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Activity > Colloquium

Colloquium (2013)

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
12013-12-27 Fri
14:20~15:20
R1203
Rosie Chen
[Max-Planck-Institut für Radioastronomie]
*Special Seminar*
Spatially and temporally resolved star formation relation and pattern in HII regions in the Galaxy and the Magellanic Clouds
22013-12-25 Wed
14:20~15:20
R1203
Masanori Nakamura
[ASIAA]
Approaching the Speed Limit: Discovering A Powerful Jet Acceleration from the Supermassive Black Hole in M87
Abstract

In 1966 M. Rees predicted that "an object moving relativistically in suitable directions may appear to a distant observer to have a transverse velocity much greater than the speed of light". Just a few years later in 1969, our curiosity became evident; J. Gubbay and others obtained a first indication of "superluminal motions" in quasars by VLBI observations. They are now widely recognized as highly relativistic outflows, initiated around the black holes/neutron stars, exhibit apparent velocities faster than light, when they align within a small viewing angle along the line of sight. "How can the flow obtain such an extremely fast speed?" is one of big unanswered questions that high-energy astrophysicists have been facing for over 40 years. We finally solve this puzzle with EVN observations towards M87 with the confirmation that an asymptotic acceleration of streaming take places from 1% to 99% of the speed of light. We conclude that the six billion solar mass black hole produces a magnetic jet exhaust nozzle, extending up to the host galaxy scale over 10^5 Schwarzschild radius. Our result constitutes a solid foundation of the magnetohydrodynamic paradigm for astrophysical jets.

32013-12-16 Mon
14:20~15:20
R1203
Aravind Natarajan
[University of Pittsburg]
*Special Seminar*
Searching for Dark Matter through Radio Observations: Present and Future
Abstract

It is now commonly accepted that most of the matter in the Universe is dark, but its identity is unknown. Weakly Interacting Massive Particles are well motivated candidates for dark matter. I will review the status of dark matter detection using direct, and collider searches. I then discuss two promising techniques for dark matter detection using radio observations: (i) Searching for excess synchrotron radiation from dwarf galaxies in the local group, and (ii) Observations of the highly redshifted 21cm line of neutral Hydrogen. I discuss recent results from the SCI-HI global 21cm experiment and future prospects.

42013-12-09 Mon
13:30~14:30
R1203
Yoshihide Kozai
[NAOJ]
*Special Seminar*
So-called Kozai Mechanism
Abstract

The so-called Kozai mechanism was formulated to understand the secular perturbations of asteroids with arbitrary eccentricity and inclination. And some dynamical difference between asteroids and comets did show up by this theory. As the potential field is that of axial symmetry, the results can be applied to any case in the same type of the potential field. In this talk I will show some examples which can be allied by this mechanism as well as some not to be applied by this.

52013-12-04 Wed
14:20~15:20
R1203
Ralph Pudritz
[Origins Institute, and Dept. of Physics and Astronomy, McMaster University.]
The early evolution of disks, jets, and protostellar spins
Abstract

The formation of disks and outflows as a consequence of the collapse of dense, magnetized, molecular cloud cores is a central problem in star formation. Collapse in a magnetized medium holds a major surprise in that magnetic braking by an ordered field can strongly surpress disk formation. A related question is why the spin rates of many young stars are so low despite their high accretion rates. How is the angular momentum problem of young stars resolved? This talk traces the early evolution of collapsing magnetized cores through the formation of disks, outflows, and accretion-powered stellar winds means by which the angular momentum problem of star formation is resolved.

62013-12-03 Tue
14:20~15:20
R1203
Robert Williams
[STScI]
*ASIAA/NTU Joint Colloquium*
Hubble Space Telescope: Piecing Together the Evolution of the Universe
Abstract

In orbit for 23 years and still operating well, in planning and development for 15 years before that, HST---at $7.5 billion---has been the most expensive scientific project in history until CERN’s LHC. It’s unique features of high spatial resolution, ultraviolet sensitivity, and low sky background together with its unified, well calibrated, publicly available data archive have produced many notable astronomical discoveries. Highlights of Hubble Telescope’s scientific mission will be discussed in the context of processes that have been key to our current understanding of the evolution of the universe from the earliest times to the present epoch. These include gravitational lensing, the Hubble deep fields which have revealed early galaxy formation, galaxy mergers that form black holes, and the initial attempts of analysis of the atmospheres of planets around other stars.

72013-11-27 Wed
14:20~15:20
R1203
Angela Speck
[University of Missouri]
Cosmochemistry & Astromineralogy: from the Big Bang to Life
Abstract

At the beginning of the Universe, all matter was in the form of hydrogen and helium: all elements bigger than helium form via nuclear fusion in stars. These newly-formed elements are ejected from stars either explosively (in the case of supernovae) or more gently over a few hundred thousand years for lower mass star like the sun. These new elements then become part of the interstellar medium, from which new stars and their planets form. Dust is a vital ingredient in understanding many astrophysical processes. It is an essential part of star formation processes; it is the key to understanding mass loss from aging stars; and it contributes to several aspects of interstellar processes such as gas heating and the formation of molecules. Such a crucial and ubiquitous constituent of our Universe needs to be well understood in its own right, if we are to understand its contributions to many aspects of astrophysics. Intermediate-mass stars (0.8-8.0 solar masses) are major contributors of new elements to interstellar space. These stars eventually evolve into asymptotic giant branch (AGB) stars. During the AGB phase, these stars suffer intensive mass loss leading to the formation of circumstellar shells of dust and neutral gas, including the new elements formed during the star's life. Using a combination of observing techniques (e.g. infrared (IR) spectroscopy, visible, IR and sub-mm imaging) and laboratory IR studies, combined with theoretical considerations (e.g. kinetics and thermodynamics of the dust-forming region; nucleosynthesis models and changing stellar chemistries) and meteoritic evidence, I will investigate the structure and evolution of the circumstellar dust and its environment.

82013-11-19 Tue
14:20~15:20
R1203
Tsz Yan Lam
[MPA]
*Special Seminar*
Eulerian-Void Assignment and its application in modified gravity model
Abstract

Void would be considered the underdenese analogy of massive halos and would constrain cosmological models. I will first discuss the recent development of a new algorithm to assign Eulerian void in the framework of the excursion set approach. I will then describe its application to modified gravity models, which has a distinctive feature compared to the statistics using massive halos.

92013-11-13 Wed
14:20~15:20
R1203
Martha Boyer
[GSFC]
Towards Characterizing AGB Stars in the Magellanic Clouds
Abstract

When low- to intermediate-mass stars (0.8 < M < 8 M_sun) begin to ascend the asymptotic giant branch (AGB), pulsations levitate material from the stellar surface and provide density enhancements and shocks, encouraging dust formation and re-processing. This dust is subsequently released to the interstellar medium via a strong stellar wind driven mainly by radiation pressure on the grains. This dusty stellar wind causes AGB stars to radiate strongly in the near- to mid-infrared, potentially affecting measurements of star-formation histories of distant galaxies at these wavelengths. The Spitzer Surveying the Agents of Galaxy Evolution (SAGE) survey of the Magellanic Clouds produced the first large-scale unbiased infrared observations of a large sample of AGB stars, enablng investigations into the dust production, the stellar evolution, and the luminosity contribution from these important stars. I will discuss some of the the SAGE AGB findings, and how the lessons from SAGE are being applied to investigations of AGB stars in other galaxies.

102013-11-12 Tue
14:20~15:10
Room 104, CCMS-New Physics Building
Ue-Li Pen
[CITA]
*ASIAA/NTU Joint Colloquium*
astrophysical tests of quantum gravity
Abstract

I discuss possible observational consequences of quantum black holes. This year, the first pulsar in orbit about a black hole was discovered. We argue that some solutions to Hawking's information loss problem, for example fuzzballs, may result in changes of lensed pulsar coherence, analogous to the Aharonov-Bohm effect. We speculate on future experimental technologies which may improve the observational prospects.

112013-11-01 Fri
14:00~15:00
R1203
Nick Kaiser
[University of Hawaii]
*Special Seminar*
Gravitational Redshifts in Clusters of Galaxies
Abstract

Wojtak, Hansen and Hjorth (Nature, 2011) have measured the long-predicted gravitational redshifts in galaxy clusters using Sloan Digital Sky Survey data. The effect is very small, corresponding to a velocity shift of only ~10 km/s in clusters with internal random motions ~600 km/s) but is in good agreement with general relativity predictions and possibly in conflict with some alternative gravity theories. Zhao, Peacock and Li (2012) showed there should also be a competing special relativistic effect - the transverse Doppler (TD) effect - of similar magnitude. In this talk I will describe how there are two more kinematic effects that need to be considered in interpreting these observations; a `light cone' effect that augments the TD shift and a competing effect caused by modulation of the surface brightness of galaxies by relativistic beaming. I will discuss how these observations constrain gravitation theory, and I shall also discuss some matters of principle concerning the interpretation of astronomical redshifts in a broader context.

122013-10-30 Wed
14:00~15:00
R1203
Chris Lintott
[University of Oxford]
The shape of galaxy evolution - Morphology in the age of Galaxy Zoo
Abstract

Despite the advent of large surveys, morphology remains an important diagnostic for studies of galaxy evolution and formation. Since 2007, the Galaxy Zoo project (http://www.galaxyzoo.org) has collected more than 250 million independent classifications of galaxies from both the Sloan Digital Sky Survey and large Hubble Space Telescope surveys, and in this seminar project Principle Investigator Chris Lintott will review the results, emphasizing the use of morphology to distinguish between secular and merger-driven evolution. Unusual objects discovered by Galaxy Zoo such as Hanny's Voorwerp, a quasar light-echo, have also provided a chance to study the evolution of AGN almost as it happens.

132013-10-29 Tue
14:00~15:00
R1203
Geoffrey Bower
[UC Berkeley]
*Special Seminar*
The Onset of Molecular Gas: CO Intensity Mapping
Abstract

Molecular gas is a poorly understood but vital component of galaxy evolution. New tools such as ALMA and EVLA are making impressive characterizations of the gas in the most massive galaxies at high redshift. But lower mass galaxies, which ultimately evolve into galaxies like the Milky Way, are undetectable through individual pointings. Intensity mapping, or the detection of aggregate emission of large angular scales, is a powerful tool for characterizing the molecular gas in low mass galaxies. I will describe our campaign using data from the SZA to detect CO at z=3 and our plans to detect molecular gas to greater redshift using the SZA, AMiBA, and new instruments.

142013-10-22 Tue
11:00~12:00
R1203
Kent D. Irwin
[Department of Physics, Stanford University, Stanford, CA 94305, USA]
*Special Seminar*
Cosmology with superconducting detectors
Abstract

Superconducting microwave detectors and polarimeters are now widely used to constrain cosmological parameters and to search for physics beyond the standard model, including inflation and neutrino mass. Measurements of the polarziation of the CMB are used to search for the signal of primordial gravitational waves, and to probe structure evolution through lensing of the CMB. Galaxy clusters are studied through the inverse Compton scattering of CMB photons off of the hot plasma in the intra-cluster medium. I will describe our work developing instruments for cosmological measurements with the CMB, including the Atacama Cosmology Telescope, the South Pole Telescope, and the MUSTANG instrument on the Green Bank Telescope.

152013-10-18 Fri
15:00~16:00
R1203
Doug Johnstone
[JCMT]
The Evolution of Star-Forming Cores in Molecular Clouds: Using Theoretical Models to Inform the Observations
Abstract

I will discuss both the observational constraints on (star-forming) cores within molecular clouds and theoretical considerations as to how these cores might form and evolve. Special consideration will be given to the notion of massive pre-stellar cores and in particular the observability of these objects. The expectation of time-dependent accretion onto deeply embedded protostars will be discussed and the observability of these fluctuations will be detailed. The importance of both single-dish sub-millimetre telescopes for large-scale surveys and interferometers for detailed high angular resolution investigations will be emphasized.

162013-10-09 Wed
14:00~15:00
R1203
Matthias Maercker
[University of Bonn]
Unwinding the secrets of thermal pulses and sculpted winds in AGB stars with ALMA
Abstract

I will present ALMA Cycle 0 observations of the CO emission around the carbon AGB star R Sculptoris. The observations show the detached shell and circumstellar medium around this star in unprecedented detail, and demonstrate the power of ALMA already during the first cycle of operations. The detached shell is formed due to the change in mass-loss rate and expansion velocity during a thermal pulse. Amazingly, the data also reveal a clear, and previously unobserved, spiral structure within and connected to the detached shell, indicating the presence of a companion star or high-mass planet. Combined with 3-dimensional hydrodynamical models, we for the first time set direct observational constraints on the changes in mass-loss rate and expansion velocity during and after a thermal pulse. By modelling the stellar wind from a binary system, we show that the observed spiral constrains the mass-loss rate and expansion velocity, the duration of the pulse, and the companion mass. The results imply a change in pulse to post-pulse mass-loss rate by a factor of 30, and a gradual decrease of the expansion velocity. We are thus able to uncover the record of mass-loss throughout the thermal-pulse cycle in unprecedented detail. The results usher in a new paradigm in our understanding of this fundamental period of stellar evolution, and the implications it has for the chemical evolution of evolved stars, the ISM, and galaxies.

172013-10-08 Tue
14:20~15:10
Room 104, CCMS-New Physics Building
Gil Holder
[McGill University]
*ASIAA/NTU Joint Colloquium*
The Cosmic Microwave Background in High Definition
Abstract

High resolution studies of the cosmic microwave background provide new views on neutrinos, dark energy, and cosmological structure formation. This new information comes through an improved understanding of the primary fluctuations imprinted in the early universe, as well as through measurements of the effects of Compton scattering and gravitational lensing by structure in the late universe. I'll report results from the South Pole Telescope, including a recent detection of the characteristic "B-mode" pattern of polarized fluctuations that is caused by gravitational lensing.

182013-10-07 Mon
14:00~15:00
R1203
Gil Holder
[McGill University]
*Special Seminar*
Mapping Dark Matter on the Largest and Smallest Scales
Abstract

I'll talk about two different gravitational lensing projects based on mm-wave data. It is now possible to map dark matter on degree scales over large areas of sky through the gravitational lensing of the cosmic microwave background, allowing new constraints on the clustering of matter and the relation between galaxies and mass. At the other end of the spectrum (on small scales), there are now large samples of galaxy-scale multiple-image gravitational lenses observed with ALMA. It should now be possible to use these lens systems to detect small-scale substructure in the dark matter halos of the lensing galaxies and establish whether the small-scale features in galactic dark matter are consistent with the predictions of cold dark matter.

192013-10-02 Wed
14:00~15:00
R1203
Lia Athanassoula
[LAM]
Bar formation and evolution: What do they depend on?
Abstract

Bar formation and evolution are strongly coupled to the redistribution of angular momentum within the galaxy. But what determines the amount of angular momentum exchanged? The latter is linked to a multitude of galaxy properties, such as the mass and velocity distributions in the disc, the halo, and, whenever relevant, the bulge, as well as the gas component and external accretion. I will discuss how each of these influences bar formation and evolution and whether and how one can obtain in simulations realistic bars and the multitude of corresponding morphological features. I will also discuss the inverse problem, i.e. how one can use bar properties to set constraints on some basic galaxy properties.

202013-09-27 Fri
14:00~15:00
R1203
Edwige Chapillon
[ASIAA]
Study of Protoplanetary disks thanks to molecular lines observations.
Abstract

Understanding the structure and evolution of disks surrounding young low-mass stars is one of the key issues to study the process of planet formation. Nevertheless the overall properties of those disks are not yet well constrained by observations. Observation of molecular lines is a useful tool to constrain the disks physical structure, as different molecules sample different physical conditions.. Beside the abundant CO, several other molecules have been detected in the outer part of the disks in the millimetre domain (e.g. HCO+, H2CO, CS, HCN, CN...). In this talk I will present results obtained with APEX and the IRAM telescopes. I will confront them to models of protoplanetary disks, in particular to the the layered structure that is predicted by all chemical model so far. Some recent ALMA outcomes will be also discussed. Study of Protplanetary disks thanks to molecular lines observations.

212013-09-13 Fri
14:00~15:00
R1203
Kouichi Hirotani
[ASIAA]
Towards a self-consistent theory of high-energy emission from pulsar magnetospheres
Abstract

In the high-energy and very-high-energy (VHE) regimes, the Fermi, VERITAS and MAGIC experiments have detected pulsed signals from the Crab pulsar up to 400 GeV. The light curves and the spectra obtained from the Crab and other rotation-powered pulsars, suggest that the gamma-ray pulsars have high-altitude emission zones, which avoid super-exponential cutoff due to magnetic pair production. I thus examine the outer-magnetospheric emission model from the basic equations for the first time and demonstrate that the model naturally explains Fermi observations such as the linear relation between their gamma-ray luminosity and the square root of the spin-down luminosity. I further apply this method to the Crab pulsar and reveal that its pulsed emission from IR to VHE can be reproduced, and give a caution on the Lorentz invariance violation tests using Fermi and VERITAS/MAGIC experiments.

222013-09-09 Mon
14:00~15:00
R1203
Stéphanie Jouvel
[Institut de Ciencies de l'Espai (IEEC-CSIC)]
*Special Seminar*
Current and future cosmological surveys: The challenges of photometric redshifts for gravitational lensing
Abstract

In this talk, I will start with an introduction on gravitational lensing and photometric redshift. I will present some of the recent results from the CLASH (Cluster Lensing and Supernovae with Hubble) survey and the Dark Energy Survey. Using what we learn from these surveys and past cosmological surveys, I will talk about survey strategy for future spectroscopic redshift campaign such as BigBOSS, DESpec and Euclid.

232013-09-06 Fri
14:00~15:00
R1203
Olivier Ilbert
[Aix Marseille Universite, CNRS, LAM (Laboratoire d'Astrophysique de Marseille)]
Photometric redshifts and stellar mass assembly in the COSMOS field
Abstract

A clear and comprehensive picture describing the physical processes which regulate the stellar mass assembly is still missing in galaxy formation scenario. Our study of the stellar mass assembly in the 2deg2 COSMOS field brings valuable clues on the physical processes at work during galaxy formation and evolution. Our analysis is based on 220,000 galaxies in the COSMOS field selected using the new UltraVISTA data release over 1.5 deg2. We derived precise 30-band photometric redshifts, with a precision better than 1% at I<22.5 and around 3% at 1.5

242013-08-28 Wed
13:30~14:30
R1203
Jamie Bock
[California Institute of Technology and Jet Propulsion Laboratory]
*Special Seminar*
Probing the Epoch of Reionization with Intensity Mapping
Abstract

Star formation during the epoch of reionization may be studied through measurements of intensity fluctuations in the redshifted 158 um line of singly ionized carbon. Intensity mapping is an attractive approach to measure galaxy clustering and its relation to underlying dark matter halos, without resolving individual galaxies with a large aperture telescope. The technique has had several notable successes in continuum band measurements with Planck and Herschel/SPIRE, and is also being used in the near-infrared with Spitzer, Akari and CIBER to study the components of the extragalactic background. The Tomographic Ionized-carbon Mapping Experiment (TIME) will measure 3-dimensional line intensity variations using a large focal plane array of mm-wave spectrometers, coupled to a wide-field dedicated 3 - 10 meter telescope. We are currently developing spectrometers lithographed on a compact silicon chip based on low-loss superconducting RF circuitry, similar to the antenna structures currently used in CMB polarimeters, that enables mass production for large spectroscopic throughput. We are also developing a precursor instrument named TIME-Pilot based on conventional spectrometer technology that can make a first detection of C+ fluctuations at predicted levels in a modest dedicated survey from the 10 meter Caltech Submillimeter Observatory.

252013-08-27 Tue
14:00~15:00
R1203
Asantha Cooray
[University of California, Irvine]
*Special Seminar*
Cosmology at Sub-mm Wavelengths: From Herschel to CCAT and Beyond
Abstract

I will summarize key science results obtained so far by two key programs that made use of the SPIRE instrument aboard the Herschel Space Observatory. These extragalactic surveys have uncovered close to a million dusty, starburst galaxies at redshifts of 1 to 5 with instantaneous star-formation rates out to several thousand solar masses per year in some cases. I will discuss properties of Herschel-selected bright and lensed sub-mm galaxies, their dust and molecular gas properties, the spatial clustering of bright and faint sub-mm galaxies, and the role of dusty starbursts in galaxy formation and evolution. I will discuss unresolved fluctuations as a way to study the fainter galaxies below the confusion limit. I will briefly introduce intensity mapping of sub-mm/far-IR spectral lines as a way to probe large-scale structure and the epoch of reionization and will end my talk with some discussion of future directions in sub-mm wavelength observations with ALMA, CCAT and SPICA.

262013-08-26 Mon
14:00~15:00
R1203
Olivier Doré
[JPL/Caltech]
*Special Seminar*
The Planck Satellite as a Large Scale Structure Survey
Abstract

Planck is the third-generation satellite aimed at measuring the cosmic microwave background, the oldest electromagnetic radiation in the Universe, coming to us from just 400,000 years after the hot big bang. Launched in May 2009, Planck has surveyed the full sky at high sensitivity and high angular resolution from 30 to 857 GHz. This broad frequency coverage gives Planck a unique view of the history of the Universe from the epoch of recombination to the present. I will present the Planck latest cosmological results, with an emphasis on Planck's sensitivity to the low redshift Universe through, e.g., the lensing of the cosmic microwave background.

272013-08-23 Fri
14:00~15:00
R1203
Naslim Neelamkodan
[ASIAA]
Discovery of extremely lead-rich hot subdwarfs: does heavy metal signal the formation of subdwarf B stars?
Abstract

Hot subdwarfs represent a group of low-mass helium-burning stars formed through binary-star interactions and include some of the most chemically-peculiar stars in the Galaxy. Stellar evolution theory suggests that they should have helium-rich atmospheres but, a majority are extremely helium poor because radiation causes hydrogen to diffuse upwards. The existence of spectroscopically different helium-rich subdwarfs poses several questions; are there distinct subgroup of hot subdwarfs, or do hot subdwarfs change their atmospheric composition during evolution. I will present the evolutionary status of hot subdwarfs both in single star and binary star systems and observational implications based on the discovery of extreme peculiar chemical signatures. Using optical spectroscopy we have reported two extreme lead rich stars in the Galaxy with 4 dex overabundances of lead relative to solar. The lead abundance is ten to 100 times that measured in normal hot subdwarf atmospheres from ultraviolet spectroscopy. The new observations are interpreted in terms of heavily stratified atmospheres and the general picture of a surface chemistry in transition from a new-born helium-rich subdwarf to a normal helium-poor subdwarf.

282013-08-16 Fri
14:00~15:00
R1203
Srinivasan Sundar
[ASIAA]
An inventory of hidden dust from extremely red evolved stars
Abstract

The injection of metal-rich material from dusty red supergiants (RSGs) and asymptotic giant branch (AGB) stars drives the chemical evolution of galaxies and the formation of the next generation of stars. It is therefore critical to constrain the dust budget from these evolved objects. Over the past few years, our group has used multi-wavelength information to estimate the total dust injection rate from RSG and AGB stars in the Magellanic Clouds. As part of our studies, we found that most of the dust (>75%) comes from a small fraction (~5%) of very dusty stars. However, the most evolved of these sources are so obscured by dust that they do not have optical or near-infrared counterparts. These extremely red objects (EROs) are thus only visible at mid-infrared and longer wavelengths. A preliminary analysis of the recently discovered extreme carbon stars in the Large Magellanic cloud (Gruendl et al. 2008) using archival Spitzer data from the SAGE program (Meixner et al. 2006) shows that these sources do indeed have very high dust production rates. The detection of such sources is therefore an important step in the determination of the dust budget. In this talk, I will summarise our work on the dust budget so far, and present our ongoing inventory of ERO candidates in the Large and Small Magellanic Clouds, as well as in M33. I will also discuss a possible search for these objects in our own Galaxy.

292013-08-02 Fri
14:00~15:00
R1203
Masaaki Otsuka
[ASIAA]
A search for fullerene C60 in Galactic Planetary Nebula
Abstract

Since their laboratory discoveries in 1985, particularly fullerene C60 have drawn considerable interest from astrochemists looking for them in interstellar conditions. Fullerenes are extremely stable and easily form in laboratories on the earth, so it had been thought that they should exist in interstellar space. However, the first confirmed detection of cosmic fullerenes was only recently reported in the C-rich planetary nebula (PN) Tc1. So far, C60 has been found in about 20 objects, however it is still unclear what kind of environment is required to formed C60 and how C60 is excited in the iterstellar scpace. To answer these questions, I have searched all the Spitzer and ISO data archival spectra of Galactic PNe since 2011 Nov. I will present recent results on my C60 PN study.

302013-07-31 Wed
14:00~15:00
R1203
Robert Laing
[ESO]
*Special Seminar*
Precision Jet Physics
Abstract

Relativistic jets are important in many areas of astrophysics: they are efficient particle accelerators, producing the highest-energy photons (and perhaps also cosmic rays) we observe; they are an inevitable consequence of accretion onto black holes, from which they efficiently extract energy, and they transport this energy to large distances, providing feedback in galaxies and clusters. After introducing the jet pheonomenon in its Galactic and Extragalactic manifestations, I will discuss the results of a long-term programme aimed at understanding the physics of large-scale jets in nearby radio galaxies. We model very deep, high-resolution VLA images in total intensity and linear polarization, exploiting the side-to-side asymmetries caused by special relativistic aberration to deduce their geometries and their variations of velocity, field structure and emissivity in three dimensions. We find that the jets decelerate and develop transverse velocity profiles as they entrain the surrounding insterstellar medium. We also show that ongoing particle acceleration is velocity-dependent and demonstrate the evolution of the magnetic field to a predominantly toroidal configuration. Finally, we deduce the mass, momentum and energy fluxes of the jets and estimate their energy input into their surroundings.

312013-07-26 Fri
14:00~15:00
R1203
Preeti Kharb
[Indian Institute of Astrophysics]
A Multi-wavelength Study of MOJAVE* Blazar Jets: Clues about their Emission Mechanisms
Abstract

I present the results of our recent and ongoing work on the deep radio (VLA), optical (HST) and X-ray (Chandra) imaging of blazar jets belonging to the MOJAVE sample. VLA imaging has revealed that blazar jets often have complex structures. Many of them are bent, show multiple hot spots and cannot be easily placed into the two primary Fanaroff-Riley categories. Multi-epoch monitoring with the VLBA has produced a comprehensive database of individual jet component speeds on parsec-scales. We have found a direct link between the jet speeds on parsec-scales and the radio lobe emission on kiloparsec-scales. Deep Chandra and HST observations of jets in selected MOJAVE blazars have indicated that the X-rays are produced via the inverse-Compton over CMB photon (IC/CMB) mechanism. However, the latest data on a hybrid morphology MOJAVE blazar suggest that the emission mechanisms may change along the length of the jet. I will briefly discuss the implications of our findings. *MOJAVE = Monitoring of Jets in AGN with VLBA Experiments

322013-07-22 Mon
14:00~15:00
R1203
Amy Lien
[GSFC]
*Special Seminar*
Probing the Cosmic Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope
Abstract

Understanding the intrinsic cosmic long gamma-ray burst (GRB) rate is essential in many aspects of astrophysics and cosmology, such as revealing the connection between GRBs, supernovae and stellar evolution. Additionally, GRB rate at high redshift provides a strong probe of star formation history in the early universe, which is hard to measure directly through other methods. Swift, a multi-wavelength space telescope, is quickly expanding the GRB category by observing hundreds of GRBs and their redshifts. However, it remains difficult to determine the true intrinsic GRB rate due to the complex trigger algorithm adopted by Swift. Current studies of the GRB rate usually approximate the Swift trigger algorithm by a single detection threshold. However, unlike the previously flown GRB instruments, Swift has over 500 trigger criteria based on photon count rate and additional image threshold for localization. To investigate possible systematic biases and explore the intrinsic GRB properties, we developed a program that is capable of simulating all the rate trigger criteria and mimicking the image trigger threshold. We use this program to search for the intrinsic GRB rate. Our simulations show that adopting the Swift’s complex trigger algorithm increases the detection rate of dim bursts. As a result, we find that either the GRB rate is much higher than previously expected at large redshift, or the luminosity evolution is non-negligible. We will discuss the best results of the GRB rate in our search, and their impact on the star-formation history.

332013-07-17 Wed
14:00~15:00
R1203
Mark Morris
[UCLA]
Past and Future Activity of the Galactic Black Hole
Abstract

An X-ray light echo now propagating through the central molecular zone of our Galaxy has revealed that a major X-ray flare took place there about 100 years ago. The high luminosity and the direction of propagation implicate the central supermassive black hole in our galaxy, which is presently very quiescent. I will discuss this evidence, and the outstanding possibilities for what might have caused this activity. This may not be a particularly rare event; a gaseous object -- possibly centered on a star -- is now plummeting toward the black hole on a highly eccentric orbit and is expected to supply new fuel for enhanced accretion activity during and after its passage through periapse in early 2014. I will present the view of this object from UCLA, based on data obtained at the Keck Observatory.

342013-07-15 Mon
14:00~15:00
R1203
Kaiki Inoue
[Kinki University]
*Special Seminar*
Probing dark matter with mini-gravitational lensing
Abstract

Recently, our group have shown that the MIR flux-ratio anomalies seen in some quadruple lens systems can be solely explained by the weak lensing effects caused by mini-halos and mini-voids in the line-of-sight. In our model, the number of halos and voids in the line-of-sight monotonically increases as a function of the source redshift, which are consistent with the observational trend. In literature, it has been postulated that the flux-ratio anomaly is mainly caused by subhalos in the lensing galaxy. Therefore, our findings may challenge this "standard" picture. Using our result, we would be able to put stringent constraints on the mass scale of dark matter particles that have a large free-streaming scale such as sterile neutrinos and super-WIMPs. In this talk, as an introduction, I review the physical mechanisms that are used for categorizing dark matter via structure formation and explain about the basics about gravitational lensing. Then I present recent results on the perturbation induced by line-of-sight mini-structures in quasar-galaxy quadruple lens systems. Finally, I briefly comment on the possible constraints on dark matter particles from our result and how we can distinguish these structures from subhalos in lensing galaxies in future observations.

352013-07-12 Fri
13:00~14:00
R1203
Robert Wittenmyer
[University of New South Wales]
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. Further observations from the Anglo-Australian Planet Search (AAPS) have revealed that some systems previously thought to contain a single, moderate-eccentricity planet are better fit by two planets on nearly-circular orbits. We have investigated apparent single-planet systems to see if the available data can be better fit by two lower-eccentricity planets. We identify nine promising candidate systems and perform detailed dynamical tests to confirm the stability of the potential new multiple-planet systems. In addition to the AAPS, 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. I then describe a plan for Minerva: an installation of four 0.7m telescopes feeding a high-resolution spectrograph, sited at Mt Hopkins in Arizona. Minerva will give exoplanetary scientists the ability to pursue dedicated radial-velocity searches for planets orbiting the nearest bright stars. In addition, a Southern hemisphere Minerva could be used to follow up on objects of interest from Antarctic telescopes such as the Chinese AST-3. I will describe the diverse science cases for this highly cost-effective facility. 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.

362013-07-05 Fri
14:00~15:00
R1203
Peter Capak
[Spitzer Science Center/Caltech]
What galaxy surveys tell us about galaxies, dark matter, and dark energy
Abstract

The field of extra-galactic astronomy is rapidly moving towards large multi-wavelength galaxy surveys such as DES, LSST, Hyper-Suprime-Cam, and Euclid which have the statistical power to measure the demographics of galaxy evolution, link galaxies to their underlying dark matter halos, and act as probes of dark energy. Back in 2003, the COSMOS survey was one of the first such large scale projects. Its data have been used in over 500 publications, and are now a prototype for Euclid, and other dedicated surveys that combine ground and space based data. I will give a summary of what COSMOS has taught us about galaxy evolution, the link between galaxy evolution and dark matter, and cosmology. I will conclude with what we expect to learn from the current generation of surveys that grew out of COSMOS such as the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH), and what we can expect from Euclid in a decade.

372013-06-28 Fri
14:00~15:00
R1203
Mar Mezcua
[Instituto de Astrofísica de Canarias (IAC)]
SUPERMASSIVE BINARY BLACK HOLE SYSTEMS
Abstract

It is widely accepted that galaxies are not isolated objects in the Universe, but are rather observed to undergo galaxy merging. If nearly all galaxies host a supermassive black hole in their center, it is expected that pairs of supermassive black holes will be formed in the course of a merger event. The detection and number estimates of binary black hole systems can, thus, help us to understand how galaxies form and grow, and shed light on the evolutionary models that rule the Universe. In this Colloquium I will present observational evidence for binary black hole systems in three kinds of extragalactic objects: X-shaped radio galaxies, ultraluminous X-ray sources, and double nucleus galaxies. I will detail our observations and analyses of these systems and the conclusions obtained when combined all observational data.

382013-06-20 Thu
14:00~15:00
R1203
M.B.N. (Thijs) Kouwenhoven
[Kavli Institute for Astronomy and Astrophysics, Peking University]
*Special Seminar*
The origin of wide binary star companions and wide planetary orbits
Abstract

Observations have revealed the presence of a significant population of wide (> 1000 AU) binary systems in the Galactic field and halo. In addition, planets in wide (> 100 AU) orbits have been detected. The origin of both of these populations is difficult to explain with theories of star formation and planet formation. We carry out N-body simulations of dissolving star clusters with a free-floating planet population, and show that dynamical capture processes can explain these wide orbits. Interestingly, the simulations also predict the existence of other peculiar systems, such as higher-order multiple systems, circumbinary planets, planets around black holes and white dwarfs, retrograde planetary orbits, and free-floating double planets.

392013-06-18 Tue
14:00~15:00
R1203
Christopher Reynolds
[University of Maryland]
*Special Seminar*
The Astrophysics of Black Hole Spin
Abstract

In addition to providing vital clues as to the formation and evolution of black holes, the spin of black holes may be an important energy source in the Universe. Over the past couple of years, tremendous progress has been made in the realm of observational measurements of spin. I will describe these efforts with particular focus on the use of X-ray spectroscopy to probe the spin of supermassive black holes in active galactic nuclei (AGN). For the first time, we are obtaining hints about the distribution of spins across the population of supermassive black holes with some interesting and unexpected consequences. After discussing spin, I will also address questions related to the driving of relativistic jets from AGN and the jet-disk connection.

402013-06-14 Fri
14:00~15:00
R1203
Freeke van de Voort
[ASIAA]
Feeding galaxies and their gaseous haloes
Abstract

Galaxies grow by accreting gas, which they need in order to form stars, from their surrounding haloes. These haloes, in turn, accrete gas from the intergalactic medium. Feedback from stars and black holes returns gas from the galaxy to the halo and can even expel it from the halo. Using cosmological simulations, I will describe this cycle of inflow and outflow, how it varies with redshift and halo mass, and its implications for star formation. I will then discuss the emission and absorption properties of the halo gas and show how to connect them to existing and future observations.

412013-06-07 Fri
14:00~15:00
R1203
Fred Adams
[University of Michigan]
Effects of Clusters on Star/Planet Formation and Possible Constraints on the Birth Environment of the Solar System
Abstract

Most stars -- and hence most solar systems -- form within groups and clusters. The first objective of this talk is to explore how these star forming environments affect solar systems forming within them. The discussion starts with the dynamical evolution of young clusters with N = 100 - 3000 members. We use N-body simulations to study how evolution depends on system size and initial conditions. Multiple realizations of equivalent cases are used to build up a robust statistical description of these systems, e.g., distributions of closest approaches and radial locations. These results provide a framework from which to assess the effects of clusters on solar system formation. Distributions of radial positions are used in conjunction with UV luminosity distributions to estimate the radiation exposure of circumstellar disks. Photoevaporation models determine the efficacy of radiation in removing disk gas and compromising planet formation. The distributions of closest approaches are used in conjunction with scattering cross sections to determine probabilities for solar system disruption. The result of this work is a quantitative determination of the effects of clusters on forming solar systems. The second objective of this talk is to use these results to place constraints on the possible birth environments for our own solar system. These latter results are more uncertain than the first ones, but provide interesting perspectives on our place in the universe.

422013-05-31 Fri
14:00~15:00
R1203
Hyosun Kim
[ASIAA]
Death Spiral of a Star with its Companion
Abstract

I will present the current status of the theoretical and observational understanding of spiral-shell patterns in the circumstellar envelopes of dying solar-type stars accompanied by the companions. This talk includes the explanation about the paper honored with the NSC 2012 postdoc publication award. Evolved stars beyond the main sequence, in particular in the Asymptotic Giant Branch (AGB) phase, can be highly obscured in dense circumstellar envelopes due to their intensive mass loss. The difficulty in detecting the obscured AGB stars leads to high uncertainties in the modeling of the late stellar evolutionary phases. In the case that the AGB star has a companion, however, the binary orbital motion leaves an imprint as a spiral-shell pattern on the circumstellar envelope. We develop a new method of determining the characteristics of such binary stars from the properties of the observed circumstellar spiral and incomplete ring patterns, revealing in the images taken with the Hubble Space Telescope and the mm/sub-mm interferometers. We use the shape of such a pattern projected on the plane of the sky as well as molecular line kinematics to further provide the three-dimensional information of the circumstellar pattern. This method is easily applicable to many sources in the AGB and pre-planetary nebula phases, whose detection is highly anticipated with the ALMA.

432013-05-28 Tue
14:20~15:15
Room 104, CCMS-New Physics Building
Professor Andrew Fabian
[Institute of Astronomy, University of Cambridge]
*ASIAA/NTU Joint Colloquium*
Astrophysical Black Holes
Abstract

Supermassive black holes are found at the centres of most galaxies and stellar mass black holes are common throughout galaxies. Observations of these astrophysical black holes will be presented and discussed. Evidence will be presented that supermassive black holes determine the final mass and shape of their host galaxies. The talk concludes with observations of the innermost regions around black holes and approaches to mapping down to the event horizon.

442013-05-27 Mon
14:00~15:00
R1203
Aaron Evans
[NRAO/UVA]
*Special Seminar*
The Great Observatories All-sky LIRG Survey: A Herschel and ALMA View
Abstract

Luminous Infrared Galaxies (LIRGs) are observed primarily to be interacting and merging galaxies. They are the sites of rampant star formation and active galactic nuclei (AGN), which are fed by abundant supplies of molecular gas. However, the very property that led to their initial discovery by IRAS as a significant galaxy population - their high infrared luminosity - also makes them difficult to study; the majority of the UV and optical light from young, massive stars and AGN is absorbed by obscuring dust and re-emitted in the infrared. The Great Observatories All-sky LIRGs Survey thus makes use of the diversity in wavelength coverage of the present space-based telescopes to probe the activity in a large (~ 100 - 200), flux-limited sample of LIRGs from the Revised Bright Galaxy Sample (RBGS). The first part of the talk will be devoted to discussing the survey as a whole. The latter part of the talk will be focussed on the mode of star formation in LIRGs as derived from recent Herschel and Spitzer observations, and on recent ALMA results of the LIRG IIZw096.

452013-05-17 Fri
14:00~15:00
R1203
Sebastian Foucaud
[NTNU]
Pushing the exploration of Dark matter and stellar mass assembly to z=7
Abstract

The past and coming few years see the advent of new generations of deep and wide surveys in optical and near-infrared, which enable us to explore the evolution of galaxies on range of redshifts and masses never explored so far. Owing to my involvement to some of the most important of these surveys, I have explored the mass assembly history of galaxies since z=2 and intend to push to z=7 with the coming Hyper-Suprime Cam Survey. 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. Clustering analyses allows us to link galaxy populations to the mass of their host haloes, and I am using this technique to probe the halo masses of galaxies up to z=2. In particular I am interested in the luminous-to-dark mass ratio and its evolution with redshift. These results implied that a halo downsizing is in place since z=2, where galaxy mass assembly happen faster in higher mass haloes at high redshifts while at lower redshifts it migrates to lower mass halos. I also demonstrate that the (stellar) baryonic mass of galaxies are not as well correlated to the mass of their dark matter haloes as expected, and even by involving gaseous mass, the budget of mass is not compatible with the baryonic fraction implied by cosmological studies (CMB). To understand better the origin of these missing baryons, I am exploring directly the mass assembly of galaxies by major mergers. I demonstrate that since z=2 while major merger plays a minor role in mass assembly of the most galaxies, it plays an increasingly important role in the lower mass galaxies, in particular at low redshift, in contradiction with the theoretical predictions. Exploiting the new Hyper-Suprime Cam on the 8.2m Subaru telescope, the HSC survey will open a new era on the exploration of the very high-redshift (z>5), which was limited to the very small fuel;d-of-view of the Hubble-Space Telescope so far. I will introduce the HSC survey and describe how I am intending to extend my exploration of the mass-assembly to z=7. Finally I will conclude on the challenges raised by the exploitation of the current and next generation of large surveys, and how they required development of topics such as Astroinformatics and Virtual Observatory.

462013-05-15 Wed
14:00~15:00
R1203
Zan Peeters
[DTM-CIW]
*Special Seminar*
The discovery of new multimicron-sized structures in meteoritic organic carbon
Abstract

The age-old question "Where do we come from?" has been central to many scientific endeavours. The field of Astrobiology has reformulated this question to "How did life originate?". Carbon is the element on which all life on Earth is based. If we want to understand the origin of life, we must look for the origin of its building blocks. A great source of organic material is provided by a class of meteorites called the carbonaceous chondrites. Several of life's building blocks are directly present in carbonaceous chondrites as small soluble molecules (e.g. amino acids, nucleobases, carboxylic acids), but the majority of the organic carbon is locked up in an insoluble macromolecular network. In this talk, I will discuss several phases of carbon in space, from interstellar molecules and laboratory experiments, to the macromolecular networks of organic carbon that are found in meteorites, and end with the latest discoveries of large (up to 10 micrometers) organic carbon inclusions in meteorites. This pathway incidentally also follows my carrier in Astrochemistry and Astrobiology, and I hope to provide more insight into the origin of the building blocks of life on Earth.

472013-05-10 Fri
14:00~15:00
R1203
Yutaro Sekimoto
[Advanced Technology Center, National Astronomical Observatory of Japan (NAOJ)]
Submillimeter-wave 10 kilo-pixel camera for future radio astronomy
Abstract

Submillimeter-wave 10 kilo-pixel camera with wide field-of-view may bring a revolution in research of cosmic microwave background and high-z submillimeter galaxies. We have been developing superconducting "CCD"-like cameras for future radio astronomy after ALMA receiver developments. ALMA is a powerful instruments with capability of high spatial and spectral resolution, however, the field of view is quite limited to 21 arc second at 300 GHz. Wide field observation with a large format imaging array isn't only a complementary for ALMA but also suitable for study of large scale structure of the universe. Microwave kinetic inductance detector (MKID) or superconducting micro-resonator is a promising technology for this purpose because large arrays can be read out using frequency-domain multiplexing with a microwave low-noise amplifier. MKID can detect higher frequencies than the gap frequency of a superconducting material, for example, Aluminum gap frequency of 90 GHz. We have demonstrated a submillimeter 100 pixel camera which consists of Aluminum antenna coupled MKIDs and Si-lens array. The dark noise equivalent power (NEP) was achieved to be 6 x 10^{-18} W/rHz. Beam pattern of the MKID camera has been measured. We are developing MKID cameras for two future projects. LiteBIRD is a future satellite to detect B-mode polarization of cosmic microwave background (CMB) led by KEK, which can explore the cosmological inflation. It consists of a small (60 cm) crossed Dragone telescope and a low-noise imaging array to observe CMB with a sensitivity of r (tensol-to-scalar ratio) ~ 0.001 at large angular scales. To reduce foreground contamination from diffuse galactic plane, it observes 50 - 270 GHz with dual-polarization imaging array. A 10m-class telescope for terahertz observations is planned by Tsukuba University at Dome Fuji (Alt. 3800 m) on Antarctica. A wide field-of-view (~1 degree) survey of submillimeter galaxies is planned with a 10 kilo-pixel array detector covering 400 GHz - 1.5 THz.

482013-05-07 Tue
14:00~15:00
R1203
Hao-Yi Wu
[University of Michigan]
*Special Seminar*
Precision cosmology from galaxy clusters and large-scale structures: the role of N-body simulations
Abstract

The number counts and large-scale distribution of galaxy clusters are powerful probes of the structure and composition of the universe. In the era of precision cosmology from deep wide surveys, dark matter N-body simulations play an essential role in modeling the non-linear gravitational effects and interpreting the survey results. In this talk, I will first discuss what we have learned from these simulations, how much we still need to improve them for upcoming surveys, and what the potential dangerous systematics are. I will then present the results from my cluster simulation project “Rhapsody” ― a statistical sample of high-resolution re-simulated clusters ― which allows us to statistically characterize the distribution of and correlation between cluster properties at fixed mass. I will focus on how we can use the understanding of the clusters’ formation history to optimize the use of cluster mass tracers, to model the covariances between different mass proxies, and to reduce systematic errors in cluster cosmology.

492013-05-03 Fri
14:00~15:00
R1203
Chow-Choong Ngeow
[NCU]
Classical Cepheids Beyond Classical Regime -- Longer Wavelength, Longer Periods and Larger Projection Factors
Abstract

Classical Cepheids are an important component in extra-galactic distance scale work, as its famous period-luminosity (PL) relation can be used to derive the Hubble constant via the calibration of various secondary distance indicators. Boosted by the HST H0 Key Project, past works on Classical Cepheids have been focused on the investigation of long period Cepheids (with pulsation periods from 10 to 60 days) in the V and I bands. One such example is the extensive calibration of VI band PL relations in literature. In this talk, I will present new directions of Cepheid research emerged in recent years. The first one is the moving of the calibration of PL relation from optical to mid-infrared (MIR). The biggest advantage of using the MIR PL relations is the extinction is negligible in these wavelengths, at which extinction is one of main systematic errors in Cepheid distance (hence propagated to the errors for Hubble constant). The MIR PL relations also hold the promise to derive Hubble constant with 2-3% accuracy in near future. The second direction is the investigation of Cepheids with periods longer than 80 days, the so-called ultra-long period Cepheids (ULPCs). These ULPCs are ignored in the past, however Bird et al (2009) proposed they can reach to a distance of 100Mpc, well beyond the ~40Mpc distance based on shorter period Cepheids using HST. An on-going search of ULPCs in M31 using PTF data is highlighted in this talk. Finally, I will ended my talk with the recent investigation of projection factor (p-factor) -- an important parameter when calibrating the PL relation using Baade-Wesselink (BW) type technique. The value of p-factor was found to be larger than the previous adopted, which could have impact on the derived Hubble constant via the Cepheid PL relations calibrated with BW methods.

502013-04-26 Fri
14:00~15:00
R1203
Satoko Takahashi
[ASIAA]
Millimeter and Sbumillimeter studies of the Orion Molecular Filaments
Abstract

I will present high angular resolution and wide-field interferometric continuum observations of the Orion Molecular Cloud (OMC) utilizing the Submilllimeter Array (SMA) and Jansky Very Large Array (JVLA), covering 25'/3.1 pc length of the the northern part of the OMC filaments. We detect at least 69 spatially resolved continuum sources associated with OMC filamentary structures through thermal dust emission. Their estimated masses and a projected source sizes range from 0.09 to 5.8 solar masses and 1010 to 19000 AU, respectively. An analysis based on the Jeans theorem suggests that these sources are most likely gravitationally unstable. Comparison of multi-wavelength datasets indicates that approximately half of the detected continuum sources are associated with outflows, infrared sources, and ionized jets. These sources show the evolutionary stage from prestellar core to Class 0/ I phases. We found the source separation within the OMC filaments peaked at 0.02 pc and 0.05 pc. This spatial distribution is part of a larger hierarchical structure, that also includes fragmentation scales of GMCs ( 5 degree/ 37 pc), large-scale clumps (1.3 pc), small-scale clumps (0.3 pc). This suggests that hierarchical fragmentation operates within the Orion A molecular cloud. Fragmentation spacings are roughly consistent with the local thermal fragmentation length in large-scale clumps ( 0.3 pc), while fragmentation spacings in dense cores measured from the SMA observations is smaller than the local fragmentation length. These smaller observed spacings can be explained by either that helical magnetic field or global filament collapse. This will be my last talk in IAA before I leave Taiwan. I also would like to make summary of my research projects and project experiences at IAA in the past years.

512013-04-19 Fri
14:00~15:00
R1203
Hao-Yu Liu
[ASIAA]
Forming the Luminous OB Clusters at the Convergences of the Large Scale Molecular Filaments
Abstract

Observations on distance <300 pc molecular clouds have shown that the nearby young YSO clusters form at the convergences of the molecular filaments. The preliminary analytical hub-filament model was proposed for describing this phenomenon. Our survey on a few most luminous Galactic OB cluster forming regions shows that their parent giant molecular clouds also have the hub-filament geometrical configuration. At the convergences of the filaments, the high density and the high external pressure may promote the accretion and the star-forming efficiency. I will elaborate the overall geometry and kinematics of the luminous OB cluster forming molecular clouds with two case studies, based on the synthesized SMA+IRAM-30m observations. One case is the molecular cloud G10.6-0.4 located in the near 3 kpc spiral arm. The other is the unique Galactic mini-starburst region W49A. We hope to shed some light on the paradigm of the formation of gravitationally bound massive cluster.

522013-04-12 Fri
14:00~15:00
R1203
Matteo Barnabè
[Dark Cosmology Centre]
The dark and luminous mass structure of lens galaxies
Abstract

Understanding the formation and evolution processes of galaxies remains among the most important unsolved problems in present-day astrophysics and cosmology. A reliable and detailed description of the mass-density profile and structural properties of galaxies through cosmic time is a much-needed step forward but – whereas nearby systems have been thoroughly analyzed – painfully little is known about more distant objects, since observational limitations make it difficult to employ the traditional diagnostic tools. During this talk I will describe a method to overcome these difficulties based on combining in a self-consistent way the information obtained from two independent and complementary techniques: strong gravitational lensing and stellar dynamics. This provides a robust way to conduct detailed studies of both elliptical and disk galaxies beyond the local Universe. I will then detail the results of the application of this method to the analysis of a sample of 16 lens elliptical galaxies in the redshift range z = 0.08 - 0.33, for which both HST imaging observations and two-dimensional kinematic maps (obtained from VLT VIMOS spectroscopical observations) are available. I will also illustrate how this approach can be extended to study in detail the dark and luminous mass structure of lens disk galaxies, and to put firm constraints on the initial mass function of massive galaxies.

532013-04-08 Mon
14:00~15:00
R1203
Fred K. Y. Lo
[NRAO]
*Special Seminar*
Mega-maser Cosmology Project
Abstract

Better measurements of H0 - the current expansion rate of the Universe, provide critical independent constraints on dark energy, spatial curvature of the Universe, neutrino physics, and validity of general relativity. The Mega-maser Cosmology Project (MCP) aims to determine the Hubble Constant at high accuracy by measuring the angular-diameter distance to galaxies in the Hubble Flow. The MCP has discovered 9 new mega-maser disks in Sy2 nuclei suitable for distance determination. A geometric distance measurement to a galaxy at 140 Mpc, via micro- arc-second astrometry of its circum-nuclear mega-maser disk, has been demonstrated. The current status of the MCP measurements of Ho, and future prospects, will be described. The MCP also enables accurate determination of the central black-hole mass in mega-maser galaxies. The large intrinsic scatter of BH masses in a narrow range of the velocity dispersion in the mega-maser galaxy bulges raise questions about the validity of the well-known M-σ relation of BH mass and the spherical component of galaxies. The relationship of the thin Keplerian accretion disks delineated by the mega-masers with the obscuring material of the AGN will also be briefly discussed. Timing permitting, other key projects at the NRAO will be also described.

542013-04-05 Fri
14:00~15:00
R1203
no colloquium this week
[ASIAA]
552013-04-02 Tue
14:20~15:20
Room 104, CCMS-New Physics Building
Toshio Matsumoto
[ASIAA]
*ASIAA/NTU Joint Colloquium*
A search for the light of the first stars; The enigma of the near-infrared background
Abstract

The first stars of the universe have attracted the strong interest of astronomers, as the first stars could re-ionized the universe and must be key objects to delineate the dark age of the universe. It has been thought that the first stars are very massive and luminous, however, it is difficult to detect individual stars even with JWST. To overcome the faintness of individual stars, we have tried to observe the near-infrared background to detect the integrated redshifted light of the first stars. This is a challenging observation, since there exist bright foreground backgrounds, however the space probes, COBE, IRTS, AKARI and Spitzer succeeded in detecting excess sky brightness and fluctuation that can not be explained with known foreground emission sources. In addition to these results, I will present the recent result of the sounding rocket experiment, CIBER, and its implications for the study of the first stars.

562013-03-29 Fri
14:00~15:00
R1203
Sheng-Yuan Liu
[ASIAA]
Chemical Signatures of Massive Star Forming Clumps
Abstract

Our understanding of the high-mass star formation process, in contrast to that of their low-mass counterpart, remains relatively poor till today. In particular, what constitutes the initial condition for massive star formation is not yet well characterized. In this talk, I will introduce recent studies of the chemical signatures of massive star forming regions through molecular line observations, with an emphasis over those of cold and dense molecular clumps that are probably associated with the earliest phase of massive star and cluster formation.

572013-03-27 Wed
14:00~15:00
R1203
Henry Hsieh
[University of Hawaii]
*Special Seminar*
Ice in the Inner Solar System
Abstract

Small bodies in the warm inner solar system have long been assumed to lack volatile material (i.e. ice) due to their close proximity to the Sun. However, recent work has pointed to the existence of preserved, and occasionally actively sublimating, water ice on objects in the main asteroid belt. These surprising discoveries carry exciting implications for our ability to understand the formation of our solar system and other extrasolar planetary systems, and possibly also the primordial delivery of terrestrial water and the origin of life on Earth itself. I will describe my own work on some of these icy inner solar system objects, known as main-belt comets, and discuss ongoing research efforts aimed at better understanding the extent and nature of preserved volatile material in the inner solar system.

582013-03-22 Fri
14:00~15:00
R1203
Neal Dalal
[University of Illinois at Urbana-Champaign]
Probing dark matter substructure with dusty galaxies
Abstract

The abundance of dark matter substructure in the halos of ordinary galaxies is sensitive to both the physics of dark matter and the physics of inflation in the early universe. Strong gravitational lensing provides one of the only probes of the abundance of DM halo substructure, but existing constraints on substructure from lensing have been weak because of the small sample sizes available. I will describe how the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) has opened a new window onto DM substructure. Large numbers of lensed, dusty star-forming galaxies at high redshift have been discovered by Herschel and the South Pole Telescope, and ALMA observations of these lensed systems will allow reconstruction of the mass distributions of the lensing galaxies with unprecedented resolution. I will describe early results from this program, and I will discuss forecasts for ALMA as a probe of the properties of dark matter.

592013-03-21 Thu
14:00~15:00
R1203
Zhi-Yun Li
[University of Virginia]
*Special Seminar*
Magnetic Braking and Protostellar Disk Formation
Abstract

The formation of stars and planets are connected through disks. Disk formation, once thought to be a trivial consequence of angular momentum conservation, is greatly complicated by the magnetic field that is observed to be present in the dense, star-forming cores of molecular clouds. Indeed, in the simplest case of perfect coupling between the magnetic field and bulk neutral core material (the ideal MHD limit), both analytic work and numerical simulations have shown that the formation of rotationally supported disks is suppressed by excessive magnetic braking in dense cores magnetized to the observed level, leading to the so-called ``magnetic braking catastrophe'' in disk formation. I will discuss possible resolutions to this fundamental problem, including non-ideal MHD effects, misalignment between the magnetic field and rotation axis, turbulence-enhanced magnetic reconnection, and outflow stripping of the slowly rotating protostellar envelope. How protostellar disks form and grow remains an open question.

602013-03-15 Fri
14:00~15:00
R1203
Tracy Beck
[STScI]
Star and Planet Formation Science with the James Webb Space Telescope
Abstract

The James Webb Space Telescope (JWST) is the next great observatory currently in development by the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA). The JWST will peer into deep space using it's 6.5 meter segmented primary mirror and it is infrared optimized to operate at 1 - 25 micron wavelengths. The four main science themes for JWST are: First Light and Reionization, the Assembly of Galaxies, the Birth of Stars and Planetary Systems, and Planetary Systems and the Origins of Life. In this talk, I will introduce you to the JWST and discuss some of its key instrument modes that will have a very strong impact on my own field of research - the birth and early evolution of stars and their planetary systems. I will also highlight some star and planet formation research projects that I have done using 8 meter-class telescopes in that will help to pave the way for future observations with JWST.

612013-03-08 Fri
14:00~15:00
R1203
Hsin-Fang Chiang
[IfA]
The Earliest Circumstellar Disks and the Variable Young Stellar Objects Survey
Abstract

My talk will include two parts. First I will take about interferometric observations and modeling of embedded young stellar objects. Protostars are surrounded by their natal envelopes in the early stage, while the earliest disks form inside the envelopes. To understand the envelope properties and to reveal the embedded circumstellar disk, we compare CARMA observations with theoretical collapse models using radiative transfer calculation and Bayesian inference. Implications of the modeling work will be discussed. Then I will introduce the Variable Young Stellar Objects Survey (VYSOS) project, which consists of two new robotic telescopes dedicated to monitor nearby star forming regions. Observations of VYSOS have started in search of new eruptive events around young stars such as FUor and EXor outbursts.

622013-03-07 Thu
14:00~15:00
R1203
Doug Simons
[CFHT]
*Special Seminar*
CFHT Status Report and Future Plans
Abstract

Presentation Summary: After a brief summary of the nature of CFHT Corp. and recent metrics illustrating the scientific success of CFHT, the future of the Observatory is described through various initiatives designed to broaden the CFHT partnership, develop new capabilities, and take steps toward the replacement of CFHT with a powerful new facility dedicated to highly multiplexed wide-field spectroscopy. CFHT, in the context of the evolving landscape on Mauna Kea will also be discussed, as CFHT positions itself among a backdrop of some older facilities being decommissioned while new Mauna Kea facilities are on the planning horizon.

632013-03-06 Wed
14:00~15:00
R1203
Tomotsugu Goto
[Dark Cosmology Centre, University of Copenhagen]
*Special Seminar*
Dark energy really exists? Detecting Integrated Sachs-Wolfe effect from WISE data.
Abstract

We estimated the cross-power spectra of a galaxy sample from the Wide-field Infrared Survey Explorer (WISE) survey with the 7-year Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy maps. A conservatively-selected galaxy sample covers ~13000sq.deg, with a median redshift of z=0.15. Cross-power spectra show correlations between the two data sets with no discernible dependence on the WMAP Q, V and W frequency bands. We interpret these results in terms of the the Integrated Sachs-Wolfe (ISW) effect: for the |b|>20 deg sample at l=6-87, we measure the amplitude (normalized to be 1 for vanilla LambdaCDM expectation) of the signal to be 3.4+-1.1, i.e., 3.1 sigma detection. We discuss other possibilities, but at face value, the detection of the linear ISW effect in a flat universe is caused by large scale decaying potentials, a sign of accelerated expansion driven by Dark Energy.

642013-03-01 Fri
14:00~15:00
R1203
Kinwah Wu
[University College London]
Cosmic magnetism: magnetic fields and polarized radio emission from galaxy clusters and large-scale structure
Abstract

Magnetic fields are present everywhere in the Universe, from substellar systems to large-scale structures, such as cosmic filaments, walls and voids. They are important in various astrophysical aspects. Without them, stars cannot be formed, and quasars cannot shine. While we have some understanding of the properties of stellar-scale magnetic fields, our knowledge of magnetic fields beyond galactic scales is very primitive. The situation will however change with the coming of new instruments, e.g. the SKA. In this talk I will first present an overview on cosmic magnetism. Then I will show results of two recent studies on cosmic magnetic fields by my collaboration. The first is a MHD simulation study of the evolution of magnetic fields of cluster and larger scales. The second is an investigation of how polarized radiation is transported through magnetized inhomogeneous multi-phase cosmological media. I will discuss how these studies will help to improve our understanding of properties, evolution and origin of the cosmic magnetic fields. I will also discuss certain technical difficulties and obstacles that we need to overcome in order to properly diagnose magnetic fields in large cosmic structures.

652013-02-27 Wed
15:30~16:30
R1203
Olivia Jones
[University of Manchester]
*Special Seminar*
Dusty evolved stars at low metallicity
Abstract

Stars on the asymptotic giant branch (AGB) are thought to be responsible for the majority of the dust injected into the interstellar medium. Infrared surveys on local group galaxies provide an ideal opportunity to investigate how the composition and quantity of dust produced by asymptotic giant branch (AGB) stars depends on metallicity on a galactic scale. Here, I discuss recent work on dust production in nearby dwarf galaxies, with particular focus on oxygen-rich dust in the Magellanic Clouds.

662013-02-26 Tue
14:20~15:10
Room 104, CCMS-New Physics Building
Motohide Tamura
[NAOJ]
*ASIAA/NTU Joint Colloquium*
Results from the Subaru Telescope SEEDS Project: Direct Imaging of Exoplanets and Their Forming Disks
Abstract

Astronomers have successfully discovered a number of extrasolar planets over the last twenty years. Our interests are now focused on direct detection of exoplanets similar to Jupiter, Saturn and Earth, understanding the similarities or diversities of such planetary systems, and how they form and evolve. Recent advances in technology, infrared imaging and the construction of large telescopes have provided dramatic progress in such studies. SEEDS (Strategic Explorations of Exoplanets and Disks) is an ongoing large survey for exoplanets and protoplanetary disks at Subaru, one of the largest optical and infrared telescopes in the world. We describe the outline of this survey and present results from its first three years, including the detection of several new planets/companions. We also show our discoveries of the detailed structures of protoplanetary disks, i.e., potential signposts of young planets.

672013-02-25 Mon
14:00~15:00
R1203
Gareth Kennedy
[National Astronomical Observatories of China, Chinese Academy of Sciences]
*Special Seminar*
Capturing stars into galactic centre accretion disks
Abstract

The high stellar densities in galactic centres, combined with an accretion disk around the massive black hole, mean that stars will inevitably interact with the disk. This interaction can cause stars to be captured into the disk and migrate inward in a process similar to planetary migration. In addition to growing the black hole, the final plunge of the star through the accretion disk and into the black hole will result in an observational signature of high energy x-rays and gamma-rays. I will present early results from the StarDisk model, developed as part of the Silk Road Project (NAOC), which will soon self-consistently model the stellar dynamics, hydrodynamics and the feedback between stars and gas in galactic centres.

682013-02-22 Fri
14:00~15:00
R1203
Subha Majumdar
[TIFR]
Energy Deposition, Entropy and AGN Feedback in Galaxy Clusters
Abstract

There are mounting evidences for AGN feedback in groups and clusters of galaxies. Understanding feedback in clusters is crucial for cluster cosmology apart from understanding the cluster thermal history. I will report the results of our study of fractional entropy enhancement in the intra-cluster medium (ICM) of the clusters from the representative XMM-Newton cluster structure survey (REXCESS). We use the `thermodynamic' entropy enhancement to make the first estimate of the total, as well as radial, non-gravitational energy deposition up to r500 for a large, nearly flux-limited, sample of clusters. We find that the total energy deposition is proportional to the cluster temperature (and hence mass), and that the centrally peaked energy deposition per particle as a function of gas mass shows a similar profile in all clusters. In the cluster core the energy deposition is also correlated with the radio luminosity. We also show that the recently proposed 'Universal' nature of cluster pressure profiles points towards 'Universal' prescription of entropy injection which is indicative of AGN heating. Taken together, the results strongly support models of entropy enhancement through AGN feedback.

692013-02-05 Tue
14:00~15:00
R1203
Ching-Cheng Hsu
[Laboratory for high energy physics, University of Bern]
*Special Seminar*
High Energy Particle Astrophysics with Cherenkov Telescopes
Abstract

High Energy experimental particle astrophysics is now a field of growing interests and has been well established. It marks the intersection of astrophysics, particle physics and cosmology. In general, particle astrophysics has two main elements. One is multi-messenger astronomy and the other is fundamental physics with cosmic messengers. It opens new windows to the universe and provides us new approaches to understanding the fundamental properties of matter and the universe. The main focus of this talk is on the development of experimental techniques for Earth-bound Cherenkov gamma-ray and neutrino detectors. Consequently, more emphasis is given to the physics results from these experiments, particularly on the physics of Active Galactic Nucleus (AGN) and related subjects. At last, the Cherenkov Telescope Array (CTA) project which is a worldwide effort experiment on Tera-electronvolt gamma-ray astronomy in the next decade will be introduced. In addition, I will also discuss the prospective CTA physics impacts on AGN research.

702013-02-04 Mon
15:00~16:00
R1203
Nicole Czakon
[Caltech]
*Special Seminar*
The Bolocam Sunyaev-Zel'dovich(SZ) Observing Program: X-ray/SZ Scaling Relations
Abstract

Galaxy clusters have become promising probes of cosmology thanks to recent advances in instrumentation. Both galaxy cluster surveys and pointed galaxy cluster observations provide insight into the nature of dark energy and dark matter. A variety of physical phenomena generate cluster observables which span from radio to X-ray. To use galaxy clusters for cosmology, however, we must combine these different wavelength observations, which scale independently with a cluster's physical properties. One of these observables, the Sunyaev-Zel'dovich (SZ) effect provides a lever arm to understand the baryonic content at the outskirts of galaxy clusters. Caltech has contributed significantly to the development of detectors and instrumentation to measure the Sunyaev Zel’dovich effect. The SZ observing program of one of the instruments, Bolocam, has fully matured over the last year. Thanks in large part to the ASIAA-branch of the CLASH program, our data has contributed to a variety of cluster analyses. I will give an overview of my work calibrating integrated SZ values with X-ray determined masses. This work includes a detailed study of sources of systematic error, including, selection function effects, large-scale signal filtering, and alternative mass models. The full Bolocam X-ray SZ catalog (BOXSZ) results are expected to be released early 2013.

712013-02-01 Fri
14:00~15:00
R1203
Hsiao-Wen Chen
[The University of Chicago]
Probing Halo Gas Kinematics with Absorption Spectroscopy
Abstract

Recent findings on the kinematic properties of the circumgalactic medium from absorption-line studies will be summarized in this talk.

722013-01-29 Tue
14:00~15:00
R1203
Rennan Barkana
[Tel Aviv]
*Special Seminar*
download PDF Detecting the First Stars from just 200 Million Years after the Big Bang
Abstract

Understanding the formation and evolution of the first stars and galaxies is one of the most exciting frontiers in astronomy. Since the universe was filled with neutral hydrogen at early times, the most promising method for observing the epoch of the first stars is using the prominent 21-cm spectral line of hydrogen. Current observational efforts are focused on a cosmic age of 500 million years, with earlier times considered much more challenging. We show that stars from a much earlier era may be observable as a result of a recently noticed effect of different motions of the dark matter and the ordinary matter in the early universe. We produce simulated maps of the first stars and show that these relative motions significantly enhance large-scale fluctuations and produce prominent structure on the scale of a degree in the 21-cm intensity distribution. The particular form expected for this structure should make it easier to confirm the existence of million solar-mass halos at early times.

732013-01-25 Fri
14:00~15:00
R1203
Adam Deller
[ASTRON]
Pinpointing pulsars in 3D
Abstract

The potential of Very Long Baseline Interferometry (VLBI) observations has increased steadily in recent years, to the point where it is now possible to accurately localise compact mJy objects - in 3D - at distances of 10 kpc. With current instrumentation, most of the known Galactic radio pulsar population is already accessible to precision mapping. I will present results from recent and ongoing VLBI programs showing how astrometric observations of both individual pulsars and pulsar ensembles can be used to provide information about stellar evolution, fundamental physics and the ISM. I will also examine how techniques which have until now been used in primarily in pulsar astrometry might give considerable benefits for other Galactic (and even extra-Galactic) targets.

742013-01-24 Thu
14:00~15:00
R1203
Kenneth Wong
[University of Arizona]
*Special Seminar*
Optimal Mass Configurations for Lensing High-Redshift Galaxies (and How to Find Them In the SDSS!)
Abstract

We investigate whether lines of sight containing multiple cluster-scale halos are the best cosmic telescopes for lensing high-redshift (z~10) sources into detectability. For lines of sight of fixed angular size and total mass, we test how the lensing cross section and the number of faint galaxies detected at high redshift change as that mass is distributed among multiple halos, as well as which physical properties of the halos are most important. We find that multiple projected halos are can result in improvement in the detection of faint, high-z sources compared to single halos of equivalent total mass due to the interactions among the lensing potentials when the projected halos overlap. Using integrated LRG luminosity density as a tracer of mass, we have identified lines of sight in the SDSS that are likely to contain the largest total integrated masses. These fields contain a diversity of single massive clusters and chance alignments of multiple halos in projection, and are likely to be among the best gravitational lenses known. Our ongoing galaxy spectroscopy in the first of these fields reveals the presence of large total masses (> 3 x 10^15 M_sun) along the line of sight and multiple cluster-scale structures.

752013-01-18 Fri
14:00~15:00
R1203
Yasuhiro Hasegawa
[ASIAA]
Planet traps in protoplanetary disks and the formation and evolution of planetary systems
Abstract

One of the most fundamental problems in theories of planet formation in protoplanetary disks is planetary migration that arises from resonant, tidal interactions between protoplanets and the natal disks. As shown by many previous studies, the interactions generally drain the angular momentum of planets so efficiently and jeopardize the existence of any planetary system around the central stars. In this talk, I will present all the key results of my PhD thesis work, wherein planet traps - specific sites in protoplanetary disks at which planets undergoing rapid type I migration are captured - are intensively investigated. We will discuss how disk inhomogeneities, one of the most general properties of planetary disks, give rise to planet traps and how planet traps affect the formation and evolution of planetary systems. Comparisons with a large number of observed exoplanets enable us to verify our picture of planet formation based on planet traps.

762013-01-15 Tue
15:00~16:00
R1203
Tony Mroczkowski
[JPL/Caltech]
*Special Seminar*
Multi-wavelength and High-Resolution Sunyaev-Zel’dovich Effect Observations of Galaxy Clusters
772013-01-04 Fri
14:00~15:00
R1203
no colloquium this week
[ASIAA]
TEL: 886-2-3365-2200 FAX: 886-2-2367-7849
General: asiaa_replace2@_asiaa.sinica.edu.tw Media Request: epo_replace2@_asiaa.sinica.edu.tw
11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C.