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Direct imaging spectroscopy of exoplanets with JWST
Kielan HochSTSciDate: Friday 19 September 2025Time: 3 pm Venue: AT 101
JWST has opened the door to spectroscopy of directly imaged exoplanets beyond 3 microns, offering a new landscape for measuring their fundamental and atmospheric properties. Directly imaged planets are in a stage of early evolution and are undergoing atmospheric processes that are critical for understanding planetary atmospheric evolution and formation. These planets, with masses of ~2-14MJup and temperatures of ~500-2000 K, remain a mystery for planet formation models—core accretion and gravitational instability. Observations that probe elemental abundances in their atmospheres can shed light on their formation. Here I present JWST Cycle 1 programs that have pioneered the use of JWST’s NIRSpec IFU to obtain spectra of substellar companions close to sunlike stars. For HD 19467 B, NIRSpec spectra show detections of CO, CO2, CH4, and H2O. We forward model the R~2,700 spectra using custom PHOENIX atmospheric model grids to constrain the abundances of these molecules, the C/O ratio, and non-equilibrium chemistry. These results highlight a need for revisions of disequilibrium chemistry models to vary the CO2 abundance with the new spectral information provided by NIRSpec. For the multi planet system YSES-1, my team obtained one of the most comprehensive datasets of a multi-planet system with spectral coverage from 1-12 microns using NIRSpec and MIRI. The spectra allow direct spectral comparison of sibling planets in unprecedented detail with spectra that show the first direct detection of silicate clouds in an exoplanet YSES-1 c and the detection of a circumplanetary disk around YSES-1 b with olivine emission that could be caused by formation of larger bodies such as moons.
Magnetic star-planet interaction
Ekatarina IlinASTRONDate: Friday 26 September 2025Time: 3 pm Venue: AT 101
The past decade has revealed that exoplanets are abundant. The evolution of their atmospheres over cosmic timescales is the next great frontier in our understanding of those planets. Star-planet interactions can determine the long-term stability and survival of planetary atmospheres. This interaction occurs in one direction, where stellar high-energy radiation and particles gradually erode the planetary atmosphere. However, recent evidence shows that the reverse is also possible: A planet in a sufficiently close orbit can influence its host star through magnetic interactions. In this talk, I will review what we know and don't know about the magnetic ways in which planets perturb their host stars, and explore the potentially destructive repercussions for these planetary troublemakers.
New insights into early galaxy formation with JWST and ALMA
Joris WitstokNiels Bohr InstituteDate: Friday 3 October 2025Time: 3 pm Venue: AT 101
Cafe AP
Date: Friday 10 October 2025Time: 3 pm Venue: AT 101
The Interplay between Massive Stars and the Interstellar Medium at Extremely Low Metallicity
Grace TelfordPrincetonDate: Friday 17 October 2025Time: 3 pm Venue: AT 101
Gravitational wave analysis with machine learning
Maximilian DaxUniversity of TuebingenDate: Friday 24 October 2025Time: 3 pm Venue: AT 101
Reaching and Teaching Neurodivergent Learners in STEM: Strategies for Embracing Uniquely Talented Problem Solvers
Jodi Asbell-ClarkeSaint Mary's UniversityDate: Friday 31 October 2025Time: 3 pm Venue: AT 101
Neutrinos and the Dark Universe: Peering into the Unknown with Liquid Argon detectors
Michela LaiQueen's U/UCRDate: Friday 7 November 2025Time: 3 pm Venue: Burke Theatre A
Beyond the dripline: neutron-unbound systems, MoNA-LISA, and Virginia State University
Thomas RedpathVirginia State UniversityDate: Friday 21 November 2025Time: 3 pm Venue: AT 101
Detection and characterization of hot dust in AGN tori using Near Infrared data
Gaia GasparSaint Mary's UniversityDate: Friday 28 November 2025Time: 3 pm Venue: AT 101
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Properties of nuclear star clusters in 41 dwarf galaxies from the MATLAS survey and implications on their formation
Melina PoulainUniversity of OuluDate: Friday 12 September 2025Time: 3 pm Venue: AT 101
Debated for decades, the formation of nuclear star clusters (NSCs) --the densest stellar objects in the Universe-- currently opposes two main scenarios: the migration and merging of globular clusters (GCs) due to dynamical friction, and the in-situ star-formation from gas infall. Studies of NSC stellar populations suggest that the former prevails in dwarf galaxies, with a possible contribution of the latter. However, timescales are such that up to now, no ongoing GC mergers were caught in the act. I will present a follow-up study of 41 nucleated dwarfs from the MATLAS survey observed with the high resolution ACS camera of the Hubble Space Telescope. About 12% of the galaxies show a complex nuclear region containing multiple star clusters and stellar tails which, I will show, establish a first direct evidence of ongoing star cluster mergers in the center of dwarf galaxies. Structural properties and photometry of the full NSC sample have been derived and compared to NSCs from galaxies in a range of mass and environment. I will showcase the results and discuss them in terms of NSC formation process. I will conclude on the future of NSC studies in the context of upcoming large surveys with deep and high spatial resolution observations, such as the Euclid Wide Survey.
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