Extracting Lens Flux From Gravitational Microlensing Events
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Date
2023-05
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The Ohio State University
Abstract
Gravitational microlensing provides a promising method for discovering exoplanets undetectable by any other method. In particular, microlensing is sensitive to exoplanets with large semimajor axes and small masses, whereas other exoplanet detection methods are better at detecting the opposite type of exoplanet. Thus, gravitational microlensing allows access to an otherwise inaccessible parameter space of planets. The upcoming NASA Nancy Gracy Roman Space Telescope will detect thousands of exoplanets using the microlensing technique. Unfortunately, extracting the properties of the host stars of microlensing events is hampered by the fact that the host star (also known as the lens star) is typically faint, and the fields where microlensing events are found are crowded, making follow-up observations of detected exoplanet host stars from the ground rarely feasible.
My project explores a potential method for characterizing the properties of the host stars of microlensing planets detected by the Roman Space Telescope, by obtaining follow-up observations with the James Webb Space Telescope (JWST), a NASA mission that was launched this past Christmas. JWST has the collecting area and angular resolution to obtain moderate-resolution spectra of bright host stars in a reasonable amount of observing time. I am simulating the properties of host star spectra obtained with JWST, leveraging the existing Pandeia Exposure Time Calculator (ETC), which can be used to simulate JWST observations given the parameters of stars within an observational scene. By simulating many spectra over a grid of properties, a library of simulated spectra is generated. Currently, my code takes an observed spectrum and determines which model best matches it, determining which effective temperature and metallicity best describe the input spectra. The software can predict a star's effective temperature, surface gravity, and heavy element abundance (or metallicity), extinction, and absolute flux.
However, these predictions only apply to single-star spectra, whereas the host star will typically be blended with light from the source star. The next step in my project, therefore, involves writing code to reliably separate combined source/lens spectra into their respective components to predict each star's attributes. I plan on testing the limits of my software to predict how distinguishable stars are from those with similar properties.
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Keywords
exoplanets, gravitational microlensing, supercomputer, simulation