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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 (2024)

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,精選影片可在本所Youtube 頻道收看。

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)

近期專題研討: 2024-07-26 Fri 12:00~13:30 [R1412]
講者:Tai-Peng Tsai
講題:Boundary gradient estimates and second derivative blow-up for Stokes equations with Navier boundary condition
摘要:This research is motivated by the boundary effect on the regularity properties of incompressible fluids, noting the recent numerical evidence of boundary singularity of inviscid fluids. For the Stokes system (for linearized viscous fluids), it is well-known that one can improve spatial regularity in the interior, but not near the boundary if it is coupled with the no-slip boundary condition (BC). We show that, under the Navier BC with either infinite or finite slip length, we have Caccioppoli type gradient estimates near a flat boundary, contrary to the no-slip BC case. However, for every finite slip length and q>1, we construct a finite energy solution of Stokes equations with nonhomogeneous Navier BC in the half space with bounded, compactly supported boundary data, bounded velocity and velocity gradient, but unbounded second derivatives in L^q locally near the boundary. To show this, we first derive the explicit Poisson kernel of Stokes equations in the half space with nonhomogeneous Navier BC for both infinite and finite slip length, and derive its estimates. Moreover, we give an alternative proof of the blow-up using a shear flow example, which solves both Stokes and Navier-Stokes equations, but has no spatial decay. This talk is based on joint work with Hui Chen and Su Liang, arXiv:2306.16480 and arXiv:2406.15995
近期學術演講: 2024-07-31 Wed 14:20~15:20 [R1203]
講者:Hyunbae Park
No. 時間地點 講者 題目/摘要 主持人
12024-07-26 Fri
12:00~13:30

R1412
Tai-Peng Tsai
[University of British Columbia]
理論天文專題研討
Boundary gradient estimates and second derivative blow-up for Stokes equations with Navier boundary condition
摘要

This research is motivated by the boundary effect on the regularity properties of incompressible fluids, noting the recent numerical evidence of boundary singularity of inviscid fluids. For the Stokes system (for linearized viscous fluids), it is well-known that one can improve spatial regularity in the interior, but not near the boundary if it is coupled with the no-slip boundary condition (BC). We show that, under the Navier BC with either infinite or finite slip length, we have Caccioppoli type gradient estimates near a flat boundary, contrary to the no-slip BC case. However, for every finite slip length and q>1, we construct a finite energy solution of Stokes equations with nonhomogeneous Navier BC in the half space with bounded, compactly supported boundary data, bounded velocity and velocity gradient, but unbounded second derivatives in L^q locally near the boundary. To show this, we first derive the explicit Poisson kernel of Stokes equations in the half space with nonhomogeneous Navier BC for both infinite and finite slip length, and derive its estimates. Moreover, we give an alternative proof of the blow-up using a shear flow example, which solves both Stokes and Navier-Stokes equations, but has no spatial decay. This talk is based on joint work with Hui Chen and Su Liang, arXiv:2306.16480 and arXiv:2406.15995

22024-07-30 Tue
15:00~16:00

R1203
Rema Ahmid
[Technical University of Denmark]
專題研討
3D printed antennas for space applications
摘要

In the rapidly advancing field of space technology, the integration of 3D printing in the manufacturing of antennas offers innovative solutions to existing challenges. This talk will explore the development and application of 3D printed antennas for space missions, drawing on my personal academic journey and research experiences. I will begin with a brief introduction of myself, Rema Ahmid, detailing my educational background and the pivotal moments that led me to specialize in space antenna technology and why I have arrived to Taiwan. My journey began during my bachelor's studies at the University of Southern Denmark, where I conducted a project on assessing CubeSats as space-based radio antennas. This project involved the use of 3D printed feed horns and was under the supervision of Roman Gold. Following this, I pursued a master's thesis at the Technical University of Denmark (DTU) and currently collaborating with IETR, Rennes, focusing on phased arrays for space applications utilizing 3D geometries and additive manufacturing. This work aimed to enhance antenna performance for GEO satellites through the development and testing of modular array architectures made using selective laser melting (SLM), a cutting-edge metal additive manufacturing technique. The thesis will contribute to the European Space Agency's MOSAIC project, emphasizing the experimental validation of these advanced antennas. Throughout the talk, I will elaborate on the technical aspects and findings from both my bachelor's and master's theses, highlighting the benefits and challenges of using 3D printing in antenna fabrication.

Satoki Matsushita
32024-07-31 Wed
14:20~15:20

R1203
Hyunbae Park
[University of Tsukuba]
學術討論會
Junsup Shim
42024-08-14 Wed
14:20~15:20

R1203
Martin Bizzarro
[StarPlan]
學術討論會
Hsien Shang
52024-08-21 Wed
14:20~15:20

R1203
Chian-Chou Chen
[ASIAA]
學術討論會
62024-09-04 Wed
14:20~15:20

R1203
Chin-Ping Hu
[National Changhua University of Education]
學術討論會
Chian-Chou Chen
72024-09-11 Wed
14:20~15:20

R1203
Sherry Suyu
[Technical University of Munich]
學術討論會
Keiichi Umetsu
82024-09-18 Wed
14:20~15:20

R1203
Uyama Taichi
[California State Northridge]
學術討論會
Michihiro Takami
92024-09-25 Wed
14:20~15:20

R1203
Chris Reynolds
[University of Maryland]
學術討論會
Min-Kai Lin
102024-10-09 Wed
14:20~15:20

R1203
Zhi-Yun Li
[University of Virginia]
學術討論會
Hsien Shang
2024年已舉辦的學術演講
12024-01-03 Wed
14:20~15:20

R1203
Cheng Chen
[University of Leeds]
學術討論會
Dancing with the binary: diverse orbital dynamics and stability around circumbinary systems
摘要

Recent observations have revealed that circumbinary disks misaligned to the binary orbit could be common in the universe. Dissipation in the disc causes it to move either towards coplanar alignment or polar alignment. In the polar configuration, the disc is perpendicular to the binary orbit, with the disc angular momentum vector aligned to the binary eccentricity vector. Since planets form inside disks, circumbinary planets may also form misaligned to the binary orbit. We explore the dynamical evolution and stability of misaligned circumbinary planets. We find that around eccentric binaries, the most stable orbits are those that are close to a polar alignment. Moreover, we find that two circumbinary planets in the same system may result in complicated orbital dynamics and resonances. These interactions could efficiently lead to the formation of free-floating planets because hosting multiple planets around a binary is more challenging than in a single star system.

 
22024-01-17 Wed
14:20~15:20

R1203
Ming-Tang Chen
[ASIAA]
學術討論會
The Greenland Telescope, Black Hole Shadow, and Photon Ring
摘要

The Greenland Telescope [i] started scientific observations in 2018. Currently, the Telescope is located at Pituffik Space Base (PSB) in the northwestern corner of Greenland and has participated in the observing campaigns of the Event Horizon Telescope (EHT) and the Global Millimeter-wave VLBI Array(GMVA). The first scientific results featuring the GLT revealed a panoramic picture of the black hole and its jet at a 3 mm wavelength [ii]. The next GLT result will come from the 2018 EHT observations, displaying a sharper black hole image at 1.3 mm. As is expected, many new and exciting research outcomes will be published from the observations after 2018.

The next stage of the GLT project aims to capture the most distinctive signature of general relativity–the photon rings. In their current planning, the EHT and its next-generation follow-up cannot resolve the features of the photon rings because of the lack of the required angular resolution. To achieve such a scientific breakthrough, we will relocate the GLT to Summit Station and conduct observations at 600 GHz and higher. I will present the status of the GLT and its plan for achieving our next goals.

[i] Ming-Tang Chen et al 2023 PASP 135 095001
[ii] Lu, R.-S., Asada, K., Krichbaum, T. P., et al. 2023, Nature, 616, 686

 
32024-01-22 Mon
14:20~15:20

R1203
Brandon Hensley
[JPL]
學術討論會
Rethinking the Nature of Interstellar Dust
摘要

Interstellar dust has long been modeled with separate silicate and graphite/amorphous carbon components. In this talk, I will argue that initially distinct populations of stardust get rapidly homogenized in the ISM into a composite material ("astrodust"). I will show that the astrodust+PAH model is compatible with current observational constraints on dust extinction and emission in the diffuse ISM, and that it provides a more natural explanation for the observed polarized emission than do two-component models. I will discuss implications for the lifecycle of dust in galaxies.

 
42024-01-24 Wed
14:20~15:20

R1203
Chandra Shekhar Saraf
[KASI]
專題研討
Tomographic cross-correlation of the CMB lensing and galaxy clustering - systematic errors from redshift bin mismatch of galaxies
摘要

The effect of gravitational lensing of the cosmic microwave background (CMB) provides a unique opportunity to obtain a picture of the gravitational potential of the large-scale structure of the Universe at very high redshifts. Tomographic cross-correlation of the gravitational potential with other tracers of the large-scale structure at known redshifts allows tracing the evolution of the structure and testing cosmological models. However, the analysis of upcoming data will require a very good understanding of any systematic errors that may bias cross-correlation measurements. In this talk we will present studies of systematic errors arising from redshift bin mismatch of galaxies with photometric redshift uncertainties. We show their impact on the cross-correlation measurement and cosmological parameter estimates for future data sets. We also present an efficient method for removing the errors.

 
52024-01-31 Wed
14:00~14:45

R1412
Hiddo Algera
[Hiroshima University]
專題研討
The Dust and Interstellar Medium Properties of Galaxies in the Epoch of Reionization
摘要

Over the last decade, ALMA has revolutionized our understanding of the interstellar medium (ISM) conditions of distant galaxies. For one, ALMA has now detected (sub-)millimeter continuum emission from dozens of galaxies at z > 6.5, establishing the importance of dust-obscured star formation already within the first 800 Myr after the Big Bang. Moreover, through various bright emission line diagnostics such as [CII]158 and [OIII]88, ALMA can be used to directly study the physical conditions and kinematics of the ISM within the earliest galaxies.

In this talk, I will review what we have learned about the dust and interstellar medium properties of high-redshift galaxies, focusing specifically on the Cycle 7 ALMA Large Program REBELS and its follow-up studies. In addition, I will present recently taken JWST/NIRSpec IFU observations of REBELS sources and discuss how we can use the combined power of ALMA and JWST to learn about early dust build-up in galaxies.

 
62024-01-31 Wed
14:45~15:30

R1412 & meet.google.com/qqi-gnyt-vxm
Sunil Simha
[UC Santa Cruz]
專題研討
Mapping the cosmic web along FRB sightlines
摘要

Fast radio bursts (FRBs) are among the newest tools in observational astrophysicists’ repertoire to study ionized gas. Their unique, millisecond-duration radio signal is subject to propagation effects in the intervening plasma. One such effect is the plasma dispersion of FRB pulses. FRB dispersion measures (DMs) quantify the net free electron column density through the sightline. FRB DMs can be precisely measured (~0.1%) and thus are sensitive to the most diffuse plasma in the intergalactic medium (IGM) that traditional probes have found challenging to illuminate. This ability to provide novel constraints on plasma has motivated studies of the circumgalactic medium (CGM) of galaxies intersecting FRB sightlines and the cosmic web filaments of the IGM. In my talk, I will highlight some of the work already done leveraging FRBs and introduce the FLIMFLAM survey. The survey is an ongoing endeavor to map foreground matter density along ~20 FRB sightlines. To this end, the survey measures spectroscopic redshifts of the foreground galaxies. Its ultimate aim is to produce statistical constraints on key parameters describing matter distribution in the universe, including the fractions of ionized baryons residing in the diffuse IGM and the virialized gas of halos. We expect our first data release by the end of 2023. Meanwhile, some of our recent work focuses on interesting sightlines that exhibit unusually large DMs. Through foreground mapping, we confirm large host galaxy DMs in some sightlines while others show numerous foreground structures. I will also discuss one sightline where foreground mapping revealed cluster gas that enhanced the DM. I will end with prospects for FRB-based analyses in the near future that I'm excited for.

 
72024-02-07 Wed
14:00~14:45

R1412
Konstantin Gerbig
[Yale]
專題研討
Novel insights in planet formation: Formation of dusty filaments & orbital alignment in binary systems
摘要

Planet formation within protoplanetary disks presents an array of unsolved questions, two of which I aim to address in this talk.

First, I'll explore how dust is concentrated to densities sufficiently high for the on-set of planetesimal formation. By drawing a parallel to the formation of underwater sand ripples, I introduce a novel linear, axisymmetric instability capable of transforming turbulent dust regions in a disk's mid-plane into dense, azimuthally stretched filaments. This process hinges on a rapid decrease in diffusivity with heightened dust concentration, a premise supported by our numerical simulations where dust-gas interactions self-generate turbulent diffusion.

Second, I will discuss planet-hosting (wide) binary systems, where recent studies suggest a prevalence of coplanar arrangement of planetary and binary orbits. I propose that this alignment, along with observed obliquity distributions in exoplanetary systems, can be attributed to viscous dissipation in the disk during binary-driven precession. Moreover, our analysis predicts that the alignment tendency should weaken as the binary stellar mass ratio increases, and indeed, I will present new evidence for this trend in TESS data of exoplanet-hosting binaries.

 
82024-02-07 Wed
14:45~15:30

R1412 & meet.google.com/tdw-qxix-tki
Chayan Mondal
[IUCAA]
專題研討
AstroSat UV Deep Field - A unique view of the distant galaxies
摘要

Observation of deep fields provides a unique scope to explore multiple aspects of extragalactic astronomy by effectively detecting the faintest objects in the distant universe. We utilize the unique angular resolution, sensitivity, and field of view of the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat to perform deep imaging of the GOODS-north field in the FUV and NUV bands reaching a 3$\sigma$ depth of ~ 27.3 AB mag. Our UV flux measurements of the identified sources complement existing rich multiband data in the GOODS-N field and enable us to probe properties of galaxies between redshift ~ 0 and 1. We study the internal dust extinction of galaxies by constraining their UV continuum slope (bet). Combining with HST F275W, F336W, and KPNO U bands, the UVIT data helped us to estimate beta of 465 galaxies between redshift 0.40 and 0.75. Our beta measurements add new data points to the least-explored redshift regime, further reinforcing the gradual reddening of the galaxy UV continuum with cosmic time. Using a sub-sample of 83 galaxies, we further constrained the beta - IRX law at redshift ~0.5. I Will also discuss how observation of AstroSat UV deep field is unique to constrain the faint end slope of UV Luminosity Function, testing the nature of SFR scaling relation, and finally to search for Lyman Continuum leaking galaxies beyond redshift ~ 1, which are important to understand galaxy evolution and cosmic reionization process.

 
92024-02-16 Fri
14:20~15:20

R1203
Chun-Hao To
[OSU]
專題研討
Multi-probe cosmology: challenges and opportunities in the next decade
摘要

In the next decade, large cosmological surveys will map billions of galaxies and measure cosmic structure to unprecedented precision via multiple cosmological probes. Using results from the Dark Energy Survey as an example, this talk will outline the challenges and opportunities of cosmological analyses in the presence of rich astrophysics and observational systematics. In particular, I will describe different cosmological probes measured from the Dark Energy Survey and summarize recent progress on joint analyses of galaxy clustering, weak lensing, and galaxy cluster abundances. I will then highlight the challenges for future, larger experiments such as Rubin Observatory's LSST and describe our progress in tackling these challenges through sophisticated simulations and an AI-enhanced analysis pipeline. I will conclude the talk by identifying a unique opportunity for overlapping imaging surveys and Cosmic Microwave Background surveys that will unlock the constraining power of small-scale weak gravitational lensing measurements.

 
102024-02-21 Wed
14:20~15:20

R1203
Ya-Lin Wu
[NTNU]
學術討論會
Monitoring accreting brown dwarfs at Lulin
摘要

Variability of mass accretion provides important information about disk evolution and the geometry of the accretion flows. While there are many studies focusing on young stars, accretion monitoring in the substellar regime has been relatively uncommon. At optical wavelengths, the H-alpha emission is a bright accretion tracer, proving an opportunity to observe young brown dwarfs with small telescopes. In this talk, I will introduce our ongoing efforts of monitoring brown dwarfs with the one-meter telescope at Lulin Observatory and present the preliminary results.

 
112024-02-26 Mon
11:00~12:00

R7S1, Cosmology Hall
Jia Liu
[IPMU]
理論天文專題研討
[Joint LeCosPA-ASIAA Seminar] Cosmology with Massive Neutrinos
摘要

Abstract: Ghostly neutrino particles continue to bring surprises to fundamental physics, from their existence to the phenomenon of neutrino oscillation, which implies their nonzero masses. Their exact masses, among the most curious unknowns beyond the Standard Model of particle physics, can soon be probed by the joint analysis of ongoing and upcoming cosmological surveys including Rubin LSST, Euclid, Roman, DESI, PFS, Simons Observatory, CMB-S4, and LiteBRID. In this talk, I will discuss ongoing works studying the effects of massive neutrinos and will draw a roadmap towards discovering the neutrino mass over the next decade. Bio: Jia Liu (https://liuxx479.github.io/) is a computational and observational cosmologist. Liu is an associate professor at Kavli IPMU in the University of Tokyo and the director of the recently established Center for Data-Driven Discovery (CD3) at Kavli IPMU. Liu received her PhD from Columbia University in 2016, was an NSF postdoctoral fellow at Princeton (2016-2019) and a BCCP postdoctoral fellow at UC Berkeley (2019-2021).

 
122024-02-29 Thu
14:20~15:20

R1203
Seamus Clarke
[ASIAA]
專題研討
Filaments in a multi-scale framework of star formation
摘要

Star formation is a process covering orders of magnitude in spatial and density scales, manifesting as a hierarchy of interacting structures. This necessitates that any complete study of this process must be multi-scale by nature. In this talk I will present my work showcasing the key role that filaments play across spatial scales and how they shape star formation, from >10 pc molecular clouds down to 100 AU protostellar disks. Using a combination of numerical hydrodynamical simulations with molecular line and dust continuum observations, I will focus on addressing a number of open questions surrounding filaments in this multi-scale framework: How do filaments fragment into cores/clumps? How does feedback interact with filaments? How are filaments shaped by their environment? I will conclude by introducing the new ASIAA-SMA key project STREAMS, which will homogeneously calculate the turbulent, magnetic and gravitational energies across multiple scales for 23 massive, star-forming clumps. With its combination of multiple datasets and large sample size, STREAMS will answer the many key, open questions about multi-scale energetics and its link to fragmentation, and high-mass star and cluster formation.

 
132024-03-05 Tue
14:20~15:20

R1203
Tomomi Sunayama
[University of Arizona]
專題研討
Precision cosmology with galaxies and galaxy clusters - projects and prospects with ongoing and future galaxy surveys
摘要

Over the next decade, large galaxy surveys will map billions of galaxies and probe cosmic structure with high statistical precision. Their ultimate goal is to develop a comprehensive model that describes the Universe from end to end. In this talk, I will introduce two of the most powerful cosmological probes: galaxy clusters and galaxy clustering. These probes offer insights into the growth of cosmic structures spanning back up to 11 billion years. By harnessing ongoing and forthcoming galaxy surveys such as the Dark Energy Spectroscopic Instrument (DESI), the Rubin Observatory's Legacy Survey of Space and Time (LSST), Subaru Prime Focus Spectrograph (PFS), and the Roman Space Telescope, we can measure the growth of structure with unprecedented precision. I will discuss the opportunities and challenges inherent in these galaxy surveys.

 
142024-03-06 Wed
14:20~15:20

R1203
Liton Majumdar
[NISER]
學術討論會
Constraining the initial conditions for the formation of extra-solar planets and their atmospheres
摘要

Protoplanetary disks serve as the sites where exoplanets are formed. Observations of these sites that give birth to planets reveal a wide range of temperatures, densities, and distribution of various molecules. The Atacama Large Millimeter/submillimeter Array (ALMA) has ushered in a new era in the study of protoplanetary disks, enabling us to explore the physics and chemistry of the outer regions of these disks. With the arrival of the James Webb Space Telescope (JWST), we can now delve much deeper into the inner regions of the disks and also investigate icy volatiles in colder regions. The combined contributions of these two instruments can provide us with greater clarity on the formation of exoplanets and the chemical inventory they inherit from protoplanetary disks. Modeling protoplanetary disks can bridge the gap between our theoretical understanding of exoplanet formation and its connection to atmospheres. Here, we introduce PEGASIS (Protoplanetary Disk and Envelope model for Emissions from GAS and Ice Absorption Simulations), a physicochemical model capable of simulating dust, cold gases, hot gases, and ices in both disks and envelopes.

 
152024-03-11 Mon
14:20~15:20

R1203
Maciek Wielgus
[Max Planck Institute for Radio Astronomy]
專題研討
Radio-bright future of studying black holes
摘要

I will discuss the exciting perspectives related to the near future observations of supermassive black holes at mm/sub-mm wavelengths. Event Horizon Telescope (EHT) is delivering images of subsequent AGN sources, while continuously expanding its capabilities, adding new facilities such as the Greenland Telescope, and testing observations at 345 GHz frequency. These observations correspond to the most central part of AGN sources we were ever able to resolve, opening tantalizing possibilities to study the region of jet formation, collimation, and acceleration and advancing our understanding of the physics of these extreme systems. Some fundamental questions to answer are related to the role of magnetic fields and general relativistic effects around a spinning black hole, location of the jet acceleration zone and its relation to the high energy emission. There is a lot to learn from observations of individual sources such as M87, Centaurus A, 3C 84, or 3C 279, but it is also extremely interesting to study a population of sources imaged at mm wavelength for the first time. In particular, our Galactic Center black hole Sagittarius A* is an uniquely interesting mm/sub-mm source, in which horizon-scale dynamics of a low accretion rate system can be studied. This is very exciting in the context of the source flaring, which we are trying to understand in a theoretical framework of the quasiperiodic flux eruptions expected for magnetically dominated accretion systems. Near future time domain analysis of a collection of mm/sub-mm light curves of Sagittarius A*, along with new coordinated multiwavelength observations, and perhaps even resolved (both in space and in time) observations of the EHT will necessarily shed light on the physical mechanism behind flares and high energy emission, as well as on the importance of magnetic fields in the systems similar to Sagittarius A*.

 
162024-03-12 Tue
14:20~15:20

R1203
Michael H. Wong
[UC Berkeley]
專題研討
10 Years of Annual Hubble Space Telescope Imaging of the Giant Planets
摘要

The Outer Planet Atmospheres Legacy (OPAL) program with Hubble was started in 2014 with the goal of studying time-domain phenomena in Jupiter, Uranus, and Neptune, with Saturn added in 2018 once the Cassini spacecraft was de-orbited. Once a year, the OPAL program images each of our four outer planets, producing pairs of global maps in multiple filters, which are made available at the MAST archive. The OPAL team (Simon, Wong, and Orton) have used the data to discover new dark spots on Neptune, discover a UV-dark oval in Jupiter's southern polar haze cap, measure changes in Jupiter's Great Red Spot over time, detect fine-scale waves, chronicle shifts in haze and cloud layers on all four planets, measure jet streams, and study the structure and evolution of convective storms. The data have also provided a valuable resource enhancing the science return from the Juno and New Horizons spacecraft missions, also supplementing observations from a growing list of observatories including JWST, Kepler, Spitzer, VLA, Keck, ALMA, IRTF, VLT, and Gemini.

 
172024-03-13 Wed
14:20~15:20

R1203
Jenny Wagner
[Bahamas Advanced Study Institute & Conferences]
學術討論會
Lensing of '69 -- Free gravitational lensing from its heuristic models
摘要

Strong gravitational lenses are massive cosmic objects, like galaxies or galaxy clusters, which can map an extended background source, like a galaxy, into several highly distorted and magnified images. Analysing the properties of those images yields important information about the distribution of the deflecting mass and the background source. Common approaches to reconstruct the source or the deflecting mass distribution model the global properties of the source and the lens. They obtain a consistent description of the entire configuration by refining the model until it matches the observation to a predefined precision.

Here, I introduce a new approach to infer local properties of the gravitational lens and to reconstruct the source only using the properties of the multiple images without assuming a lens or a source model. The approach can be applied to galaxy or galaxy-cluster lenses in the same way and yields the maximum information all lens models agree upon. Showcasing two example lenses, I highlight 1) how to obtain a smoothness scale for dark matter with it from only three multiple images in a newly discovered cluster and 2) how to identify and resolve limits of lens models that may lead to highly unrealistic dark matter properties.

Since data is still sparse at the moment but of increasing level of detail, a model selection to find an appropriate mass density profile is also needed to reduce the increasing amount of computing time when fitting a detailed lens model to the data. Most models are currently based on heuristical fitting functions inferred from simulations. Hence, they lack an explanation for their suitability based on fundamental physical principles. To overcome this issue, I will show how the most common mass density profiles, in particular the famous Navarro-Frenk-White profile found in many simulations, can be derived from symmetry arguments and conservation laws.

References: - Lens method overview: https://arxiv.org/abs/1906.05285 - Examples: https://arxiv.org/abs/2207.01630 and https://arxiv.org/abs/2306.11779 - Derivation of power-law models: https://arxiv.org/abs/2002.00960

 
182024-03-19 Tue
14:20~15:20

R104, CCMS-New Phys. building
Anne Dutrey
[Laboratoire d'Astrophysique de Bordeaux]
中研院/臺大學術討論會
From protoplanetary Disks to Planet Formation
摘要

Understanding planet formation is a major challenge in modern astrophysics. Planets form in protoplanetary disks orbiting around young stars. These disks are gas and dust residuals inherited from the parent clouds which form stars. It is only recently, with the advent of large mm/submm arrays such as ALMA (Atacama Large Millimeter Array, Chile) and its precursors, in particular the IRAM (Institute of Radio Astronomy Millimetric) array (France), that this field has slowly emerged in the early nineties. In this talk, I will present how our understanding on planet formation has evolved in the last 30 years. For this purpose, after an introduction describing the context, I will focus on the observations and analyses of two emblematic objects: the young low-mass triple system GG Tauri and the young single HAe (2.4 Msun) star AB Auriga. Starting from unresolved images of their protoplanetary disks 30 years ago, I will show how we are now beginning to unveil their nascent planetary systems.

 
192024-03-20 Wed
14:20~15:20

R1203
Kotaro Kohno
[University of Tokyo]
學術討論會
ALMA and JWST observations of emission-line galaxies in the early Universe
摘要

I will present recent observational studies of emission-line galaxies using ALMA and JWST. First, I will discuss the physical and chemical properties of a highly magnified (up to μ~160) and intrinsically faint (sub-L*) galaxy at z = 6.072, known as Cosmic Grapes, located behind the massive cluster RXC J0600-2007. This unique source has been uncovered as a bright 1-mm-wave line emitter by the ALMA Lensing Cluster Survey (ALCS) and subsequent investment of approximately 160 hours of observing time with ALMA, JWST, and MUSE/VLT reveals its highly clumpy nature. I will also demonstrate how the joint analysis of emission lines by ALMA and JWST provides constraints on fundamental parameters, such as electron density, in a metal-poor, low-mass galaxy at z = 8.496, situated behind the lensing cluster SMACS 0723.3-7327. A [OIII]5007 emission line selected galaxy at z = 8.343 behind the lensing cluster MACS J0416-2403, a part of JWST cycle 2 program MAGNIF, will also be reported. A serendipitously uncovered millimeter-wave emission line galaxy reveals the presence of a submillimeter-galaxy-like, dust-enshrouded extreme starburst event hosted by an isolated yet gas-rich grand-design barred spiral galaxy at z = 2.467. Discovery of a CO-bright (i.e., gas-rich) quiescent galaxy at z = 1.146 will also be discussed. Lastly, based on these studies, I will discuss how next-generation submillimeter-wave telescopes, like the LST/AtLAST, equipped with a large-format imaging spectrograph, will revolutionize our understanding of galaxy evolution in the early universe.

 
202024-03-22 Fri
11:00~13:00

R1412
Susana Lizano
[UNAM, Morelia]
理論天文專題研討
Dust in Transition Protoplanetary Disks
摘要

I will discuss transition protoplanetary disks observed by ALMA which have a large inner dust cavity. They are believed to be in the process of planet formation although other central clearing mechanisms are possible. Several of these disks show asymmetric emission that has been associated with vortices where the dust can be trapped and grow to form planetesimals. I will discuss the analysis of the dust properties in the asymmetric transition disks HD142527 and work needed to further elucidate the properties of this dust trap.

 
212024-03-27 Wed
11:00~13:00

R1203
James Stone
[Institute for Advanced Study]
理論天文專題研討
Modeling Luminous Accretion Flows Around Black Holes
摘要

New general relativistic MHD models of black hole accretion flows in luminous systems (such as quasars and X-ray binaries) that include full radiation transport will be described. These models are designed to study the steady-state structure of the accretion disk near the horizon, and the effect of radiation on the launching of relativistic jets from spinning black holes. Moreover, they enable not only the interpretation of the spectra and variability of these sources, but also predictions about the rate of growth of black holes in the early universe, and measurement of the energy and momentum feedback into the surrounding medium, a process likely to be important in galaxy formation. These calculations use a new version of the Athena++ adaptive mesh refinement code based on the Kokkos library that runs on both CPUs and GPUs. A brief description of this new code, as well as other applications and extensions underway, will also be given.

 
222024-03-27 Wed
14:20~15:20

R1203
Anders Johansen
[University of Copenhagen]
學術討論會
Rapid accretion of rocky planets and the outgassing of their first atmospheres
摘要

Terrestrial planets have traditionally been thought to form by collisions between protoplanets taking place mostly after the dissipation of the protoplanetary disc, on time-scales of 30-100 million years. I present here a new model where terrestrial planets grow instead by accreting small pebbles in the protoplanetary disc within 3-5 million years. I discuss how the immense pebble accretion heat leads to extensive melting of the growing planets and to the emergence of deep magma oceans. Volatiles such as water, carbon and nitrogen are accreted with the pebbles and partitioned between atmosphere, magma ocean and core. The end of the accretion phase leads to rapid crystallisation of the magma ocean and outgassing of the first atmosphere. I will finally discuss how the atmospheric composition of young planets is key to understanding the origin of life.

 
232024-03-28 Thu
14:20~15:50

R1203
Yusei Koyama,
Takashi Moriya,
Daisuke Suzuki

[Subaru, NAOJ, Osaka Univ]
專題研討
ULTIMATE-Subaru and SUPER-IRNET: toward the bright future of the Subaru Telescope
摘要

ULTIMATE-Subaru is a next large instrumentation program at Subaru, to develop a wide-field (20-arcmin in diameter) ground-layer adaptive optics (GLAO) system and a wide-field NIR imager (WFI) on Subaru, to strengthen the capability of Subaru Telescope in NIR. ULTIMATE will deliver an improved image quality of FWHM~0.2-arcsec (at K-band) in moderate conditions of Maunakea over the full 20-arcmin FoV. While HSC/PFS are the leading instruments for dark nights, ULTIMATE will be a primary facility instrument for bright nights of Subaru in late 2020s and beyond. In this series of seminar talks, we will introduce science cases of ULTIMATE for (1) galaxy and structure formation, (2) time domain astronomy, (3) Galactic Center observations - for all of which the new capabilities of deep, sharp, wide-field IR observations are critical. Taking this opportunity, we will also introduce the "SUPER-IRNET" program, to promote everyone in the community in Taiwan to join this activity. ULTIMATE-Subaru is a next large instrumentation program at Subaru, to develop a wide-field (20-arcmin in diameter) ground-layer adaptive optics (GLAO) system and a wide-field NIR imager (WFI) on Subaru, to strengthen the capability of Subaru Telescope in NIR. ULTIMATE will deliver an improved image quality of FWHM~0.2-arcsec (at K-band) in moderate conditions of Maunakea over the full 20-arcmin FoV. While HSC/PFS are the leading instruments for dark nights, ULTIMATE will be a primary facility instrument for bright nights of Subaru in late 2020s and beyond. In this series of seminar talks, we will introduce science cases of ULTIMATE for (1) galaxy and structure formation, (2) time domain astronomy, (3) Galactic Center observations - for all of which the new capabilities of deep, sharp, wide-field IR observations are critical. Taking this opportunity, we will also introduce the "SUPER-IRNET" program, to promote everyone in the community in Taiwan to join this activity.

 
242024-04-03 Wed
14:20~15:20

R1203
Emmanuel Schaan
[SLAC]
學術討論會
Backlighting the large-scale structure with the cosmic microwave background
摘要

Upcoming large-scale structure (LSS) and cosmic microwave background (CMB) experiments offer a unique opportunity to turn the Universe into a particle physics laboratory and determine the nature of dark matter, dark energy, and the masses of the neutrinos. I will present innovative methods to jointly analyze these datasets and unleash their full constraining power. My group's research explores two powerful ways of using the CMB as a backlight for the LSS: revealing the invisible dark matter (gravitational lensing) and baryons (Sunyaev-Zel'dovich and patchy screening effects) via their shadows on the CMB. These methods will yield percent-precision maps of the dark and baryonic matter on cosmic scales, from combinations of CMB experiments like the Atacama Cosmology Telescope, Simons Observatory and CMB-S4 with LSS experiments like the Dark Energy Spectroscopic Instrument and the Rubin Observatory. These will not only shed light on dark matter, dark energy and the neutrinos, but they will also constrain models of inflation and transform our understanding or galaxy formation.

 
252024-04-16 Tue
14:20~15:20

R104, CCMS-New Phys. building
David Schlegel
[Lawrence Berkeley National Laboratory]
中研院/臺大學術討論會
Massive Redshift Surveys and First Results from the Dark Energy Spectroscopic Instrument (DESI)
摘要

The current generation of redshift surveys will provide three-dimensional maps of the Universe with tens of millions of galaxies spanning much of the observable universe. These maps explore physics beyond the standard model, including the physics of dark energy and early universe inflation. I will present new measurements of cosmic expansion and dark energy from the first year of the Dark Energy Spectroscopic Instrument (DESI). DESI is mapping the sky with a 5000-fiber robotic focal plane and 10 optical spectrographs. I will describe the design of the instrument, the survey, and the analysis of the first 5 million galaxies and quasars.

 
262024-04-17 Wed
14:20~15:20

R1203
David Schlegel
[LBNL]
學術討論會
First Results from DESI and Future Spectroscopic Surveys
摘要

The Dark Energy Sepctroscopic Instrument (DESI) is mapping 40 million galaxies and quasars to precisely measure the expansion history of the universe. I will present results from the DESI Year 1 data. I will describe the science goals and survey design for the second-generation survey of the Dark Eenergy Spectroscopic Instrument (DESI-2) and the successor Spec-S5. These surveys are designed to improve constraints on dark energy and to probe the inflationary epoch. High-redshift (z>2) galaxies will be selected using a combination of broad-band and medium-band imaging. The more ambitious scope of Spec-S5 relies upon significant upgrades to the telescopes, fiber robots and spectrographs.

 
272024-04-18 Thu
14:20~15:20

R1203
Toshifumi Futamase
[Tohoku University]
專題研討
Gravitational Flexion Measurement in Weak Lensing and JWST Applications
摘要

High-precision data obtained by new-generation observational instruments such as JWST and EUCLID are expected to bring new developments to dark energy research. As these datasets surpass conventional data both in quantity and quality, there arises a need for more accurate analytical methods. Weak gravitational lensing stands out as a valuable tool for probing dark matter and dark energy. Traditionally, gravitational shear, a combination of the second derivative of the lens potential, has been measured to reconstruct mass distribution. However high-quality space imaging data are expected to contain more detailed information of the lensing potential. We have developed a new method to measure the gravitational flexion, which corresponds to certain combinations of the third derivatives of the lens potential. Measuring flexion enables a more accurate mass reconstruction. In this talk, I will introduce our method of measuring flexion and present the results of flexion measurement for the JWST cluster SMACS0723.3-7327.

 
282024-04-24 Wed
14:20~15:20

R1203
Salvatore Orlando
[INAF]
學術討論會
Supernova Remnants as Probes of the Life and Death of Massive Stars
摘要

The remnants of core-collapse supernovae (SNe) exhibit intricate morphologies and a highly non-uniform distribution of stellar debris. In the case of young remnants (less than 5000 years old), their properties encode valuable insights into the inner processes of the SN engine, including nucleosynthetic yields and large-scale asymmetries originating from the early stages of the explosion. Additional characteristics of the remnants can reflect the nature of the progenitor stars and the interactions between the remnants and the circumstellar medium (CSM), shaped by the progenitor's mass-loss history. Hence, investigating the connection between young SNRs, parent SNe, and progenitor massive stars can be of paramount importance to delve into the physics of SN engines, and to investigate the final stages of massive star evolution and the elusive mechanisms governing their mass loss. In this talk, I will review recent advances in modeling young to middle-aged SNRs, focusing on investigations aimed at linking the observed physical and chemical properties of SNRs to their progenitor stars and SN explosions, thus telling us about life and death of massive stars.

 
292024-04-26 Fri
12:00~13:20

R1412
Maurice van Putten
[Sejong University, Korea]
理論天文專題研討
Hubble Expansion Beyond ΛCDM in Big Bang Quantum Cosmology
 
302024-05-14 Tue
14:20~15:20

R1203
Shang-Min Tsai
[UC Riverside]
專題研討
A Comprehensive Framework for Modeling Photochemistry, Climate, and Habitability
摘要

Exoplanet science has rapidly progressed, not only we have discovered more than 5000 planets since the first discovery in the 1990s, the field is transitioning from the stage of detection to atmospheric characterization. The diversity of exoplanets broadens our understanding of planetary science and provides a profound perspective on the evolution of our world. In this talk, I will give an overview of exoplanet characterization methods and the fundamental processes governing atmospheric composition. I will highlight recent JWST findings, including the first detection of photochemistry in an exoplanet atmosphere and its implications for understanding planet formation in tandem with disk observations and simulations. I will address the necessity of moving beyond 1D modeling, to account for global and temporal properties. By employing a 2D--3D modeling framework, I reveal distinct spectral features and limb asymmetries relevant to transit and phase-curve observations. I will discuss the puzzles surrounding the most common class of planets, known as sub-Neptunes, which curiously find no analogues in our Solar System. I will demonstrate how studying their atmospheres can help break the internal structure degeneracies. Lastly, did JWST detect signs of life on the sub-Neptune exoplanet K2-18b? I will share our recent insights into probing microbial life on oceanic sub-Neptune exoplanets. In closing, I will present my vision for collaborations with the multidisciplinary expertise at ASIAA.

 
312024-05-15 Wed
14:20~15:20

R1203
Janet Chen
[NCU]
學術討論會
Transient Zoo from ePESSTO+
摘要

The current generation of wide-field sky surveys and efficient spectroscopic follow-up observations have led to unexpected discoveries of rare and exotic phenomena among stellar transients. Since 2019, I have co-led the advanced Public ESO Spectroscopic Survey of Transient Objects (ePESSTO+) programme, a collaborative effort involving over 300 experts and early career researchers in supernovae, gamma-ray bursts, and nuclear transients. Our programme contributes crucial data on gravitational wave counterparts, superluminous supernovae, fast-evolving and gap transients, and tidal disruption events through observations with the ESO 3.58-m New Technology Telescope. These efforts substantially expand our observational scope, exploring transient diversities, and enhancing our cosmic understanding. In this talk, I will provide an overview of the current state of optical follow-up of transients and focus on the scientific outcomes from ePESSTO+. Additionally, I will introduce my newly established GREAT lab and discuss our ongoing projects with Lulin Observatory.

 
322024-05-22 Wed
14:20~15:20

R1203
Harish Vedantham
[ASTRON]
學術討論會
Radio flashes from plasma storms around exoplanets
摘要

Low frequency (< few hundred MHz) radio observations uniquely probe several processes that determine the habitability of exoplanets such as coronal mass ejections and exoplanet magnetic fields. Radio observations of such phenomena in the solar system are commonplace. I will argue that the extrasolar frontier is now also within reach thanks to powerful new low-frequency telescopes such as LOFAR. I will describe an observational program using LOFAR to systematically survey the low-frequency radio sky for stellar, brown dwarf and exoplanetary emissions with unprecedented sensitivities. I will present some early successes of this campaign including (a) the discovery of evidence for magnetic interaction between a star and its planet (b) the discovery of a cold brown dwarf directly in the radio band using its magnetospheric emissions and (c) solar-type radio bursts on nearby stars possibly associated with coronal mass ejections. I will end with an outlook for harnessing radio astronomy’s unique diagnostic capabilities to advance stellar and exoplanet science.

 
332024-05-29 Wed
14:20~15:20

R1203
Stephen Appleby
[APCTP]
學術討論會
Cosmology from the topology of Large Scale Structure
摘要

The distribution of galaxies in the low redshift Universe provides information on the initial conditions, energy content and evolution of the Universe from its almost Gaussian primordial state to the highly non-linear cosmic web that we observe today. In this talk I will introduce a class of statistics that are capable of extracting both Gaussian and non-Gaussian information from the matter distribution. The so-called Minkowski Functionals and their rank-2 tensorial generalisation are a class of topological descriptors of a field which can be used to measure cosmological parameters, test the degree of non-Gaussianity as a function of scale and also provides a mechanism to test statistical isotropy. I will describe these statistics, explain how we extract them from galaxy catalogs and elucidate what they can tell us about the properties of the Universe.

 
342024-05-30 Thu
14:00~15:00

R1203
Chao-Chin Yang
[Department of Physics and Astronomy The University of Alabama, U.S.A.]
專題研討
From pebbles to planets: planetesimal formation and pebble accretion
摘要

From pebbles to planets: planetesimal formation and pebble accretion Abstract: Even though thousands of extrasolar planetary systems have been detected, a comprehensive picture of how planets are formed from their natal protoplanetary disks remains to be drawn. I will review our current understanding of the dust-gas dynamics in protoplanetary disks and its consequences on the formation of planets via the core accretion scenario. Specifically, I will examine how and under what conditions cm-/mm-sized dust pebbles can actively concentrate themselves to high density for km-scale planetesimals to form, the initial mass function of planetesimals, and how pebble accretion assists planet formation, along with some supporting observational evidence.

 
352024-06-18 Tue
14:20~15:20

R1203
Keiichi Maeda
[Kyoto U.]
專題研討
Insights into the final evolution of massive stars: studying circumstellar environments around supernovae
摘要

It has recently recognized that supernovae showing signatures of strong interaction with the circumstellar media (CSM) are very heterogeneous, with various observational characteristics in the light curve and spectral evolutions. It must reflect diverse natures in the CSM compositions (hydrogen-rich and -free) and distribution (corresponding either to steady-state mass loss or change in the mass-loss rate), ultimately connected to much more diverse stellar evolutionally channels than previously thought. I will provide a biased review on the "interacting" SN populations, covering so-called type IIn, Ibn, Icn, and Ic-CSM supernovae, through optical and radio observations.

 
362024-06-19 Wed
14:20~15:20

R1203
Jenny Greene
[Princeton]
學術討論會
Little Red Dots in JWST
摘要

I will discuss a fascinating new object we have discovered with JWST/NIRCam imaging and grism spectroscopy at z>4. With compact sizes (<100 pc), red rest-frame optical colors, and ubiquitous broad Balmer lines, these objects have many hallmarks of accreting supermassive black holes. However, they have x100 the number density of UV-selected quasars, and appear to have very massive black holes compared to their hosts. Also, unlike most known accreting black holes, they show no signs of hot dust or X-ray emission. I discuss our ongoing efforts to understand the nature of the Little Red Dots, and what they may teach us about the coevolution of black holes and galaxies.

 
372024-06-20 Thu
10:30~12:00

R1203
Keiichi Maeda,
Janet Chen,
Yen-Chen Pan,
Ken Chen

[Kyoto U., NCU, ASIAA]
專題研討
Kyoto-NCU-ASIAA supernovae discussion
 
382024-06-20 Thu
14:00~15:00

R1203
Tien-Hao Hsieh
[MPE]
專題研討
PRODIGE - Envelope to Disk with NOEMA - A streamer feeding the SVS13A protobinary and the complexity of the COM emission
摘要

We conducted NOrthern Extended Millimeter Array (NOEMA) observations toward the Class 0/I protobinary system SVS13A as part of the PROtostars & DIsks: Global Evolution (PRODIGE) program. SVS13A is composed of two protostars VLA4A and VLA4B with a separation of ∼90 au, for which VLA4A is undergoing an accretion burst that enriches the chemistry of the surrounding gas. This gives us an excellent opportunity to probe the chemical and physical conditions as well as the accretion process. We study the kinematic structures of SVS13A via DCN (3–2) line, and the C18O (2–1) line at about hundred au scale. By combining our observations with previous ALMA high-angular-resolution observations, we find that the binary system (or VLA4A) might be fed by an infalling streamer from envelope scales (∼700 au). If this is the case, this streamer contributes to the accretion of material onto the system with a rate of at least 1.4 × 10−6 Msun yr−1. We further analyzed 12- 11 lines of CH CN and CH 13CN and six selected O-bearing COMs: CH3OH, aGg’-(CH2OH)2, C2H5OH, CH2(OH)CHO, CH3CHO, and CH3OCHO. Although the COM emission is not spatially resolved, we constrained the source sizes to ~0.3 − 0.4 arcsec (90−120 au) by conducting uv-domain Gaussian fitting. Interestingly, the high-spectral-resolution data reveal complex line profiles with multiple peaks; although the line emission is likely dominated by the secondary,VLA4A,at Vlsr = 7.36 kms−1,the numbers of peaks (∼2−5), the velocities, and the linewidths of these six O-bearing COMs are different. The local thermodynamic equilibrium (LTE) fitting unveils differences in excitation temperatures and emitting areas among these COMs. We further conducted multiple-velocity-component LTE fitting to decompose the line emission into different kinematic components. As a result, the emission of these COMs is decomposed into up to six velocity components from the LTE modeling. The physical conditions (temperature, column density, and source size) of these components from each COM are obtained. We conclude that accretion shocks induced by the large-scale infalling streamer likely exist and contribute to the complexity of the COM emission. This underlines the importance of high-spectral-resolution data when analyzing COM emission in protostars and deriving relative COM abundances.

 
392024-06-26 Wed
14:20~15:20

R1203
Chrystian Luciano Pereira
[Observatorio Nacional]
學術討論會
Rings Around Small Solar System Objects: Discoveries and Detection Limits
摘要

Until 2013, ring systems were known only around the four giant planets. This perspective shifted when a stellar occultation revealed the presence of two rings around the minor planet (10199) Chariklo (Braga-Ribas et al. 2014), a Centaur object. In January 2017, another occultation revealed the existence of a ring encircling the dwarf planet (136108) Haumea (Ortiz et al. 2017). The third minor body with a confirmed ring system is the big Transneptunian Object (50000) Quaoar. Intriguingly, Quaoar’s ring system is far beyond the classical Roche limit (∼1,780 km). The innermost ring lies about 2,520 km from the Quaoar center (Pereira et al. 2023), and the outermost ring lies about 4,100 km. The latter presents significant longitudinal variations concerning optical depth and width (Morgado et al. 2023). Similarly, observations of flux variations in occultation light curves over two decades of the Centaur (2060) Chiron suggested the presence of material in its surroundings. Published works have interpreted these materials as rings, shells, and jets, but a definitive classification is premature. In this context, stellar occultations by Chiron were conducted in 2018 and 2019 (Braga-Ribas et al. 2023), 2022 (Ortiz et al. 2023), and 2023 to characterize the observed structure, revealing that the material around Chiron presents an evolving structure, which can result from outbursts feeding putative rings. We have also identified objects that presented outbursts and thus could be capable of hosting rings, such as the Centaurs Echeclus (Pereira et al. 2024) and 29P/Schwassmann-Wachmann 1. Stellar occultations by them were observed and used to search for rings or other confined signatures. In cases where detection was not achieved, we obtained upper limits for detecting additional structures. This ongoing work can result in discovering new ring systems, other confined structures, or even small satellites around these small bodies in the solar system. These results and implications will be presented in this talk.

 
402024-06-28 Fri
12:00~13:30

R1412
Shih-Hsien Yu
[Institute of Mathematics, Academia Sinica]
理論天文專題研討
Heat Equation and Wave Train
摘要

In this talk, we will introduce a way to integrate the heat equation with rough heat conductivity. The solution of heat equation is constructed and one can describe the qualitative and quantitative behavior of the solution. One will also comment the generality of the approach.

 
412024-07-02 Tue
14:20~15:20

R1203
Eva Lilly
[Planetary Science Institute]
學術討論會
A Hundred Sleeping Beasts: Dynamical Triggers of Cometary Activity in Centaurs
摘要

The Centaur population is comprised of small, likely icy bodies on dynamically unstable orbits transitioning from the trans-Neptunian region to the inner Solar system. Centaurs represent an interesting stage in the dynamical evolution of primordial small bodies scattered by planetary perturbations from the deep freeze of the TNO reservoir where they have been stored for billions of years. They enter the giant planet region as largely primordial objects and carry information about the composition of their parent populations to our doorstep.

Here we present a thermodynamical study of Centaurs, complemented with a visual survey conducted with the Gemini telescopes aimed to search for cometary activity and to identify possible activity triggers in the members of the Centaur population. Through the duration of our survey only one Centaur in our sample - C/2014 OG392 (PANSTARRS) appeared active. Both results from our survey and the thermodynamical modeling indicate that the orbital history plays a critical role in the thermal processing of Centaurs and their potential for onset of cometary activity. Our in-depth analysis of orbital evolution revealed that within the past several hundred years every known active Centaur underwent a rapid orbital change leading to significant decrease in semi-major axis we call an `a-jump’, which led to a major increase in the average-per orbit insolation. Such a-jumps typically occur after close encounters with Jupiter or Saturn and are not present in recent orbital histories of inactive Centaurs. A single Centaur can typically undergo several a-jumps throughout its lifetime leading to the depletion of volatiles and thermal processing of the nucleus. Our results also show that most of the targets of our survey dynamically evolved interior to ~14 AU over the past 1000 years, which is a region where several processes could trigger phase transitions of volatiles leading to outgassing. However, the apparent inactivity of inspected Centaurs, including objects with perihelia near Jupiter, indicates they are either dormant or volatile-depleted, supported by the fact that apart from C/2014 OG392 their orbital history doesn’t show significant a-jumps typical for active Centaurs, adding further evidence that the orbital evolution of Centaurs is the key to understanding the cometary activity in members of the population.

 
422024-07-03 Wed
14:20~15:20

R1203
Ruobing Dong
[University of Victoria]
學術討論會
Observational Planet Formation
摘要

It is hard to see a plane cruising at 10 km, as the plane is tiny and faint in the sky. But, if we can see the contrail trailing behind the plane, we know where the plane is. Now, astronomers are applying the same principle to study how planets form by detecting and characterizing the structures that baby planets produce in their birth cradles — protoplanetary disks. This is a new field largely driven by discoveries made by some of the largest and most advanced telescopes ever built. I will introduce the current status of the field and highlight some of the latest developments as well as unsolved problems.

 
432024-07-10 Wed
14:20~15:20

R1203
Naomi Hirano
[ASIAA]
學術討論會
Panchromatic study of the extremely dense prestellar core on the verge of first core formation
摘要

The prestellar core G208.68-19.02-N2 (G208-N2) in the Orion Molecular Cloud 3 (OMC3) has been studied with the ALMA in Band 4 (2 mm), 6 (1.3 mm and 1.1 mm), 7 (0.83 mm, ACA), 8 (0.75 mm), 9 (0.45 mm), and 10 (0.35 mm). The dust continuum emission revealed a filamentary structure with a length of ~5000 au and an average H2 volume density of ~6 x 10^7 cm^-3. At the tip of this filamentary structure, there is a compact "nucleus" with a radius of ~150--200 au and a mass of ~0.1 M_sun. The nucleus does not have a counterpart at wavelength shorter than 0.35 mm. In addition, there is no sign of CO outflow localized to this nucleus. The spatial distributions of the molecular lines reveal significant chemical segregation in G208-N2. Although N2D+ and H2D+ trace the filamentary structure, they do not exhibit pronounced peak toward the nucleus. Instead, the emission peaks of DCO+, H2CO and CH3OH appear in the vicinity the nucleus. In this talk, we will discuss the possible evolutionary stage, i.e. prestellar of first hydrostatic core, of this enigmatic object.

 
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台北市106216羅斯福路四段1號 中央研究院/台灣大學天文數學館11樓