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Activity > Colloquium

Colloquiums and Seminars(2020)

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 Colloquium: 2020-07-22 Wed 14:20~15:20 [R1203]
Speaker:Ellis Owen
Topic:Star-forming galaxies and the unresolved cosmic gamma-ray background
Abstract:The diffuse cosmic gamma-ray background (CGB) is thought be due to unresolved emission from AGN and star-forming galaxy (SFG) populations. The gamma-rays typically arise from the decay of neutral pions formed by hadronic processes in AGN jets (e.g. photo-pion interactions), or within the interstellar media of SFGs (via proton-proton interactions). Efforts to study the diffuse CGB have been carried out by gamma-ray telescopes EGRET and Fermi-LAT between energies of 30 MeV to 820GeV. However, the upcoming Cherenkov Telescope Array (CTA) will be capable of probing the TeV sky to a greater depth than current facilities and will undertake a blind, high-resolution survey of 25% of the extragalactic sky over 3 years between 50 GeV and 10 TeV. In this talk I will outline how SFG populations may imprint a signature in the CGB, and discuss the prospects for its detection. I will consider how CGB signatures may allow us to infer new information about the redshift evolution of SFG populations using spatial power spectral techniques, and will show how this could be further studied with complementary multi-wavelength and multi-messenger surveys.
No. Time/Place Speaker Topic / Abstract
download PDF: download talk PDF file
12020-10-07 Wed
14:20~15:20
R1203
Hsiang-Kuang Chang
[NTHU]
Colloquium
22020-08-26 Wed
14:20~15:20
R1203
Chow-Choong Ngeow
[NCU]
Colloquium
32020-08-19 Wed
14:20~15:20
R1203
Ya-Hui Yang
[NCU]
Colloquium
42020-08-12 Wed
14:20~15:20
R1203
Shigehiro Nagataki
[Riken]
Colloquium
CANCELLED
52020-07-22 Wed
14:20~15:20
R1203
Ellis Owen
[NTHU]
Colloquium
Star-forming galaxies and the unresolved cosmic gamma-ray background
Abstract

The diffuse cosmic gamma-ray background (CGB) is thought be due to unresolved emission from AGN and star-forming galaxy (SFG) populations. The gamma-rays typically arise from the decay of neutral pions formed by hadronic processes in AGN jets (e.g. photo-pion interactions), or within the interstellar media of SFGs (via proton-proton interactions). Efforts to study the diffuse CGB have been carried out by gamma-ray telescopes EGRET and Fermi-LAT between energies of 30 MeV to 820GeV. However, the upcoming Cherenkov Telescope Array (CTA) will be capable of probing the TeV sky to a greater depth than current facilities and will undertake a blind, high-resolution survey of 25% of the extragalactic sky over 3 years between 50 GeV and 10 TeV. In this talk I will outline how SFG populations may imprint a signature in the CGB, and discuss the prospects for its detection. I will consider how CGB signatures may allow us to infer new information about the redshift evolution of SFG populations using spatial power spectral techniques, and will show how this could be further studied with complementary multi-wavelength and multi-messenger surveys.

62020-07-08 Wed
14:20~15:20
R1203
Emeric Le Floc'h
[CEA Saclay]
Colloquium
CANCELLED
72020-07-01 Wed
14:20~15:20
R1203
Wen-Ping Chen
[NCU]
Colloquium
Dwindle Dwindle Little Stars --- Hunting for Substellar Objects Young and Old Rich and Poor
Abstract

With insufficient masses to sustain core hydrogen fusion, substellar objects continue to cool and fade after birth. Those heavier than 13 jupiter masses, called brown dwarfs, manage to ignite deuterium or lithium in the cores, thereby maintaining hydrostatic equilibrium for a short period of time. Those less massive than this do not undertake any nuclear reaction whatsoever in their lives and evolve like planets. So far a few thousand brown dwarfs and planetary-mass objects are known, almost exclusively found in the Galactic field in the solar neighborhood, i.e., they are already aged. Searching for the youngest substellar objects by spectroscopy is hampered by their faintness and often confusion with foreground or background contaminations. We describe our efforts to identify substellar candidates in nearby star-forming regions of 1 to 3 Myr old, when brown dwarfs are being formed or in their infancy. Our sample of substellar populations in star clusters, with known ages and distances, provides stringent constraints to confront theoretical modeling of ultracool atmospheres, and of chromospheric activity. We also present how these least-massive members as the most vulnerable members in stellar dynamics get ejected, leading to eventual disintegration of star clusters.

82020-06-17 Wed
14:20~15:20
R1203
Hsiang-Yi Karen Yang
[NTHU/UMD]
Colloquium
Cosmic-ray Feedback in the Universe
Abstract

Energetic feedback from stars and supermassive black holes (SMBHs) is key ingredient in the formation and evolution of galaxies and clusters, as shown by state-of-the-art cosmological simulations. However, predictive powers of these simulations are limited by the important but often neglected microphysics -- physical processes that are unresolvable and not captured by purely hydrodynamic simulations. One of such examples is cosmic rays (CRs). In this talk, I will discuss how CRs could influence feedback processes across different mass scales, including AGN feedback in galaxy clusters, Fermi bubbles within our Milky Way Galaxy, and galactic winds in dwarf galaxies. In particular, I will discuss how the detailed microscopic processes of CR transport could have dramatic impacts on the macroscopic properties of galaxies and clusters.

92020-05-27 Wed
14:20~15:20
R1203
Yao-Lun Yang
[University of Virginia]
Colloquium
The ALMA View of Complex Chemistry toward Embedded Protostars
Abstract

Planet formation may start during the embedded phase of star formation. In this scenario, the chemistry of embedded disks may directly determine the chemical composition of the forming planets. In recent years, observations discover several embedded protostars that have developed complex chemistry at the disk-forming region. However, only a few observations attempt to constrain the occurrence of complex molecules at embedded protostars and their relationships to star formation processes. I will present the first result of the Perseus ALMA Chemistry Survey (PEACHES), which aims to unbiasedly survey the chemistry toward 47 embedded protostars with a spatial resolution comparable to the size of disk-forming region. In PEACHES, we identify a variety of molecules and their isotopologues, including CCH, c-C3H2, SO, SO2, CH3OH, CH3CN, CH3OCHO, CH3OCH3, and C2H5OH. I will discuss the detection statistics of these molecules with respect to the physical properties of these protostars, such as their evolutionary stages and disk properties. I will also discuss the correlations of these complex molecules and the comparison with the chemistry of the protostars at other regions and environments. The occurrence rate of different complex molecules learned from the PEACHES survey will provide a primer for constraining chemical evolution during the star formation.

102020-05-20 Wed
14:20~15:20
R1203
Chorng-Yuan Hwang
[NCU]
Colloquium
From Dark Matter to Supermassive Black Holes
Abstract

Galaxies are believed to form in dark matter halos. In principle, we should be able to constrain the physical parameters of some dark-matter candidates by studying the properties of galactic halos. On the other hand, galaxy formation is believed to connect to the formation of the supermassive black hole located at the center of the galaxy; therefore, the formation and properties of active galactic nuclei (AGNs) should also be related to the dark matter halos. In this talk, I would like to show our results related to the studies of galaxies and AGNs and discuss possible effects on the connection between the dark matter halos and the supermassive black holes. I will also discuss some constraints about the properties of dark matter obtained from our investigations.

112020-05-13 Wed
14:20~15:20
R1203
Hsin-Yu Chen
[Black Hole Initiative Fellow, Harvard University]
Colloquium
Gravitational-wave observations from quarks to the Universe
Abstract

Advanced LIGO-Virgo have detected tens of stellar mass compact binary mergers, including binary black holes, binary neutron stars, and potentially neutron star-black hole mergers. These binary merger detections carried plenty of information about the binaries and the Universe. In this talk I will focus on a few topics we learned from the gravitational-wave detections: the electromagnetic counterparts of binary mergers, the neutron star equation-of-state, and the expansion rate of the Universe. I will first summarize current status of the field and the future projections. I will then discuss future plans to expand and improve the study.

122020-04-29 Wed
14:20~15:20
R1203
Hidetoshi Sano
[NAOJ]
Colloquium
CANCELLED
132020-04-22 Wed
14:20~15:20
R1203
Denis Burgarella
[Laboratoire d'Astrophysique de Marseille]
Colloquium
CANCELLED
142020-04-08 Wed
14:20~15:20
R1203
Nanda Kumar
[Centro de Astrofísica da Universidade do Porto]
Colloquium
CANCELLED
152020-04-01 Wed
14:20~15:20
R1203
Hajime Sotani
[RIKEN]
Colloquium
CANCELLED
162020-03-11 Wed
14:20~15:20
R1203
Ray-Kuang Lee
[Institute of Photonics Technologies, National Tsing Hua University]
Colloquium
Frequency-dependent squeezed vacuum source for broadband quantum noise reduction in advanced gravitational-wave detectors
Abstract

The astrophysical reach of current and future ground-based gravitational-wave detectors is mostly limited by the quantum noise, induced by vacuum fluctuations entering the detector output port. The replacement of this ordinary vacuum field with a squeezed vacuum one has proven to be an effective strategy to mitigate such quantum noise and it is currently used in advanced detectors. However, current squeezing cannot improve the noise in the whole spectrum, because of the Heisenberg uncertainty principle: when shot noise at high frequencies is reduced, radiation pressure at low frequencies is increased. A broadband quantum noise reduction is possible by using a more complex squeezing source, obtained reflecting the squeezed vacuum off a Fabry-Perot cavity, known as filter cavity. In this talk, I will report our recent implementation of squeezed vacuum states at 1064 nm. With a bow-tie optical parametric oscillator (OPO) cavity, and our home-made balanced homodyne detectors, noise reduction up to 10dB below the vacuum is measured. Applications of our squeezer to the gravitational wave detection will be reported, for the first demonstration of a frequency dependent squeezed vacuum source able to reduce quantum noise of advanced gravitational-wave detectors in their whole observation bandwidth. The experiment uses a suspended 300 m long filter cavity at National Astronomical Observatory of Japan (NAOJ), similar to the one planned for KAGRA, Advanced Virgo and Advanced LIGO, and capable to impress a rotation of the squeezing ellipse below 100 Hz.

172020-03-04 Wed
14:20~15:20
R1203
Ray Li
[NTHU]
Colloquium
RIFT: A Robotic Telescope System for Cosmic Transients
Abstract

RIFT is the abbreviation of Robotic Imagers For Transients, which will be the first robotic multiple-telescope observatory dedicated to the study of multi-messenger transients in Taiwan. The project has been approved by MOST and will be funded through the Young Scholar Fellowship Program, hopefully from 2020. In this talk, I will present the configuration of RIFT, our five-year plan, and the science that RIFT can do.

182020-02-25 Tue
14:20~15:20
R1203
Takuya Inoue
[Doshisha University]
Seminar
The effect of our local motion on the Sandage-Loeb test of the cosmic expansion
Abstract

Redshifts of an astronomical body measured at multiple epochs (e.g., separated by 10 years) are different due to the cosmic expansion. This so-called Sandage-Loeb test offers a direct measurement of the expansion rate of the Universe. However, acceleration in the motion of Solar System with respect to the cosmic microwave background also changes redshifts measured at multiple epochs. If not accounted for, it yields a biased cosmological inference. To address this, we calculate the acceleration of Solar System with respect to the Local Group of galaxies to quantify the change in the measured redshift due to local motion. Our study is motivated by the recent determination of the mass of Large Magellanic Cloud (LMC), which indicates a significant fraction of the Milky Way mass. We find that the acceleration towards the Galactic Center dominates, which gives a redshift change of 7 cm/s in 10 years, while the accelerations due to LMC and M31 cannot be ignored depending on lines of sight. We create all-sky maps of the expected change in redshift and the corresponding uncertainty, which can be used to correct for this effect.

192020-02-18 Tue
14:20~15:20
R1203
Seongjoong Kim
[Tokyo Institute of Technology]
Seminar
Deriving the dust properties in the TW Hya disks with the synthetic ALMA multiband analysis
Abstract

The multiwavelength analysis is one of the useful tools to understand the dust properties in protoplanetary disks. I study the synthetic ALMA multiband analysis to find the best three ALMA band combination for deriving the accurate dust temperature Tdust, optical depth τν, and dust opacity power-law index β (κν ∝ ν^β) using the ALMA archival data of the TW Hya disk. Through this approach, I can directly derive the three unknowns (Tdust, τν, β) without any assumptions on some of the dust properties. The synthetic multiband analysis results show that the Band [10,6,3] set is the best combination for minimizing the uncertainties of the dust properties derived from ALMA observations. The band combinations with Band 9 or 10 and with the large frequency intervals between the bands in the set give us stronger constraints on the dust properties. Also, large β and low Tdust are preferable for reducing the uncertainties of the dust properties. Some of those conditions are interpreted that the combination of optically thick and thin bands are required for obtaining stronger constraints on the dust properties. To examine the consistency of the synthetic analysis results, I apply the multiband analysis to ALMA archival data of the TW Hya disk at Band 4, 6, 7, and 9. I confirm that the trend of the synthetic model is consistent with the derivations from the real data. Additionally, I examine my synthetic analysis results with ALMA Band 1 which has been developing in ASIAA. The results show that the ALMA band combinations with Band 1 will improve the constraints on the dust properties.

202020-02-12 Wed
14:20~15:20
R1203
Po-Yu Chang
[National Cheng Kung University, Institute of Space and Plasma Sciences]
Colloquium
Studies of high-energy-density plasma (HEDP) on a 1-kJ pulsed-power system
Abstract

A 1 kJ pulsed-power system was built for studying various topics related to high-energy-density plasma, a regime with pressure greater than 1 MBar in general. Astrophysics and space sciences can be studied experimentally using the pulsed-power system due to the magnetohydrodynamic scaling. The pulsed-power system consists of twenty 1 μF capacitors, two rail-gap switches, two parallel plate transmission lines, and a cylindrical vacuum chamber orientated vertically. Two capacitors are first connected in series forming a brick. Five bricks are connected in parallel forming a wing. Finally, two wings are connected in parallel forming the whole capacitor bank, i.e., 5 μF in total. The system is charged to 20 kV. When it is discharged, a peak current of 110±20 kA with a rise time of 1.51±0.06 μs, i.e., a power of ∼ 700 MW, is provided. It is the pulsed current that will be used to drive different loads for different experiments. In particular but not restricted, supersonic plasma jets are generated via imploding conical-wire arrays made of tungsten wires using the pulsed-power system. The supersonic plasma jets will be used to simulate solar winds in the laboratory. When the generated supersonic plasma jet flows around an obstacle with or without surrounding plasma, either the Martian bow shock or wake cavity behind the moon will be studied based on the hydrodynamic similarity between the solar system and the laboratory. Besides generating plasma jets using conical-wire arrays, we are also developing a new scheme of generating plasma jets by compressing argon plasma plume, which will be generated by a plasma gun, using conical-theta pinches. Therefore, experiments can be conducted with higher repetition rates. To diagnose different experiments, a suite of ultrafast x-ray imaging systems such as time-integrated pinhole camera with an exposure time of 1 μs, a streak camera with a temporal resolution of 15 ps, and a framing camera with a temporal resolution of ns are being built by ourselves. Interferometry using a q-switch laser with the single longitudinal mode is planned to be used for plasma density measurements. Collective thomson scattering will be used for measuring local electron temperatures, ion temperatures, electron densities, and ion densities of the plasma. The laser pulse will be compressed using stimulated brillouin scattering (SBS) in water so that a temporal resolution of sub- ns can be achieved. Although all diagnostics are being developed, we have started imploding conical-wire arrays. Time-integrated images in visible light will be shown. This work was supported by the Ministry of Science and Technology (MOST), Taiwan, under Award Number 105-2112-M-006-014-MY3.

212020-02-05 Wed
14:20~15:20
R1203
Alex Teachey
[Columbia]
Colloquium
The Search for Exomoons in Survey and Targeted Observations
Abstract

Exomoons remain amongst the most elusive targets in observational astronomy. Nevertheless, these worlds stand to provide an unprecedented window into the formation and evolution of planetary systems. If the Solar System is any guide, we can expect exomoons will be geologically active and diverse, with the potential for hosting volatiles, atmospheres, and even life. Moreover, a thorough understanding of the population and occurrence rates of exomoons will help to place our own Solar System in a galactic context, speaking to the commonality of our own history. And though there are a variety of known pathways for moon formation, the discovery of exomoons may yet reveal heretofore unanticipated system architectures that defy easy explanation, thereby enriching our theoretical understanding of system formation. In this talk I will present my dissertation research, focusing first on a population study of exomoons in the Kepler data. I will then highlight my work related to the HST observation of Kepler-1625b, potentially the first transiting exomoon discovery. Finally, I will discuss my ongoing efforts to detect candidate exomoon signals in the Kepler data through deep learning, and argue that both targeted and survey observations have a role to play in finding exomoons going forward.

222020-01-15 Wed
14:40~15:40
R1203
Jongho Park
[ASIAA]
Colloquium
Acceleration and Collimation of the M87 Jet
Abstract

It is widely accepted that relativistic jets in AGNs are accelerated by strong magnetic fields. The magnetohydrodynamic (MHD) models of jet acceleration predict that (i) jet is gradually collimated by the pressure of an external medium confining the jet and (ii) jet collimation and acceleration occur simultaneously. Indeed, systematic collimation has been revealed in the jet of M87 inside the Bondi radius by many recent very long baseline interferometry observations. However, both the nature of the external confining medium and the presence of gradual jet acceleration in the jet collimation zone have not been well constrained by observations. In the first part of my talk, I briefly introduce our recent study of Faraday rotation in the M87 jet, where information on the external medium is imprinted. We found that the magnitude of the Faraday rotation measure systematically decreases with increasing distance from the black hole in the jet collimation zone. Our data is consistent with a picture that substantial winds, non-relativistic un-collimated gas outflows launched from hot accretion flows, confine the jet, resulting in the observed jet collimation. In the second part, I present the results of our recent kinematic analysis of the high-cadence monitoring data observed with the East Asian VLBI Network (EAVN) and of the Very Long Baseline Array (VLBA) archival data. We found that the jet is gradually accelerated from non-relativistic to relativistic speeds over a broad distance range that coincides with the jet collimation zone, which is in good agreement with the prediction of the MHD models.

232020-01-08 Wed
14:20~15:20
R1203
Daichi Hiramatsu
[UCSB]
Colloquium
Recent Advancements in Core-collapse Supernova Observation Through the Global Supernova Project
Abstract

Supernovae are among the most influential events in every astrophysical scale. New wide-field and high-cadence transient surveys enable us to watch supernovae from the moment of explosion. Paired with rapid and continuous monitoring facilities, these observations reveal unprecedented features that bridge our understanding of their progenitor systems to explosion mechanisms. From the discovery to follow-up, the Global Supernova Project is a world-wide collaboration of +150 supernova observers and theorists facilitated with the Las Cumbres Observatory and various other ground and space telescopes. In this talk, I will highlight the recent advancements in core-collapse supernova observation, especially in the context of the Global Supernova Project.

TEL: 886-2-3365-2200 FAX: 886-2-2367-7849
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