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NTHU Institute of Astronomy
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Home > Recent Colloquia
Title: The Challenges and Joy of Doing Astronomy
Speaker: Professor Kong, Albert 江國興 (NTHU)
Time: 15:30pm 29nd Sep. 2017 (Friday)
Vanue: R521, IoA, 2nd General Building 綜二館R521
From solar eclipses, compact objects, to gravitational waves, I will share my experience of being an observational astronomer and show you how one can adopt new techniques in a rapidly changing world of astronomy.

Title: Cosmological simulation with Dust Formation and Destruction with ISM physics

Speaker: Dr. Aoyama, Shohei 青山尚平 (Academia Sinica Institute of Astronomy and Astrophysics)

Time: 3:30pm 22nd Sep. 2017 (Friday)

Vanue: R521, IoA, 2nd General Building 綜二館R521


Dust is an essential component in understanding star formation properties of galaxies both observationally and theoretically. When we consider the absorption of UV light by dust, the dust abundance and the grain size distribution are both important. Dust is formed and destroyed in multiple processes, which depend on the local metallicity, density and temperature. We implement these processes of dust into hydrodynamic simulation code GADGET3-Osaka taking into account of the evolution of dust size distribution. In order to realize it, we include dust formation end destruction processes in ISM, which are not only generation and destruction by supernovae but also accretion, coagulation and shattering. We obtained the time evolution of the abundance Ωdust(z), the mass function and the relation between dust-to-gas mass ratio to metallicity of each galaxy and radial profiles of dust grains. They agree with the corresponding observations.


Time: 2pm, Monday, August 14
Venue: R521, IoA, 2nd General Building
Speaker: Prof. Alex Lazarian (University of Wisconsin-Madison) 
Title: New way to study interstellar magnetic fields: velocity gradients

 I shall discuss two new techniques of magnetic field tracing using spectral line data. The techniques employ the gradients of velocity in order to trace magnetic fields in the diffuse interstellar media as well as to trace regions of star formation associated with the gravitational collapse. The differences between these techniques is that they use different observationally available measures, i.e. the first one uses the velocity centroids and the other uses velocity channel maps. I shall provide the theoretical foundations of the techniques that are based on our modern understanding of MHD turbulence, the numerical testing of the techniques as well as the comparison of the directions obtained with the velocity gradients using GALFA HI data and those of magnetic field as traced by Planck as well as 13CO data and far infrared polarimetry with BLASTPOL.

Special Seminar

Title:  Large Millimeter Bolometric Arrays for Cosmic Microwave Background Observations


Shuay-Pwu Patty Ho (Princeton University)


2pm-3pm, Thursday, August 3 at General Building II R521, IoA


The cosmic microwave background (CMB) continues to reveal new aspects of the large scale universe. For example, current projects are searching for evidence of primordial gravitational waves, for signatures sensitive to the sum of the neutrino masses, and for further understanding of the formation and growth of large structures under the influence of gravity in the accelerating universe. Technologies for ground-based and balloon-borne instruments measuring the polarization of the CMB have been well established and advanced in the last decade.

Two upgraded bolometric polarimeters on the Atacama Cosmology Telescope (ACT), the ACT Polarimeter (ACTPol) and the Advanced ACTPol, have made and will make sensitive measurements of the temperature and polarization in the Cosmic Microwave Background (CMB) with arcminute resolution.  In this talk, I will focus on the instrumentation of these state-of-the-art arrays, especially the Advanced ACTPol ones. I will conclude with the results coming from the two-season cosmological results presented in Louis et al. (2016) and describe the current progress on the all three ACTPol seasons.


Special Seminar

Title:  Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks

Masato Kobayashi (Nagoya University, Japan)

2pm-3pm, Monday, July 10 at GEN II R521


Recent radio observations show that giant molecular cloud (GMC) mass functions noticeably vary across galactic disks (e.g., Colombo et al. 2014). High-resolution magnetohydrodynamics simulations show that multiple episodes of compression are required for creating a molecular cloud in the magnetized interstellar medium (e.g., Inoue et al. 2012). To understand time evolution of GMC mass functions, we formulate the evolution equation for the GMC mass function to reproduce the observed profiles, for which multiple compressions are driven by a network of expanding shells due to H II regions and supernova remnants. We also introduce the cloud-cloud collision (CCC) terms in the evolution equation in contrast to previous work. In this seminar, I would like to present computed time evolutions and the following two suggestions:

(1) the GMC mass function slope is governed by the ratio of GMC formation timescale to its dispersal timescale whereas the CCC effect is limited only in the massive end of the profile,

(2) almost all of the dispersed gas contributes to the mass growth of pre-existing GMCs in arm regions whereas less than 60 percent contributes in inter-arm regions. Our results suggest that measurement of the GMC mass function slope provides a powerful method to constrain those GMC timescales and the gas resurrecting factor in various environments across galactic disks.

Time Coordinate: 3:30 pm 9th June 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: He-Feng Hsieh and Ing-Guey Jiang (NTHU)

Title: Imaging the Exoplanets


Imaging method is a viable pathway to detect exoplanet and characterize the planetary atmosphere. However, imaging exoplanets is challenging due to the small angular separation and extreme intensity contrast between the exoplanet and its host star (~1e-4 for self-luminous giant planets and ~1e-10 for rocky planets). Collaborating with Nanjing Institute of Astronomical Optics & Technology, Chinese Academy of Sciences, we are developing next generation Adaptive Optic (AO) systems aiming to detect and characterize rocky exoplanets. The design of AO systems, the observation strategy, data reduction techniques, and the method for retrieving physical properties of imaged objects will be introduced in this talk.


Time Coordinate: 3:30 pm 2nd June 2017 (Friday)

Space Coordinate: NTHU General Building II, R521


Speaker A: Chia-Hsuan Cheng (NTHU)

Title: Variations of the x-ray flux from the globular cluster black hole


Speaker B: Ren-Yi Deng (NTHU)

Title: Predicting the spectrum of ejection velocities of hypervelocity stars

Time Coordinate: 3:30 pm 26th May 2017 (Friday)

Space Coordinate: NTHU General Building II, R521


Speaker A: Hao-Yuan Duan (NTHU)

Title: Kinematics of a Young Low-mass Star-forming Core


Speaker B: Sheng-Jun Lin (NTHU)

Title: Detection of Interstellar Ortho-D2H+ with SOFIA

Title: Statistical analysis of the observational data of Gamma Ray Bursts (GRBs)

Speaker: Dr. Jakub Ripa  (Leung Center for Cosmology and Particle Astrophysics National Taiwan University)

Time: 12:20pm, May 25 (Thu), 2017

Location: Room 501, The 2nd General Building

Time Coordinate: 3:30 pm 12th May 2017 (Friday)

Space Coordinate: NTHU General Building II, R521


Speaker A: Pou-Ieng Cheong (NTHU)

Title: ALMA Observations of Spiral Accretion Flows Towards Extremely Young Protostars


Studying the accretion flows toward extremely young protostars is an important step for understanding how the protostars and the protoplanetary disks are assembled in the early stage of star formation. The accretion flows are commonly seen in the MHD numerical simulations; however, it is rarely observed toward young protostars. Here we present our ALMA observations of the accretion flows around the extremely young protostar VLA1623A with a Keplerian disk likely just formed (Murillo, Lai, et al. 2013). "Dendrogram" algorithm (Goodman et al. 2009) are used to identify the accretion flows, and we find the three brightest "branches" and their associated "leaves" likely correspond to the spiral structure flowing toward the central young cluster. We further compare the three accretion flows in the position-position-velocity cube to the CMU model (Ulrich 1976; Cassen & Moosman 1981) which describe the velocity structure of the gas accreting to the central protostar with constant angular momentum. We find that our identified branch structures well match with the CMU model.


Speaker B: Li-Wen Liao (NTHU)

Title: Anatomy of the internal bow shocks in protostellar jet

Time Coordinate: 3:30 pm 5th May 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Dr. Lung-Yih Chiang (ASIAA)

Title: Excessive shift of the CMB acoustic peaks of the Cold Spot area


Measurement of the acoustic peak positions of the cosmic microwave background (CMB) temperature anisotropies has been instrumental in deciding the geometry and content of the universe. Acoustic peak positions vary from patch to patch in different parts of the sky due to statistical fluctuation. We present the statistics of the peak positions of small patches from ESA Planck data. It is found that the peak positions have significantly high variance compared to the 100 CMB simulations with best-fit LambdaCDM model with lensing and Doppler boosting effects included, both of which can significantly shift the peaks of small patches. 

Examining individual patches, we find the one containing the mysterious "Cold Spot", an area near the Eridanus constellation where the temperature is lower than Gaussian theory predicts, displays large synchronous shift of peak positions towards smaller multipole numbers (i.e. larger scales) with significance lower than 1.11 x 10^{-4}. The combination of large synchronous shifts in acoustic peaks and lower than usual temperature at the Cold Spot area results in a 4.73 sigma detection (significance p~1.11 x 10^{-6}) against the LambdaCDM model, prompting us to propose one of the possible accounts for both anomalies: some localised unknown force to stretch the space around the Cold Spot area so that the acoustic peak positions are shifted towards large scales and the temperature is dragged down.

Time Coordinate: 3:30 pm 28th April 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Dr. Kevin Jun-Yi Koay (ASIAA)

Title: Interstellar scintillation as micro-arcsecond scale probes of compact radio AGNs


The variability of compact AGNs on timescales of hours and days observed at cm-wavelengths is predominantly caused by scattering in the ionized interstellar medium (ISM) of our Galaxy. With the ISM as an AU-scale interferometer, interstellar scintillation (ISS) provides an exquisite probe of the micro-arcsecond scale structure of AGNs. I present results from the Micro-arcsecond Scintillation-Induced Variability (MASIV) Survey of ~500 compact AGNs and its follow-up observations.

I will discuss the dependence of ISS on intrinsic AGN properties, including their gamma-ray loudness, radio spectral indices, optical spectral classification, redshift, and intrinsic variability. I will show how we have used ISS to probe the source size-redshift relation of compact AGNs, and place strong constraints on the turbulent properties of the intervening intergalactic medium.

Future surveys of ISS with highly-sensitive instruments such as the SKA will potentially probe the micro-arcsecond structure of faint (~100 muJy to 10 mJy) AGNs, thereby complementing studies at comparable angular resolutions with Space-VLBI and mm-VLBI which are limited only to the brightest AGNs.

Time Coordinate: 3:30 pm 21st April 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Prof. Guo-Chin Liu (Tamkang University)

Title: CMB Anomalies and CMB induced Polarization in Distant Galaxy Clusters

Time Coordinate: 3:30 pm 14th April 2017 (Friday)

Space Coordinate: NTHU General Building II, R521


Speaker A: Sheng-Feng Chung (NTHU)

Title: High-frequency quasi-periodic oscillations in black hole binaries


Speaker B: Pattana Chintarungruangchai (NTHU)

Title: The Hot Exo-Neptune GJ3470b

Time Coordinate: 3:30 pm 7th April 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Dr. Rosemary Pike (ASIAA)

Title: Exploring the 5:1 Neptune Resonance: Dynamics, Population, and Origin

The long-term evolution of objects in the outer n:1 resonances with Neptune provide clues to the evolutionary history of the Solar System. Based on 4 objects with semi-major axes near the 5:1 Neptune resonance, we estimate a substantial and previously unrecognized population of objects, perhaps more significant than the population in the 3:2 (Plutino) resonance. Understanding the characteristics and trapping history for objects in these populations is critical for constraining the dynamical history of the solar system. The 4 objects detected in the Canada-France Ecliptic Plane Survey (CFEPS) were classified using dynamical integrations. Three are resonant, and the fourth appears to be a resonance diffusion object, part of a population which exited the resonance through chaotic diffusion. The dynamical behavior of the known objects, suggests that the trapping mechanism for the 5:1 resonance is resonance sticking from the scattering objects. This is consistent with the measured surface colors of the objects. However, our investigations of Solar System evolution models show that they do not emplace a sufficiently large population into this resonance, and the source of this large population remains unexplained.

Time Coordinate: 3:30 pm 31st March 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Dr. Hyosun Kim (ASIAA)

Title: Circumstellar Spirals/Shells/Arcs: the Messages from Binary Stars


A growing consensus has been developing in the past few decades that binarity is key in providing an understanding of the morphological diversities of the circumstellar envelopes (CSEs) surroudning stars in the Asymptotic Giant Branch (AGB) to Planetary Nebula (PN) phase. However, despite extensive efforts to detect companions of AGB stars and the central stars of PNe, the number of detected binaries in particular with their orbital properties derived are still small. As a consequence, the possible roles of binaries in the shaping of PN and in the CSEs of AGB stars have yet to be clarified.

On the other hand, recurrent (ring/spiral/arc) patterns are often found in the CSEs of AGB stars and the outer halos of pre-PNe and PNe. Such patterns provide a fossil record and can be used to trace the temporal history of the mass loss dynamics during the AGB phase. In this regard, recent molecular line observations using radio interferometric facilities such as ALMA and JVLA have revealed the spatio-kinematics of such patterns. Numerical simulations of binary interactions producing spiral-shells have been extensively developed and are now becoming increasingly sophisticated, revealing new probes for extracting the stellar and orbital properties from these patterns.

I will review the recent theoretical and observational investigations on the circumstellar spiral-shell patterns and discuss their implications in linking binary properties to the asymmetric ejection events in the post-AGB phase.

Time Coordinate: 3:30 pm 24th March 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Dr. Min-Kai Lin (ASIAA)

Title: Hydrodynamic processes in planet formation


Planet formation is rapidly developing field in astronomy. We are in an era of not only regular detections of extra-Solar planets, but also the planet formation process itself. Recent observations of protoplantary disks reveal stunningly detailed sub-structures such as gaps, rings, spirals and lopsided asymmetries. Understanding the origin of these structures, for example due to unseen planets or dynamical instabilities, can place constraints on the physical conditions for planet formation. I will discuss some works on hydrodynamic processes important to protoplanetary disk/planet evolution and in explaining observations. These include gravitational instabilities, vortex formation, and the vertical shear instability for generating turbulence in disks. I will also present a new effort to study dusty protoplanetary disks through a set of modified fluid dynamic equations.

Time Coordinate: 3:30 pm 17th March 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Dr. Hsi-Wei Yen (European Southern Observatory, Germany)

Title: Formation and Evolution of Protoplanetary Disks


Protoplanetary disks are sites of planet formation. It is essential to study how protoplanetary disks form in dense cores and evolve, to understand the environment of planet formation. In this presentation, I will introduce our observational studies on protoplanetary disks at different evolutionary stages, from the formation and growth of protoplanetary disks around deeply embedded young protostars (Class 0 stage), to the gas dynamics of the material surrounding protoplanetary disks around more evolved protostars (Class I stage), and to the properties of a larger sample of protoplanetary disks around young stellar objects after the main accretion phase (Class II stage).

Two talks on 3/14 (Tue) and 3/17 (Fri)

Location: Room 521

Time: 12:10 pm


(1) Speaker: Prof. Wenwu Tian (Calgary University, Canada & National Astronomical Observatories of China)

Time: 12:10pm, 3/14 (Tue), 2017

Title: Supernova remnants and the origin of cosmic rays


I will first give a short introduction to Supernova Remnant (SNR), then focus on a recent hotspot of SNR research: Studying the origin of cosmic rays by TeV gamma-ray survey in the Galactic plane. TeV SNRs show great promise to increase our understanding of cosmic rays. By neutral hydrogen (HI) 21 cm continuum and HI line observations to some TeV SNRs, we have measured their kinematic distances which help improving our understanding of cosmic rays' origin.


(2) Speaker: Dr. Jeng-Lun Chiu (Space Sciences Lab, UC Berkeley, USA)

Time: 12:10pm, 3/17 (Fri), 2017

Title: The Compton Spectrometer and Imager (COSI) Project


The Compton Spectrometer and Imager (COSI) project is an effort to develop the next generation Compton telescope of higher sensitivity. COSI is currently a balloon-borne telescope project. The heart of COSI is an array of 12 cross-strip germanium detectors, each with 15mm x 80mm x 80mm dimension and full 3D position resolution of less than 2 mm^3. COSI performs Compton spectroscopic imaging in the 0.2-10 MeV gamma-ray band with a field of view about 50 degrees across and capability of polarization measurement. It is also well suitable for monitoring transient events. Several COSI balloon flights have been conducted. The most recent flight was launched from Wanaka, New Zealand, in May 2016 with a super-pressure balloon flying for 47 days. During this flight, COSI discovered GRB160530A and detected several sources, including the 511-keV emission from the galactic center, the Crab, Cen A, and Cyg X-1. The COSI collaboration is now working for the next flight in spring 2019, to launch again from Wanaka, New Zealand, for a 100-day flight. I will report the current status of the COSI project. COSI is a join effort of several institutions in Taiwan, US and France.