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Activity > Colloquium

Colloquium (2009)

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
12009-12-17 Thu
14:00~15:00
R1203
Dr. Nozomu Tominaga
[Konan University]
Core-collapse supernovae in early and distant universe
Abstract

Massive stars being larger than 8Msun explode as core-collapse supernovae (CCSNe) at the end of their life. CCSN is a predominant metal producer and so bright as to be observed even if it takes place at high redshift. I briefly introduce physics of CCSNe first and then focus on CCSNe in the early universe and distant universe: 1. Extremely metal-poor (EMP) stars in Galactic halo, formed in the early universe, tell us the nature of CCSNe in the early universe and indicate their similar variations to present CCSNe and gamma-ray bursts (GRBs). 2. CCSNe are generally accepted to be much fainter than Type Ia SNe. However, when a shockwave emerges from a stellar surface, CCSNe emit a bright X-ray or UV flash (L>10^44erg/s), called shock breakout first observed in 2008. I present a radiative hydrodynamical calculation of the shock breakout and propose that it will attain the first direct detection of CCSNe at z>1.

22009-12-17 Thu
16:30~17:30
R1203
Dr. Luis Ho
[Carnegie Observatories]
Coevolution of Black Holes and Galaxies: Recent Developments
Abstract

I will review observational progress in defining and refining the various empirical scaling relations between black hole masses and host galaxy properties. I will emphasize ways in which the intrinsic scatter can be quantified, and present evidence that the scatter correlates with physical properties. I will discuss how to extend the scaling relations to active galaxies, and summarize preliminary efforts to probe the evolution of these scaling relations with redshift. I will present new measuremnts of the cold ISM content in AGN host galaxies, and constraints they place on currently popular models of AGN feedback. Lastly, I will discuss a new class of low-mass black holes in bulgeless and dwarf galaxies that serve as local analogs of seed supermassive black holes.

32009-12-16 Wed
14:00~15:00
R1203
Dr. Tomoki Morokuma
[NAOJ]
Variability Surveys for Low-Luminosity Active Galactic Nuclei
Abstract

I first introduce our activities on Subaru/Suprime-Cam surveys for time-varying objects such as active galactic nuclei, supernovae, and high proper motion stars. The combination of the large aperture of the Subaru telescope and the wide field-of-view of Suprime-Cam gives us a large statistical sample of these interesting objects. I here also show a brief summary of the next generation wide-field camera on Subaru, Hyper Suprime-Cam (HSC). In the latter part of my talk, I will focus on AGN studies using the Suprime-Cam multi-epoch imaging data in the Subaru/XMM-Newton Deep Survey (SXDS) field. By combining the deep X-ray data with optical variability, we found a significant fraction of optical-variability-selected AGN which were not detected in X-ray. We discuss properties of such interesting AGN and our plan with HSC to understand the nature of these AGN.

42009-12-08 Tue
14:00~15:00
R1203
Prof. Frederick M. Walter
[SUNY Stony Brook]
All the low mass objects - Where do they all come from?
Abstract

The Galaxy is littered with substellar mass objects - brown dwarfs and possibly free-floating massive planets. Do they form as stars, as an extension of a continuous mass function? Are they the remains of underdone embryos, either eroded in the harsh environment of OB associations, or ejected from dense clusterings? We can investigate the origins of the very low mass objects by examining the mass function and its spatial variations in nearby fossil star formation regions - the OB associations. I shall report on an on-going investigation of the Orion OB1a and b associations, the largest of the nearby fossil star forming regions. Our JHK survey using CPAPIR on the SMARTS/CTIO 1.5m telescope is complete to about 1 mag deeper than 2MASS over about 15 square degrees. Excesses in the color-magnitude diagram suggest an abundance of substellar mass objects, with space densities from a few hundred to 10^3 per sq deg. Optical and near-IR spectra, and optical/IR spectral energy distributions confirm the expectations from the photometry. Our deep optical and near-IR photometry in the region will result in a catalog of some 10^4 substellar mass objects complete in some areas to a limiting mass of about 2 Jovian masses, and perhaps a deeper understanding of the low mass end of the mass function.

52009-11-24 Tue
14:00~15:00
R1203
Prof. Steve Strom
[NOAO]
The Evolution of Circumstellar Disks: What Kinds of Planets Form in What Kinds of Disks?
Abstract

We will review the range of initial conditions that obtain for circumstellar disks surrounding stars of masses 0.2 < M/Msun < 10 and discuss the physical factors that influence their evolution. Starting from these basics, we will outline current thoughts regarding the formation of planets and the effects of planet formation on the physical state and observable properties of the disk. Next, we will summarize the statistical distribution of spectral energy distributions diagnostic of disk evolutionary states. By combining this information with other measurable quantities -- disk mass, accretion rate and the distribution of various gas tracers -- we are able to infer which disks have likely formed systems dominated by Jovian or supra-Jovian mass planets, and which are likely dominated by planetesimals or low mass planets. We conclude that there is substantial evidence that initially more massive disks have formed Jovian mass planets.

62009-10-30 Fri
14:00~15:00
R716
Prof. Sebastien Foucaud
[NTNU]
Witnessing the formation and evolution of massive galaxies
Abstract

Understanding the formation of the most massive galaxies that are the brightest, biggest and yet elusive objects in the Universe is topic that deeply puzzles and interests Astronomers today. While the large-scale structure and cosmological properties are globally understood, the mass assembly and star-formation in the massive systems continues to challenge existing models. As the large-scale behaviour of galaxies is ruled by their dark matter content, an estimate of the mass of their dark matter halos is crucial to gain a good understanding of the history of their mass assembly. Panchromatic deep and large near-infrared surveys, such as the UKIDSS-UDS and AEGIS-POWIR surveys, are the ideal tools to study distant massive galaxies. I will detail the deepest of these surveys, the Ultra-Deep Survey (UDS) which covers 0.6 sq degrees for a depth of the current world-wide available release of K=21.3, H=22.0, J=22.5 (Vega). I will introduce the most recent work I am leading thanks to these near-infrared surveys, to describe the properties of massive galaxies at 1

72009-10-23 Fri
14:00~15:00
R716
Dr. Induk Lee
[NCU]
Bright Quasar Survey at Low Galactic Latitude
Abstract

I will present the result of second phase of Seoul National University Bright Quasar Survey in Optical (SNUQSO). From this survey, we discovered 176 new bright quasars/Seyferts (0.0520 deg) to avoid stellar contamination and Galactic extinction at low Galactic latitude (|b|<20 >>> deg), or also known as the "zone of avoidance". In order to find quasars at the zone of avoidanace, we have made an algorithm to find quasars with high efficiency using optical, NIR, X-ray, and radio information. Using this algorithm, we selected quasar/Seyferts candidates which are J<16 magnitude at low Galactic latitude. The observation were carried out using the 1.8m telescope at the Bohyunsan Optical Astronomy Observatory (BOAO), the 2.1m telescope at the Kitt Peak National Observatory (KPNO), and the 1.8m telescope at the IUCAA Girawali Observatory for the Northern hemisphere, and the 1.5m telescope at the Cerro Tololo Inter-American Observatory (CTIO) for the Southern hemisphere, during 2006-2008. We found that the efficiency depends on NIR color. For candidates within 1.2 < J-K < 2.3, we can search quasars/Seyferts with >40% of efficiency. We also found that the surface number density of the quasars/Seyferts we discovered is 0.012 deg^{-2}, and comparable with other quasar survey programs which use radio information for bright quasars/Seyferts. These objects will be useful for many astrophysical applications, such as (i) building a complete census of quasar population; (ii) studying the Galactic matters using absorption lines; (iii) studying stellar proper motion using these objects as reference points; and (iv) studying AGN host galaxies using adaptive optics (AO) with many bright stars nearby for a better AO PSF characterization.

82009-10-20 Tue
14:00~15:00
R716
Dr. Shep Doeleman
[MIT Haystack Observatory]
Observing an Event Horizon: Very Long Baseline Interferometry of the Galactic Center
Abstract

There is now very strong evidence that SgrA*, the compact source of radio, IR, and x-ray emission at the Galactic Center, marks the position of a 4 million solar mass black hole. Only 8 kilo-parsecs away, Very Long Baseline Interferometry (VLBI) has the potential to model, and eventually image, emission on scales of a few Schwarzschild radii, at the innermost accretion region of this black hole. This requires pushing the VLBI technique to short wavelengths where scattering by the ionized ISM is reduced and the intrinsic structure of SgrA* can be observed. VLBI observations in April 2007 and April 2009 at a wavelength of 1.3mm have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. More sensitive observations, using additional VLBI stations, are planned over the next few years, and will be sensitive to time variable structures predicted by models of flaring activity in SgrA*. I will describe the instrumentation efforts that enable these observations, discuss what current and future VLBI observations of SgrA* tell us about this closest super-massive black hole, and outline plans to assemble an 'Event Horizon Telescope'.

92009-10-15 Thu
14:00~15:00
R716
Dr. Tsz Yan Lam
[IPMU]
Signature of primordial non-Gaussianity on large scale structure
Abstract

Cosmological probes of primordial non-Gaussianity have recently attracted much attention due to its ability to discriminate between different inflationary models. In this talk I will present the signatures of primordial non-Gaussianity on large scale structure. I will first describe its effect on the distribution of the underlying dark matter field. I will show how to generalize Doroshkevich's celebrated formulae for the eigenvalues of the initial shear field assoicated with Gaussian statistics to the local non-Gaussian f_{nl} model. Then I will discuss how to extend the excursion set approach to compute the halo mass function when the primordial perturbation is non-Gaussian. The result will then compare with measurements from N-body simulations.

102009-09-11 Fri
14:00~15:00
R716
Dr. Yen-Ting Lin
[IPMU]
Evolution of galaxies in massive halos
Abstract

A key issue in cosmology is the formation of massive (>L*), early type galaxies. To reconcile their predominant old stellar populations and the uniformity in physical properties with the hierarchical buildup of structures within the LCDM framework, poorly understood processes such as feedback (interaction between galaxies and their immediate environment via e.g. radio outflows) and "dry" mergers (mergers involving gas-poor galactic systems) have been invoked in leading galaxy formation theories. I will discuss the roles of mergers and feedback in shaping the massive galaxy populations, using galaxies that reside in groups and clusters. In the first half of the talk the importance of mergers will be assessed with a new statistic for the brightest cluster galaxies. In the second half I will focus on the physical properties of the radio-loud AGNs in the local Universe, and present a model for the evolution of powerful radio galaxies that can account for the source counts from 0.15 GHz to 150 GHz, and radio luminosity function out to z~2.

112009-09-08 Tue
14:00~15:00
R716
Dr. Makoto Miyoshi
[NAOJ]
Very Long Baseline Interferometry (VLBI) for Sagittarius A*
122009-09-02 Wed
15:00~16:00
R716
Prof. Walter Gear
[Cardiff University]
CMB Polarization, whispers from the Big-Bang
Abstract

I will describe the origin of and the current status of measurements of the polarization properties of the cosmic microwave background radiation. In particular I will focus on the search for the so-called 'B-mode' signature of gravitational waves created at the time of inflation in the very earliest Universe which many projects worldwide are now being developed for, and will describe the Clover project which I am currently leading.

132009-09-01 Tue
14:00~15:00
R716
Dr. Keiichi Asada
[ASIAA]
Probing the structure of the magnetic field in the jets from active galactic nuclei
Abstract

Jets emanating from the active galactic nuclei are one of the largest objects in the universe. Some jets travel more than 1 Mpc, keeping highly collimated structure. Based on statistical studies, it has been known that jets are highly accelerated, in some cases, up to bulk Lorentz factors of 30. It seems that we are reaching an important clue to understand the jet phenomena. However, the most essential subjects, how jets are formed, accelerated and collimated, are still unclear. Focusing to this issue, we have probed the structure of the magnetic field in the jet using multi-frequency VLBI polarimetry. As the results, we have revealed that several jets might have a helical magnetic field, which is frequently invoked by many MHD models. We would like to talk on this issue and introduce the related progress based on VLBI observations.

142009-08-31 Mon
14:00~15:00
R104
Dr. Jean Charles Cuillandre
[CFHT]
Optical Wide Field Imaging at CFHT
Abstract

The summit of Mauna Kea (14,000 feet) offers the best viewing of the Cosmos in the northern hemisphere, and the film "Hawaiian Starlight" delivers a pure esthetic experience from the mountain into the Universe. Seven years in the making, this cinematic symphony reveals the spectacular beauty of the mountain and its connection to the Cosmos through the magical influence of time-lapse cinematography scored exclusively (no narration) with the awe-inspiring, critically acclaimed, Halo music by Martin O'Donnell and Michael Salvatori. Daytime and nighttime landscapes and skyscapes alternate with stunning true color images of the Universe captured by an observatory on Mauna Kea, all free of any computer generated imagery. The inspiration and technology of the film for both the terrestrial cinematography and astronomical imagery using CFHT's large optical CCD mosaics will be presented.

152009-08-14 Fri
14:00~15:00
R716
Dr. Masahiro Machida
[NAOJ]
Fragmentation and binary formation in the star formation process
Abstract

Observations have shown that about 50-80% of stars are members of binary or multiple systems. Since the binary frequency of pre-main sequence stars is higher than that of field stars, it is considered that stars are born as binary or multiple systems. These systems are formed by fragmentation of the collapsing cloud. However, we cannot directly observe fragmentation process, because it is embedded in a dense cloud core. Numerical simulation is the most effective tool for investigating the cloud fragmentation, and can clarify the binary formation process. In this talk, I will present recent development of numerical simulations for star formation in the collapsing gas cloud, focusing fragmentation and binary formation process. The cloud fragmentation is closely related to the magnetic field and angular momentum of the natal cloud. The magnetic field suppresses fragmentation, while the cloud rotation promotes it. I will discuss the implication of the binary separation in a very young cluster.

162009-08-13 Thu
14:00~15:00
R716
Dr. Toshiya Ueta
[University of Denver]
Interaction between Stellar Winds and the Interstellar Medium around Evolved Stars
Abstract

Recent far-IR observations done by Spitzer and AKARI have provided refined evidence for shock interactions between stellar winds and the interstellar medium (ISM). Characteristic bow-shock structures have been found around not only high mass loss stars like supergiants but also low/intermediate mass loss stars like AGB stars. These new far-IR data at higher spatial resolution have revealed detailed structures of the wind-ISM shock interactions, from which conditions local to the wind-ISM system can be investigated. I would like to highlight some recent findings.

172009-07-31 Fri
14:00~15:00
R716
Dr. Makoto Inoue
[ASIAA]
Very Long Baseline Interferometry (VLBI) in ASIAA (part I)
Abstract

We are planning to initiate a VLBI project in ASIAA. Two main streams under consideration are sub millimeter VLBI and space VLBI. Both have been approaching to super massive black hole (SMBH) and its vicinity by the superb spatial resolutions. Hopefully we will see a shadow of SMBH against bright accretion disk within a few years, which presumably enables us to study physics on black hole with General Relativity, accretion flow mechanism onto disk, and the formation mechanism of relativistic jets. In this talk of Part I, brief introduction on VLBI system and general idea of VLBI works in ASIAA are given.

182009-07-28 Tue
14:00~15:00
R716
Prof. Charles Liu
[American Museum of Natural History]
Galaxy Evolution At The Faint End Of The Luminosity Function
Abstract

We have examined the faint-end slope of the rest-frame V-band luminosity function (LF), with respect to galaxy spectral type, of field galaxies with redshift z<0.5, using a sample of 80,820 galaxies with photometric redshifts in the Cosmic Evolution Survey (COSMOS) field. For all galaxy spectral types combined and separated, the faint-end slopes grow shallower with increasing redshift. The steepness of that slope at lower redshift could be qualitatively explained by large numbers of faint dwarf galaxies, perhaps of low surface brightness, which are not detected at higher redshifts. Some properties of one particular strongly evolving population, compact emission line galaxies, are presented in detail.

192009-07-27 Mon
14:00~15:00
R716
Dr. Marc Kuchner
[NASA Goddard Space Flight Center]
Reading the Signatures of Extrasolar Planets in Debris Disks
Abstract

An extrasolar planet sculpts the famous debris disk around Fomalhaut; probably many other debris disks contain planets that we could locate if only we could better recognize their signatures in the dust that surrounds them. But the interaction between planets and debris disks involves both orbital resonances and collisions among grains and rocks in the disks---difficult processes to model simultaneously. I will describe new 3-D models of debris disk dynamics that incorporate both collisions and resonant trapping of dust for the first time, allowing us to decode debris disk images and read the signatures of the planets they contain.

202009-07-17 Fri
14:00~15:00
R716
Dr. Rowin Meijerink
[Caltech]
Radiative transfer modeling on AU-scales of mid-infrared water lines from protoplanetary disks
Abstract

The material that formed the present-day Solar System originated in feeding zones in the inner solar disk located at distances within ∼ 20 AU from the Sun, known as the planet-forming zone. Meteoritic and cometary material contain abundant evidence for the presence of a rich and active chemistry in the planet-forming zone during the gas-rich phase of Solar System formation. It is a natural conjecture that analogs can be found among the zoo of protoplanetary disks around young stars. The study of the chemistry and dynamics of planet formation requires 1) tracers of dense gas at 100-1000 K and 2) imaging capabilities of such tracers with 5-100 (0.5-20 AU) milli-arcsec resolution, corresponding to the planet-forming zone at the distance of the nearest star-forming regions. We show that the rich infrared (2-200 micron) molecular spectrum recently found to be common in protoplanetary disks represents such a tracer and thus offers a unique opportunity for constraining both the structure and chemistry of planet-forming regions, beginning with current infrared imaging spectrometers and extending to the next generation of Extremely Large Telescopes and beyond. We have developed a set of non-LTE radiative transfer tools specifically designed to simulate mid-infrared line imaging observations with present and future facilities. The toolset is applied to spectroscopic observations of water vapor in protoplanetary disks with the Spitzer Space Telescope to show that the water vapor abundance in the disk surface must be truncated beyond ∼ 1 AU, in excess of what is possible with static chemistry models. We speculate that the depletion of water is due to vertical turbulent diffusion of water from the superheated surface to regions below the snow line, where the water can freeze out and settle to the midplane as part of the general dust settling. We suggest that such a vertical cold finger effect will be efficient due to the lack of a replenishment mechanism of water to the surface.

212009-07-03 Fri
14:00~15:00
R716
Prof. Li-Yong Zhou
[Nanjing University]
Dynamics of Neptune Trojans
222009-06-19 Fri
14:00~15:00
R716
Dr. Rosie Chen
[University of Virginia]
Massive Star Formation in HII Complexes in the Large Magelllanic Cloud
Abstract

Recent Spitzer mid-IR observations have revealed a large number of individually resolved massive young stellar objects (YSOs) in the Magellanic Clouds (MCs), providing an excellent opportunity to study massive star formation with metallicity and galactic environment different from the Milky Way. We use the HII complexes N44 and N159 in the Large Magellanic Cloud (LMC) to perform a detailed study of star formation in a mild starburst, as they not only contain a large number of YSOs, but also host regions of star formation at different evolutionary stages and are not as complicated and confusing as the 30 Doradus giant HII region. We have used Spitzer IRAC and MIPS observations and complementary ground-based uBVIJK observations to identify candidate massive YSOs in these two HII complexes. We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our sample of YSO candidates in N44 and N159, more than half of them are resolved into multiple components or extended sources in high-resolution ground-based images. We have modeled the SEDs of YSOs that appear single or dominant within a group. We find good fits for Types I and I/II YSOs, but Types II and II/III YSOs show deviations between their observed SEDs and models that do not include PAH emission. We have also found that some Type III YSOs have central holes in their disk components. YSO counterparts are found in ultracompact HII regions and their stellar masses determined from SED model fits are compared with those estimated from the ionization requirements of the HII regions. The distribution of YSOs is compared with those of the underlying stellar population and interstellar gas conditions to illustrate a correlation between the current formation of O-type stars and previous formation of massive stars. Evidence of triggered star formation is also presented.

232009-06-18 Thu
14:00~15:00
R716
Dr. Stephane Guilloteau
[Laboratoire d'Astrophysique de Bordeaux]
Searching for disk dissipation
Abstract

Identifying the proto-planetary disk dissipation mechanisms is an important step towards understanding the planetary system formation process and the variety of planetary systems produced. Accretion onto the star, viscous spreading of the disk, planet formation and photo-evaporation are among the main processes contributing to the disk disappearance. I will present some examples of attempts to pinpoint which process dominates from mm observations of a few disks. I will focus on two recent findings - the role and nature of inner cavities found in disks - using CO as a potential tracer of disk dissipation

242009-06-16 Tue
14:00~15:00
R716
Dr. Darek Lis
[Caltech]
Herschel/HIFI: A Window to the Molecular Universe
Abstract

The Herschel Space Observatory, the fourth ESA `cornerstone’ mission, will be launched in April 2009. With a 3.5 m primary mirror, it will be the largest submillimeter space telescope. The Heterodyne Instrument for Far Infrared (HIFI) will cover the wavelength range 625—157 ìm. With its wide instantaneous IF bandwidth, high frequency resolution and near-quantum noise limit sensitivity, it will allow detailed studies of the chemical composition, physical conditions, and kinematics of ISM sources. Unbiased spectral line surveys over the full HIFI frequency range will be carried out in a number of ISM sources, providing the complete molecular census of these regions. Submillimeter wavelengths give access to high-energy transitions, excited in the immediate vicinity of newly formed stars, where molecules evaporating from grain mantles drive rich high-temperature chemistry. HIFI will also provide access to important classes of interstellar molecules that cannot be observed from the ground, including fundamental transitions of most hydrides and ro-vibrational transitions of carbon chains and rings. Transitions of light hydrides and deuterides can be studied, by means of absorption spectroscopy against bright continuum emission from high-mass star-forming regions, in foreground clouds with diverse properties and visual extinction values. Some chemically complex molecules, such as C3 and c-C3H2 have been detected in the diffuse ISM, and studies of diffuse clouds are of great interest for understanding initial steps of the interstellar chemistry. Key hydrides and deuterides containing the heavy elements C, N, O, F, and Cl will be observed with HIFI. These observations will address the role of high-temperature, non-equilibrium reactions in the formation of interstellar molecules, and the question of how such reactions are driven. They will also improve our understanding of the role of grain-surface reactions in formation of interstellar molecules and the growth of large carbon chains, bridging the gap between molecules and aggregates.

252009-06-05 Fri
14:00~15:00
R716
Dr. Tze-Yang Lee
[University of Tennessee]
2D Core Collapse Supernova Simulations with the CHIMERA code
Abstract

Even after four decades of effort, the numerical simulation of core collapse supernova still pose one of the most fascinating and challenging problems in astrophysics. “CHIMERA” is a multi-physics and multi-dimensional code developed to simulate core collapse supernovae. It is composed of three major modules, which describe different physical process: hydrodynamics, neutrino transport, and nuclear reaction network. The ORNL supernova group has performed a series of 2D core collapse simulations by the CHIMERA code. I will discuss the results of these simulations.

262009-05-26 Tue
14:00~15:00
R716
Dr. Darren Reed
[Los Alamos National Lab]
Uncloaking the dark universe with cosmological numerical simulations
Abstract

I will discuss what can cosmological numerical simulations help us to learn about structure formation from the epoch of the first galaxies to the present day, in the context of decrypting the nature of dark matter and dark energy. The galaxies and clusters that we observe in the universe form within the gravitational potential wells of dark matter structures (halos), whose growth is driven by gravitational instability. The numbers, distribution, and internal structures of dark matter halos extracted from simulations can probe dark matter and dark energy. For example, the cluster mass function and its evolution are sensitive to the properties of dark energy. However, large substructures within many clusters present a challenge for determining cluster mass. On smaller scales, within galaxy halos, the properties of the dark matter particle could have many observable consequences, including the numbers of luminous satellites, the distribution of central dark matter, and the theorized dark matter annihilation signal. One difficulty is that the small scale distribution of dark matter within galaxies may be affected profoundly by the interplay via gravity between baryons and dark matter as gas cools and contracts to form stars and galaxies, especially at early times. Thus, in order to understand the dark universe, it will be essential to model structure and galaxy formation starting from the epoch of the ``first'' galaxies.

272009-05-14 Thu
14:00~15:00
R716
Dr. Leonid .I. Gurvits
[Joint Institute for VLBI in Europe, The Netherlands]
Square Kilometre Array, the radio telescope of the XXI century and its space science frontier
Abstract

The Square Kilometre Array (SKA) is a global international project aimed at constructing a next generation radio telescope. After full completion, the telescope will operate at frequencies from several hundred megahertz to tens of gigahertz. I will discuss scientific drives which define the set of engineering requirements to the SKA. I will also present several ongoing radio astronomy research projects which can be considered as an “SKA precursory science” in the very different domains ranging from cosmological to the studies of the Solar System. The coming two decades will see a burst of space and planetary science missions including cosmological and astrophysical telescopes positioned in the Sun-Earth L2 point and a fleet of planetary probes and missions to Mercury, Venus, Mars, outer planets and their satellites. In all these missions a multi-facet support from SKA would greatly enhance the mission scientific return. Although not among the SKA Key Science themes, the SKA-based research in the planetary science area will deliver high-impact results. For example, SKA-based tracking of planetary probes during their approach to and landing on the surface of planets will yield an extremely valuable “health-check” of the spacecraft and scientific measurements beyond ability of the present and prospective “standard” deep space tracking facilities. Such the experiments proved to be highly rewarding even with much less sensitive than SKA present day radio telescopes and their networks. VLBI tracking of planetary probes involving SKA will provide an unprecedented combination of sensitivity and angular resolution, bypassing any other methods of estimating state vectors of planetary probes. In addition, SKA will enable Direct-to-Earth (DtE) data delivery of the mission-critical information as a back-up to the nominal data transmission schemes with relaying the data via orbiters and fly-by spacecraft. I will emphasise those scientific applications of SKA to the space and planetary science missions scheduled for in-situ operations in the 2020’s, during the first decade of the SKA life.

282009-04-30 Thu
14:00~15:00
R716
Dr. Chih-Hao Li
[Harvard]
Astro-comb, a novel tool in the search for exo-Earths
Abstract

The long term goal is to search for Earth-like extrasolar planets. Searches for exoplanets using the periodic Doppler shift of stellar lines have recently achieved a precision of 60 cm/s which is sufficient to find a 5 Earth-mass planet in a Mercury-like orbit from a Sun-like star. In order to find a 1-Earth-mass planet in an Earth-like orbit, a precision of 5 cm/s is necessary. An approach that combines a laser frequency comb with a Fabry-Perot cavity has been suggested as a promising approach. In this talk, I report the successful operation of such a laser comb ("astro-comb") with up-to-40 GHz (~1 A) line spacing, generated from a 1-GHz source, without compromise of long-term stability, reproducibility and resolution, at the Whipple Observatory. This astro-comb is well matched to the resolving power of the TRES, the high-resolution astrophysical spectrograph for the Tinglinghast telescope. The astro-comb should allow more than a 10-fold improvement in Doppler-shift sensitivity, with significant impact to many fields, including the search for extra-solar Earths and the direct measurement of the universe expansion.

292009-04-24 Fri
14:00~15:00
R716
Dr. Patrice Theule
[Universite de Provence]
Low-temperature thermal reactions on interstellar ices
Abstract

Different types of chemical reactions are occurring in interstellar ices. New and more complex molecules are formed and eventually desorbed into the gas phase when the ice is submitted to energetic processes, thermal or not. This is especially the case in star formation regions. I will give three examples of thermal reactions occurring at low temperature and correlate the work done in laboratory with IR spectra taken by ISO or Spitzer.

302009-04-23 Thu
15:30~16:30
R716
Dr. Wei Zheng
[Johns Hopkins University]
Search for the Youngest Galaxies via Cosmic Lens
Abstract

We have carried out an extensive search for i- and z-band dropouts in approximately two dozens of cluster fields with deep ACS, NICMOS and ground-based near-infrared imaging data. The gravitational lensing effect in these clusters amplifies the distant objects behind them, enabling us to find bright galaxies at z~6-8 that are otherwise extremely faint. We discuss three interesting cases of our findings and compare the results with GOODS and UDF. Cluster lensing will be effective in searches for bright galaxy candidates for spectroscopy with future large telescopes such as JWST.

312009-04-03 Fri
14:00~15:00
R716
Dr. Mike Cai
[ASIAA]
X-winds: A Fragile Truce
322009-03-16 Mon
12:00~13:00
R716
Prof. Masanori Iye
[NAOJ]
High redshift galaxy survey, laser guide star adaptive optics, and extremely large telescope
Abstract

Let me talk on three subjects in an informal way. First I would like to make a brief review on the current status of high redshift galaxy surveys and their implications regarding the cosmic re-ionization. Second will be a status report on the development of Subaru laser guide star adaptive optics system and some science objectives. Finally, touched on will be the extremely large telescope projects which will come true in the next decade. Let's think about our future.

332009-02-20 Fri
14:00~15:00
R716
Prof. Keiichi Wada
[NAOJ]
Intrinsic Structures of "Galactic Shocks" and Origin of Spiral Arms
Abstract

I am going to talk about our recent 3D hydrodynamic simulations on ``Galactic spiral shocks'', in which self-gravity of the ISM, radiative cooling, and star formation followed by energy feedback from supernovae are considered. This is an essential improvement over previous numerical models, or analytic solutions. We found that the classic galactic shock solutions (Fujimoto 1968; Roberts 1969 are unstable and transient, and they shift to a globally quasi-steady, inhomogeneous pattern due to the nonlinear development of instabilities. I will also show new results from our project for modeling spiral galaxies and our Galaxy using self-consistent N-body/gas simulations.

342009-02-12 Thu
14:00~15:00
R716
Prof. Leo Blitz
[UC Berkeley]
The Odd Dark Matter Halo of the Milky Way
Abstract

Recent all sky surveys of atomic hydrogen in the Milky Way have made it possible to reevaluate the surface density, the warp and the thickness of the neutral gas layer with unprecedented accuracy. As a result it is possible, for the first time, to trace the spiral arms out to the edge of the gas disk, and to show that the warp is well described by the superposition of three and only three bending modes. To make sense of the HI distribution, it is necessary to ascribe an significant asymmetry to the dark matter halo of the Galaxy. The magnitude of this deviation from axisymmetry is a noteworthy constraint to simulations of the growth of structure in the Universe.

352009-02-11 Wed
14:00~15:00
R716
Prof. Ed Churchwell
[Univ. of Wisconsin]
A New View of the Galaxy: The GLIMPSE Survey
362009-02-11 Wed
15:30~16:30
R716
Prof. Richard Crutcher
[UIUC]
Testing Star Formation Models with Observations of Magnetic Fields
Abstract

In this talk, I report the results of two very recent studies to test the strong and weak magnetic field models of star formation and determine observationally which dominates the star formation process. One study is the measurement of the differential mass/flux ratio between cloud envelope and core. Ambipolar diffusion requires that this ratio increase from envelope to core, while turbulent simulations usually show a decrease. The comparison of GBT and Arecibo telescope measurements of the Zeeman effect in OH toward dark cloud cores has given a clear result for this test. Two, the problem with Zeeman measurements in general is that only the line-of-sight component B(los) of the total magnetic vector B(total) can be measured. A Bayesian analysis of a set of 141 H I, OH, and CN Zeeman measurements of the line-of-sight component B(los) has provided clear information about the probability density function (pdf) of the total strength B(total) of the magnetic vector and its scaling with density. This Bayesian study also provides a clear test to distinguish between the two models of star formation. The results of these new observations and analyses will be described and the implication for ambipolar diffusion versus turbulence discussed. Finally, I will consider future observations with new instruments that promise to further advance our understanding of the role of magnetic fields in star formation.

372009-01-20 Tue
13:30~14:30
R716
Dr. Kevin Xu
[IPAC/Caltech]
Local Benchmarks for Evolution of Major-Mergers -- Binary Galaxies in 2MASS
Abstract

It has been suggested that the strong decline of the cosmic star formation rate (SFR) since z=1 is mostly due to the evolution of star formation associated with galaxy interactions/mergers. However, this has been challenged in recent literature. A quantitative constraint on the evolution of interaction-induced star-formation in the universe is very important for future development of the galaxy evolution theory. In this talk, I will present a study on samples of nearby close major-merger pairs of galaxies selected from the 2MASS database in K-band. This is to provide a highly accurate and unbiased local (z=0) benchmark for studies on evolution of interacting galaxies.

382009-01-16 Fri
14:00~15:00
R716
Dr. Ekaterina Koptelova
[NCU]
Variability study of lensed quasars
Abstract

The quasar lensing is now regarded to be a powerful tool in astrophysical studies. The main information is obtained from the brightness variations of the quasar images at different epochs and wavebands. Since the time needed for the light to travel from the source to the observer is different for different images, brightness variations intrinsic to the quasar are seen at different moments in each image. The time delay between the detection of the brightness variations in quasar images is directly related to the Hubble parameter. These time delays are determined from the cross-correlation analysis of accurate and well-sampled light curves of quasar images. The lensed quasars may also exhibit photometric variability associated with microlensing by the compact objects located in the lensing galaxy. Microlensing-induced variability can help to study the physical properties of the lensing galaxy and quasar. Analysis of the microlensing light curves in several bands can be used to constrain the size and energy profile of the quasar accretion disk.

392009-01-15 Thu
14:00~15:00
R716
Dr. Chaitra Narayan
[None]
Vertical equilibrium in a disk galaxy
Abstract

The stars and gas in a disk galaxy settles down into equilibrium distribution along the vertical direction because of two opposite forces – gravity and pressure. We study a disk under vertical equilibrium to basically calculate its scale height using a semi-analytic method. The scale height of atomic hydrogen gas particularly at large distances from the galactic centre is sensitive to external gravitational force. So it was used to study dark matter distribution or in general, the laws of gravity in our Galaxy. I would also like to outline a proposal where a galaxy's light distribution and its rotation curve can be used to put a constraint on the mass of its central super massive black hole, by modeling vertical structure of the disk. Finally, I would briefly mention other interesting issues that can be investigated under vertical equilibrium.

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.