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學術活動 > 學術演講及專題研討

學術演講及專題研討 (2020)

本所學術演講每週三下午2:20~3:20邀請國內外學者報告最新天文發展,歡迎大家參與。

中研院/臺大聯合學術演講系列中,我們將邀請世界知名研究人員報告物理科學領域最新發展及長程展望。

連絡窗口: 研討會委員 (talks_replace2@_asiaa.sinica.edu.tw)

近期學術演講: 2020-04-08 Wed 14:20~15:20 [R1203]
講者:Nanda Kumar
講題:CANCELLED
No. 時間地點 講者 題目/摘要
download PDF: 下載 PDF
12020-07-08 Wed
14:20~15:20
R1203
Emeric Le Floc'h
[CEA Saclay]
學術討論會
22020-05-27 Wed
14:20~15:20
R1203
Shigehiro Nagataki
[Riken]
學術討論會
32020-05-20 Wed
14:20~15:20
R1203
Chorng-Yuan Hwang
[NCU]
學術討論會
42020-04-29 Wed
14:20~15:20
R1203
Hidetoshi Sano
[NAOJ]
學術討論會
CANCELLED
52020-04-22 Wed
14:20~15:20
R1203
Denis Burgarella
[Laboratoire d'Astrophysique de Marseille]
學術討論會
CANCELLED
62020-04-15 Wed
14:20~15:20
R1203
Karen Yang
[NTHU/UMD]
學術討論會
CANCELLED
72020-04-08 Wed
14:20~15:20
R1203
Nanda Kumar
[Centro de Astrofísica da Universidade do Porto]
學術討論會
CANCELLED
82020-04-01 Wed
14:20~15:20
R1203
Hajime Sotani
[RIKEN]
學術討論會
CANCELLED
92020-03-25 Wed
14:20~15:20
R1203
Ellis Owen
[NTHU]
學術討論會
CANCELLED
102020-03-11 Wed
14:20~15:20
R1203
Ray-Kuang Lee
[Institute of Photonics Technologies, National Tsing Hua University]
學術討論會
Frequency-dependent squeezed vacuum source for broadband quantum noise reduction in advanced gravitational-wave detectors
摘要

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.

112020-03-04 Wed
14:20~15:20
R1203
Ray Li
[NTHU]
學術討論會
RIFT: A Robotic Telescope System for Cosmic Transients
摘要

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.

122020-02-25 Tue
14:20~15:20
R1203
Takuya Inoue
[Doshisha University]
專題研討
The effect of our local motion on the Sandage-Loeb test of the cosmic expansion
摘要

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.

132020-02-18 Tue
14:20~15:20
R1203
Seongjoong Kim
[Tokyo Institute of Technology]
專題研討
Deriving the dust properties in the TW Hya disks with the synthetic ALMA multiband analysis
摘要

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.

142020-02-12 Wed
14:20~15:20
R1203
Po-Yu Chang
[National Cheng Kung University, Institute of Space and Plasma Sciences]
學術討論會
Studies of high-energy-density plasma (HEDP) on a 1-kJ pulsed-power system
摘要

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.

152020-02-05 Wed
14:20~15:20
R1203
Alex Teachey
[Columbia]
學術討論會
The Search for Exomoons in Survey and Targeted Observations
摘要

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.

162020-01-15 Wed
14:40~15:40
R1203
Jongho Park
[ASIAA]
學術討論會
Acceleration and Collimation of the M87 Jet
摘要

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.

172020-01-08 Wed
14:20~15:20
R1203
Daichi Hiramatsu
[UCSB]
學術討論會
Recent Advancements in Core-collapse Supernova Observation Through the Global Supernova Project
摘要

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.

電話: 886-2-3365-2200 傳真: 886-2-2367-7849
一般事務: asiaa_replace2@_asiaa.sinica.edu.tw 媒體連絡: epo_replace2@_asiaa.sinica.edu.tw
台北市10617羅斯福路四段1號 中央研究院/台灣大學天文數學館11樓