Spring 2024 IfA Colloquia
Talks home
Date
Speaker
Affiliation
IfA Host
Title (click for abstract)
Jan 3 (W)
Maria Vincenzi
Duke University
Rubin
Jan 18 (Th)
Kamber Schwarz
Max Planck Institute for Astronomy
Williams
Jan 25 (Th)
Adina Feinstein
University of Colorado
van Saders
Jan 29 (M)
Seth Siegel
Perimeter Institute for Theoretical Physics
Liu
Feb 1 (Th)
Taeho Ryu
Max Planck Institute for Astrophysics
Shappee
Feb 2 (F)
Feb 5 (M)
Megan Mansfield
University of Arizona
van Saders
Feb 8 (Th)
Darryl Seligman
Cornell University
Williams
Feb 12 (M)
Anowar Shajib
University of Chicago
Liu
Feb 13 (Tu)
Feb 15 (Th)
Luis Welbanks
Arizona State University
Magnier
Feb 20 (Tu)
Ian Wong
NASA GSFC
Meech
Feb 22 (Th)
Chris Ashall
Virginia Tech University
Magnier
Mar 12 (Tu)
12:15pm; IfA Mānoa Library
Aparna Venkatesan
University of San Francisco
Liu
Apr 10 (W)
John R. Weaver
UMass Amherst
Sanders
Apr 17 (W)
Theron Carmichael
UH IfA
Huber
Apr 24 (W)
Peter Senchyna
Carnegie Observatories
Bresolin
Apr 26 (F)
Shadia Habbal
UH IfA
Bresolin
May 1 (W)
Bruce Macintosh
UC Santa Cruz/UC Observatories
Liu
May 8 (W)
Karen Meech
UH IfA
Bresolin
May 20 (M)
10:00am
NASA WB-57 Research Aircraft Team
NASA/JSC
Habbal
May 24 (F)
Naoyuki Tamura
Subaru/NAOJ
Sanders
Talks are held at 11:45am HST Wednesdays in the IfA Mānoa Auditorium (C-214) unless otherwise noted.
For additional information, please contact Dr. Fabio Bresolin.
Missed a talk? See if there’s a recording at the IfA YouTube channel!
Cosmological results from the Dark Energy Survey SN program
Maria Vincenzi
NASA Einstein Fellow
Duke University
The Dark Energy Survey SN sample is the largest and deepest Type Ia Supernova sample from a single telescope to date. It includes 1600 photometrically identified SNe Ia with high-quality multi-band light curves and spectroscopic redshifts, 15% of which are spectroscopically confirmed thermonuclear supernovae. With a redshift range spanning between 0.1 to 1.2 and a well-defined selection function, this SN sample constitutes an ideal dataset for cosmological analysis. We present the cosmological results from this unique sample and show that the DES SNe, combined with publicly available low-z SN samples, provides the best constraints on the Dark Energy equation of state w from SN Ia, with total uncertainty (statistical and systematic) ~0.03. Looking towards the future, I will discuss how future optical ground-based surveys like Rubin, and space-based near-Infrared observatories like the Euclid Space Telescope and the Nancy Grace Roman Space Telescope, will revolutionise how we do SN Ia cosmology and potentially answer some of the most pressing questions of modern cosmology.
Characterizing the Realistic Evolution of Planet-Forming Disks
Kamber Schwarz
Postdoctoral Research Fellow
Max Planck Institute for Astronomy
Website
Planets are formed in protoplanetary disks of gas and dust around young stars. Where and when a planet forms determines its ultimate composition. However, our ability to determine exoplanet compositions from observations is extremely limited. To truly understand what planets are made of we must instead observe the planet-forming material in the natal disk. These protoplanetary disks are dynamic objects. Material moves through the disk and experiences a wide range of temperature, irradiation, and ionization conditions. Simultaneously, chemical reactions change the composition of the disk material. The full extent of chemical variation, both across a single system’s evolution and between systems, is not well understood. I will lay out the tension between observational constraints on chemical timescales in disks and current protoplanetary disk models. I will then present how my research provides new insight into the evolution of protoplanetary disks by combining multi-wavelength observations across evolutionary stages with new chemo-dynamic models. This approach provides a holistic understanding the physical and chemical conditions during planet formation.
Hunting for Missing Carbon and Oxygen in Protoplanetary Disks with JWST
Kamber Schwarz
Postdoctoral Research Fellow
Max Planck Institute for Astronomy
Website
Protoplanetary disks are dynamic objects. Solids grow in size and drift inward, potentially enriching the gas of the inner disk in volatile molecules transported from the outer disk as ices. Concurrently, the formation of substructures such as rings and vortices may prevent this material from being delivered to the inner disk, changing the chemical composition of the material available to forming planets. JWST allows us to characterise the properties of gas and dust in the inner regions of protoplanetary disks with unprecedented sensitivity and spectral resolution. It also provides insight into the usually hidden ice inventory throughout the disk. I will present the first results from several JWST projects focused on the chemical composition of disks, as well as discuss new analysis packages I am developing to aid in the interpretation of JWST spectroscopic observations.
Evolution of Exoplanets and their Broader Environments
Luke Bouma
51 Pegasi b Postdoctoral Fellow
Caltech
Website
Over the past three decades, exoplanet science has revealed planetary archetypes with a wide range of sizes, compositions, and orbital characteristics. A major frontier in the study of these exoplanets aims to measure their properties and to understand how those properties result from the processes of star and planet formation. While the earliest formation stages are challenging to observe directly, a suite of ground and space-based telescopes is beginning to clarify the processes that occur shortly after protoplanetary disk dispersal. In this talk, I will discuss these advances, focusing on: (i) young transiting exoplanets that orbit close to their host stars, (ii) the dissolving stellar associations that harbor such exoplanets, and (iii) prospects for measuring precise ages for large numbers of field stars, including those with detected exoplanets. I will close by highlighting several future directions in the study of exoplanet evolution which will be enabled by existing and upcoming datasets.

Artist’s conception of a gas giant orbiting a red dwarf K star (system name OGLE-2003-BLG-235L)
Image credit: NASA, ESA, and G. Bacon (STScI)
Complex Periodic Variables Are A Purely Stellar Phenomenon
Luke Bouma
51 Pegasi b Postdoctoral Fellow
Caltech
Website
Space-based photometry surveys have recently shown that one to a few percent of fully convective M dwarfs younger than ~200 million years exhibit complex, but highly structured and periodic optical light curves. The most likely interpretation, after correcting for the line-of-sight viewing angle, is that up to a quarter of these stars host transient circumstellar clumps of either gas or dust that orbit at the corotation radius for hundreds of stellar rotation cycles. I’ll review the evidence for this interpretation, and will discuss how some recent work that I’ve led has helped winnow down possible sources of the circumstellar material. While there are still many open questions about these new objects, I’ll highlight some connections to stellar magnetism and close-in exoplanets, and will point out a few possible paths for better understanding this phenomenon. In particular, I’ll preview some new ground-based spectroscopy that suggests that the circumstellar clumps of material are mostly composed of hydrogen, and therefore that the phenomenon is purely stellar.
A Tale of Planetary Adolescence and Evolution
Adina Feinstein
NASA Sagan Postdoctoral Fellow
University of Colorado
Website
Within the past decade, we have discovered only a dozen young (< 300 Myr) short-period exoplanets, compared to ~5,600 mature exoplanets. The radii of these young planets are larger than older planets on similar orbital periods. The leading hypothesis is that these young planets have inflated atmospheres because they are still contracting. Inflated atmospheres are more susceptible to photoevaporation — atmospheric removal driven by high energy stellar irradiation. These effects are intensified in the earliest stages of planetary evolution, when young stars are more active and produce extreme levels of X-ray and Ultraviolet (UV) radiation on a variety of timescales. Even though it is challenging to study exoplanets around active stars, observational constraints of these targets provide crucial insights into our understanding of exoplanet formation and evolution. In this talk, I will present several benchmark studies of young stars and their planets spanning from the UV to the infrared (IR). I will present the results of several large statistical surveys of stellar flares with the Transiting Exoplanet Survey Satellite, and detailed characterization of stellar flares with the Hubble Space Telescope. I will present atmospheric follow-up characterization of young short-period exoplanets in the UV, optical, near-IR, and IR. Finally, I will present models of flare-driven atmospheric escape, discuss the contributions of stellar flares in removing gas-dominated planetary atmospheres, and highlight future steps in understanding these challenging young systems.

Artist’s rendering of a young red dwarf star stripping a planet’s atmosphere
Image credit: NASA, ESA, and D. Player (STScI)
Evolution of Flare Activity in GKM Stars Younger than 300 Myr
Adina Feinstein
NASA Sagan Postdoctoral Fellow
University of Colorado
Website
Stellar flares are short-duration (< hours) bursts of radiation associated with surface magnetic reconnection events. Stellar magnetic activity generally decreases as a function of both age and Rossby number, a measure of the relative importance of the convective and rotational dynamos. Young stars (< 300 Myr) have typically been overlooked in population-level flare studies because of the lack of long baseline observations and challenges with flare-detection methods. With this motivation, we analyzed young stars that were observed with the Transiting Exoplanet Survey Satellite (TESS) at 2-minute cadence over its 5 years of operations thus far. In this talk, I will discuss how stellar flare rates and distributions change as a function of age and spectral type. Additionally, I will discuss how these rates change as a function of Rossby number and Far- and Near-Ultraviolet luminosity of the host star. Finally, I will present candidates for which we see dramatic annual flare rate and distribution changes. These changes are likely indicative of stellar activity cycles, and proves a promising new activity metric to use moving forward.
Mapping the Large-scale Structure of the Cosmos with Tremendous Radio Arrays
Seth Siegel
Research Scientist
Perimeter Institute for Theoretical Physics
The current cosmological paradigm, LambdaCDM, is remarkably successful at describing the large-scale properties of our Universe. However, it leaves us with a number of questions regarding the nature of dark energy, the nature of dark matter, and the physics of the very early Universe. By mapping the 3D matter distribution over large volumes, we can perform powerful tests of proposed answers to these questions and a sensitive search for anomalies which may inspire entirely new ways of thinking. Observing the redshifted 21 cm line from neutral hydrogen at radio frequencies is a promising technique for characterizing the 3D matter distribution over most of cosmic history. Efficiently mapping the 21 cm signal has recently become possible as advances in signal processing, high-speed networking, and high-performance computing have enabled the construction of “digital radio telescopes” capable of performing interferometry with arrays of thousands of receivers. In addition to measuring the 21 cm signal, these telescopes can simultaneously monitor the sky at millisecond cadence for fast radio transients due to high-energy astrophysical events. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is an early example of such a telescope. CHIME recently reported the detection of 21 cm emission from the neutral hydrogen surrounding galaxies and quasars between redshifts 0.8 and 1.4. In this talk, I will describe the experiment, discuss challenges encountered when commissioning and calibrating this new type of telescope, and provide an overview of our first detection. I will then evaluate the prospects for using CHIME—and its successor, the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD)—to measure the power spectrum of 21 cm emission and probe the origin of cosmic acceleration.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, British Columbia
Image credit: CHIME
Mapping the Large-scale Structure of the Cosmos with Tremendous Radio Arrays
Seth Siegel
Research Scientist
Perimeter Institute for Theoretical Physics
Fast radio bursts (FRBs) are a mysterious class of radio transient whose physical origin has eluded explanation for well over a decade. They are characterized as bright, millisecond pulses of radio emission that are highly dispersed, indicating that they occur at cosmological distances. In addition, a small fraction of FRBs have been found to repeat. Over the past 5 years, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) has increased the total number of FRBs detected by over an order of magnitude as a result of its wide field of view, high sensitivity, and powerful real-time search backend. This has led to new insights into the origin and properties of FRBs. In this talk, I will summarize recent results from CHIME/FRB. I will then discuss the design and optimization of a next-generation search for FRBs that will be deployed on the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) and present forecasts for the detection rate. Finally, I will describe how a large sample of well-localized FRBs from CHIME and CHORD will provide a unique probe of the distribution of baryons in the Universe.
Tidal disruption events: Unresolved problems, challenges, and future prospects
Taeho Ryu
MPA Fellow
Max Planck Institute for Astrophysics
Website
What happens if a main-sequence star orbits very close to a supermassive black hole in a galactic center? If the star approaches within tens of times the event horizon of the black hole, the black hole’s intense tidal forces would tear the star apart in a matter of hours. This dramatic event, also known as a tidal disruption event, may sound like a Sci-Fi movie. However, since its first detection in the 1990s, the number of detected events has been steadily growing thanks to ongoing surveys and telescopes, such as Pan-STARRS, ATLAS, and ASAS-SN, reaching approximately one hundred. The prospect of future surveys and advanced telescopes, exemplified by the Vera C. Rubin Observatory, promises a surge in detections by several orders of magnitude over the next decade. These events offer a unique opportunity to enhance our understanding of the population of dormant massive black holes, which are otherwise challenging to identify, and distant galactic centers that can not be directly resolved. However, as the observational catalog expands, our theoretical understanding lags behind and struggles to elucidate various features unveiled by detected events. In this talk, I will address some of the unresolved problems of tidal disruption events, along with relevant challenges and emerging frontiers crucial to advancing our comprehension. I will present the results of my efforts to address these long-lasting problems with various methods, including relativistic hydrodynamics simulations and stellar evolution calculations. Lastly, I will discuss promising future directions and numerous opportunities in this field.

Artist’s conception of a tidal disruption event (TDE) in Arp 299.
Image credit: Sophia Dagnello, NRAO/AUI/NSF; NASA, STScI
Pushing the limits of numerical simulations for stellar collisions and binary mass transfer—From days to billions of years
Taeho Ryu
MPA Fellow
Max Planck Institute for Astrophysics
Website
Two crucial processes for the evolution of stellar binaries are collisions and mass transfer. Two stars, either in an eccentric binary or as two singles in dense stellar clusters, can physically collide, which can create bright electromagnetic transients or exotic outcomes, such as blue stragglers. Although it would take only days between the first contact and the formation of collision products, this brief period can critically determine the final fate of the colliding stars that could evolve over millions or billions of years. On the other hand, in binary mass transfer, material is transferred from one star to the other. This process, relatively gentle compared to stellar collisions, plays a crucial role in determining the final outcome of a compact binary such as gravitational wave sources. Although the duration of mass transfer can be as long as the main-sequence lifetimes, the process involves the crossing of streams on the time scale of days. How can we connect two widely different time scales (days vs stellar lifetime) of the two processes? In the talk, I will present my ongoing projects where I examine the magnetohydrodynamics of the two processes as well as the long-term evolution of the outcomes, by combining several state-of-the-art numerical methods. In particular, in the first part of my talk, I will discuss the amplification of magnetic fields in collision products and their long-term evolution in the context of blue straggler formation. In the second part, I will present some results of my 3D hydrodynamics simulations for stable mass transfer over a wide range of mass ratio, including stellar extreme mass-ratio inspirals consisting of stars and supermassive black holes. In both parts, I will also discuss the future directions of my research on each topic.
Studying exoplanet atmospheres in the era of JWST and the ELTs
Megan Mansfield
NASA Sagan Postdoctoral Fellow
University of Arizona
Website
The recent launch of JWST and the upcoming extremely large telescopes (ELTs) will revolutionize our understanding of exoplanet atmospheres by providing observations at an unprecedented level of detail. In this talk, I will discuss two methods for studying the atmospheres of exoplanets. First, I will discuss the recently developed method of high-resolution cross-correlation analysis, which can be used to precisely measure abundances and thermal structures from ground-based telescopes. I will present the first results from a large program to measure high-resolution transmission spectra of 10 giant exoplanets using the IGRINS instrument on Gemini-S. I will describe the goals of this ongoing program and show first results constraining the carbon-to-oxygen ratio of the ultra-hot Jupiter WASP-76b. I will then describe the advances in this observational style which will be enabled by the next-generation ELTs.
Second, I will present a method of using JWST to quickly determine which M dwarf planets host atmospheres through secondary eclipse observations. I will give an overview of the application of this method in the first two years of JWST science, including new, unpublished results from my own program to observe the hot terrestrial planet Gl 486b in secondary eclipse. Finally, I will briefly discuss synergies between space-based and ground-based observations in studying exoplanet atmospheres.

Artist’s rendering of the ultra-hot Jupiter WASP-18b, which orbits its star once every 23 hours
Image credit: NASA/GSFC
Studying exoplanet atmospheres in the era of JWST and the ELTs
Megan Mansfield
NASA Sagan Postdoctoral Fellow
University of Arizona
Website
Exoplanet eclipse and phase curve observations have revealed information about energy transport and thermal structures of planetary atmospheres. However, this information has been fundamentally limited by these observational techniques, which only probe spatially-integrated fluxes. The launch of JWST in 2021 enabled the new technique of spectroscopic eclipse mapping, which uses measurements during secondary eclipse ingress and egress to construct a brightness map resolved in latitude, longitude, and altitude. No other observational technique can simultaneously resolve exoplanet atmospheres in all three dimensions. In this talk, I will present early results of a spectroscopic eclipse map of the ultra-hot Jupiter WASP-18b, the first such map produced from JWST data. I will describe the methods used to extract spatially-resolved information from secondary eclipse observations and what this information reveals about compositional and thermal gradients across the dayside of the planet. Finally, I will discuss the prospects for eclipse mapping other exoplanets with JWST.

Spectrum of exoplanet WASP-18b as resolved by JWST’s NIRISS instrument
Image credit: NASA/JPL-Caltech (R. Hurt/IPAC)
New Populations of Solar System Small Bodies and What They Tell Us
Darryl Seligman
NSF Postdoctoral Researcher
Cornell University
Website
Small bodies not only trace the formation and evolution of their host systems, but also deliver material to planets vital for the development of life. In recent years, an entirely new class of planetesimals has been discovered in the solar system: dark comets. The dark comets are near-Earth objects which exhibit significant nongravitational accelerations only explainable by the outgassing of volatiles, without any evidence of cometary tails. These still-enigmatic objects are challenging our understanding of the behavior and properties of comets and asteroids. In this talk, I will review what has been learned to date from the known dark comets and present new results that clearly show that there are two distinct, but possibly related, families of dark comets. I will provide circumstantial evidence that the outer dark comets are the progenitor population for the inner dark comets. These objects therefore allow us to trace the various stages in the life cycle of a previously undetected, but vast, population of small bodies that may have provided material to the Earth essential for the development of life. One of the dark comet candidates, 1998 KY26, is already the target for the extended Hayabusa2 mission. I will discuss what we can learn about the Earth, the Solar System and exoplanets from future ground and space-based observations of small bodies.

Artist’s illustration of Earth Trojan asteroid 2020 XL5 (discovered by Pan-STARRS1 in 2020); in this illustration, the asteroid is shown in the foreground in the lower left. The two bright points above it on the far left are Earth (right) and the Moon (left). The Sun appears on the right.
Image credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine
Interstellar Interlopers
Darryl Seligman
NSF Postdoctoral Researcher
Cornell University
Website
1I/ʻOumuamua was the first macroscopic interstellar object discovered traversing the inner Solar System. In this talk, I will review the mysterious properties that 1I/ʻOumuamua exhibited, including an elongated shape and a surprisingly low velocity with respect to the local standard of rest. Most intriguing, 1I/ʻOumuamua appeared unresolved and asteroid-like, yet moved under the action of nongravitational acceleration. I will present our recent hypotheses that can explain 1I/ʻOumuamua’s unusual behavior via the release of radiolytically produced and entrapped molecular hydrogen. The interstellar interlopers and their divergent properties provide our only window so far onto an enormous and previously unknown galactic population. Existing all sky surveys and the forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST) are poised to further transform our understanding of interstellar interlopers, and I will discuss the feasibility of future discoveries and characterization via ground-based observations as well as possible intercept missions.

Artist’s impression of the first detected interstellar asteroid, 1I/’Oumuamua (detected by Pan-STARRS1 in 2017)
Image credit: ESO/M. Kornmesser
The strong-lensing revolution in the JWST-Rubin-Roman era: From resolving the Hubble tension to constraining baryonic feedback
Anowar Shajib
NHFP Einstein Fellow
University of Chicago
Website
Despite the remarkable success of the Lambda Cold Dark Matter (LCDM) cosmological model, several challenges have recently emerged. One of the most prominent is the “Hubble tension”: the Hubble expansion rate (H0) measured using the Cepheid-calibrated distance ladder of type Ia supernovae and the value extrapolated from the cosmic microwave background using LCDM disagree by 5 standard deviations. To confirm that new physics beyond the LCDM model is needed to resolve this disagreement, we must rule out any unknown systematic errors in these measurements using another independent probe. Strong gravitational lensing time delays provide such a probe that can independently constrain H0 to 1% precision and potentially confirm new physics. This will be made possible by the very large samples of galaxy-scale lenses to be discovered by the Rubin and Roman Observatories—two orders of magnitude larger than current samples—and with follow-up data from JWST. These surveys will also provide new samples of exotic lenses to competitively constrain dark energy parameters and to study the impact of baryonic feedback on the evolution of massive galaxies to redshift z~1. Strong lensing in the Rubin-Roman era thus promises a revolution in the study of both cosmology and galaxy evolution.
Project Dinos: A joint lensing-dynamics view of how baryonic processes have shaped the internal structure of massive elliptical galaxies
Anowar Shajib
NHFP Einstein Fellow
University of Chicago
Website
Project Dinos website
I will present “Project Dinos”, whose goal is to constrain the internal structure or the mass distribution of massive elliptical galaxies from joint lensing-dynamics analysis, and to uncover the details of the baryonic processes that have shaped them. To that end, Project Dinos has assembled a “supersample” of strong lenses consisting of archival samples with available Hubble Space Telescope (HST) imaging and ground-based stellar velocity dispersion measurements, such as the SLACS, SL2S, and BELLS. In Project Dinos, we perform state-of-the-art lens modeling of these systems from the HST imaging, adopting improved mass models beyond the simple singular isothermal ellipsoid (SIE) mass distribution that was used in most previous analyses of these samples. We have released the first sample of 77 uniformly modeled lenses from Project Dinos, which is the largest to date with power-law models. I will present our result on the consistency of the power-law mass profile in elliptical galaxies based on the joint lensing-dynamics analysis performed using these lens models. I will then describe the near-future plan to constrain the impact of baryonic feedback and the stellar initial mass function based on this sample, and then to expand the sample size to ~300 with a new, approved HST program in the next 3-4 years.
Addressing the challenges in understanding the nature of exoplanet atmospheres from their spectra
Luis Welbanks
NASA Sagan Postdoctoral Fellow
Arizona State University
Website
The 2020s and beyond will be the era of spectroscopy of exoplanet atmospheres. In just 3 years, our field has made dramatic advancements, moving from having very limited wavelength coverage and precision data from the Hubble Space Telescope (HST), to having high-precision spectroscopy over a wide wavelength range (~0.4 to 20μm) with the James Webb Space Telescope (JWST). These exquisite observations come with the opportunity to perform detailed reconnaissance of exoplanet atmospheres, explore their chemical and physical properties, and perform population-level studies to test our hypotheses for planet formation and planetary processes. Thanks to these advancements we could very well be the first generation in human history to answer whether we are alone in the universe.
However, any interpretation is only as good as our understanding of the limits of the data and the model assumptions themselves, a point often overlooked. Whether exploring hot gas giants or temperate terrestrial exoplanets, the future of the field depends on our models’ ability to interpret atmospheric properties from observed spectra. This new era in exoplanetary sciences invites us to overcome previous artificial boundaries between observers and theorist and merging both disciplines to fully exploit this wealth of data. In this talk, I will present my efforts to deliver a holistic view of exoplanet atmospheres, answering not only what exoplanet atmospheres are made of, but also which data drive our inferences, how reliable these inferences are, and their place within the larger astronomical context. I will present several early ground-breaking results from observations with JWST. From these observations we detect and constrain several chemical species that were previously elusive, including methane (CH4), ammonia (NH3), sulfur dioxide (SO2), carbon monoxide (CO), and carbon dioxide (CO2), alongside several precise water (H2O) measurements. I will discuss the challenges we are currently facing, and the advancements required for inferring the complete chemical inventory of our diverse exoplanet sample. Our findings underscore the transformative power of JWST and pave the way for future, in-depth atmospheric investigations of a larger exoplanet population.

Gas giant WASP-107b orbits a highly active K-type main sequence star about 200 light years from Earth. Helium was detected in the escaping atmosphere of the planet — the first detection of this element in an exoplanet atmosphere.
Image credit: ESA/Hubble, NASA, M. Kornmesser
Deciphering the broadband transmission spectra of exoplanets with JWST
Luis Welbanks
NASA Sagan Postdoctoral Fellow
Arizona State University
Website
The James Webb Space Telescope promised to revolutionize our understanding of exoplanetary atmospheres by providing us with transmission spectra at wavelengths never probed before and with unprecedented precisions. During this talk I will present, for the first time, the observations that demonstrate how JWST is delivering on its promise. I will begin by presenting the first complete broadband spectrum of WASP-39b from 0.5 to 12μm as observed by JWST/NIRSpec-PRISM, JWST/NIRSpec-G395H, JWST/NIRCam, JWST/NIRISS, and JWST/MIRI from a cohesive synthesis data effort. Then, I will present the panchromatic spectrum of WASP-107b from 0.8 to 12μm using both JWST and HST. I will discuss the important lessons learned from interpreting these first-of-their-kind broadband JWST spectra, leveraging different modelling strategies, with key recommendations for upcoming observations with this space telescope. I will share our findings on the chemical composition of these planets—as described by the multiple molecular features observed and their inferred chemical abundances—and the planets’ properties such as atmospheric metallicity and elemental enhancements. Finally, I will discuss how these observational and technical advancements open a new avenue for atmospheric characterization of a diverse planetary population with JWST and upcoming facilities.

A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by Webb’s Near-Infrared Spectrograph (NIRSpec) July 10, 2022, reveals the first clear evidence for carbon dioxide in a planet outside the solar system. This is also the first detailed exoplanet transmission spectrum ever captured that covers wavelengths between 3 and 5.5μm.
Illustration credit: NASA, ESA, CSA, and L. Hustak (STScI)
Science credit: The JWST Transiting Exoplanet Community Early Release Science Team
The Dynamic Solar System: Observational explorations of icy planetesimals as probes of planetary migration
Ian Wong
Postdoctoral Researcher
NASA Goddard Space Flight Center
Research Assistant Professor
American University
Website
For over a century, astronomers have sought to improve our understanding of solar system history by placing the existing body of observational data within the explanatory framework of planetary formation and evolution models. While earlier theories posited a relatively simplistic view of planet formation, with the planets forming close to their present-day locations, new discoveries in the past several decades have begun to favor a substantially more dynamic evolutionary history. Current theories describe a period of dynamical instability that occurred after the end of planet formation, during which the orbits of the giant planets migrated outward from an initially more compact configuration. While these models consistently reproduce many aspects of the present-day Solar System, definitive confirmation of dynamical instability models has remained elusive. The key to unveiling the detailed evolutionary history of the middle and outer Solar System is a more complete understanding of the diverse populations of icy planetesimals spanning the giant planet region, including the Jupiter Trojans, Kuiper Belt objects, and Centaurs. These enigmatic objects serve as tracers of past dynamical evolution, and the specific trajectories of early-stage planetary migration have critical implications for their observable properties. In this talk, I will provide an overview of the current state of knowledge regarding these small bodies, with a focus on the wide-ranging observational studies I have carried out over the past decade to characterize their surface properties and place them within the broader context of solar system evolution. Special attention will be given to the immense leap in knowledge brought about by JWST during its first year of operation and the promising future avenues of research that will be enabled by upcoming surveys, such as the Legacy Survey of Space and Time (LSST) at the Rubin Observatory.
JWST observations of Chiron: A unique active Centaur beyond 18 AU
Ian Wong
Postdoctoral Researcher
NASA Goddard Space Flight Center
Research Assistant Professor
American University
Website
Centaurs are inward-scattered objects from the Kuiper belt that lie on unstable orbits within the giant planet region. Their closer heliocentric distances compared to Kuiper belt objects have made them particularly valuable for probing the detailed properties of outer solar system bodies. Meanwhile, the higher levels of irradiation provide a unique window into the differential effects of thermal processing on the surface properties of icy planetesimals. Chiron is one of the largest Centaurs, with a mean radius of 90 km. Notably, Chiron belongs to the enigmatic subpopulation of active Centaurs, which show sporadic periods of cometary outgassing. In March 2021, Chiron was observed to outburst while it was at a heliocentric distance of 18.8 AU. This report of Centaur activity is the most distant to date by a significant margin and challenges our prevailing understanding of the mechanisms that trigger and sustain outgassing on these objects. A holistic picture of Chiron’s surface and coma promises to revolutionize our understanding of Centaur activity and the properties of primitive icy planetesimals near and far. In July 2023 and January 2024, we obtained observations of Chiron with the Near Infrared Spectrograph (NIRSpec) on JWST. These data reveal a wide range of surface ice species, including a surprisingly high abundance of CO2 ice. In addition, the spatial information provided by NIRSpec’s integral field unit has yielded maps of individual molecular constituents within the coma. In this talk, I will present the results of these Chiron observations, place them within the context of other active bodies observed with JWST, and discuss the broader implications for our understanding of distant cometary activity and the formation and evolution of icy planetesimals throughout the Solar System. I will also discuss fruitful avenues of future study that will capitalize on synergies between ground- and space-based facilities as we look forward to the Legacy Survey of Space and Time (LSST).
The Infrared Revolution: Supernovae with the James Webb Space Telescope
Chris Ashall
Assistant Professor
Virginia Tech University
Website
As cauldrons of nucleosynthesis, supernovae (SNe) provide the interstellar medium with heavy elements and are key to its isotopic composition. Yet, we do not fully understand the details of how they explode, what their progenitors are, or how they contribute to the dust budget of the cosmos. The launch of the James Webb Space Telescope has transformed our view of the universe, and recent results have demonstrated that JWST data may provide the missing information required to finally comprehend the physics driving these cosmic explosions.
In this talk I will showcase how JWST is pushing our understanding of SNe into a new era. My talk will be centered around the groundbreaking results obtained from the six JWST programs lead by my research team. This includes some of the first ever JWST observations of transients as well as their connection with models. I will discuss both thermonuclear SNe (SNe Ia), and core collapse SNe (CC SNe). For SNe Ia, I will show how JWST observations can be used to accurately measure the mass of the primary white dwarf, chemical asphericities within the explosion, and the details of the flame physics. For CC SNe, I will demonstrate how JWST data can be used to observe the formation and growth of both molecules (e.g. CO and SiO) and dust for a variety of events. Overall, these results have profound implications for the application of SNe Ia as cosmological distance indicators, and the role of SNe as producers of early-universe cosmic dust. Finally, I will project forward and discuss the future of the JWST transient field, as well as the connection between JWST and the Nancy Grace Roman Space Telescope.
One-minute colloquium
Presented by the IfA Community
Participants will have a single slide and one (1) minute to present their research.
For newcomers, this is a great introduction to what goes on at IfA. For the old-timers, it’s always interesting to see what your peers have been up to for the past year.
A Global View of the Cosmic Ray Spectrum
Damiano Caprioli
Associate Professor
University of Chicago
Website
The regularity of the cosmic ray (CR) spectrum is one of the most striking astrophysical phenomena. I discuss how novel kinetic (particle-in-cells) plasma simulations of non-relativistic shocks are helping us understanding that supernova remnants are the most prominent sources of Galactic CRs. Ion acceleration efficiency and magnetic field amplification are obtained as a function of the shock properties and compared with theoretical predictions, multi-wavelength observations of individual remnants, and in-situ measurements at heliospheric shocks.
Moreover, I outline an original mechanism (the “espresso mechanism”) for the acceleration of nuclei up to ~1020 eV in the relativistic jets of powerful active galactic nuclei. The combination of the “supernova-remnant paradigm” for the origin of Galactic CRs and the “espresso” mechanism provides a unified description of the spectrum.
Who Owns the Night Sky? Lessons from Partnerships with Indigenous Communities
Aparna Venkatesan
Professor
University of San Francisco
Website
Space exploration is increasingly privatized, from Earth’s orbital space to the Moon and beyond. This has led to increasing congestion and environmental degradation of low-Earth orbits; along with dramatic rises in ground-based light pollution, this is leading to brightening night skies worldwide. The loss of dark skies impacts ground-based astronomical observations (which I discuss in a separate talk this week) as well as the scientific-cultural practices and sky traditions of many cultures worldwide. I share perspectives and invaluable lessons from over a decade of collaborations with numerous Indigenous communities, including Maunakea, wayfinding and Native Hawaiian communities in the past three years. Space is an ancestral global commons, and the skies represent our shared heritage needing advocacy and protection more than ever.
The Cost of Brightening Night Skies on Ground-Based Astronomy
Aparna Venkatesan
Professor
University of San Francisco
Website
Dramatic rises in ground-based light pollution in recent years as well as increasingly congested low-Earth orbits are leading to brightening night skies worldwide, with consequences reaching far beyond this decade. I share calculations of the potentially large future rise in global sky brightness from space objects in low Earth orbit (LEO), including qualitative and quantitative assessments of how ground-based astronomical observations may be affected. Debris proliferation is especially a concern: all log-decades in debris size may contribute approximately the same amount of night sky radiance, and given the rising risk of debris-generating events in LEO, this could lead to rapid rises in global night sky brightness. This will in turn lead to increased loss of astronomical data and diminished opportunities for ground-based discoveries as faint astrophysical signals become increasingly “lost in the noise”. This will affect many constituencies beyond professional astronomy that are reliant on dark and quiet skies, including Indigenous communities’ sky traditions, animal/bird migratory patterns, amateur astronomy, astrotourism, human/animal circadian rhythms, and the seasonal and pollination cycles of plants. Globally coordinated regulatory policies and mitigation strategies are urgently needed to protect the shared environment and intangible heritage of space and dark skies for future generations.
Temporal and Spatial Variability of Ultra-Hot Jupiters
Ji Wang
Assistant Professor
Ohio State University
Website
In this analog presentation, I will talk about recent developments in observing ultra-hot Jupiters (UHJs). For these close-in planets that are tidally-locked, their day-side temperatures are comparable to the coolest stars. In such extreme conditions, interesting phenomena happen, including strong winds that blow from the day-side to the night-side at speeds that have been seen in the solar system. More intriguingly, the wind speed is changing over time scales from weeks to years. Another unique phenomenon for UHJs is the detection of neutral and ionized atomic species (e.g., Fe and Fe⁺). The detection signal of the atomic species sometimes varies as a function of orbital phases, implying spatially inhomogeneous distribution due to varying physical and chemical conditions. In conclusion, despite being firstly detected and studied for almost three decades, hot Jupiters remain puzzling and continue offering opportunities to peering into physical processes under extreme conditions.
Cosmic Evolution of Star Formation and Gas in Galaxies
Nick Scoville
Francis L. Moseley Professor of Astronomy, Emeritus
Caltech
Website
In the last decade, there has been tremendous progress in understanding the overall evolution of the interstellar gas in galaxies and the processes leading to stars (and planetary system formation). From observations of nearby galaxies we gain insight into star formation processes, while from comprehensive surveys out to redshift ~ 6 (and some detections at z ~ 10), we now have a quantitative picture of the early cosmic evolution of interstellar gas. Despite the great observational progress, there is a diversity of understanding. I will highlight those issues where recognizing a few paradoxes can lead to surprising but fundamental understanding—e.g., the role of spiral structure, the trigger of star cluster formation, the lifetimes of molecular clouds, and the role of atomic gas. Lastly, some open discussion of Pop III star formation at redshift 20 – 30.
In Search of Giants: Tracing the History of the Most Massive Galaxies in Our Universe
John R. Weaver
Postdoctoral Research Associate
University of Massachusetts Amherst
Website
Recent surveys of the distant Universe have revealed a landscape that challenges our preconceptions of galaxy evolution. Of this formative epoch, the most luminous, star-forming systems are thought to be the progenitors of massive elliptical galaxies lying within the rarest, most overdense regions of the primordial web of dark matter from which they sprung. Scarce on even degree-scales, only in the last decade have sufficiently deep, wide-field near-infrared surveys found them, albeit in limited numbers. With the launch of Euclid in conjunction with efforts in Hawaiʻi, we are now expanding this search into the 20x larger volume necessary to identify the first statistical samples of these cosmic beasts. Nearly simultaneously, JWST has enabled detailed spectroscopic study of the ISM conditions that permit their rapid growth. I will present an overview of our efforts to chart the assembly and evolution of the most massive galaxies in our Universe, including brand new spectroscopic observations that are finally beginning to reveal their origins.
Tackling the Inflated Radius Problem in Transiting Brown Dwarfs
Theron Carmichael
NSF MPS-Ascend Postdoctoral Fellow
University of Hawaiʻi Institute for Astronomy
Website
This work explores the discrepancies between the transiting brown dwarf population and substellar age-radius models by examining radius inflation mechanisms in brown dwarfs and giant planets and comparing the effects of these as a function of mass. To do this, I compare the relative ages of over 90% of known transiting brown dwarfs via a homogeneous analysis of their host star ages. Both low-mass and high-mass brown dwarfs show clear signs of radius inflation at ages beyond 1 Gyr, but it is unclear whether or not the inflation mechanisms are shared between low- and high-mass brown dwarfs. Here I present an overview of transiting brown dwarfs and discuss possible radius inflation mechanisms affecting them.
New windows on the earliest massive star populations with JWST and HST
Peter Senchyna
Carnegie Postdoctoral Fellow
Carnegie Observatories
Website
The first generations of massive stars fundamentally shaped the Universe we live in today, from forging the first metals to reionizing the neutral early Universe. Yet despite their importance, our understanding of these first metal-poor young stellar populations remains highly uncertain. I will describe new results from JWST spectroscopy and our emerging view of the massive star populations inhabiting the most luminous galaxies in the reionization era. As expanding samples of z > 6 spectra continue to reveal surprising challenges to model expectations, work on metal-poor young stellar populations more close to home remains of significant and growing relevance. I will describe new results from HST and other facilities targeting metal-poor stellar populations in a range of nearby galaxies. Many of these disparate observations underscore the importance and complexity of binary interaction in shaping metal-poor massive stars, which has significant implications for our understanding of the very early galaxies they dominated.
The Solar Wind Sherpas’ 8 April 2024 Total Solar Eclipse Expedition
Shadia Habbal
Astronomer
University of Hawaiʻi Institute for Astronomy
The Solar Wind Sherpas will report on their most ambitious total solar expedition in modern times. This presentation will showcase the observations we wanted to gather to address our science goals as well as the trials and tribulations of this expedition.
Direct Imaging of Extrasolar Planets and the Gemini Planet Imager
Bruce Macintosh
Director
University of California Observatories
Professor
UC Santa Cruz
Direct detection of extrasolar planets—spatially resolving a planet from its host star while blocking, moving, or post-processing the starlight—is a powerful complement to transit, RV, and microlensing approaches. Direct detection is sensitive to planets in wider orbit, and allows spectroscopic characterization of planetary atmospheres. One of the most effective instruments in this regime has been the Gemini Planet Imager (GPI). GPI was a facility instrument combining advanced adaptive optics, a diffraction-controlling coronagraph, and an infrared integral field spectrograph on the Gemini South Telescope. From 2014-2019 we carried out the Gemini Planet Imager Exoplanet Survey (GPIES), which observed 532 young (10-200 Myr) nearby stars. I will summarize the key results of the GPIES program, including constraints on giant-planet distributions and atmospheric properties.
We have also extensively characterized GPI’s performance. Based on that, the GPI 2.0 project upgrades the existing instrument with faster adaptive optics, better coronagraph designs, and new spectrograph modes. When deployed on Gemini North, GPI 2.0 will be able to search younger stars in the Taurus and Ophiucus star-forming regions, and be sensitive to Jupiter-like “cold start” planets. I will summarize the science drivers that guided the GPI 2.0 upgrade and the project’s status.
In the even longer run, direct imaging is the best path to characterizing true Earth analogs—planets orbiting in the habitable zone of sunlike stars, beyond the reach of practical transit spectroscopy. Such detection will require a dedicated space mission incorporating an advanced coronagraph—now known as the Habitable Worlds Observatory. I will give a brief update on HWO and the prospects for someday characterizing earthlike planets.
Small Bodies: Primitive Witnesses to the Birth of a Habitable Solar System
Karen Meech
Astronomer
University of Hawaiʻi Institute for Astronomy
No one knows if our solar system, with a planet possessing the necessary ingredients for life within the “habitable zone”, is a cosmic rarity. We also don’t know if the gas giants in our solar system played a role in delivering the materials essential to life to the habitable zone. Our solar system does not have a common arrangement of planets; does this have implications for Earth’s habitability? The answers to these questions are contained in the leftovers of the process of forming our solar system. Today, we observe these remnants of the birth of our solar system as comets and icy asteroids. Decades of small body observations from both ground and space, along with contributions from all-sky surveys, are confirming old theories and uncovering new information that will help piece together how at least one inhabited solar system planet became habitable. In this talk, I will explore how recent discoveries and interdisciplinary investigations are addressing the question of how Earth became habitable, and what we can expect using new tools such as JWST, the LSST, and future missions.
Airborne Scientific Observing Opportunities Onboard the NASA WB-57 Research Aircraft
NASA WB-57 Research Aircraft Team
NASA/Johnson Space Center
Opportunities for low-cost access to space for astronomical observations have been rather limited, with balloons being the most utilized. The design of enclosures on the NASA’s WB-57 research aircraft, known as spearpods on the wings and noseball ahead of the cockpit, offer special opportunities for astronomical observations that have been poorly exploited. In this informal presentation we will discuss how the two available NASA WB-57 research aircraft have been used during the total solar eclipse observations on 21 August 2017 and 8 April 2024 to enable the operation of state of the art imaging and spectroscopic instrumentation with great success. We underscore how the spearpods and noseball can accommodate a variety of instrumentation, and welcome engagement from the community to take advantage of this airborne platform.

The WB-57 is a mid-wing, long-range (2,500 miles) aircraft capable of operation for extended periods of time from sea level to altitudes in excess of 60,000 feet. This PDF brochure has more info, and check out their website, specifically the Design and Integration section, if you’re really interested in the science and operations of the aircraft.
Image credit: NASA Aircraft Operations Division
The Subaru Prime Focus Spectrograph—Taking final steps to science operation
Naoyuki Tamura
Project Manager & Project Systems Engineer
Prime Focus Spectrograph [PFS] Project
Professor
Subaru Telescope, National Astronomical Observatory of Japan
PFS Project Overview
PFS Project Official Website
The international collaboration led by Kavli IPMU, the University of Tokyo, and including the National Astronomical Observatory of Japan (NAOJ) has been developing a next-generation facility instrument, the Prime Focus Spectrograph (PFS), for the Subaru telescope. After successive progresses and achievements over more than a decade, the instrumentation is now in the final phase of the commissioning process. In this talk, I will try to summarize the current status of the PFS instrument and prospects for the upcoming science operation phase, as well as present a brief overview about the path the project has been traveling.

Credit: PFS Project
Reference: “Prime Focus Spectrograph (PFS) in Final Phase of Commissioning”