Additional Event Information

• Special Talks

  Speaker: Sarah Moran (STScI)
  Title: Silicate Cloud Morphologies as Thermal Tracers in Substellar Atmospheres
  Abstract: Silicate clouds detections in hot Jupiters, directly imaged planets, and brown dwarfs are becoming commonplace thanks to JWST’s MIRI instrument. The morphologies of these cloud particles can offer insights into their formation conditions, acting as tracers of atmospheric transport and thermal gradients. I will discuss my recent efforts to include temperature dependent properties of silicate materials into cloud modeling tools, as well as present my recent laboratory experiments investigating the time- and temperature-dependent optical properties of synthetic SiO2 in the form of silica, quartz, and its high temperature polymorph tridymite, and of natural samples of mixed mineralogies. I show that the inclusion of temperature dependence, polymorph, and crystalline vs. amorphous mineralogy all have a large effect in the inferred SiO2 cloud absorption feature in exoplanet data, as well as the inferred atmospheric conditions in which the aerosol is located.

  Speaker: Ciarán Rogers (STScI)
  Title: MORPOP - The NIRSpec MSA Orion Proplyd Program Overview and First Results
  Abstract: We have observed more than 100 externally irradiated planet-forming discs and the surrounding nebula with the NIRSpec micro-shutter assembly (MSA) in the Orion Nebula Cluster (ONC). Included in this sample are 50 discs with spatially extended cocoons of gas and dust. These objects are known as ‘proplyds’. These are the first near-infrared spectra obtained for these targets.

  Proplyds are exposed to intense external UV radiation from a nearby high-mass star with spectral-type O. UV heats the disc surface enough to exceed the escape velocity of the central star, leading to dramatic form of mass-loss for the disc. This process is known as external photoevaporation. The extent to which external photoevaporation alters the evolution of the disc, and its ability to form planets, remains largely unknown. 

  The core goal of MORPOP is to leverage a statistically significant sample proplyds and other irradiated discs in the ONC to investigate the impact of external irradiation/photoevaporation on planet-forming discs.

  NIRSpec spectra provide diagnostics to determine the mass-loss rate and accretion rate of proplyds simultaneously for the first time. Combined, these processes set the disc lifetime, and hence the maximum planet formation timescale. Chemistry of the inner-disc and outer-disc surface layers are probed by the rich molecular spectra of many proplyds, revealing the chemical inventory of irradiated discs. Using the Meudon PDR code, the winds of the proplyds provide insight into the dust-to-gas ratio and PAH-to-gas ratio of material leaving the disc. Atomic lines from the cocoon trace the exact intensity of UV radiation reaching the disc. The wide wavelength coverage, high signal-to-noise ratio, and statistically significant sample of targets allow for several dozen atomic, molecular and dust species to be detected, and their response to UV radiation studied.

  In this talk, the proplyd spectra will be shown for the first time. Their spectral properties will be discussed, and some of the first results will be presented.
  
  Speaker: Elizabeth Tarantino (STScI)
  Title: The Origin and Nature of Dust at Low Metallicities: A JWST Case Study on the Nearby Dwarf Galaxy Sextans A
  Abstract: The formation, composition, and evolution of dust at low metallicities is poorly characterized, yet critical for understanding the lifecycle of dust at high redshifts. Since the far distances of these early galaxies prohibit detailed study, we use observations of nearby metal-poor galaxies that mimic the pristine gas conditions of these distant galaxies to constrain models of dust formation and destruction. In this talk, I will present JWST imaging and spectroscopy of the 7% Solar metallicity galaxy Sextans A to (1) characterize the abundance and properties of the smallest dust grains, polycyclic aromatic hydrocarbons (PAHs), and (2) determine the dust production and composition from asymptotic giant branch (AGB) stars. While mid-infrared PAH emission is ubiquitous in high-metallicity galaxies, metal-poor galaxies show a sharp decline in the fraction of PAHs relative to total dust abundance. I will discuss how JWST's exceptional sensitivity and resolution allow us to detect and resolve PAH emission in Sextans A into compact 3–10 pc clumps, marking the lowest metallicity detection of PAHs to date. Additionally, I will explore the dust production mechanisms in Sextans A, focusing on AGB stars. Dust formed through the winds from stars on the AGB branch can significantly contribute to a galaxy's overall dust budget, but it remains unclear whether metal-poor AGB stars can produce substantial dust reservoirs. I will show JWST mid-infrared imaging and spectroscopy that reveal dust features, indicating that metal-poor AGB stars with metallicities as low as 7% Solar are capable of producing dust. Our results offer vital insights into dust formation and survival pathways at low metallicities, which can inform models of cosmic dust evolution at high redshifts.