncertain and model dependent. Our photometry provides an external measurement of the random errors on total magnitudes from the widely used Virgo Cluster Catalog, which we estimate to be σ(BT )≈ 0.13 mag for the brightest galaxies, rising to ≈ 0.3 mag for galaxies at the faint end of our sample (BT ≈ 16). The distribution of axial ratios of low-mass ("dwarf") galaxies bears a strong resemblance to the one observed for the higher-mass ("giant") galaxies. The global structural parameters for the full galaxy sample—profile shape, effective radius, and mean surface brightness—are found to vary smoothly and systematically as a function of luminosity, with unmistakable evidence for changes in structural homology along the red sequence. As noted in previous studies, the ugriz galaxy colors show a nonlinear but smooth variation over a ~7 mag range in absolute magnitude, with an enhanced scatter for the faintest systems that is likely the signature of their more diverse star formation histories.

532012-04-06 Fri
14:00~15:00
R1203
Dr. Frank Shu
[ASIAA]
download PDF Molten Salt Breeder Reactors
Abstract

We explain the basics of nuclear fission, starting with the history of how most of the world came to use the once-through fuel cycle of light water reactors, explaining why the light water dream dissolved, and concluding that reprocessing and breeding are necessary to remove public concerns about waste management, safety, and sustainability of the nuclear option. We point out why the long overlooked technologies of molten salt reactors coupled to the thorium fuel cycle is superior in terms of cost, passive safety, and weapons non-proliferation to the current usage of nuclear power. We discuss an approach using novel materials to build two-fluid molten salt reactors on a rapid enough schedule to make Taiwan and the world free of plutonium and net CO2 emission by mid-century. Of particular interest may be the possibility of leveraging the capacity of such facilities by coupling nuclear power to the production of high-throughput biofuels.

542012-03-27 Tue
14:20~15:20
Physics R104
Prof. Chung-Pei Ma
[UC Berkeley]
*ASIAA/NTU Joint Colloquium*
Monster Black Holes
Abstract

Black holes are among the most fascinating astrophysical objects and have long entranced the public. For over three decades, the giant elliptical galaxy Messier 87 has hosted the most massive known black hole in the local Universe. I will describe the recent discovery of two record-breaking black holes, each with ten billion solar masses, in an ongoing survey of centers of nearby massive galaxies. The existence of these supermassive black holes have interesting implications for the growth of the largest galaxies in the Universe.

552012-03-26 Mon
14:00~15:00
R1203
Prof. Chung-Pei Ma
[UC Berkeley]
*Special Seminar*
How to Find a Job in Academia!
562012-03-21 Wed
14:00~15:00
R1203
Dr. Chao-Chin Yang
[UCO/LICK, UC Santa Cruz]
*Special Seminar*
Thermal Instability-Driven Turbulent Mixing in Galactic Disks
Abstract

Observations show that open clusters and moving groups in the Solar neighborhood are extremely chemically homogenous, with typical star-to-star abundance variations of only ~0.01 dex. On a larger scale, radial metallicity gradients in majority of nearby disk galaxies are relatively shallow, if not flat, especially towards large galactocentric distances. The physical mechanism behind these phenomena, however, remains unclear. We conduct magnetohydrodynamical simulations of a local shearing sheet of a thin, thermally unstable, gaseous disk driven by a background stellar spiral potential, with the metals modeled as passive scalar fields. By Fourier and statistical analyses, we quantify the redistribution of metals and its variation within each gravitationally bound structure. We find that turbulence driven by thermal instability is very efficient at mixing metals, regardless of the presence or absence of stellar spiral potentials or magnetic fields. This in turn helps explain the chemical homogeneity of star clusters and radial metallicity gradients in disk galaxies.

572012-03-20 Tue
14:00~15:00
R1203
Dr. Roberto De Propris
[CTIO]
*Special Seminar*
Galaxy Mergers
Abstract

I will describe the importance of mergers for theories of galaxy formation in a LCDM context and how these affect not only the evolution of stellar mass but also the gross properties of galaxies (such as morphology, activity, star formation). I will then discuss results from our measurements of the local merger rate from close galaxy pairs in the MGC and 2SLAQ survey and new results from the GAMA and the 2SUISS surveys.

582012-03-14 Wed
14:00~15:00
R1203
Dr. Hiromi Seta
[Saitama university]
*Special Seminar*
Suzaku Observations of Radio lobes in Active Galaxies
Abstract

The jet from active galactic nuclei (AGNs) is one of the most gigantic features of energy concentration and dissipation in the universe. The dissipated energy and material are deposited in the radio lobes, which should exhibit footprints of the past activities of the jet in its surface brightness distribution of the non-thermal emission. The radio and X-ray observations are useful to estimate the energy in the lobes respectively probing the synchrotron and inverse Compton emission off of relativistic electrons. However, the observations of radio lobes are difficult, in particular, in the X-rays, as the emission is extended and low in surface brightness and is often overwhelmed by thermal emission of the host galaxies. We use the Suzaku X-ray Observatory, which has a wide-band spectroscopic capability with an unprecedentedly low and stable background. We observed Fornax A, which is one of the closest and largest radio lobes from the radio galaxy NGC1316. We estimated the non-thermal energy density using the emission above the 10 keV band, in which thermal contamination is negligible. We also identified thermal emission associated to the lobe, which has not been recognized before. We found a spatial difference in the brightness distribution of the X-ray emission, which we speculate was caused from the varying jet orientation in the past.

592012-03-12 Mon
14:00~15:00
R1203
Dr. Sherry Suyu
[UC Santa Babara]
*Special Seminar*
Exploring the Dark Universe with Gravitational Lensing
Abstract

Understanding the nature of dark energy and dark matter is one of the biggest challenges in modern cosmology. Strong gravitational lens systems provide a powerful tool for measuring cosmological parameters and for probing dark matter in galaxies. I will describe how strong lens systems with measured time delays between the multiple images can be used to determine the "time-delay distance" to the lens, which is primarily sensitive to the Hubble constant. I will present the prospects for using time-delay lenses to measure the Hubble constant to 1% precision and accuracy, which will provide critical independent constraints on the nature of dark energy, the spatial curvature of the Universe and neutrino physics. To study properties of dark matter, I will show how a combination of lensing and stellar kinematics can be used to disentangle dark matter and baryons in spiral galaxies, measure the shape of dark matter halos, and probe the stellar initial mass function. In addition, a novel approach to determine the dark matter halo sizes of galaxies in groups and clusters will be presented. I will discuss the prospects for measuring the inner dark matter profiles in galaxies and determining the efficiency of tidal stripping in galaxy groups/clusters, both of which will provide key insights into the co-evolution of galaxies and dark matter.

602012-03-09 Fri
14:00~15:00
R1203
Dr. Stephane Guilloteau
[Laboratoire d'Astrophysique de Bordeaux (LAB), Floirac, France]
download PDF Molecular and continuum surveys as tools to determine the structure of protoplanetary disks: part II
Abstract

The study of protoplanetary disks is essential to understand how planetary systems form. Because of the small apparent sizes of these discs, and of their low temperatures, mm interferometry is a key to unveil the physical conditions in which planets may form. In the first part, we shall show what has been learned from the still relatively rare high resolution molecular line observations in terms of temperature and chemistry, and how this compares to our a priori concepts of proto-planetary disks, in particular the layered structure that all chemical models predict. The complete inventory of molecules will be presented, and perspectives for ALMA discussed. In the second part, the informations derived from molecules will be compared to those derived from dust observations. Progress towards constraining the disk mass, a fundamental yet largely unconstrained parameter will be reported. Beyond this simple number, we will explore how the dust to gas ratio can be studied, in particular in view of the recent and on coming progress in observational facilities.

612012-03-02 Fri
14:00~15:00
R1203
Dr. Anne Dutrey
[Laboratoire d'Astrophysique de Bordeaux (LAB), Floirac, France]
download PDF Molecular and continuum surveys as tools to determine the structure of protoplanetary disks: part I
Abstract

The study of protoplanetary disks is essential to understand how planetary systems form. Because of the small apparent sizes of these discs, and of their low temperatures, mm interferometry is a key to unveil the physical conditions in which planets may form. In the first part, we shall show what has been learned from the still relatively rare high resolution molecular line observations in terms of temperature and chemistry, and how this compares to our a priori concepts of proto-planetary disks, in particular the layered structure that all chemical models predict. The complete inventory of molecules will be presented, and perspectives for ALMA discussed. In the second part, the informations derived from molecules will be compared to those derived from dust observations. Progress towards constraining the disk mass, a fundamental yet largely unconstrained parameter will be reported. Beyond this simple number, we will explore how the dust to gas ratio can be studied, in particular in view of the recent and on coming progress in observational facilities.

622012-03-01 Thu
15:30~16:30
R1203
Dr. Ryoko Ishioka
[Subaru telescope]
*Special Seminar*
Optical and near-Infrared observations of cataclysmic variables and related objects
Abstract

Cataclysmic variables are well defined interacting binaries at a late stage of binary evolution. They are a wonderful laboratory for the study of many astrophysical processes. One of the most fundamental parameters of binary systems is the orbital period. The orbital period distribution of cataclysmic variables has been used as a tool to test models of binary formation and evolution. Among many subclasses of cataclysmic variables, SU UMa-type dwarf novae are characterised by a periodic modulation, called superhumps, during their long outbursts. The superhumo period is a few percent longer than the orbital period, so it can be a good approximation of the orbital period. In addition, when the orbital period is known, the superhump period excess over the orbital period gives us an estimate of the mass ratio, another fundamental binary parameter. I will introduce our work on the superhumo period variation in SU UMa-type dwarf novae based on the photometric observations led by the Variable Star Network collaboration. I will also talk about a peculiar cataclysmic variable reacently discovered, and infrared spectroscopies of cataclysmic variables and post common envelope binaries in the period gap of cataclysmic variables, whose aim is to get further clue to understand binary evolution.

632012-02-29 Wed
14:00~15:00
R1203
Dr. Chien-Hsiu Lee
[NCU]
*Special Seminar*
download PDF PAndromeda - First results from the high-cadence monitoring of M31 with Pan-STARRS 1
Abstract

The Pan-STARRS 1 (PS1) survey of M31 (PAndromeda) is designed to identify gravitational microlensing events, caused by bulge and disk stars (selflensing) and by compact matter in the halos of M31 and the Milky Way (halo lensing, or lensing by MACHOs). With the 7 deg2 FOV of PS1, the entire disk of M31 can be imaged with one single pointing. Our aim is to monitor M31 with this wide FOV with daily sampling (20 mins/day). In the 2010 season we acquired in total 91 nights toward M31, with 90 nights in the rP1 and 66 nights in the iP1. The total integration time in rP1 and iP1 are 70740s and 36180s, respectively. As a preliminary analysis, we study a 40′ × 40′sub-field in the central region of M31, a 20′ × 20′ sub-field in the disk of M31 and a 20′ × 20′ sub-field for the investigation of astrometric precision. We demonstrate that the PSF is good enough to detect microlensing events. We present light curves for 6 candidate microlensing events. This is a competitive rate compared to previous M31 microlensing surveys. We finally also present one example light curve for Cepheids, novae and eclipsing binaries in these sub-fields.

642012-02-24 Fri
14:00~15:00
R1203
Cheng-Yu Kuo
[ASIAA]
The Megamaser Cosmology Project : Accurate Determination of the Hubble Constant and the Masses of the Supermassive Black Holes at the centers of Megamaser Galaxies
Abstract

The primary goal of the Megamaser Cosmology Project is to determine the Hubble constant H0 3\% accuracy in order to constrain the equation of state parameter w of dark energy. The key to achieving this goal is to measure accurate distances to galaxies well into the Hubble flow (50 - 200 Mpc). A proven method to measure accurate angular-diameter distances involves sub-milliarcsecond resolution imaging of H2O maser emission from sub-parsec circumnuclear disks at the center of active galaxies, a technique established by the study of NGC 4258 with VLBI. As the Megamaser Cosmology Project discovers and images megamaser disks, an important result, in addition to the Hubble constant determination, is the accurate measurement of the masses of the supermassive black holes at the centers of these megamaser galaxies In this talk, I will present the latest results on the Hubble constant determination from the Megamaser Cosmology Project. In addition, I will also show the black hole mass measurements and their impact on our understanding of hte famous M-sigma relation.

652012-02-17 Fri
14:00~15:00
R1203
Prof. Tom Broadhurst
[Basque U., Bilbao, Spain]
Taiwan Attack on Dark Matter
Abstract

This talk includes our latest Hubble Treasury data for massive cluster of galaxies and how the tension we find with with standard particle-CDM may point towards a Bose-Einstein Condensate (BEC) form of CDM. We aim to discriminate between these contending possibilities for CDM with direct spectroscopic measurements of the motion of dark matter during cluster collisions and with predictions from improved BEC simulations.

662012-02-16 Thu
14:00~15:00
R1203
Prof. Toshifumi Futamase
[Tohoku Univ.]
*Special Seminar*
download PDF A New Approach to nonlinear evolution of cosmological density perturbation
Abstract

An accurate theoretical prediction of the density power spectrum has a fundamental importance in the observational cosmology. We have recently developed a new formalism to study this problem by employing the Wiener-Hermite expansion technique. The calculated power spectrum agrees with N-body result within 3% accuracy over the range k=0.5-0.8 at z+0.5-3.0.

672012-02-10 Fri
13:15~14:45
R1203
Olivier Le Fevre
[Laboratoire D'Astrophysique de Marseille]
download PDF Next Generation Observational Facilities and Galaxy Surveys (this talk is part of the lecture of the high-z school)
682012-02-03 Fri
14:00~15:00
R1203
Prof. Yasushi Suto
[The University of Tokyo]
download PDF Colors of a second Earth
Abstract

We develop a simple method to estimate the fractional areas of different surface types on earth-like exoplanets from multi-band photometry. Our attempt is to reproduce the scattered light curves as a sum of the 5 surface types, i.e., ocean, soil, vegetation, snow and cloud. We would like to answer an ambitious, but well-defined, scientific question: "If we discover an exoplanet identical to the Earth in the near future, can we infer the presence of vegetation observationally ?''. This is why we intentionally and specifically adopt the major surface types of the Earth, including vegetation, into the analysis even though our method is thus inevitably model-dependent. We apply our method to mock scattered light curves of the Earth and to the real data from the Earth observing satellite. In an idealized situation where the photometric errors are only photon shot noise, we are able to reproduce the fractional areas of those components fairly well. We may be even able to detect a signature of vegetation from the distinct feature of photosynthesis on the Earth, known as the red edge. In our reconstruction method, Rayleigh scattering due to the atmosphere has an important effect, and for terrestrial exoplanets with atmosphere similar to our Earth, it is possible to estimate the presence of oceans and an atmosphere simultaneously. References: 1. Yuka Fujii, Hajime Kawahara, Yasushi Suto, Atsushi Taruya, Satoru Fukuda, Teruyuki Nakajima, and Edwin L. Turner: “Colors of a second Earth I: estimating the fractional areas of ocean, land and vegetation of Earth-like exoplanets” The Astrophysical Journal 715, 866—880, 2010. 2. Yuka Fujii, Hajime Kawahara, Yasushi Suto, Satoru Fukuda, Teruyuki Nakajima, Timothy A. Livengood, and Edwin L. Turner: “Colors of a second Earth II: Effects of clouds on photometric characterization of Earth-like exoplanets” The Astrophysical Journal 738, 184(1-15), 2011.

692012-02-02 Thu
15:30~16:30
R1203
Prof. Yasushi Suto
[The University of Tokyo]
*Special Seminar*
download PDF Cosmological implications of inhomogeneities in intra-cluster gas
Abstract

Almost all the theoretical/empirical models of galaxy clusters do not take into account the local density and temperature inhomogeneities in intra-cluster gas. Given the recent progress in observations, a proper account of those inhomogeneities is overdue. We use the cosmological SPH simulations of galaxy clusters to evaluate the degree of inhomogeneities in intra-cluster gas, and find that they have important implications on the cluster temperature determination and on the estimate of the Hubble constant through the Sunyaev-Zel'dovich effect.

702012-01-19 Thu
16:00~17:00
R1203
Dr. Ray Furuya
[NAOJ/Subaru Telescope]
*Special Seminar*
The Initial Conditions for Gravitational Collapse of Star-Forming Molecular Cloud Core
Abstract

Without accurate knowledge of the initial conditions of gravitational collapsing process of a molecular cloud core, one cannot understand how a low-mass protostar forms. One of the major limiting factors is that the initial conditions of core collapse are not necessarily revealed by observations in detail. In this context, we performed a study of the natal molecular cloud core and its environment. The core is believed to harbor an extremely young low-mass protostar that has not generated an extensive molecular outflow, yielding a rare opportunity to investigate core-collapsing process free from the disturbance by the outflow. Our observations suggest that the gas in the molecular cloud core is infalling onto the protostar, and that the non-thermal velocity dispersions, tracing the ambient turbulent velocity fields, in the medium-density gas are clearly smaller than those in the low-density gas. We discuss these results with comparisons of theoretical models and the implications for initial conditions of star formation in general.

712012-01-13 Fri
14:00~15:00
R1203
Keitaro Takahashi
[Kumamoto University]
download PDF Square Kilometer Array and related activity in Japan
Abstract

Square Kilometer Array (SKA) is the next-generation cm-wave radio telescope which will have a sensitivity better than the existence telescopes by more than one order. It is expected to make a tremendous impact on many fields of astrophysics and cosmology, such as cosmic reionization, cosmic magnetism and pulsar study. In Japan, a consortium was established with more than 100 members and many researchers are studying SKA-related topics. In this talk I will review the SKA plan, science and Japanese activity toward SKA. Possible Taiwan-Japan collaborations are also argued.

722012-01-12 Thu
14:00~15:00
R1203
Dr. Yin-Zhe Ma
[U. of British Columbia]
*Special Seminar*
*** Canceled ***
732012-01-06 Fri
14:00~15:00
R1203
Tony Wong
[University of Illinois]
The Molecular Cloud Population of the Large Magellanic Cloud
Abstract

With the Magellanic Mopra Assessment (MAGMA), we have recently completed a CO imaging survey of the most luminous giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) with the Mopra mm-wave telescope. In this talk I will describe recent progress in deepening our understanding of GMC evolution using CO surveys of the LMC. Molecular gas is found in regions with high gas columns, but high gas columns do not guarantee CO detection. The inferred properties of the GMCs depend a great deal on the analysis technique, and the expected size-linewidth correlation only becomes apparent on large scales. The velocity gradients across GMCs are similar to those found in the surrounding atomic gas and do not appear indicative of rotation. Examining the CO detection statistics towards candidate young stellar objects (YSOs), we find that more luminous YSOs are more likely to show detectable CO emission. Conversely, more luminous GMCs are more likely to contain YSOs. On the other hand, the virial parameter of a GMC has little influence on whether it is likely to exhibit massive star formation. Our results support a tight linkage between molecular gas and star formation but call into question the assumption that GMCs are gravitationally bound (and thus long-lived) entities.

TEL: 886-2-3365-2200 FAX: 886-2-2367-7849
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11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C.