Tyler Richey-Yowell

Title: The UV and X-Ray Evolution of Low-Mass Stars

Abstract: Low mass stars (< 1 solar mass) are some of the best candidates for hosting planets with detectable life as a result of these stars' long lifetimes and relative planet to star mass and radius ratios. An important aspect of these stars to consider is the amount of ultraviolet (UV) and X-ray radiation incident on planets in their habitable zones due to the ability of UV and X-ray radiation to alter the chemistry and evolution of planetary atmospheres. In this talk, I will discuss the photometric evolution of the UV and X-ray flux for K and M stars, both intrinsically and in their respective habitable zones. Our results suggest that there may not be a K dwarf advantage compared to M stars in the UV, but perhaps one may still exist for K stars in the X-ray.

Aishwarya Iyer 

Title: The SPHINX Grid: New Model Atmospheres to Derive Fundamental M-Dwarf Properties

Abstract: About 70-80% of stars in our solar and galactic neighborhood are M dwarfs. They span a range of low masses and temperatures relative to solar-type stars, facilitating molecule formation throughout their atmospheres. Standard stellar atmosphere models primarily designed for FGK stars face challenges when characterizing broadband molecular features in spectra of cool stars. Here, we introduce SPHINX—a new 1-D self-consistent radiative-convective thermochemical equilibrium chemistry model grid of atmospheres and spectra for M dwarfs in low-resolution (R~250). We incorporate the latest pre-computed absorption cross-sections with pressure-broadening for key molecules dominant in late-K, early/main-sequence-M stars. We then validate our grid models by acquiring fundamental properties (Teff, log(g), [M/H], radius, and C/O) for 10 benchmark M+G binary stars with known host metallicities and 10 M dwarfs with interferometrically measured angular diameters. Incorporating a Gaussian-process inference tool Starfish, we account for correlated and systematic noise in low-resolution (spectral stitching of SpeX, SNIFS, and STIS) observations and derive robust estimates of fundamental M dwarf atmospheric parameters. Additionally, we assess the influence of photospheric heterogeneity on acquired [M/H] and find that it could explain some deviations from observations. We also probe whether the model-assumed convective mixing-length parameter influences inferred radii, effective temperature, and [M/H] and again find that may explain discrepancies between interferometry observations and model-derived stellar parameters for cooler M dwarfs. Mainly, we show the unique strength in leveraging broadband molecular absorption features occurring in low-resolution M dwarf spectra and demonstrate the ability to improve constraints on fundamental properties of exoplanet hosts and late brown dwarf companions.

Nuri Park

Title : Connecting Coronal Mass Ejections (CMEs) to Far-Ultraviolet Flares Nuri Park, Evgenya Shkolnik, Joe Llama

Abstract: A contributing factor to the habitability of exoplanets is the extent of the host star’s stellar activity, such as flares and coronal mass ejections (CMEs), as these eruptive events affect the planet atmosphere’s chemistry and stability. While stellar flares are routinely detected and characterized, the physical characteristics of CMEs remain elusive due to limits of the current CME-detection methods. In this context, the Sun can serve as a guide in constraining the stellar CMEs, at least for the Sun-like stars. A series of previous studies reported that some solar X-ray flares are associated with CMEs and show a positive correlation in their physical properties (e.g., flare X-ray peak flux and CME mass). We have now found a parallel correlation of CME mass to far-ultraviolet (FUV) flares, which is a more accessible and diagnostic wavelength for stellar flare detection due to its high sensitivity to stellar upper-atmosphere activity. With these correlations, we can begin to make statistical inferences on the CME impacts on planets orbiting Sun-like stars.

Peter Smith

Title: S'more Roasting Marshmallows - The Atmosphere of WASP-121 b is 13CO-enriched

Abstract: Atmospheric characterization of exoplanets often focuses on bulk metallicity and volatile ratios in order to tie composition back to formation history. Recently, isotopologues have become detectable in the atmospheres of exoplanets, opening an entirely new avenue of understanding these worlds in the form of isotope ratios. Here, I report the detection of 13CO in the atmosphere of ultra-hot Jupiter WASP-121 b, the first detection of an isotopologue in this type of planet. Under a wide range of modelling assumptions, we consistently find that the planet's atmosphere is 13CO-enriched. I will discuss the implications of this and how the carbon isotope ratio can be used as a diagnostic for a variety of physical and chemical processes.

Host: TBA

Seminar held in 538 Davey or please email CEHW-SEMINAR-QUESTIONS@lists.psu.edu to attend virtually