STScI/JHU 2026 HotSci Series -- July 1st

Speaker: Natalia Oliveros Gomez (JHU) Title: Linking Variability and Atmospheric Structure in the Benchmark Brown Dwarf Binary WISE 1049AB Abstract: We present a combined observational and modeling analysis of the benchmark brown dwarf binary system, WISE 1049 AB (L7.5+T0.5). This analysis incorporates spectroscopic variability and atmospheric retrievals from JWST NIRSpec/MIRI observations (GO-2965). NIRSpec time-resolved spectroscopy reveals that component B exhibits higher variability amplitudes than component A across all molecular bands (H₂O, CH₄, and CO). Component A shows a pattern of variability in CO and CH₄ that differs from what would be expected if the variability were solely caused by clouds, as is the case with H₂O variability. These trends suggest the presence of additional processes, such as thermochemical instabilities, affecting object A more than object B. To improve the interpretation of these observations, we performed atmospheric retrievals on NIRSpec/MIRI time-averaged spectra and explored multiple cloud configurations. Preliminary results suggest that each object is best described with different cloud slabs, and WISE 1049A exhibits stronger signatures of chemical disequilibrium than WISE 1049B. Together, these results suggest that differences in cloud composition and chemistry play a significant role in shaping the observed variability. We propose that viewing geometry may further modulate the differences in these effects across objects. Our study highlights the importance of integrating time-domain observations and retrieval frameworks to develop a comprehensive understanding of substellar atmospheres in the JWST era. Speaker: Steven Goldman (STScI) Title: Tracing AGB Dust Production in DDO 68: A Local Analog of High-Redshift Galaxies Abstract: Using Hubble/WFC3 medium-band imaging, we have identified the largest sample of extremely metal-poor (2% solar) AGB stars in an individual galaxy, determined their chemical compositions (carbon-rich or oxygen-rich), and isolated those actively producing dust. Theoretical work predicts that oxygen-rich AGB stars and silicate dust production should be strongly suppressed at a few percent solar metallicity. Contrary to these expectations, we find a substantial population of oxygen-rich AGB stars producing dust in this regime. These stars directly challenge the predicted metallicity threshold for silicate dust formation and demonstrate that oxygen-rich AGB stars can contribute to dust production in extremely metal-poor environments. These results place strong new constraints on dust evolution models and may explain the origin of the dust reservoirs observed in high-redshift galaxies. Using a similar three-filter imaging strategy, the Nancy Grace Roman Space Telescope will enable comparable wide-field surveys in a fraction of the time. Spectroscopic follow-up with James Webb Space Telescope/MIRI will characterize the dust properties of the most extreme dust producers and reveal the underlying physics of metal-poor silicate dust formation. Speaker: Justus Gibson (STScI) Title: Ultra-Red Flattened Objects Observed with JWST at Cosmic Noon Abstract: The infrared capabilities of the James Webb Space Telescope has facilitated the discovery of galaxies that were missed by previous generations of UV/optical telescopes including the Hubble Space Telescope. Among the galaxy populations that were missed by HST is a population of extended and extremely red galaxies discovered with JWST/NIRCam imaging only a few months after the first data products were available. These galaxies were selected based on their brightness at 4.4 microns (m- 24.5) in JWST imaging and their faintness in HST imaging as well as having extended sizes and red F200W - F444W colors. In this talk, I will present an extensive study of this population, enabled by JWST imaging of the GOODS north and south fields from the JADES survey, revealing 56 of these objects located between 2 -z - 4 which are characterized by extended red light distributions, high stellar masses, high star-formation rates, and significant dust attenuation throughout their extents. Interestingly, while appearing to resemble disk-like galaxies, detailed modeling of their axis-ratio distribution surprisingly favors a scenario in which these galaxies have prolate (tube) shaped geometries despite residing in a stellar mass regime where galaxies are expected to be almost entirely disk or spheroid dominated. I will discuss their integrated and resolved stellar population properties derived from fits to the observed JWST spectral energy distributions and what their morphologies tell us about their place in our picture of galaxy formation and evolution.