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Dynamic modeling of the X-ray spectra and line profiles for the massive-star binary eta Carinae

Presentation #110.99 in the session “Stellar/Compact (Poster)”.

Published onApr 01, 2022
Dynamic modeling of the X-ray spectra and line profiles for the massive-star binary eta Carinae

X-ray observations of the massive binary-star system eta Carinae provide important insights to the nebula-enshrouded system, most notably the existence of a secondary star with a fast stellar wind that is responsible for producing the observed thermal X-ray emission as it shocks with the much slower primary stellar wind. The X-ray scenario is especially complex around periastron where four observation cycles with RXTE, Swift, and NICER have revealed a variable rise into a well-repeated drop in X-ray flux, followed by a variable-length X-ray minimum of 2-3 months, and then a recovery in the X-ray flux level before slowly varying over the remainder of the 5.5-yr orbit. This behavior is highly indicative of an eccentric binary where 1) high stellar orbital speeds around periastron create an asymmetry in the X-ray absorption profile about periastron, and 2) the small stellar separation at periastron shuts down the X-ray production between the stars due to the primary wind encroaching into the acceleration zone of the secondary wind. To disentangle these effects, we perform 3D hydrodynamic simulations of the colliding winds in eta Carinae, and then synthesize their thermal X-ray emission from their resultant density, temperature, and velocity structure. This allows us to generate model X-ray light curves, spectra, and line profiles that we compare directly with the relevant X-ray observations, most recently the NICER light curves and spectra and the Chandra line profiles. While key observables are well reproduced, such as the flux level and shape of line profiles on the rise to periastron, other observables are not as well reproduced, including the line-profile shape at apastron and the recovery of the X-ray light curve after the extended minimum. The latter discrepancy is consistently higher than is observed for the range of parameter space we have modeled, though other features of the X-ray emission are sensitive to a simulation’s given parameters. This presentation will show the latest status of our hydrodynamic simulations and X-ray synthesis, noting both their successes and shortcomings. We will also include ideas for future models that will hopefully have improved model-to-observable comparisons over a larger set of observations.

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