Colloquiums and Seminars

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   _replace_to_@_   asiaa.sinica.edu.tw)

Next Colloquium:
2025-02-19 Wed 14:20~15:20 [R1203]
Speaker:
Paul Tiede & Iniyan Natarajan (CfA/SAO)
Topic:
1. Reference HOPS Calibration Pipeline for millimetre-VLBI Arrays, 2. Interpol: A Polarized Imaging and Calibration Code for Heterogeneous VLBI Arrays
Abstract:
1. Reference HOPS Calibration Pipeline for millimetre-VLBI Arrays
We present a new version of the EHT-HOPS calibration pipeline (Blackburn et al. 2019), designed to process data from the evolving EHT array, for handling both current and future configurations. This updated pipeline supports the calibration of multiple years of EHT data and similar VLBI arrays, accommodating changes in instrumentation, frequency bands, and array configurations (with and without ALMA). The refactored pipeline improves performance, code integration, and usability, features updated diagnostics, and supports hybrid polarization bases, tested using 2017 M87 data. Planned future developments include complex bandpass and full polarization calibration, parallel processing, and integration with new data formats to generate standardized calibrated data products for all EHT campaigns.

2. Interpol: A Polarized Imaging and Calibration Code for Heterogeneous VLBI Arrays
Very Long Baseline Interferometry (VLBI) has paved the way for groundbreaking astrophysical discoveries, such as black hole jets, planet formation, and imaging of the shadow of a black hole. However, transforming the raw VLBI data into an interpretable image is a formidable challenge. VLBI imaging requires modeling an entire image from a sparse sampling of Fourier components and the complicated instrument response to the incident electric field. While the instrument response and image are traditionally analyzed separately, distinguishing instrumental effects from source structure is complex and non-linear for heterogeneous VLBI arrays such as the EHT or GMVA. In this talk, I will present Interpol, a novel Bayesian simultaneous imaging and calibration algorithm implemented in the VLBI software Comrade. Interpol can reconstruct the full Stokes polarized image and instrumental response for circular, linear, and mixed feed arrays. We demonstrate Interpol on various VLBI arrays, including the VLBA, Event Horizon Telescope, and VLBA sources, demonstrating improved image resolution with fewer image artifacts and discuss its place relative to Polconvert, a common tool used to convert ALMA data from linear to a circular feed basis.
Next ASIAA/NTU Joint Colloquium:
2025-02-18 Tue 14:20~15:20 [R104 CCMS-New Phys]
Speaker:
Daniel Wang (UMass & ASIAA)
Topic:
[CANCELLED] Exploring the Galactic Core: The mysteries of Sagittarius A* - our supermassive black hole
Abstract:
The presence of supermassive black holes (SMBHs) in galaxies is well known. But why most of them remain silent in today's Universe is poorly understood. Sgr A* at the center of our Milky Way Galaxy is an asymptotic example of such a low-luminosity SMBH. The proximity of Sgr A* provides a unique opportunity to observe and understand the dynamics of black hole activity and its interplay with its Galactic nuclear environment. Based primarily on deep X-ray observations and computer simulations, I will discuss what Sgr A* has been doing recently and how this interplay may have determined the life cycle of black hole activity and other galactic nuclear processes that profoundly affect the structure and evolution of our Galaxy. Such studies, complemented by observations of other nearby SMBHs and their environments, provide insights into the functioning of galactic ecosystems and astrophysical processes under extreme conditions.
Next Seminar:
2025-02-18 Tue 11:00~12:00 [R1203]
Speaker:
Yuya Fukuhara (Institute of Science Tokyo)
Topic:
Hydrodynamical simulations of the vertical shear instability with dynamic dust and cooling rates in protoplanetary disks
Abstract:
Turbulence in protoplanetary disks affects dust evolution and planetesimal formation. The vertical shear instability (VSI) is one of the candidate turbulence-driving mechanisms in the outer part of the disks. Since the VSI requires rapid gas cooling, dust particles in disks can influence and potentially control VSI-driven turbulence. However, VSI-driven turbulence has strong vertical motion, causing vertical diffusion of dust particles. We perform global two-dimensional hydrodynamical simulations of an axisymmetric protoplanetary disk to investigate how the VSI drives turbulence and maintains a balance between dust settling and diffusion. These simulations account for the dynamic interplay between dust distribution, cooling rates, and VSI-driven turbulence. We find that VSI mixing, dust settling, and the local dust cooling reach an equilibrium, forming a thick dust layer with a dimensionless vertical mixing coefficient of approximately $10^{-3}$. The ability of VSI to sustain this equilibrium depends on dust size and dust-to-gas mass ratio. Larger grains or lower mass ratios weaken the turbulence, leading to dust settling. Our results suggest that in VSI-dominated disks, dust grows under turbulence with intensity varying by dust size. Finally, I will talk about the application of the early disk stage and further planet formation.
Time/Place
Speaker
Topic / Abstract
Host
2025-02-18 Tue 11:00~12:00 R1203
Yuya Fukuhara
Institute of Science Tokyo
*Seminar*
Hydrodynamical simulations of the vertical shear instability with dynamic dust and cooling rates in protoplanetary disks
Min-Kai Lin
2025-02-18 Tue 14:20~15:20 R104 CCMS-New Phys
Daniel Wang
UMass & ASIAA
*ASIAA/NTU Joint Colloquium*
[<b>CANCELLED]</b> Exploring the Galactic Core: The mysteries of Sagittarius A* - our supermassive black hole
2025-02-19 Wed 14:20~15:20 R1203
Paul Tiede & Iniyan Natarajan
CfA/SAO
*Colloquium*
1. Reference HOPS Calibration Pipeline for millimetre-VLBI Arrays, 2. Interpol: A Polarized Imaging and Calibration Code for Heterogeneous VLBI Arrays
Keiichi Asada
2025-02-25 Tue 14:20~15:20 R104 CCMS-New Phys
J. Xavier Prochaska
UC Santa Cruz
*ASIAA/NTU Joint Colloquium*
Three Decades of Science in Silhouette
Ting-Wen Lan
2025-03-05 Wed 14:20~15:20 R1203
Shiang-Yu Wang
ASIAA
*Colloquium*
The status of the Transneptunian Automated Occultation Survey (TAOS II)
2025-04-15 Tue 14:20~15:20 R104 CCMS-New Phys
Ting-Wan Chen
NCU
*ASIAA/NTU Joint Colloquium*
Ting-Wen Lan
2025-05-27 Tue 14:20~15:20 R104 CCMS-New Phys
Sut-Ieng Tam
NYCU
*ASIAA/NTU Joint Colloquium*
Ting-Wen Lan
2025-10-15 Wed 14:20~15:20 R1203
Aaron Yung
STScI
*Colloquium*
Ke-Jung Chen
Past talks in 2025
2025-01-02 Thu 14:20~15:00 R1203
Kung-Yi Su
Harvard
*Seminar*
Self-regulation of black hole accretion via jets in atomic cooling halo
 
2025-01-08 Wed 13:00~14:00 R1203
Sal Fu
University of California, Berkeley
*Seminar*
Detailed Views of the Baryon Cycle of Dwarf Galaxies via Narrowband Imaging
 
2025-01-08 Wed 14:20~15:20 R1203
Claudio Ricci
Universidad Diego Portales
*Colloquium*
The mm continuum emission of accreting supermassive black holes
 
2025-01-17 Fri 14:20~15:20 R1203
Sunmyon Chon
MPA
*Colloquium*
Transition of the initial mass function in the early universe
 
2025-01-21 Tue 14:20~15:20 R1203
Sunmyon Chon
MPA
*Seminar*
Formation of massive seed BHs in the metal-enriched universe
 
2025-01-22 Wed 14:20~15:20 R1203
Fuheng Eric Liang
Heidelberg University
*Colloquium*
Cold molecular gas (cloud) properties in nearby galaxies
 
2025-01-23 Thu 14:20~15:20 R1203
Daniel Wang
UMass/ASIAA
*Seminar*
Nearby low-metallicity dwarf galaxies: feedback and end-products
 
2025-02-05 Wed 14:20~15:20 R1203
Chia-Yu Hu
NTU
*Colloquium*
High-resolution simulations of the interstellar medium coupled with a dust-evolving chemistry network
 
2025-02-10 Mon 10:00~11:00 R1412
Kaustav Mitra
Yale University
*Seminar*
Constraining galaxy formation models and cosmology using the smallest scales of redshift survey data
 
2025-02-12 Wed 14:20~15:20 R1203
Nhat-Minh Nguyen
IPMU
*Colloquium*
Decoding the Cosmos: Field-Level Inference from Galaxy Maps