Date: Wednesday 29-Jan-2025
Speaker: Dr. Shreyas Vissapragada (Carnegie Observatories)
Title: Observing Atmospheric Evolution in Extrasolar Planets
Atmospheric escape has driven the long-term evolution of most known planetary atmospheres, including terrestrial planet atmospheres in our Solar System. In this talk, I will discuss the wealth of information we can learn from studying atmospheric escape in extrasolar planets, focusing on three main observational efforts. I will first introduce The Unintentional NIRISS Escape Survey (TUNES), a JWST archival program aimed at automating detections of escaping helium using low-resolution NIRISS/SOSS data, which is providing unanticipated constraints on outflow morphology sculpted by star-planet interactions. Next, I will discuss a Magellan/WINERED survey to precisely constrain helium absorption in a sample of 50 sub-Neptunes, achieving population-level constraints on atmospheric escape in small planets. Finally, I will describe the Search for Transiting Exoplanets in Lyman-alpha (STELa): the largest HST program ever awarded to study exoplanets. With 625 orbits allocated over 3 years, STELa endeavors to measure absorption from escaping hydrogen in every nearby (<100 pc) system where it could possibly be observed. These three programs are part of a broader shift towards population-level constraints on exoplanet atmospheres.
Date: Wednesday 05-Feb-2025
Speaker: Dr. ChangHoon Hahn (Princeton University)
Title: The New Frontier in Cosmology and Astrophysics
Galaxy surveys of the next decade will observe billions of galaxies over unprecedented cosmic volumes. They will produce detailed 3D maps of galaxies that encode the growth and expansion histories of the Universe. They will also observe photometry and spectroscopy that encode how galaxies and quasars evolve across cosmic history. Recent developments in machine learning (ML) and AI provide unique opportunities to fully extract this information. I will illustrate how the galaxy surveys I am leading (DESI, PFS), combined with the cutting-edge ML/AI methods I have pioneered, will address fundamental questions in cosmology and about galaxies that are out of reach with conventional methods. I will show how to test the standard "Lambda-CDM" cosmological model in new regimes and with unmatched precision to probe the nature of dark energy. Furthermore, I will demonstrate how my ML/AI methods can extract detailed properties of millions of galaxies to precisely track their evolution, constrain the physical processes that drive their evolution, and unlock the discovery space of the next-generation surveys.
Date: Wednesday 12-Feb-2025
Speaker: Dr. Ekta Patel (University of Utah)
Title: New Insights on Local Group Dynamics in the Era of Precision Astrometry
High-precision astrometric data from space observatories, such as the Hubble Space Telescope and Gaia, are revolutionizing our ability to reconstruct the history of the Local Group. In particular, 6D phase space measurements (three-dimensional position and velocity) now make it possible to rewind the clock and trace the orbital histories of nearly all Local Group satellites to their cosmic origins. These new datasets, combined with high-resolution simulations, pave the way for a revised model of the Local Group’s dynamical history and its current dark matter content. In this talk, I will review recent advancements in our understanding of the Milky Way and its halo substructures, and juxtapose those with the Andromeda system, where much remains to be learned. Looking ahead, I will discuss how these two systems can serve as benchmarks for future studies of analogous galaxies beyond the Local Group, powered by the deep, wide-field surveys enabled by Roman and Rubin.
Date: Wednesday 19-Feb-2025
Speaker: Dr.Charles Law (University of Virginia)
Title: Protoplanetary Disk Chemistry as a Window into Planet Formation
Planets assemble in dusty, gas-rich disks around young stars, and the properties of exoplanetary systems, including their architectures, atmospheres, and potential habitability, trace their origins back to disk conditions. In this talk, I will describe how advancements in observational capabilities enabled by facilities, such as ALMA and JWST, now provide access to the composition, structure, and chemistry of these disks in unprecedented detail. I will focus on how such observations have revealed complex, highly-structured, and vertically-extended disks, and the implications for planet formation occurring in these systems. I will also highlight our efforts to use molecular lines to trace the earliest stages of this process, which offers a powerful, new method to directly detect young protoplanets still embedded in their natal disks. To conclude, I will discuss how ongoing and future programs are poised to push the frontiers in our understanding of the chemistry of planet formation and ultimately, allow us to link exoplanet characteristics to their birth environments.
Date: Wednesday 26-Feb-2025
Speaker: Dr. Kartheik Iyer (Columbia University)
Title: Reading stories written in starlight: Understanding what shaped the past lives of galaxies with novel astrostatistical methods
The light from galaxies that we observe with telescopes on the ground and in space contains emission from its component stars, gas and dust. The spectra (or spectral energy distributions; SEDs) of galaxies therefore tell us stories of how galaxies form and evolve over time, and help us understand the complex processes that regulate galaxy growth over vastly different spatial and temporal scales. Modern galaxy surveys have observed millions of galaxies (and counting!) with unprecedented sensitivity across a wide range of wavelengths, enabling the reconstruction of galaxy star formation histories (SFHs). Meanwhile, large cosmological hydrodynamical simulations help us connect the physical processes that shape galaxies (cosmological accretion, feedback and baryon cycling, mergers, and more) to the imprints they leave in galaxy SFHs. My research focuses on building a new temporal picture of galaxy evolution by developing novel mathematical frameworks and computational tools to extract information from observations and connect them to theoretical models. I will discuss how this work (i) has led to the development of new methods and data products (Dense Basis, GP-SFH, Katachi) that are valuable to the wider scientific community, (ii) is being applied to observations from JWST, leading to exciting discoveries about how galaxies form stars in the early universe, and (iii) will address the unique challenges (and opportunities!) posed by large, noisy datasets from upcoming observations. While it is always an exciting time to be an astronomer, recent advances in the adjacent fields of astrostatistics and machine learning have opened up new windows for us to identify subtle signals in large populations of galaxies. As we prepare for the next generation of astronomical facilities, these methods - and the interdisciplinary approaches they represent - will be crucial for understanding how galaxies like our Milky Way came to be.
Date: Wednesday 05-Mar-2025
Speaker: Dr. Luke Bouma (Carnegie Observatories)
Title: Hot and Cold: The Circumstellar Environments of Young Low-Mass Stars
Over the past decade, photometric surveys conducted from space have opened tremendous opportunities for deepening our understanding of how exoplanets and stars evolve. Red dwarf stars in particular are enabling the study of close-in rocky exoplanets. However, the circumstellar particle and radiation environments of these stars differ from those of Sun-like stars, and these environments are observationally challenging to study. In this context, an important surprise has been the discovery that a small fraction of young red dwarfs show optical light curves with complex periodic variability, suggesting the presence of transiting clumps of opaque material corotating with the star for months to years. The composition, and even the existence, of this material have been debated. I'll give an overview of this new area of study, describe competing interpretations of the data, and present new ground-based observations that argue for this phenomenon being associated with extended clumps of circumstellar plasma. In the coming decade, a firehose of data from Roman, Rubin, JWST, Gaia, and TESS will continue to drive data-driven discovery in exoplanet and stellar astrophysics; these specific stars offer one case study of what can be learned from the surprises.
Date: Wednesday 12-Mar-2025
Speaker: Dr. Sarah Moran (GSFC)
Title: Cloudy and Hazy Worlds in the Era of JWST
Aerosols are everywhere. I will discuss two avenues where our understanding of photochemical hazes and condensation clouds has advanced for exoplanetary atmospheres. Both kinds of aerosols fundamentally shape the atmospheric chemistry of a variety of exoplanets, with subsequent impacts on observations from Hubble to JWST to upcoming missions like the planned Habitable Worlds Observatory. First, I will present results on the properties of photochemical haze particles produced from laboratory studies and the ways we may begin untangling these properties with JWST's instrumentation for the most promising planetary targets. Second, I will focus on updates to our understanding of exoplanet clouds. Clouds made of silicate materials are thought to be the dominant cloud species that affects our interpretations of hot Jupiters, but the underlying laboratory data typically used for such interpretation does not fully capture the complexity of these materials. I will discuss my recent efforts to properly account for this complexity by considering mineral polymorphs and non-spherical cloud particle models. Properly accounting for the full chemical and physical complexity of both condensate and photochemical aerosol particles in exoplanet atmospheres will let us use them as atmospheric tracers of planetary conditions.
Date: Wednesday 26-Mar-2025
Speaker: Dr. Massimo Stiavelli (STSci)
Title: Studying high redshift galaxies with the James Webb Space Telescope
I will provide a brief overview of origin and status of the James Webb Space Telescope project. I will then move to describe the results we obtained on the properties of high redshift galaxies focusing in particular on the chemical abundances measured in these objects and what they tell us about their evolution. I will conclude with some considerations on the future directions of the search of primordial galaxies.
Date: Wednesday 02-Apr-2025
Speaker: Dr. Stefanie Milam (GSFC)
Title: "**Special-Mike A'Hearn Lecture** The Solar System Revisited with JWST: New Views, Discoveries, and Questions"
The James Webb Space Telescope (JWST) has been astonishing the public and science community since the summer of 2022 after a nail-biting deployment sequence and extensive commissioning campaign. The complex space telescope operates with exquisite sensitivity at infrared wavelengths with imagers and spectrometers on board covering 1-28 microns. These instruments are already returning amazing spectra and images of small and large bodies in our solar system, revealing the composition and dynamic processes of these objects not readily accessible with other observatories or even planetary missions.
After only a few years, JWST has already provided fundamental insight into the composition and dynamics of planetary/satellite atmospheres/exospheres and rings as well as the composition of small bodies. We are learning more about the distribution of volatiles and processed materials across the different reservoirs of planetesimals and providing new observational constraints on the formation of the solar system. More importantly, the unprecedented resolution and spectral imaging are leading to new questions as well as revolutionizing planetary science for the outer solar system. The nominal launch and efficient operations in place ensure a JWST science mission lifetime of up to 20 years, enabling new discoveries and exploration for future generations. This presentation will highlight some of the amazing science in the solar system being revealed and some perspectives on what is to come.
Date: Wednesday 9-Apr-2025
Speaker: Dr. Jeff Bennett (DEI Lecture)
Title: Climate Change for Astronomers - Paving a Pathway to a Post-Global Warming Future
Many people, and especially young people, express despair when it comes to the topic of climate change, which is unsurprising given that the media often portrays our climate future as a choice between bleak and bleaker. But it doesn't have to be that way, because if we understand the science behind global warming, then we can also see pathways to its solution. In this presentation, I'll show you how I try to approach the topic with inspiration, not (only) fear, by providing simple ways to discuss global warming science, consequences, and solutions---and how these solutions could lead to a "post-global warming" future in which today's young people will someday be able to speak of the threat of global warming in the past tense. I'll focus in particular on the role that astronomy plays in our understanding of global warming, and on why this gives astronomers a unique opportunity to educate the public about this critical topic.
Date: Wednesday 16-Apr-2025
Speaker: Dr. Ilse Cleeves (University of Virginia)
Title: Imagining Other Worlds: How Planet-Forming Disks Can Shed Light on What is Possible
The last decade of ALMA has transformed our view of planet-forming environments in all respects. High resolution images have revealed a diverse array of structured belts of millimeter-sized dust and a variety of distinct molecular compositions both within disks and between different disk systems. How does this diversity translate into the initial conditions for the formation of planets and the compositions (gas and solid) that they receive? Are planets likely to receive water and organic material at formation, or at some later phase from a belt of volatile-rich icy comets? I will present recent work including on-going efforts from the ALMA "Disk-Exoplanet C/Onnection" Large Program highlighting how our picture of the chemical and physical environment of planet formation has radically shifted in recent years and how multiwavelength observational campaigns, including new observations with JWST, can help us identify patterns in the apparent variety of protoplanetary environments.
Date: Wednesday 23-Apr-2025
Speaker: Dr. Rachel Osten (STSci)
Title: Stellar Flares in a New Light
The Sun and other stars on the main sequence with an outer convection zone undergo sporadic increases in brightness over short timescales; these flares are the most dramatic examples of variability these stars will experience while they are on the main sequence. The radiation and particles involved in these events have the potential to impact not only the star itself, but the surrounding environment which may include a planet-forming disk or even close-in planets. The study of flares on the Sun and other stars has a long history, yet results in the last few years from observations and modelling in the stellar regime are upending our understanding, revealing complexities to a simple solar-stellar connection. In this talk I will focus on recent progress in studying flares as part of stellar eruptive events and earching for signatures of stellar coronal mass ejections; new information about particle acceleration revealed with mm and ultraviolet flare observations; and the emerging crisis about what optical flares tell us about the flare process.
Date: Wednesday 30-Apr-2025
Speaker: Dr. Burcin Mutlu-Pakdil (Dartmouth University)
Title: "The Smallest and Faintest Galaxies: Clues to the Nature of Dark Matter and Galaxy Formation"
The smallest and faintest galaxies around the Milky Way are the most ancient, most metal-poor, and most dark-matter-dominated systems known. These extreme objects offer unique access to small scales where the stellar and dark matter content can be studied simultaneously. They hold the promise of major breakthroughs in understanding the nature of dark matter and a more complete picture of galaxy formation. Thus, their discovery and characterization are among the most important goals in the field. In this talk, I will share our ongoing observational efforts to detect these faint systems around the Milky Way and beyond, and upcoming advances in the era of deep and wide imaging instrumentation, with a focus on their implications.
Date: Wednesday 07-May-2025
Speaker: Dr. Harley Katz (University of Chicago)
Title: The Spectral Revolution at Cosmic Dawn: Interpreting High-Redshift JWST Observations with Next-Generation Models
JWST has revealed a remarkably diverse population of high-redshift galaxies, reshaping our understanding of early galaxy formation. However, interpreting these spectral data presents a fundamental theoretical challenge. In this talk, I will first highlight key early JWST results and the limitations of existing models in extracting physical properties from spectra. I will then introduce a new suite of simulations that incorporate non-equilibrium primordial, metal, and molecular chemistry alongside on-the-fly radiation transfer. These next-generation models enable first-principles forward modeling of JWST observations, offering new insights into the physical processes governing the formation and evolution of the first galaxies.
