Monday, Jan.14
9:30 -
Welcome and "Visitors/TDLI/DOA Astrophysics Jamboree"
Each participants (visiting fellows and select local faculty/postdocs)introduce themselves and their research
(either review their research or discuss a specific research project), about 5 mins and 2-5 slides for each speaker
[Visiting fellows: please email your slides (pdf) to Dong Lai by Sunday night;local faculty/postdocs: email your slides
to Pengjie Zhang]
Lunch break
2:00 - 3:00
Liang Dai (IAS)
Near Caustic Lensing As a Probe of Lens Fine Structure
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Tuesday, Jan.15
9:30 - 10:30
Kenta Hotokezaka (Princeton)
Electromagnetic counterparts to GW170817 and astrophysical implications
Coffee Break
11:00 - 12:00
Wenbin Lu (Caltech)
Energetics and Polarization Properties of Fast Radio Bursts
Lunch break
2:00 - 3:00
Yuan-Sen Ting (IAS)
Milky Way, machine learning, big data
3:30 - 4:30
Informal discussion about faculty job opportunities at STJU/TDLI
(with Profs. Wei Ku, Pengjie Zhang, Xiaohu Yang, etc)
6 pm
Banquet on campus
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Wednesday, Jan.16
9:30 - 10:30
Cristobal Petrovich (CITA)
On the origin of the shortest-period planets
11:00 - 12:00
Kento Masuda (Princeton)
Mutual Inclinations of Exoplanetary Orbits
Afternoon free
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Thursday, Jan.17
9:30 - 10:30
Hao Zhou (LANL)
Very-High-Energy Gamma-Ray Astrophysics with HAWC
11:00 - 12:00
Xiangcheng Ma (UC Berkeley)
Galaxy formation in the first billion years of the Universe: progress,
questions, and future
Lunch
2:00 - 3:00
Xingjiang Zhu (Monash)
Pulsars, gravitational waves and fuzzy dark matter
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Friday, Jan.18Informal discussions (and short talks)
End at noon
Abstarct List
Liang Dai (IAS)
Near Caustic Lensing As a Probe of Lens Fine Structure
The phenomenon of strong gravitational lensing offers a way to studyforeground mass without detecting electromagnetic emissions. When asource happens to lie near a lensing caustic, its magnification factorformally diverges. A remarkable example of lensing in this extremeregime was already uncovered in HST observations of a massive lensingcluster, behind which a single star at z ~ 1.5 is magnified by afactor of a few hundreds and becomes detectable to telescopes. Itturns out that the phenomenology of near caustic lensing is extremelysensitive to any lumpiness in the lens mass profile, making it anideal probe of baryonic or dark matter substructures. I will talkabout, in the context of lensing near a cluster’s caustic,strongly-coupled microlensing due to stellar objects, substructurelensing due to sub-galactic cold dark matter halos, as well as theeffect of surface density fluctuations in competing dark mattermodels. By discussing the implications of those phenomena forforthcoming observations, I will emphasize that the study of nearcaustic lensing can provide us with valuable clues to the physicalnature of dark matter.
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Kenta Hotokezaka (Princeton)
Electromagnetic counterparts to GW170817 and astrophysical implications
The neutron star merger GW170817 is the first gravitational-wave (GW) event accompanied by electromagnetic radiation: prompt gamma-rays, uv/optical/IR kilonova, and broadband non-thermal afterglow. The signatures of kilonova in GW170817 are consistent with the picture that a substantial amount of material is ejected at merger and the ejecta is composed of r-process nuclei. In particular, the light curve from 0.5 to 70 days after the merger can be explained well with the radioactive power of r-process nuclei. I will discuss what we can learn from this observation about the composition of the ejecta and also discuss the nebular emission of kilonvoae. The second part of my talk, I will focus on the superluminal jet in GW170817 observed by VLBI. Using the afterglow light curve data and VLBI images, the jet's Lorentz factor, kinetic energy, and viewing angle are determined. I will discuss the implication of this jet to short gamma-ray bursts and how these observations can improve the GW distance measurement, which leads to the improvement of the local Hubble constant measurement from the GW-only analysis.
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Wenbin Lu (Caltech)
Energetics and Polarization Properties of Fast Radio Bursts
Fast radio bursts (FRBs) are bright millisecond-duration transientevents, first detected at ~GHz frequencies by the ParkesTelescope. Currently, about 50 FRBs are detected from randomdirections across the sky. One source discovered by the AreciboTelescope, FRB 121102, was found to generate numerous bursts. Thisallowed follow-up observations to pin-point its host galaxy, which isat a distance of ~1 Gpc.
The high brightness temperatures (> 1e35 K) of FRBs mean that theemission process must be coherent. We use the typical FRB energeticsto constrain the plasma conditions for a wide variety of coherentemission processes. We find that none of the maser mechanisms in theliterature can explain the high luminosity without invokingunrealistic or fine-tuned plasma conditions. The most favorablemechanism is curvature emission by charge clumps near the surface of amagnetar (B > 1e14 G). We also show that propagation effects throughthe magnetosphere can explain the nearly 100% linear polarization andsmall variation of polarization angles for multiple bursts from FRB121102, provided that the underlying neutron star has rotation periodlonger than about 0.3 second and its magnetic inclination is less thanabout 20 degrees.
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Xiangcheng Ma (UC Berkeley)
Galaxy formation in the first billion years of the Universe: progress,questions, and future
Understanding the formation of galaxies in the first billion years ofthe Universe is one of the key questions in galaxy evolution as wellas cosmic reionization. Despite the remarkable progress on findinglarge samples of z>5 galaxies in the past few years, many bigquestions still remain unsolved. By reviewing recent progress andmajor challenges in this field, I will introduce a suite ofhigh-resolution cosmological zoom-in simulations of galaxies down toz=5, taking advantage of the realistic models of the multi-phase ISM,star formation, and stellar feedback from the Feedback in RealisticEnvironments (FIRE) project. With unprecedented resolution anddetails, these simulation provide a realistic sample of modelgalaxies, which can play a unique role in planning and interpretingcurrent and future observations. I will discuss several key results wehave learned from these simulations, including (i) the formation ofglobular clusters in z>5 galaxies and their complications in measuringthe faint-end galaxy ultraviolet luminosity functions (UVLFs) at theseredshifts, (ii) the effects of dust attenuation on the UV propertiesand IR emission of high-redshift galaxies, and (iii) the escapefractions of ionizing photons from z>5 galaxies and their connectionto strong emission line properties. I will also discuss how theseresults motivate future theoretical and observational work.
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Kento Masuda (Princeton)
Mutual Inclinations of Exoplanetary Orbits
Unlike the solar system planets, orbits of exoplanets are occasionallyhighly eccentric and tilted with respect to the stellarrotation. These observations naturally question the universality ofyet another regularity in the solar system: alignment of the planetaryorbits. I will discuss observational efforts to constrain mutualorbital inclinations in exoplanetary systems containing planetseclipsing their host stars (transiting planets), and summarize what wehave learned from them.
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Cristobal Petrovich (CITA)
On the origin of the shortest-period planets
The shortest-period exoplanets are not only the most readily detectedby transit and radial velocity surveys, but also offer one of the bestbenchmarks to test models of planet formation and evolution. In fact,the longest-standing puzzle in exoplanet science began with thediscovery of the shortest-period gas giants, the so-called hotJupiters. First, I will argue that most hot Jupiters possibly migratedby weak gravitational interactions with outer giant planets and tidesacting on them. The nature of these interactions is likely imprintedon a population of eccentric planets at the verge of migration, and Iwill discuss a novel mechanism based on the interactions with adispersing protoplanetary disk evidenced by a particular exoplanetsystem. Second, I will promote the picture of migration even furtherto explain the origin of a population of shortest-period rocky planetswith sub-day orbits revealed by Kepler. I will argue that theseplanets acquired their tight orbits by weak chaotic interactions,similar to those driving the long-term orbital evolution of Mercury;our Solar system's shortest-period planet. Finally, I will discuss howTESS and Gaia together will inform us about the origin of theseenigmatic planetary systems.
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Yuan-Sen Ting (IAS)
Milky Way, machine learning, big data
Understanding physical processes responsible for the formation andevolution of galaxies like the Milky Way is a fundamental but unsolvedproblem in astrophysics. Fortunately, most stars are long-lived. Assuch, using the stars as "fossil records" (what is known as Galacticarchaeology) can offer unparalleled insight into the assembly ofgalaxies. In recent years, the landscape of Galactic archaeology israpidly changing thanks to on-going large-scale surveys (astrometry,photometry, spectroscopy, asteroseismology) which provide a few ordersof magnitude more stars than before. In this talk, I will discuss new"phenomenological" opportunities enabled by large surveys. I willalso discuss how machine-learning tools could leverage the big dataabout the Milky Way by maximally harnessing information from stellarspectra as well as the time-series photometric fluxes of stars.
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Hao Zhou (LANL)
Very-High-Energy Gamma-Ray Astrophysics with HAWC
The High Altitude Water Cherenkov (HAWC) Observatory, located incentral Mexico at 4100 m above sea level, is sensitive to gamma raysfrom a few hundreds GeV to above 100 TeV. HAWC has an instantaneousfield of view of 2 steradians and continuously observes two third ofthe sky each day. HAWC performs unbiased sky survey of the TeVgamma-ray sources in the northern hemisphere. There are variety ofscience topics we can study with HAWC. It is an important instrumenttargeting the century-old puzzle of the origin of cosmic rays. Thecontinuous time coverage and wide field of view also makes HAWCcritical in the era of multi-wavelength and multi-messenger astronomy.I will present recent highlights from the HAWC observatory.
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Xingjiang Zhu (Monash)
Pulsars, gravitational waves and fuzzy dark matter
Pulsars are unique cosmic laboratories with a range of astrophysicalapplications. Observations of binary pulsar systems provided the firstindirect evidence for the existence of gravitational waves and were astrong motivation for the highly successful LIGO/Virgo detectors thatmade a number of breakthrough discoveries in the past couple ofyears. The exceptional rotational stability of millisecond pulsars canbe exploited to construct a pulsar timing array, which is essentiallya Galactic-scale detector for nanohertz gravitational waves. In thistalk, I will discuss three broadly related research topics. First, Iwill present a new framework that allows population properties ofbinary neutron stars to be inferred from radio and gravitational-waveobservations. In particular, I will show that it will soon becomepossible to probe neutron star equation of state and magnetic fieldevolution with Advanced LIGO and radio telescopes like FAST andSKA. Second, I will provide updates on the international pulsar timingarray efforts and highlight some new limits on the expected signalamplitude of the gravitational wave background formed by supermassivebinary black holes. Lastly, I will present fresh constraints on fuzzydark matter using the Parkes Pulsar Timing Array.
