April 16, 2021

The ExoExplorer Science Series presents talks by cohort members David Coria (U Kansas) and Jason Williams (USC/Carnegie) on April 16, 2021 from 1-2 pm Pacific / 4-5 pm Eastern. Connection information below

David Coria (U Kansas)

"The Missing Link: Connecting Exoplanets and Galactic Chemical Evolution via Stellar Abundances"

This research project seeks to: (1) test the feasibility of determining stellar ages from isotopic measurements; and (2) identify how unexplored stellar abundances correlate with galactic chemical evolution, formation, interior, age, metallicity, activity, and planetary properties for a wide range of host stars. Past isotopic searches have been hindered by limited sensitivity & resolution, strong telluric absorption, and the opacity due to millions of other molecular absorption lines that dominate the observed spectrum of cool stars. Now, however, isotopic abundance analysis is not only possible via high resolution spectroscopy but is also the next logical step for many cool stars. I am measuring the first multi-isotopic (carbon monoxide) abundances in a sample of FGKM stars, to identify possible discrepancies in planetary chemical evolution and accretion models. These isotopic abundance measurements may provide a new means of determining stellar ages and help identify the “missing link” between current Galactic Chemical Evolution models and inconsistent observations. Since most of spectral lines useful in isotopic analysis have low statistical significance and are barely discerned by eye when considered individually, I use a custom list of the strongest lines and create a single line profile for each isotopologue. We create a single, high- S/N line profile by taking the weighted mean, after continuum-normalizing, of each line to create a stacked absorption line. I then create corresponding line profiles for synthetic stellar models corresponding to various enrichments of the targeted isotopologue and compare them to the observed spectra in order to determine final abundances. I will repeat this process for a sample of solar twins, stars in FGK(+M) binaries, stars in known moving groups, and (eventually) any exoplanet host stars that exhibit isotopic signatures. This will provide host star parameters for the currently lacking database as well as the necessary foundations for corollary exoplanet characterization studies and ultimately contribute to the exploration of galactic, stellar, and planetary origins and evolution.

Jason Williams (USC/Carnegie)

"The Design and Construction of Henrietta, a high-precision low resolution near-infrared spectrograph to explore exoatmospheres"

When JWST comes online in 2022, it will usher in a golden age of exoatmosphere characterization. Given that available time for exoatmosphere studies will be limited with JWST, it will be impossible for it to survey most exoplanet atmospheres. Thus, it is critically important not only that we have the capability to prioritize the most promising targets for JWST follow-ups, but also multiple instruments available to study the multitude of targets JWST won’t get a chance to survey. These considerations have led to the design of Henrietta, a high-precision, low resolution near-infrared spectrograph for the 1-m Swope Telescope at Las Campanas Observatory. I will talk about why high-precision ground-based spectrophotometry is so challenging in the infrared and how Henrietta’s design choices seek to mitigate these issues. If successful, Henrietta will operate near the photon noise limit and will have ample amounts of telescope time. This will not only provide a consistent stream of targets to JWST, but will also be extremely scientifically productive in its own right - allowing us to begin to place exoplanet atmospheres in a statistical context - and serve as a pathfinder instrument for future ground-based exoatmosphere instruments.

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