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中央研究院天文及天文物理研究所
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Activity > Colloquium

Colloquium (2017)

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.

The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.

Contact: Colloquium Committee (talks_replace2@_asiaa.sinica.edu.tw)

NEXT Colloquium: 2017-07-26 Wed 14:20~15:20 [R1203]
Speaker:Xinwen Shu
Topic:Supersoft AGNs: signature of super Eddington accretion, IMBH, TDE or new AGN spectral state?
Abstract:Supersoft AGNs are a new class of AGNs which lack significant hard X-ray emission above ~2 keV. They may host intermediate mass black holes (IMBH) accreting in a poorly explored regime of parameter space, such as super Eddingtong accretion and extreme coronal condition. Their X-ray spectra are dominated by a soft thermal component, a form similar to disk blackbody emission in stellar-mass BHs in their high/soft state. Though only three supersoft AGNs are reported to date, they show distinct X-ray variability behavior, some of them could be associated with TDE. In this talk, I will present the multi-wavelength characteristics of RX J1301.9+2746, the most distinct source of this kind. In particular, I will show our follow-up JVLA observations which reveal fast intraday radio variability, confining its origin likely from a compact jet. Such the unexpected presence of jets in a supersoft AGN challenges canonical theories of jet formation. All the results suggest that this AGN is an ideal laboratory for studying the universality of accretion/ejection coupling in BH accreting systems.
NEXT Special Seminar: 2017-08-07 Mon 14:20~15:20 [R1203]
Speaker:Hua-bai Li
Topic:TBA
Abstract:TBA
No. Time/Place Speaker Topic / Abstract
download PDF: download talk PDF file
12017-12-13 Wed
14:20~15:20
R1203
TBD
[ASIAA]
Note: the date is provisional. (Hiro's collaborator)
22017-12-06 Wed
14:20~15:20
R1203
TBD
[ASIAA]
Note: the date is provisional (Hiro's collaborator).
32017-11-22 Wed
14:20~15:20
R1203
Bernhard Brandl
[Leiden University]
Note: the date is provisional.
Abstract

TBA

42017-09-20 Wed
14:20~15:20
R1203
Li-Ting Hsu
[ASIAA]
TBD
Abstract

TBD

52017-09-13 Wed
14:20~15:20
R1203
I-Non Chiu
[ASIAA]
TBD
Abstract

TBD

62017-09-06 Wed
14:20~15:20
R1203
George Djorgovski
[Caltech]
Exploring the Time Domain
Abstract

TBA

72017-08-24 Thu
14:20~15:20
R1203
Roger Wesson
[UCL]
*Special Seminar*
TBA
Abstract

TBA

82017-08-23 Wed
14:20~15:20
R1203
Mike Barlow
[UCL]
Observations of Supernova Dust and Molecules
Abstract

Although a number of models for the formation of dust in the ejecta of core-collapse supernovae (CCSNe) had predicted that between 0.1 and 1.0 Msun of dust could be formed per event, it was not until the 2009-2013 Herschel mission that direct observational evidence was obtained for the presence of such large masses of dust in several young supernova remnants, including Cas A, the Crab Nebula and SN 1987A. High angular resolution submillimetre observations of SN 1987A with ALMA subsequently confirmed that its cold dust emission originated from the inner expanding ejecta. The presence of dust in CCSN ejecta can also be diagnosed and quantified from red-blue asymmetries in their late-time optical emission line profiles. I will summarise current results for SN dust masses based on these methods.
The ALMA observations of the ejecta of SN 1987A also revealed strong CO and SiO rotational line emission. Broad CO line emission has also been detected from the reverse shock region of Cas A, while ArH+ (argonium) rotational lines were first detected by Herschel from the Crab Nebula. These molecular lines have opened up the possibility of measuring supernova isotope ratios for the first time.

92017-08-16 Wed
14:20~15:20
R1203
Ing-Guey Jiang
[NTHU]
TBD
Abstract

TBD

102017-08-09 Wed
14:20~15:20
R1203
Testuya Hashimoto
[NTHU]
112017-08-08 Tue
14:20~15:20
R1203
Shuay-Pu Ho
[Princeton]
*Special Seminar*
TBA
Abstract

TBA

122017-08-07 Mon
14:20~15:20
R1203
Hua-bai Li
[CUHK]
*Special Seminar*
TBA
Abstract

TBA

132017-08-02 Wed
14:20~15:20
R1203
Wing Ip
[NCU]
News from Rosetta
Abstract

After a long journey, almost as long as the planning period, the Rosetta spacecraft finally reached the target comet, 67P/Churyumov-Gerasimenko, in August 2014. For nearly two years, Rosetta provided close-up looks of a cometary nucleus that came from the time of the solar system formation and a far-away place. In this talk, we will give a summary of some of the major results obtained by different instruments onboard the spacecraft and the Philae Lander. The research results produced by the NCU group will be described in passing.

142017-07-26 Wed
14:20~15:20
R1203
Xinwen Shu
[Anhui Normal University]
Supersoft AGNs: signature of super Eddington accretion, IMBH, TDE or new AGN spectral state?
Abstract

Supersoft AGNs are a new class of AGNs which lack significant hard X-ray emission above ~2 keV. They may host intermediate mass black holes (IMBH) accreting in a poorly explored regime of parameter space, such as super Eddingtong accretion and extreme coronal condition. Their X-ray spectra are dominated by a soft thermal component, a form similar to disk blackbody emission in stellar-mass BHs in their high/soft state. Though only three supersoft AGNs are reported to date, they show distinct X-ray variability behavior, some of them could be associated with TDE. In this talk, I will present the multi-wavelength characteristics of RX J1301.9+2746, the most distinct source of this kind. In particular, I will show our follow-up JVLA observations which reveal fast intraday radio variability, confining its origin likely from a compact jet. Such the unexpected presence of jets in a supersoft AGN challenges canonical theories of jet formation. All the results suggest that this AGN is an ideal laboratory for studying the universality of accretion/ejection coupling in BH accreting systems.

152017-07-19 Wed
14:20~15:20
R1203
Wladimir Lyra
[CSUN]
Evolution of Circumstellar Disks and Planet Formation
Abstract

During the first million years of evolution, nascent planetary systems are embedded in dense disk-shaped clouds of gas. These "circumstellar disks" are home to a myriad of hydrodynamical processes, which bring about turbulence and the emergence of viscous-like behavior, enabling accretion of gas onto the forming star. Meanwhile, micron-sized dust grains embedded in the disk are growing into pebbles and rocks. Turbulence has a positive effect on these small solids, concentrating them into transient high pressure regions for long enough to achieve gravitational collapse through pebble accretion into km-sized bodies, forming the first planetesimals. Giant storm systems in the disk, similar to Jupiter's Great Red Spot, may exist in quiescent zones of the disk. These are even more prone to collecting solid material, producing the first terrestrial planets and cores of giant planets. In this talk I will discuss the state of the art and recent advances in the field of planet formation, as well as pressing problems such as the structure observed in high resolution images of circumstellar disks, and how to interpret them.

162017-07-18 Tue
14:20~15:20
R1203
Chuhong Mai [CANCELLED]
[ASU]
*Special Seminar*
Exploring Exoplanet Cloud Assumptions with JWST Transmission Spectra [CANCELLED]
Abstract

Transit transmission spectroscopy of extrasolar planets is a powerful tool for determining their atmospheric properties. However, the presence of high altitude clouds and hazes can have a significant influence on transit transmission spectra, obscuring information from the deeper atmosphere. Understanding the impact of clouds on transit transmission spectra is essential if we are to properly interpret their spectra and subsequent conclusions about the atmospheric composition. The James Webb Space Telescope (JWST) is expected to characterize transiting exoplanet atmospheres with high resolution and signal to noise. In this work we demonstrate how different assumptions about cloud properties can impact transit transmission spectra by simulating JWST observational data of archetypal exoplanets from hot Jupiters to Super Earths. And we perform the Bayesian retrieval (algorithm: nested sampling) to determine the degree of constraint on these assumptions. These assumptions include simple gray cloud approximation, the general extinction curve for cloud conden-sates, and cloud properties (mixing ratio, cloud base pressure, particle radius and verticle extent) in a parameterized realistic cloud model. We also plan to expand our 1-D model assumptions to pseudo 3-D non-uniform clouds (patchy clouds). The goal is to provide useful predictions for how transmission spectra from JWST can implicate and constrain the presence, properties and vertical distributions of clouds in exoplanet atmospheres.

172017-07-12 Wed
14:20~15:20
R1203
Renyu Hu
[JPL]
Studying Planetary Atmospheres in an Exoplanet Era
Abstract

The number of planets we know increased by two orders of magnitude in the past decade. Many of the planets discovered outside the solar system, i.e., the exoplanets, have surprising traits, including having orbital periods of a mere few days, being larger than Earth and smaller than Neptune, and having atmospheric compositions where data suggest deviation from chemical equilibrium. These discoveries necessarily reorient our study of planetary atmospheres. I will discuss how observations of exoplanet atmospheres help us better understand the physical and chemical processes that control planetary atmospheres as well as the evolution of planets. For example, strong stellar irradiation and intermediate size of some exoplanets enable the formation of helium atmospheres, resulting in distinctive remote sensing spectral features. Transit observations of Hubble and JWST thus provide the opportunity to study the atmospheric evolution of super-Earths and sub-Neptunes. Looking ahead, I will conclude by describing pathways forward to directly image and characterize cold planets at wide orbital separations and search for potential signs of life from alien worlds.

182017-06-30 Fri
14:20~15:20
R1203
Charling Tao
[Tsinghua University]
*Special Seminar*
What do we know about the Dark Universe?
Abstract

In this talk I will review our present knowledge about the Dark Universe and the main research areas which are currently shedding some light. Cosmology has become a science. We measure with precision the extent of our ignorance. The Universe today is dominated by dark energy and dark matter. Dark Energy could well reduce to the cosmological constant, and within 10 years, we should have results from many surveys which either will find a deviation from a cosmological constant or we will have to explain why the dark energy is so close to a cosmological constant and is not. Unless there is a modification of gravity, our Galaxies and the universe has Dark Matter which nature is still unknown. I will describe some of the attempts to unveil its nature, and maybe open up in the future a new field of Dark Matter astronomy, as we are witnessing today the beginning of gravitational waves astronomy.

192017-06-29 Thu
14:20~15:20
R1203
Chia-Hsun Chuang
[AIP Potsdam]
*Special Seminar*
The Map of the Universe Based on the Positions of Quasars
Abstract

During the first two years of the SDSS’s Extended Baryon Oscillation Spectroscopic Survey (eBOSS), astronomers measured accurate three-dimensional positions for more than 147,000 quasars. We have created the first map of the large-scale structure of the Universe based entirely on the positions of quasars. But to use the map to understand the expansion history of the Universe, we had to go a step further, using a technique involving studying “baryon acoustic oscillations” (BAOs). BAOs are the present-day imprint of sound waves which travelled through the early Universe, when it was much hotter and denser than the Universe we see today. People have previously used the BAO technique on nearby galaxies and then on intergalactic gas distributions to push this analysis farther and farther back in time. The current results cover a range of redshift where they have never been observed before (z ~ 1.5). The results of the new study confirm the standard model of cosmology that researchers have built over the last twenty years. In this standard model, the Universe follows the predictions of Einstein’s General Theory of Relativity -- but includes components whose effects we can measure, but whose causes we do not understand. Along with the ordinary matter that makes up stars and galaxies, the Universe includes dark matter - invisible yet still affected by gravity - and a mysterious component called “Dark Energy”. Dark Energy is the dominant component at the present time, and it has special properties that cause the expansion of the Universe to speed up.

202017-06-28 Wed
14:20~15:20
R1203
Juan-Carlos Algaba
[KASI]
Interferometric Monitoring of Gamma-Ray Bright AGNs: Exploring the Variability of the Flat Spectrum Radio Source 4C38.41
Abstract

The Interferometric Monitoring of Gamma-ray Bright AGNs (iMOGABA) is a monitoring program for about 30 gamma-ray bright AGNs using the Korean VLBI Network (KVN) at simultaneous frequency bands (22, 43, 86 and 129 GHz) aimed at studying the origins of the gamma-ray flares of AGNs. Here We present observations of the flat spectrum radio quasar 4C 38.41 as part of the iMOGABA program combined with additional observations in radio, optical, X-rays and gamma-rays carried out between the period 2012 March - 2015 August. The monitoring of this source reveals a significant increase in its activity in the radio bands, which correlates with other bands from sub-millimeter to gamma-rays. The epochs of the maxima for the two largest gamma ray flares seem to coincide with the ejection of two respective new VLBI components. The evolution of the flares probes the adiabatic losses in agreement with the shock-in-jet model. Derived synchrotron self absorption magnetic fields, of the order of 0.1 mG, do not seem to dramatically change during the flares, and are much smaller than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle dominated emitting region. This is consistent with considerations suggesting that this region may be located near but downstream the acceleration and collimation region.

212017-06-21 Wed
14:20~15:20
R1203
Yu-Yen Chang
[ASIAA]
Host Galaxies of Obscured AGNs and their Environment
Abstract

I will present our recent results on mid-infrared selected active galactic nuclei (AGNs). We derived their stellar masses, star formation rates, dust properties, AGN contributions, as well as obscurations by fitting their optical to far-infrared photometry through the state-of-art spectral energy distribution (SED) technique. Our obscured AGNs by infrared selection are not significant different from the star-forming sequence. We confirm our previous finding about compact host galaxies of obscured AGNs at z~1, and find that galaxies with 20-50% AGN contributions tend to have smaller sizes, by~25-50%. Besides, we show that high merger fraction up to 0.5 happens to the most luminous (LIR ~46 ergs/s) AGN host and non-AGN galaxies, but not to the whole obscured AGN sample. Moreover, merger fraction has dependence on the total and star-forming infrared luminosity, rather than the decomposed AGN infrared luminosity. Our results suggest that major merger is not the main driver of AGN activities, and obscured AGNs might be triggered by internal mechanisms, such as secular process, disk instabilities, and compaction in a particular evolutionary stage. I will also discuss the role of environment on these obscured AGNs, based on new data from JCMT Large Programs.

222017-06-19 Mon
14:20~15:20
R1203
Yapeng Zhang
[CUHK]
*Special Seminar*
Magnetic field orientations and star formation rates
Abstract

The relation between star formation rates (SFRs) and magnetic field is still a mystery. Through a comparison between the surveys of SFRs and a study of cloud–field alignment—which revealed a bimodal (parallel or perpendicular) alignment—we show that the perpendicular alignment tends to have lower SFRs per solar mass. This indicates that B-fields are a primary regulator of SFRs: a perpendicular cloud-field alignment has higher magnetic flux than parallel cases and the support of the gas against self- gravity is stronger. Moreover, cloud fragmentation and magnetic field alignment is found to be selfsimilar (e.g. Li et al. 2015). Whether the bimodal SFR is also selfsimilar can only be answered with a higher resolution of magnetic- field detection. I will also introduce APol, the ASTE Polarimeter, which I am leading to build for this purpose.

232017-06-16 Fri
14:20~15:20
R1203
Kohei Hayashi
[Kavli Institute for Astronomy and Astrophysics]
*Special Seminar*
Dark matter in the Galactic dwarf spheroidal galaxies
Abstract

The dwarf spheroidal galaxies (dSphs) in the Milky Way are excellent laboratories to shed light on fundamental properties of dark matter because these galaxies are the most dark matter dominated systems. DSph galaxies also have the advantage that we can measure very accurate line-of-sight velocities for resolved member stars. Therefore, using these high-quality data, we are able to constrain internal structure of their dark halos. In the first part of my talk, I will present the constraint on candidate dark matter particles through indirect searches for their annihilations from non-spherical dark halo in the Galactic dSphs. I also show that Prime Focus Spectrograph mounted on Subaru telescope will play an important role in getting an insight into the nature of dark matter particles by synergy between space and ground-based telescopes. In the second part, I will propose the universal dark halo scaling relation for the dSphs. This scaling relation would not be largely affected by any baryonic feedbacks, hence it is good tracer to compare between observed and simulated dark halos. Using high-resolution N-body simulations based on Lambda cold dark matter (LCDM) universe, we find that this relation from observed dSphs is in good agreement with those from pure dark matter simulations. Therefore, LCDM models can reproduce the observed dark halo properties even on small mass scales without baryonic uncertainties.

242017-06-14 Wed
14:20~15:20
R1203
Naonori Sugiyama
[Kavli IPMU]
Kinematic Sunyaev-Zel'dovich Effect
Abstract

Over the past few years, cosmologists have been able to make the first detections of the kinematic Snuyaev-Zel'dovich (kSZ) effect by combining galaxy data with measurements from CMB experiments. The kSZ effect is well-suited for studying properties of the optical depth of halos hosting galaxies or galaxy clusters. As the measured optical depth via the kSZ effect is insensitive to gas temperature and redshift, the kSZ effect can be used to detect ionized gas that is difficult to observe through its emission, so-called "missing baryons". This work presents the first measurement of the kSZ signal in Fourier space. While the current analysis results in the kSZ signals with only evidence for a detection, the combination of future CMB and spectroscopic galaxy surveys should enable precision measurements. This talk emphasizes the potential scientific return from these future measurements.

252017-06-13 Tue
14:20~15:20
R1203
Masahiro Takada
[Kavli IPMU]
*Special Seminar*
Microlensing constraints on 10^{-10}Msun-scale primordial black holes from high-cadence observation of M31 with Hyper Suprime-Cam
Abstract

We use the Subaru Hyper Suprime-Cam (HSC) to conduct a high-cadence (2 min sampling) 7~hour long observation of the Andromeda galaxy (M31) to search for the microlensing magnification of stars in M31 due to intervening primordial black holes (PBHs) in the halo regions of the Milky Way (MW) and M31. The combination of an aperture of 8.2m, a field-of-view of 1.5 degree diameter, and excellent image quality (~ 0.6'') yields an ideal dataset for the microlensing search. If PBHs in the mass range M_PBH=[10^{-13},10^{-6}]Msun make up a dominant contribution to dark matter (DM), the microlensing optical depth for a single star in M31 is tau~10^{4}-10^{-7}, owing to the enormous volume and large mass content between M31 and the Earth. The HSC observation allows us to monitor more than tens of millions of stars in M31 and in this scenario we should find many microlensing events. To test this hypothesis, we extensively use an image subtraction method to efficiently identify candidate variable objects, and then monitor the light curve of each candidate with the high cadence data. Although we successfully identify a number of real variable stars such as eclipse/contact binaries and stellar flares, we find only one possible candidate of PBH microlensing whose genuine nature is yet to be confirmed. We then use this result to derive the most stringent upper bounds on the abundance of PBHs in the mass range. When combined with other observational constraints, our constraint rules out almost all the mass scales for the PBH DM scenario where all PBHs share a single mass scale.

262017-06-07 Wed
14:20~15:20
R1203
Changbom Park
[Korea Institute for Advanced Study (KIAS)]
Satellites of Isolated Early-type Galaxies and the Missing Satellite Galaxy Problem
Abstract

The standard galaxy formation scenario in the popular LCDM cosmogony has been very successful in explaining the large-scale distribution of galaxies. However, one of the failures of the theory is that it predicts too many satellite galaxies associated with massive galaxies compared to observations, which is called the missing satellite galaxy problem. Isolated groups of galaxies hosted by massive early-type galaxies are ideal laboratories for finding the missing physics in the current theory. We discover through a deep spectroscopic survey of galactic satellite systems that bright isolated early-type galaxies have almost no satellite galaxies fainter than the r-band absolute magnitude of about -14. The cutoff in the satellite galaxy luminosity function is at somewhat brighter magnitude of about -15 for early-type satellites. Physical properties of the observed satellites depend sensitively on the host-centric distance. All these are strong evidence that galactic satellites can be significantly affected due to astrophysics of satellite-host galaxy interaction. Previously, the faint end of the luminosity function of satellite galaxies has been measured only for late-type host systems or down to absolute magnitudes brighter the cutoff. Our work expands our knowledge to early-type host systems and down to absolute magnitude much fainter than -14. A recent state-of-the-art hydrodynamic simulation of galaxy formation does not reproduce such a cutoff in the satellite galaxy luminosity function. But the past history of the simulated satellites demonstrates that many satellite galaxies evolve to become fainter than the cutoff magnitude by the present epoch through fatal encounters with the host or other satellite galaxies. This leaves the hope that the missing satellite galaxy problem could be mitigated if the astrophysics of galaxy interaction is more elaborated in the theory.

272017-06-06 Tue
14:20~15:20
R104, CCMS
Changbom Park
[Korea Institute for Advanced Study (KIAS)]
*ASIAA/NTU Joint Colloquium*
Cosmology with the Large-scale Structures of the Universe
Abstract

In the first part of my talk I will briefly review sciences with the large-scale structures of the universe. In particular, I will introduce how the growing galaxy redshift data can be used to constrain cosmological models and galaxy formation theories. In the second part a new method for measuring the cosmological parameters governing the expansion history of the universe will be introduced. The method uses the Alcock-Paczynski (AP) test applied to the overall shape of the galaxy two-point correlation function along and across the line-of-sight. We applied this method to simulated data and also to a recent galaxy survey data to obtain an impressive constraint on the dark energy equation of state and matter density parameter Ωm.

282017-06-05 Mon
14:20~15:20
R1203
Chin-Ping Hu
[The University of Hong Kong]
*Special Seminar*
Magnetic Field Effects on Pulsars
Abstract

Pulsars are fast-rotating neutron stars with strong magnetic fields. Magnetars are an extreme group of pulsars with extraordinarily strong magnetic fields of $10^{14}$--$10^{15}$ G, and remarkable for the bursting activities and high X-ray luminosities powered by their high magnetic field. However, recent discoveries blurred the boundary between magnetars and rotation-powered pulsars (RPPs). In this talk, I will introduce the recent works on the high-magnetic-field RPPs, especially the youngest ones of J1846-0258, J1119-6127, and B1509-58. Young and high-magnetic-field RPPs have surface temperatures between the magnetars and canonical RPPs, indicating that high-magnetic-field RPPs are potential bursters and may contain toroidal magnetic fields according to the magneto-thermal evolution model. This model implies that the toroidal field could play an important role in bursting rate and the temperature anisotropic. Our recent work on the statistics of magnetars' pulse profiles agreed on this implication well. Finally, I will introduce the possible connection between the magnetars and the accreting pulsars in ultraluminous X-ray sources. Toroidal or multi-polar magnetic fields are necessary to interpret the high luminosities and the observed spin-up rates, indicating that ultraluminous pulsars are possibly powered by magnetars.

292017-06-02 Fri
15:20~16:20
R1203
Ming Sun
[University of Alabama Huntsville]
Study Baryon Physics with Galaxy Groups and Clusters
Abstract

Galaxy groups and clusters are the least massive systems where the bulk of baryons are accounted for and also the most massive systems that are gravitationally bound. Baryons locked into stars and baryons remaining diffuse provide orthogonal constraints on cosmic structure formation, which makes groups and clusters ideal systems to study baryon physics. In this talk, I will summarize our results on X-ray scaling relations of local galaxy groups and clusters. By stacking the Chandra data of 320 galaxy clusters, we are able to track the X-ray emission beyond the virial radius and unambiguously detect the steepening of the density profile with radius (beta ~ 1 at r_200 and beyond). The universal baryon fraction is also recovered at r_200. The stacked emission is also significantly different along the major and minor axes of the hot gas distribution, implying the detection of cosmic filaments. We further applied the weak self-similarity of the emission measure profiles at large radii to obtain good constrains of cosmological parameters, which provides an independent, direct method solely based on observed quantities. The stacking work has also been extended to lower-mass halos like galaxy groups and I will highlight our recent results on a local galaxy group with over 400 ks Chandra data. In the end, I will discuss our results on a sample of the most massive MaxBCG clusters, which sheds light on the puzzling offset between the Planck stacked SZ signals and the predicted values from the X-ray pressure template.

302017-05-24 Wed
14:20~15:20
R1203
Takahiro Nishimichi
[IPMU]
Analytical and numerical approaches to cosmic large scale structures
Abstract

Theoretical tools for accurate predictions of cosmological structure formation are significantly updated in this decade in light of recent and future observational programs. They include efficient calculations of perturbative expansion based on re-organization of the diagrams and emulators constructed based on a series of numerical simulations. I will present our recent studies on this topic with particular attention to their limitations and future prospects.

312017-05-18 Thu
14:30~15:30
R1203
Eleonora Ammannito
[Italian Space Agency]
*Special Seminar*
Mineralogical mapping across the main belt, Vesta and Ceres as test cases
Abstract

From July 2011 to August 2012, Dawn spacecraft orbited around Vesta. It escaped then for Vestan gravitational well and since January 2015 is acquiring data at Ceres. The Visible InfraRed mapping Spectrometer (VIR) mapped Vestan and Cerean surfaces acquiring VIS/NIR spectra (0.5 µm -5.0µm) with resolutions ranging from 70m to 800m. Vesta and Ceres have a completely different composition. Vestan surface is dominated by basalt and is genetically linked to HED meteorites. Ceres on the other hand has on the surface mainly aqueous alteration products like clays and does not have a clear match in the meteorite collection. These two different surfaces are indicative of a different evolutionary path of the two most massive objects of the main belt.

322017-05-17 Wed
11:00~12:00
R1107
Karl Ziemelis
[Nature]
*Special Seminar*
Inside Nature
Abstract

Since its launch in 1869, Nature has seen its mission as two-fold: facilitating the prompt communication of the most important scientific developments to the relevant research communities, while at the same time fostering a greater appreciation of these great works of science amongst the wider public. Although the publishing landscape for scientific research is currently undergoing a period of unprecedented change, these core principles remain largely unchanged. In this talk, I will endeavour to shed light on how Nature editors apply these principles in practice, and so determine which few of the many excellent research submissions that we receive make it through to publication.

332017-05-17 Wed
14:20~15:20
R1203
Martin Bureau
[University of Oxford]
3D Observations of Molecular Gas in Galaxies: From Global Dynamics to Supermassive Black Holes
Abstract

I will first briefly review the molecular gas content of early-type galaxies. I will show not only that they unexpectedly harbour much cold gas, but also that it is the best tracer of the circular velocity, thus allowing accurate spatially-resolved dynamical mass measurements in galaxies across the Hubble sequence. Second, I will explore the use of molecular gas for studies of the Tully-Fisher (luminosity-rotational velocity) relation of galaxies to high redshifts. I will highlight the work done to establish local (z=0) benchmarks and will discuss the challenges posed by systematic effects when comparing nearby and distant galaxies. Third, I will demonstrate that CO can be used to easily and accurately measure the mass of the supermassive black holes lurking at galaxy centres. I will discuss substantial ongoing efforts to do this and present many spectacular new ALMA measurements, that open the way to literaly hundreds of measurements across the Hubble sequence with a unique method. I will also hint at how the same data allow to study the spatially-resolved properties of giant molecular cloud populations in non-local galaxies for the first time, providing a new tool to understand and contrast the star formation efficiency of galaxies on cloud scale.

342017-05-10 Wed
14:20~15:20
R1203
Kevin Koay
[ASIAA]
Interstellar scintillation as micro-arcsecond scale probes of compact radio AGNs
Abstract

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 can use 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 radio telescopes 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 at present are limited only to the brightest AGNs.

352017-05-03 Wed
14:20~15:20
R1203
Xiaohu Li
[ASIAA]
Progress, Challenges, and Opportunities in the Study of “Molecular Factories” in Space
Abstract

On the Asymptotic Giant Branch (AGB), stars that have reached the end of their lives eject gas and dust to their surroundings, forming a circumstellar envelope (CSE) containing a rich variety of complex molecules. These CSEs are true “molecular factories” in space, attracting great interests from both astronomers and chemists. Thanks to the progress from high-quality observations (e.g., Herschel, ALMA, etc.) and the improvement in the accurate reaction rates of the most abundant molecules, plus the development of new astrochemical models, much of successes have been made in the understanding of the compositions and chemistry of these “molecular factories”. In this talk, I will briefly introduce our previous and recent work during the investigation of the CSEs of all types of AGB stars. I will also talk about major challenges and opportunities we have in the next few years.

362017-04-26 Wed
14:20~15:20
R1203
Ai-Lei Sun
[ASIAA]
The many facets of AGN feedback -- a multi-wavelength view of galactic outflows
Abstract

Active galactic nuclei (AGN) feedback is now a standard ingredient in galaxy evolution models. Popular models suggest that during the quasar phase, gas is driven out of the galaxy in the form of outflows, shutting off star-formation and black hole growth, leading to the observed quiescent galaxy population and the black hole -- galaxy correlations, but many assumptions require observational supports. Observations have discovered galactic outflow in the luminous quasar, but their structure is surprisingly complex, involving a wide range of gas phases from cold molecules to hot X-ray emitting gas. Multi-wavelength coverage is needed for a comprehensive picture. I summarize recent optical, radio, and X-ray observations of AGN outflows in nearby luminous quasars, and what do we learn about their occurrence rate, composition, and energetics, as well as the life cycles of AGN feedback. I end with discussing how on-going and future optical surveys could help us study this rare and intriguing phenomenon of AGN feedback.

372017-04-24 Mon
14:20~15:20
R1203
Jesus Toala
[ASIAA]
*Special Seminar*
X-ray Emission as a probe of Stellar Evolution
Abstract

Very massive stars are the main actors in shaping and chemically enriching the ISM in the galaxies we see. They do so by a combination of their stellar winds, proper motions, strong ionising photon fluxes, and supernova explosions. These produce cavities in the ISM that can be studied with X-ray observatories. In this talk I review our current understanding of the production of diffuse X-ray emission towards the nebulae carved by massive stellar feedback.

382017-04-21 Fri
14:20~15:20
R1203
Laurent Pagani
[Observatoire de Paris]
*Special Seminar*
Deuterium, a swiss-knife to study star-formation
Abstract

Though we understand the main steps which lead from diffuse gas to a newborn star with its nascent planets, a number of details remain obscur and need clarification. One of the least understood steps is the formation and collapse of the prestellar core, in the dark cloud. This is due to the core being extremely cold (down to 6 K), deeply embedded in the cloud and largely depleted of most molecular species. Therefore almost no tracer is available to study this phase in detail. Apart from dust itself (it would require a second talk to discuss it), the main tracers are H2D+, N2H+, N2D+ and DCO+ (the NH3 family is another possibility). 3 species out of 4 carry a Deuterium. Why are they abundant enough to be detected when the cosmic D/H ratio is as low as 10^-5 and what can we learn from their presence ? In the presentation, I will illustrate 3 different measurements we can perform thanks to the peculiar deuterium chemistry: the age of clouds, the age of prestellar cores and the depletion profile of CO and N2 in these cores, which is a prerequisite to study the interaction of grain surface chemistry (ices) with the gas phase in the dense cores. Deuterium appears as a swiss-knife to study star formation.

392017-04-19 Wed
14:20~15:20
R1203
Andrew Youdin
[University of Arizona]
The Route to Planetesimals
Abstract

It has long been difficult to understand how dust grains could grow past the “meter-size barrier” to become super-km scale planetesimals, the solid building blocks of planets.  Daunting obstacles include the  rapid radial drift of solids towards the star and the tendency of many collisions to result in destruction or bouncing instead of growth. The route to planetesimals focuses on two broad mechanisms.  First finding the circumstances that may lead to more effective collisional growth towards or even beyond the meter-size barrier.  Second, (aero)dynamical mechanisms to concentrate smaller solids into gravitationally bound planetesimals.  The classic dynamical mechanism is a gravitational instability of the particle disk.  In the streaming instability mechanism, drag forces and radial drift can automatically produce strong particle clumps.  Recent simulations have explored the viability of the streaming instability across a broad range of parameter space.  I will asses the viability of the streaming instability and other planetesimal formation mechanisms, including a discussion of the large scale dust structures observed in protoplanetary disks.

402017-04-12 Wed
14:20~15:20
R1203
Hayato Shimabukuro
[Observatoire de Paris]
21cm cosmology meets artificial neural networks
Abstract

The 21 cm signal from the Epoch of Reionization should be observed within the next decade. To extract from the observed data constraints on the parameters describing the underlying astrophysical processes, inversion methods must be developed. Here we test possible inversion method for EoR parameter reconstruction: artificial neural networks (ANN). We find that the quality of the parameter reconstruction depends on the sensitivity of the power spectrum to the different parameters at a given redshift, that including thermal noise and sample variance decreases the quality of the reconstruction and that using the power spectrum at several redshifts as an input to the ANN improves the quality of the reconstruction.

412017-04-06 Thu
14:20~15:20
R1203
Ellis Owen
[University College London]
*Special Seminar*
The impacts of cosmic ray heating on star formation in high-redshift galaxies
Abstract

Young galaxies with strong star formation activity are likely sources of cosmic ray particles. At high-energies, these particles interact with the baryon and radiation fields of the galactic environment via hadronuclear, photo-pair and photo-pion processes to produce charged and neutral pions, neutrons and protons. At lower energies, they can interact by collisional ionization. In both cases, the effect is to drive a heating process in the interstellar medium and beyond. The distribution of this heating effect is governed by the galactic magnetic field in the case of low-energy cosmic rays which effectively become ‘locked’ and diffuse predominantly along field lines. At high-energies, the cosmic ray heating is governed more strongly by the multi-phase interstellar density field, with the particles being more freely able to diffuse throughout the magnetic field. This talk addresses the interactions between these low and high-energy particles and the partially ionised gases and dense molecular clouds in starbursting protogalactic environments. We calculate the energy deposited by cosmic rays as they propagate in and around their host galaxy and demonstrate how this affects the thermal conditions and star formation in the host galaxy and its neighbours.

422017-03-30 Thu
14:20~15:20
R1203
Werner Krauth
[Ecole Normale Supérieure]
*Special Seminar*
Research and higher education in France, between Organizations, Schools and Universities
Abstract

A mirror of the multi-faceted research environment in most countries in the world, and in particular in Europe, the French academic environment is organized by a considerable number of actors, in a way that is not totally transparent from the outside. Nevertheless, the system produces a very stable environment, and provides opportunities for research and study at the highest level of excellence. In this presentation, I will (attempt to) provide an introduction to French research organization, with a focus on my discipline, physics, and on my own institution, Ecole normale supérieure, in Paris.

432017-03-29 Wed
14:20~15:20
R1203
Kenny Vilella
[Institute of Earth Sciences, Academia Sinica]
What thermal convection can tell us about planetary observations: applications to Pluto and habitability of exoplanets
Abstract

Thermal evolution of planetary bodies is mainly controlled by its interior thermal convection and affect importantly its atmosphere and surface processes. The observations of its direct and indirect implications provides important constraints. For instance, the polygonal network found on the nitrogen glacier Sputnik Planitia (SP) on Pluto's surface (Stern et al. 2015), indicates that thermal convection operates within SP, which in turn suggests a large glacier thickness. Thermal convection, therefore, gives information that help the interpretation of planetary observations. For instance, the thickness of SP inferred by thermal convection indicates that a deep ocean is required to explain the location of SP on the equator. Thermal convection and planetary observations are therefore closely linked.

Here I present different approaches to study thermal convection and I emphasize the important link between our work and planetary observations. First, I investigate thermal convection within SP suggested by its surface polygonal network. Based on complex 3D-numerical simulations conducted for a large range of convective system, I conclude that only internal heating may produce such a surface pattern. However, there is no clearly identified source of internal heating within SP. I propose that the surface temperature variations caused by the variation in Pluto's orbit may be an appropriate source of heating. Second, I follow a parameterized approach to predict the occurrence of partial melting in exoplanets. Partial melting being necessary to maintain an atmosphere over a long period of time, which is a prerequisite for the presence of life. I found that moderate size planets are the most likely to be habitable, which show the importance of detecting Earth-size exoplanets.

442017-03-24 Fri
14:20~15:20
R1203
Hyosun Kim
[ASIAA]
*Special Seminar*
Beloved Celestial Patterns: the Evidences of Hydrodynamic Interactions
Abstract

Hydrodynamic interactions are ubiquitous. I have devoted myself in various topics related to hydrodynamic interactions encoded in the celestial patterns surrounding various astronomical objects including evolved stars, young stellar clusters, merging black hole pairs, etc. In this talk, I will show that these various phenomena have similarities and cross-connection in a theoretician's point of view and provide some potential applications and directions.

452017-03-23 Thu
14:20~15:20
R1203
Ke-Jung Chen
[NAOJ]
*Special Seminar*
Lighting up the Universe with Extreme Supernovae
Abstract

Recent all-sky transient searches have discovered new and unexpected explosion types that fall outside traditional SN classification schemes. These exotic outliers in many cases are due to the deaths of massive stars and therefore may have been prevalent in the primordial universe because the Pop III IMF is thought to be top-heavy. Depending on the mass of the progenitor, these outliers may be faint, magnetar-powered, pair-instability, or general relativistic instability SNe, all of which have unique observational signatures. Some of these events are superluminous, 10-100 times brighter than normal supernovae, and may produce energetic UV, X-ray, or gamma-ray bursts. Their extreme luminosities enable their detection at z > 10 and they are ideal probes of the primordial universe at cosmic dawn, prior to the advent of the first galaxies. Here, we examine these exotic explosions with state of the art 3D radiation-hydro simulations that bridge all spatial scales from the central engine to breakout into the IGM, where observational signatures can be computed. We discuss the coevolution of radiation and turbulent mixing in SN ejecta and present realistic light curves for these explosions for JWST and the coming generation of extremely large telescopes (ELTs). Detection rates for Pop III SNe can place useful constraints on the primordial IMF, and their nucleosynthetic yields can be used to study the chemical compositions of extreme metal poor stars.

462017-03-22 Wed
14:20~15:20
R1203
Ziri Younsi
[University of Frankfurt]
Imaging Black Holes - Shadows, Accretion and Variability
Abstract

In the coming months and years mm-VLBI observations of supermassive black holes using the Event Horizon Telescope (EHT), most notably of Saggitarius A* and M87, are expected to verify the existence of astrophysical black holes through detection and measurement of the black hole shadow. Although the mathematical description of a black hole shadow is straightforward, its observational appearance is strongly governed by the (thermo)dynamics and geometrical structure of the surrounding accretion flow. This accretion flow, particularly on event horizon-scales, is turbulent and time variable, and must be modelled using general-relativistic magnetohydrodynamical (GRMHD) simulations. The propagation of radiation and therefore the appearance of shadow images, spectra and lightcurves are calculated using GR radiation transport (GRRT). Here we combine GRMHD and GRRT calculations to derive observational predictions of what upcoming VLBI observations of Sagittarius A* are expected to observe, addressing questions concerning variability therein and also discussing the possibility of testing the Kerr black hole hypothesis and constraining other black hole solutions and theories of gravity.

472017-03-20 Mon
14:20~15:20
R1203
Andrew Mann
[University of Texas at Austin]
*Special Seminar*
Tracing Planetary Evolution from Formation to Maturity
Abstract

Planets are not born in their final state; rather, they change significantly over their lifetimes. Understanding how planets evolve has been a central question since the discovery of the first exoplanets. The first few hundred million years are thought to be the most formative, but planets in this age range are also the most difficult to identify and characterize. Instead, research has focused on inferring the history of planets through patterns in the population of older systems. In this talk I will discuss how this paradigm is shifting, as novel search techniques and new missions have enabled our discovery of Earth- to Jupuiter-size planets as young as 10 Myr. These discoveries have altered our understanding of how planets migrate and lose atmosphere, but raise further questions about the physical drivers of these changes. The upcoming TESS mission will discover hundreds more young planets, including analogues of a young Earth. Combined with follow-up from new NIR spectrographs (e.g., SPIRou on CFHT, IRD on Subaru), the TESS sample will enable new tests of planet formation and evolution through population statistics. Eventually, JWST, SPICA, and 30m-class telescopes can be used to study the atmospheres of young, rocky planets, providing unique insight into the history of potentially habitable planets.

482017-03-16 Thu
14:20~15:20
R1203
Toshiya Namikawa
[Stanford University]
*Special Seminar*
Cosmology with cosmic microwave background polarization
Abstract

One of the promising cosmological probes in the next decades is the CMB polarization. While CMB temperature anisotropies have been already measured very precisely, CMB polarization, in particular a twisting pattern in the polarization map (B mode) is not well measured. The detection of B mode at more than degree angular scale opens new window into the inflationary universe and high energy physics beyond the standard model. Precise polarization data also enables us to measure gravitational lensing of CMB which is a key probe to understand the properties of neutrinos, dark matter and dark energy. In this talk, I will present analysis of the gravitational lensing and cosmic birefringence measurements with CMB polarization data taken from BICEP2/Keck Array experiments. I will also talk about synergy between CMB experiments and galaxy surveys such as the galaxy-lensing cross correlation with Subaru-Hyper Suprime Cam and CMB experiments, and delensing B mode with mass tracers.

492017-03-15 Wed
14:20~15:20
R1203
Sofia Wallstrom
[ASIAA]
The death throes of massive stars
Abstract

Massive evolved stars affect their local surroundings as they go through phases of intense mass-loss and eventually explode as supernovae, adding kinetic energy and freshly synthesised material to the interstellar medium. Over time, these processes affect the chemical evolution of the interstellar medium on a galactic scale. I will here present my PhD research, which probed the death throes of massive stars at various stages. First, CO observations were used to study the circumstellar environment of a massive star, the yellow hypergiant IRAS 17163-3907. Observations with APEX and ALMA ACA reveal a complex environment with several distinct components: a fast recent stellar wind of 100 km/s, a clumpy CO ring which appears to be a torus ejected by the star several thousand years ago, and a unidirectional bright spur extending from the star to the clumpy ring. These asymmetries are not seen in infrared dust observations, and demonstrate the complexity of massive evolved stars and the need for high resolution molecular observations to understand them. Next, observations of CO lines in the supernova remnant Cassiopeia A were used to study the effect of the reverse shock on supernova ejecta. A large column density of warm CO was found, which has most likely re-formed after the passage of the reverse shock. The high temperature and density implies that thermal conduction by electrons may be an important process for the evolution of dense ejecta knots, with implications for the survival of supernova dust. Finally, the contribution of massive stars to galactic chemical enrichment was investigated indirectly with measurements of isotopic ratios in a molecular absorber at z=0.68 towards B0218-211. The ratios at z=0.68 were found to be very different from those in the solar neighborhood, but similar to the ratios found in another absorber at z=0.89 and in starburst galaxies. The interpretation of these ratios is as a signature of enrichment mainly by massive stars.

502017-03-14 Tue
14:20~15:20
R1203
Simeon Bird
[Johns Hopkins University]
*Special Seminar*
Simulating Neutral Hydrogen, Galaxy Clusters and Primordial Black Holes
Abstract

It has recently become possible to perform large-scale cosmological simulations incorporating gas and enough physical processes to roughly reproduce the distribution of matter observed in the Universe. Our simulations have allowed us to resolve several long-standing problems in astrophysics, as well as suggesting new lines of investigation. I will describe in particular my work on the distribution of neutral hydrogen absorbers and galaxy clusters, both of which have implications for cosmology. I will then discuss my recent work on the implications of the LIGO gravitational wave detection for primordial black holes, which raises the exciting possibility that LIGO may have detected the dark matter.

512017-03-13 Mon
14:20~15:20
R1203
Baobab Liu
[ESO]
*Special Seminar*
Star formation: previous developments and future
Abstract

Limited by the coarse angular resolutions and/or the poor sensitivities of the previous generation (sub)millimeter telescopes (SMT, CSO, IRAM, SMA, Herschel, Planck), significant efforts and resources have been devoted to improving the constraints on a few "macro phenomenological correlations", such as the star-formation (e.g., Kennicutt-Schmidt law), Larson's laws, etc. While these laws are almost treated as fundamental physics laws, and have been routinely compared with any new observational measurements, the micro physics including how the stellar cluster-formation is related to an interplay between the supersonic gas motions and self-gravitational contractions, remain poorly understood. As an example, the meaning of the term "turbulence" has been rather ambiguous for the community of star-formation. In this talk, I will present our preliminary developments about how images of molecular cloud structures with extremely high spatial and intensity dynamic ranges may enable discriminating a variety of physical conditions, and how such developments can be prosecuted with the facilities of Taiwan and EAO.

522017-03-09 Thu
14:20~15:20
R1203
Geoff Bower
[ASIAA]
*Special Seminar*
Localization of the Fast Radio Burst 121102
Abstract

Fast radio bursts (FRBs) are millisecond-duration, highly-dispersed radio wavelength pulses. Based on their large dispersion measure, FRBs appear to originate from extragalactic distances implying extreme luminosities that are not seen in any galactic sources. Progress in understanding FRBs has been slow because the discovered events have had >arcminute localization, making association with galaxies or galactic objects impossible. Currently, there are more theories than FRBs, which number about 20. I will describe here the first arcsecond localization of an FRB. Using the Very Large Array (VLA) and other radio telescopes, we have shown that FRB 121102 is associated with a faint persistent radio source and a faint galaxy. Gemini observations provided the redshift (z~0.2) and identification of the galaxy as a dwarf with significant star formation and low metallicity. I will discuss the implications of this discovery for our understanding of FRBs and the possibility of using FRBs to study the intergalactic medium.

532017-03-08 Wed
14:20~15:20
R1203
Xuan Fang
[University of Hong Kong]
Peering into the Halo of the Andromeda Galaxy Using Planetary Nebulae
Abstract

It has been widely accepted that in hierarchical cosmology, a large galaxy evolves through accretion/merging of smaller galaxies. The effects of such galaxy interaction are imprinted in the outer disk or halo of a galaxy in the form of stellar condensations (i.e., substructures) like tidal streams. As the nearest large spiral system, the Andromeda Galaxy (M31) is an excellent candidate to study galaxy interaction and evolution. In order to study the halo and substructures of M31 using planetary nebulae (PNe) as tracers of chemistry and kinematics, we carried out very deep spectroscopic observations of a carefully selected sample of PNe using the 10.4m Gran Telescopio Canarias (GTC, La Palma). The target PNe are located in different regions: the substructures (the Northern Spur and the Giant Stream), the outer halo (or the exodisk) of M31, and M32. Our chemical study reveals: 1) the halo PNe, as far as ~180 kpc from galactic center, have oxygen abundances close to the solar value, supporting the current view that the external regions of M31 are the result of complex interaction and merger process; and 2) the substructure PNe have lower oxygen abundances, indicating a different origin.

542017-03-07 Tue
14:20~15:20
R1203
Quan-Zhi Ye
[Caltech]
*Special Seminar*
Aging comets and their meteor showers
Abstract

Active comets lost a significant amount of volatile every time they pass through perihelion. As a result, comets will have less materials for sublimation, and one would expect that comets will continue to fade as they evolve. However, it is also suggested that the active lifetime of a comet can consists of multiple active stages separated by temporary dormant phases, making it difficult to identify true secular fading caused by aging of comets. The era of modern astronomy is unfortunately not long enough to cover the typical lifetime of a comet (usually a few hundred orbits); however, comets produce dust during their active stages, which are potentially detectable as meteor activity at the Earth. Here I discuss the effort of understanding cometary aging by examining different parts of the evolution spectrum of Jupiter-family comets (JFCs), a group of comets that dominates the cometary influx in the near-Earth space, using telescopic and meteor observations as well as dynamical investigation.

552017-03-06 Mon
14:20~15:20
R1203
Paulo Freire
[Max-Planck-Institut für Radioastronomie]
*Special Seminar*
Testing the nature of gravitational waves with observations of binary pulsars
Abstract

In this talk, I will review some of the principles of pulsar timing, and review some of the results from the timing of binary pulsars from previous work. These include the observation of gravitational waves (GWs) in the energy loss of the "Hulse-Taylor" double neutron star, almost 40 years before the LIGO observation. I then introduce ongoing work, which tests the emission of GWs with far more accuracy than in the Hulse-Taylor pulsar, and new detections of the emission of gravitational waves in pulsar-white dwarf systems, which introduce strong constraints on the nature of GWs. In particular, we are able to exclude, within observing precision, any dipolar components of gravitational radiation, showing that they are almost purely quadrupolar. These results are then used for some of the most stringent tests of general relativity and alternative theories of gravity ever accomplished.

562017-03-01 Wed
14:20~15:20
R1203
Samantha Lawler
[NRC Herzberg]
Does our Solar System Need to have Another Planet?
Abstract

The orbital element distribution of trans-Neptunian objects (TNOs) with large pericenters has been suggested to be influenced by the presence of an undetected, large planet at >200 AU from the Sun. To find additional observables caused by this scenario, we present here the first detailed emplacement simulation in the presence of a massive ninth planet on the distant Kuiper Belt. We perform 4 Gyr N-body simulations with the currently known solar system planetary architecture, plus a 10 M_earth planet with similar orbital parameters to those suggested by Trujillo & Sheppard or Batygin & Brown, and thousands of test particles in an initial planetesimal disk. We find that including a distant super-Earth-mass planet produces a substantially different orbital distribution for the scattering and detached TNOs, raising the pericenters and inclinations of moderate semimajor axis (50 < a < 500 au) objects. We test whether this signature is detectable via a simulator with the observational characteristics of four precisely characterized TNO surveys. We find that the qualitatively very distinct solar system models that include a ninth planet are essentially observationally indistinguishable from an outer solar system produced solely by the four giant planets. We also do not find any evidence for clustering of orbital angles in our simulated TNO population, and further simulations find that an additional planet causes significant changes in the orbits of known distant TNOs. Wide-field, deep surveys targeting inclined high-pericenter objects will be required to distinguish between these different scenarios.

572017-02-22 Wed
14:20~15:20
R1203
Pham Ngoc Diep
[Vietnam National Satellite Center/Vietnam Academy of Science and Technology]
Millimetre/Submillimetre Astronomy Studies of Evolved Stars, Protostars and High Redshift Galaxies
Abstract

The observation of molecular emission at millimetre and submillimetre wavelengths gives access to the study of stars having a large and cool circumstellar envelope as well as of the gas reservoirs of galaxies, in particular remote galaxies with redshift in the 2 to 5 range at the epoch of maximum star formation rate. The observation of the continuum emission underneath the molecular excitation lines provides important information on the dust content. Using Plateau de Bure and archival ALMA observations, we have been able to reconstruct in space, under simplifying hypotheses such as of invariance by rotation about an axis, both the morphology and the kinematics of such sources. Examples will illustrate these studies, including Asymptotic Giant Branch stars, protostars and gravitationally lensed high redshift galaxies.

582017-02-21 Tue
14:20~15:20
R1203
TBA
[TBA]
*Special Seminar*
TBA
Abstract

TBA

592017-02-15 Wed
14:20~15:20
R1203
Marc W. Buie
[Southwest Research Institute]
Exploring the Outer Solar System with Occultations
Abstract

The Research and Education Collaborative Occultation Network (RECON) is a project to use occultations to probe basic properties of outer solar system objects. Occultation measurements can be done with relatively small telescopes but the principle challenge is in predicting events. RECON uses a strategy of a large set of fixed sites to overcome the prediction challenge. Our system uses 28-cm telescopes with high-sensitivity integrating video cameras hosted by schools across the Western United States. Our network consists of 56 stations with an average spacing of 50 km between stations. With this system, we reduce the prediction quality needed by an order of magnitude compared to a traditional “chase-the-shadow” deployment while also probing over a 2000 km region near the body. Such data can measure the sizes and shapes of the occulting body as well as detecting very close binary systems or rings and dust environments. RECON has ofetn been described as a citizen-science project but it is really more of a new collaborative research model. This presentation will review how the project was setup and is operated and provide examples of recent scientific results from our efforts.

602017-02-08 Wed
14:20~15:20
R1203
Peter Roelfsema
[SRON]
A joint infrared space observatory - SPICA revised and upgraded
Abstract

The infrared wavelength domain allows measurements to directly assess the physical state and energy balance of cool matter in space, thus enabling the detailed study of the various processes that govern formation evolution of planets, stars and galaxies over cosmic time. Infrared space missions to date were hampered by either having a warm or a relatively small size telescope, limiting the practically achievable sensitivity. With SPICA we propose to take the next step in mid- and far-infrared research by combining a large, cold telescope with instruments employing modern ultra-sensitive detectors.
SPICA is to be launched in the late 2020s as a joint ESA-JAXA mission with instruments provided by Japanese and European consortia. The mission concept foresees a 2.5-meter diameter telescope cooled to below 8K, with the optical axis oriented perpendicularly to the axis of the spacecraft. Like on PLANCK, ‘V-grooves’ to provide passive cooling are combined with mechanical coolers to provide for an effective cryogenic system, as is needed for the cooling of the telescope assembly and the science instruments. With cooling not dependent on a cryogen the mission lifetime is expected to extend significantly beyond the required 3 years.
With the combination of low telescope background and instruments with state of the art detectors SPICA will provide spectroscopic capabilities at a uniquely high sensitivity of 2-5 x10-20 W/m2 (5σ/1hr). The instruments will offer resolutions ranging from R~50 through 3000 in the 17-230 μm domain as well as R~30.000 spectroscopy between 12 and 18 μm. Additionally the instruments will support efficient 17-35 μm broad band mapping, and small field spectroscopic imaging in the 35-230 μm range.
SPICA’s extreme spectroscopic sensitivity will give at least two orders of magnitude improvement over what has been attained to date. With this exceptional leap in performance new domains in infrared astronomy become accessible. For example, with this high sensitivity astronomers will be able to detect the [OIV] line in relatively average galaxies out to a redshift z~3. Thus, the evolution of galaxies can be followed through their most active periods in cosmic time from about 10 billion years ago to what they look like today. Also, we will be able to observe dust features from even earlier epochs, out to redshifts of z~7-8, thus providing insight into dust formation in the very early phases of the universe. Similarly, this new facility will allow us to study dust formation and evolution from very early epochs onwards, and to compare the formation history of planetary systems to that of our own solar system.

612017-01-18 Wed
14:20~15:20
1F auditorium
Dominik Riechers
[Cornell]
The Intricate Role of Cold Gas and Dust in Galaxy Evolution at Early Cosmic Epochs
Abstract

Dusty starburst galaxies at very high redshift represent an important phase in the early evolution of massive galaxies. They typically represent large-scale, gas-rich major mergers that trigger intense, short-lived bursts of star formation, which consume most of the available gas and drive the morphological transition to spheroids. At early cosmic epochs, these hyper-luminous galaxies commonly trace regions of high galaxy overdensity, and may be directly related to the formation of galaxy clusters and their giant central ellipticals. Molecular and atomic gas plays a central role in our understanding of the nature of these often heavily obscured distant systems. It represents the material that stars form out of, and its mass, distribution, excitation, and dynamics provide crucial insight into the physical processes that support the ongoing star formation and stellar mass buildup. I will discuss the most recent progress in studies of the cold gas content of dusty starburst galaxies at high redshift, back to the first billion years of cosmic time using CARMA, the Jansky Very Large Array, the Plateau de Bure interferometer, and the Atacama Large (sub)Millimeter Array (ALMA). I will also highlight our recent successful first detections of the interstellar medium in "normal" (~L*) galaxies at z>5 with ALMA, and discuss the impact of our findings on future studies back to even earlier epochs.

622017-01-11 Wed
14:20~15:20
R1203
Francesco Costagliola
[Chalmers University of Technology]
Tracing the AGN/Starburst co-evolution in compact obscured nuclei
Abstract

Observations at all redshifts suggest that the AGN and starburst evolution across cosmic time are tightly linked. The recent discovery of ubiquitous giant molecular outflows revealed that even low-luminosity AGN can have a profound impact in the evolution and star-formation history of galaxies. The compact obscured nuclei of IR-luminous galaxies have been suggested to be the ideal targets to study the early stages of the Starburst/AGN interaction. However, because of the large extinction, standard Starburst/AGN tracers cannot be used to probe the central regions of these objects and new, more sensitive methods must be developed. Here I will report some of the latest results in the study of obscured AGN/Staburst activity including observations with ALMA and the JVLA.

632017-01-10 Tue
14:20~15:20
R1203
Koju Chuang
[Leiden University]
*Special Seminar*
Formation of Complex Organics in Dark Clouds - Sweet results from the laboratory -
Abstract

Complex organic molecules (COMs) have been not only observed in hot cores of low- and high-mass protostars, but also were detected recently in cold dense clouds. Besides energetic processing of ices that were shown to produce organic species, it is interesting to understand COM formation also under dense cloud conditions, i.e., without the presence of embedded energy sources. We present our latest laboratory study of the low-temperature (15 K) solid state formation of three complex molecules – methyl formate (HC(O)OCH3), glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) – through recombination of active intermediate radicals. These free radicals are formed via H-atom addition and abstraction reactions along the CO→H2CO→CH3OH hydrogenation network, which starts from CO gas accreted on the grain that successively reacts with H-atoms to form H2CO and CH3OH. The present work extends on a recent CO hydrogenation study and aims to resemble the physical-chemical conditions typical of dark molecular clouds. We confirm that H2CO, once formed by hydrogenation of CO, not only leads to CH3OH through forward addition reactions, but is also subject to backward abstractions induced by H-atoms, yielding CO again. In a similar way, H2CO is also the product of abstraction reactions of CH3OH. In this work, we show that the dominant intermediate radicals of CH3OH abstraction and H2CO addition reactions are CH2OH and CH3O, respectively. By considering both addition and abstration reactions, more reactive intermediates (HCO, CH3O and CH2OH) are produced in the ice mantle than previously thought, focussing on sequential H-atom addition reactions only. Inclusion of both types of reactions also enhances the probability to form COMs through radical-radical recombination without the need of UV photolysis or cosmic rays bombardment as external triggers. The formation of COMs realized in this way, is proven by RAIRS and TPD, also using isotopically labelled species.

642017-01-09 Mon
14:20~15:20
R1203
Erwin Lau
[Yale]
*Special Seminar*
Modeling baryonic physics in galaxy clusters
Abstract

Galaxy clusters play an important role in modern precision cosmology. As the most massive virialized objects in the universe, their abundance depends sensitively on cosmological parameters. However, uncertainties in galaxy cluster physics pose serious challenges to using forthcoming observations to make advances in cosmology with galaxy clusters. In this talk, I will highlight how we can improve our understanding of galaxy cluster physics with the state-of-the-art numerical simulations and semi-analytical modelling. In particular, I will present results from the "Omega500" simulation, a high-resolution hydrodynamic simulation suite of galaxy cluster formation that follows the evolution of dark matter and baryons in a realistic cosmological setting. I will also outline upcoming challenges in the computational modelling of major physical processes in galaxy clusters, and how we can address them in anticipation of upcoming multi-wavelength cluster surveys in the next decade.

652017-01-04 Wed
14:20~15:20
R1203
Allison Man
[ESO]
How to quench a massive galaxy?
Abstract

The progenitors of the local-day elliptical galaxies have formed the bulk of their stars in the first few Gyr of the Universe. This implies that already by z=2, there is a population of massive galaxies that have terminated their star formation somehow, and become quenched. Many plausible mechanisms have been proposed to explain early quenching in massive galaxies (e.g., active galactic nuclei feedback, halo quenching, morphological quenching). However, until recently the observations at hand are insufficient to allow us to distinguish between these mechanisms. I will review our knowledge on this topic thus far, and present efforts to tackle this decade-old question.

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