Academia Sinica Institute of Astronomy & Astrophysics
中央研究院天文及天文物理研究所
Go Back
Activity > Colloquium

Colloquiums and Seminars(2019)

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. Seminars on more specialized topics are also held on a regular basis.

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)

NEXT Seminar: 2019-01-22 Tue 11:00~12:00 [R1203]
Speaker:Seog-Tae Han
Topic:A development of compact triple band receiver for millimeter-wave radio astronomy
Abstract:We have developed a compact triple-band receiver which enables simultaneous observations in the three frequency intervals K(18–26 GHz) band, Q(35–50 GHz) band, and W(85–115 GHz) band. The quasi-optics design enables the triple-band receiver to fit into a single cryostat with some of the mirrors and dichroic filters outside the cryostat. The total receiver system is 600 mm(W) x 980 mm(L) x 370 mm(H) including the optical circuit. When compared with the present KVN optical bench of size 2600 mm x 2300 mm x 60 mm, the system is significantly more compact and is tailorable for use in telescopes with a small receiver cabin. The receiver performance and test observation results will be presented. We have shown that it is possible to design a quasi-optical circuit that has simultaneous observation capability for three or four frequency bands for millimeter and sub-millimeter receivers. Ultimately, this concept may lead to development of much more compact multi-frequency receiver systems for mm-wave and sub-mm radio telescopes.
NEXT Colloquium: 2019-01-23 Wed 14:20~15:20 [R1203]
Speaker:Tomohisa Kawashima
Topic:Black hole shadow and relativistic jet image in M87
Abstract:he Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array aiming for imaging black hole (BH) shadows on event horizon scales, and exploring fundamental properties of BHs as well as physics of accretion flows/relativistic jets. M87 is one of the prime target of EHT, because the expected diameter of the black hole shadow is larger than the beam size of EHT. Theoretical studies of BH shadow and relevant disk-jet images are very important to estimate the mass and spin of black holes and to reveal the physics of accretion flow and launching mechanism of relativistic jets. We have recently developed a new general relativistic radiative transfer (GRRT) code and have carried out calculations of the black hole shadow in M87, assuming a simple model of accretion flow or disk-jet model based on GRMHD simulations (Nakamura et al. 2018 and in prep.). Based on the simple accretion flow model, we have newly found that the BH spin can be constrained by measuring the dark-crescent feature which appears in the rapidly spinng BHs. We also introduce our recent GRRT calculation results of disk-jet models based on GRMHD simulations from horizon to mili-arcsecond scale (i.e., one thousand gravitational radius scale). The resultant image shows the limb-brightened jet far from the black hole, that is consistent with the VLBI observation images.
No. Time/Place Speaker Topic / Abstract
download PDF: download talk PDF file
12019-07-17 Wed
14:20~15:20
R1203
Satoshi Ohashi
[RIKEN]
*Colloquium*
22019-07-10 Wed
14:20~15:20
R1203
Frank Eisenhauer
[MPE]
*Colloquium*
The present science/technical achievements of VLTI and future prospects
Abstract

TBA

32019-07-03 Wed
14:20~15:20
R1203
Yusuke Tsukamoto
[Kagoshima University]
*Colloquium*
42019-06-26 Wed
14:20~15:20
R1203
Sara Sadavoy
[CfA]
*Colloquium*
52019-06-12 Wed
14:20~15:20
R1203
Abdurrouf
[ASIAA]
*Colloquium*
TBA
Abstract

TBA

62019-05-29 Wed
14:20~15:20
R1203
Albert Zijlstra
[Jodrell Bank Centre for Astrophysics, University of Manchester]
*Colloquium*
TBA
72019-05-22 Wed
14:20~15:20
R1203
Thavisha Dharmawardena
[ASIAA]
*Colloquium*
82019-05-15 Wed
14:20~15:20
R1203
Di Li
[NAOC]
*Colloquium*
Present science/technical achievements of the Five hundred meter Aperture Spherical Telescope and future prospects
Abstract

TBA

92019-05-08 Wed
14:20~15:20
R1203
Bo Zhao
[MPE]
*Colloquium*
102019-04-24 Wed
14:20~15:20
R1203
Martin Bureau
[Oxford]
*Colloquium*
WISDOM: Probing Supermassive Black Holes and their Immediate Environments with ALMA
Abstract

I will present key results from the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM), a high resolution survey of molecular gas in galaxy nuclei. First, I will show that CO can be used to easily and accurately measure the mass of the supermassive black holes lurking at galaxy centres. I will discuss substantial ongoing efforts to do this, and present many spectacular new ALMA measurements, the latest of which rival the best black hole measurements to date. This opens the way to literally hundreds of measurements across the Hubble sequence (in both active and non-active galaxies) with a unique method. Second, I will briefly show how the same data allow to study the spatially-resolved properties of the giant molecular clouds in all the galaxies studied. This will yield cloud censuses in non-local galaxies (including early-type galaxies) for the first time, providing a new tool to understand and contrast the star formation efficiency across galaxies. Already, it appears that basic cloud properties are not universal and vary systematically along the Hubble sequence, contrary to long-held assumptions.

112019-04-10 Wed
14:20~15:20
R1203
Yuji Matsumoto
[ASIAA]
*Colloquium*
122019-04-03 Wed
14:20~15:20
R1203
Tien-Hao Hsieh
[ASIAA]
*Colloquium*
132019-03-27 Wed
14:20~15:20
R1203
Qing Bo Ma
[Guizhou Normal University]
*Colloquium*
142019-03-20 Wed
14:20~15:20
R1203
Kathryn Volk
[University of Arizona]
*Colloquium*
152019-03-14 Thu
14:20~15:20
R1203
Annalisa Pillepich
[MPIA]
*Colloquium*
162019-03-06 Wed
14:20~15:20
R1203
Wen-Pin Hsieh
[ASIES]
*Colloquium*
A journey to the Earth and icy bodies’ interiors
Abstract

Physical properties of constituent materials in the Earth and planetary interiors are key to determine their formation history and thermo-chemical structures, etc. In particular, knowledge of the thermal conductivity of these constituent materials under relevant pressure-temperature conditions plays critical roles in understanding many geophysical phenomena within the Earth and planetary bodies, such as the temperature profile and dynamics of the mantle and core, as well as the heat flux across the core-mantle boundary. Recently we have successfully combined ultrafast optics with high pressure diamond cells to precisely measure lattice thermal conductivity of Earth’s mantle and core materials and water-volatile mixtures under extreme conditions. Modeling of our new data show significant influences of hydration, iron, aluminum, and volatiles on the thermal states and dynamics of the Earth and icy bodies. I will also discuss some future directions that are important to further understand the thermal history of the Earth and icy bodies.

172019-03-05 Tue
14:20~15:20
R1203
Liton Majumdar
[JPL]
*Seminar*
Multi-wavelength Astronomy and the Origin of Planetary Systems
Abstract

One of the most exciting developments in astronomy is the discovery of planets around stars other than our Sun. More than two thousand exo-planets have now been detected. But how do these planets form, and why are they so different from those in our own solar system? Which ingredients are available to build them? Thanks to powerful ground-based telescopes such as the Atacama Large Millimeter Array (ALMA) and soon the James Webb Space Telescope (JWST), we are now in a position to address these age-old questions scientifically. The formation of stars and planetary systems takes place in "molecular clouds". These dense, cold, dust enshrouded regions of the interstellar medium exhibit a high degree of molecular complexity. I will discuss how this complexity develops in protostellar envelopes, and how far it progresses before the molecules are incorporated as ices into planetesimals in protoplanetary disks and delivered to planets in the habitable zone.

182019-02-27 Wed
14:20~15:20
R1203
Takafumi Ootsubo
[JAXA]
*Colloquium*
192019-02-26 Tue
14:20~15:20
R1203
Kohei Hayashi
[ICRR, University of Tokyo]
*Seminar*
TBA
Abstract

TBA

202019-02-22 Fri
14:20~15:20
R1203
Veronica Allen
[NASA/GSFC]
*Seminar*
212019-02-20 Wed
14:20~15:20
R1203
Orkan Umurhan
[SETI Institute / NASA Ames]
*Colloquium*
222019-02-13 Wed
14:20~15:20
R1203
Fang-Chun Liu
[NTNU]
*Colloquium*
232019-01-30 Wed
14:20~15:20
R1203
Masato Shirasaki
[NAOJ]
*Colloquium*
Gravitational lensing effect of large-scale structures and its correlations to multi-wavelength extragalactic background
Abstract

Modern galaxy surveys aim at collecting billions of distant galaxies with precise measurement of their redshifts and shapes. Gravitational lensing effect causes an arc-shaped distortion in images of distant galaxies and offers a unique method to probe underlying mass density distribution in the universe. The information of cosmic mass density from gravitational lensing analyses is thought to be the basis for understanding the nature of multi-wavelength extragalactic background. I will introduce two representative examples of cross correlations of gravitational lensing with extragalactic emission at different wavelength. One is the correlation with gamma-ray background emission, and another is the correlation with thermal Sunyaev-Zel'dovich (tSZ) effect in cosmic microwave background. The former allows us to explore a possible signature of annihilating dark matter, while the latter provides meaningful information of the physics of intra-cluster medium. I will summarize the results of cross correlation analyses performed so far, and discuss some key issues remaining unsolved in the analyses. Those include accurate modeling of dark-matter substructures in cluster-sized objects and the statistical relationship among dark mater halos, blazars in gamma rays, and flat-spectrum sources in radio.

242019-01-29 Tue
14:20~15:20
R1203
Hai Yu
[Nanjing University]
*Seminar*
TBA
Abstract

TBA

252019-01-23 Wed
14:20~15:20
R1203
Tomohisa Kawashima
[NAOJ]
*Colloquium*
Black hole shadow and relativistic jet image in M87
Abstract

he Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array aiming for imaging black hole (BH) shadows on event horizon scales, and exploring fundamental properties of BHs as well as physics of accretion flows/relativistic jets. M87 is one of the prime target of EHT, because the expected diameter of the black hole shadow is larger than the beam size of EHT. Theoretical studies of BH shadow and relevant disk-jet images are very important to estimate the mass and spin of black holes and to reveal the physics of accretion flow and launching mechanism of relativistic jets. We have recently developed a new general relativistic radiative transfer (GRRT) code and have carried out calculations of the black hole shadow in M87, assuming a simple model of accretion flow or disk-jet model based on GRMHD simulations (Nakamura et al. 2018 and in prep.). Based on the simple accretion flow model, we have newly found that the BH spin can be constrained by measuring the dark-crescent feature which appears in the rapidly spinng BHs. We also introduce our recent GRRT calculation results of disk-jet models based on GRMHD simulations from horizon to mili-arcsecond scale (i.e., one thousand gravitational radius scale). The resultant image shows the limb-brightened jet far from the black hole, that is consistent with the VLBI observation images.

262019-01-22 Tue
11:00~12:00
R1203
Seog-Tae Han
[KASI]
*Seminar*
A development of compact triple band receiver for millimeter-wave radio astronomy
Abstract

We have developed a compact triple-band receiver which enables simultaneous observations in the three frequency intervals K(18–26 GHz) band, Q(35–50 GHz) band, and W(85–115 GHz) band. The quasi-optics design enables the triple-band receiver to fit into a single cryostat with some of the mirrors and dichroic filters outside the cryostat. The total receiver system is 600 mm(W) x 980 mm(L) x 370 mm(H) including the optical circuit. When compared with the present KVN optical bench of size 2600 mm x 2300 mm x 60 mm, the system is significantly more compact and is tailorable for use in telescopes with a small receiver cabin. The receiver performance and test observation results will be presented. We have shown that it is possible to design a quasi-optical circuit that has simultaneous observation capability for three or four frequency bands for millimeter and sub-millimeter receivers. Ultimately, this concept may lead to development of much more compact multi-frequency receiver systems for mm-wave and sub-mm radio telescopes.

272019-01-17 Thu
14:20~15:20
R1203
Jongho Park
[Seoul National University]
*Seminar*
Faraday Rotation in the Jet of M87 Inside the Bondi Radius: Indication of Winds from Hot Accretion Flows Confining the Relativistic Jet
Abstract

Active galactic nuclei (AGNs) often produce highly collimated relativistic jets, one of the most energetic phenomena in the Universe. Theoretical models predict that AGN jets can be accelerated to nearly speed-of-light by magnetic fields if they are confined by an external medium. Winds, nonrelativistic un-collimated gas outflows launched from accretion flows onto the supermassive black holes in AGNs, are primary candidates for this medium. Recent observations have indeed revealed gradual collimation and acceleration of the jet in M87, a nearby AGN that possesses a black hole with a mass of three to six billion Suns which provides a unique opportunity to investigate the region under the influence of the black hole's gravity. However, it has not been possible to either probe the external medium by observations or verify the general picture of jet collimation and acceleration. Here we report radio observations of Faraday rotation (the rotation of the plane of polarization by intervening magnetic fields) in the M87 jet, where information on the external medium (which is not directly observable) is imprinted. The Faraday rotation systematically decreases with increasing distance from the black hole from 5,000 to 200,000 Schwarzschild radii, in good agreement with the gas density being inversely proportional to the distance. This behavior matches the theoretically expected signature of moderately magnetized winds, which can naturally serve as the external confining medium. The sign of the Faraday rotation is predominantly negative, suggesting that jet and accretion axis are misaligned and the jet emission exposes only one side of the toroidal magnetic fields in the winds. Our results demonstrate that winds are indeed a key element of the black hole inflow-outflow system.

282019-01-16 Wed
14:20~15:20
R1203
Ryo Tazaki
[Tohoku]
*Colloquium*
Probing grain growth in protoplanetary disks via millimeter-wave polarization
Abstract

Dust coagulation in protoplanetary disks is the first step of planetesimal formation. However, a pathway from dust aggregates to planetesimals remains unclear. Both laboratory and numerical studies have so far shown that the structure of a dust aggregate plays important roles in planetesimal formation. However, the aggregate structure has been poorly constrained by disk observations. Recently, ALMA opens a new window to observe (sub-)millimeter-wave polarization of disks, which is expected to provide additional constraints on dust aggregate properties. In this study, we perform 3D radiative transfer simulations in order to study how the structure of dust aggregates affect millimeter-wave polarization from disks. As a result, it is found that relatively compact particles are favorable to explain observed millimeter-wave scattering polarization of disks, whereas highly porous and fractal particles fail to explain the observations. Furthermore, it is also shown that observed millimeter-wave scattering polarization is consistent with grain radii of a few hundreds of microns, which are an order of magnitude smaller than that previously estimated. We discuss a possibility that these relatively small grains are due to efficient fragmentation of CO2-ice coated grains in disks.

292019-01-15 Tue
14:20~15:20
R1203
Chao-Chin Yang
[University of Nevada]
*Seminar*
Planetesimal Formation through the Streaming Instability
Abstract

The formation of kilometer-scale planetesimals is one of the most difficult stages in the course of planet formation around young stars. It is faced with several major barriers. Direct dust growth by coagulation is limited, up to mm to cm in size, due to inefficient sticking, bouncing, and fragmentation at collision. Even if the dust grains manage to grow past cm in size, they continually lose angular momentum to their surrounding gas due to constant head wind, leading to rapid orbital decay to the star. One promising mechanism for circumventing these barriers is the streaming instability, in which the solids actively participate in the dust-gas dynamics to concentrate themselves to high density, leading to direct gravitational collapse and the formation of planetesimals.
I will review our current understanding of the streaming instability and planetesimal formation. Specifically, how the instability operates, under what conditions it drives strong concentration of solid materials, the initial mass function of the resulting planetesimals, and its interaction with turbulent gas will be examined.

302019-01-09 Wed
14:20~15:20
R1203
Kenji Kurosaki
[Nagoya University]
*Colloquium*
Thermal Evolution and Obliquity of Solar System Ice giants
Abstract

Our solar system has two ice giants, Uranus and Neptune. The intrinsic luminosity and the obliquity are different between Uranus and Neptune, though they have similar mass and radius. In particular, Uranus has a tilted rotation axis, which is supposed to be caused by a giant impact. In general, an impact event also changes the internal compositional distribution and drives mass ejection from the planet. The present luminosity of a planet infers not only the present atmospheric composition but also the origin of the accretion energy that the planet gained during its formation and impact event. I will talk thethermal evolution history and the impact event that reproduces the present Uranus’s intrinsic luminosity and obliquity. We demonstrate that the latent heat of those species keeps the atmosphere hot and thus the emission flux high for billions of years, resulting in acceleration of the cooling of ice giants. Also, we find that young ice giants with highly enriched atmospheres are much brighter in mid-infrared than those with unenriched atmospheres. This provides important implication for future direct imaging of extrasolar ice giants. We also perform hydrodynamics simulations for the impact events of Uranus-size ice giants composed of a water core surrounded by a hydrogen envelope using two variant methods of the smoothed particle hydrodynamics. We suggest the range of possible initial conditions for the giant impact on proto-Uranus that reproduces the present rotation tilt of Uranus and sufficiently provides the total angular momentum of the satellite system that can be created from the fragments from the giant impact.

Page Top
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.