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The Habitable Zones of Rapidly Rotating Main Sequence A/F Stars

Presentation #102.211 in the session Poster Session.

Published onJun 20, 2022
The Habitable Zones of Rapidly Rotating Main Sequence A/F Stars

One of the fundamental properties of A-type and F-type stars is that they rotate rapidly throughout their lifetimes. Unlike G/K/M dwarfs, these stars do not slow their spin rates over time, but rather maintain their high primordial rotation rates over the course of their main sequence lifetimes. Rapid stellar rotation can dramatically change a star’s luminosity and spectral energy distribution and, therefore, can impact the habitability of any surrounding planets. A-type and F-type stars commonly rotate near their breakup speeds, which causes two effects relevant to planet habitability. First, these stars flatten into oblate spheroids with shorter polar radii and elongated equatorial radii. The stars’ distorted shapes change their total sizes and luminosities, which directly changes the total energy received by a planet. Second, rapid rotation induces a pole-to-equator temperature gradient on the surface of these stars (known as gravity darkening). Their polar regions can be up to several thousand Kelvin hotter than their equatorial regions, which impacts the stars’ total luminosities and their spectral energy distributions. In this project, we investigate how rapid rotation in A/F stars affects the locations of their habitable zones. We find that in general, rapid rotation causes the habitable zone to reside closer in than for a non-rotating equivalent star. We also find that gravity darkening dramatically reduces A/F stars’ UV emission, which combats the common assumption that A/F stars emit too much UV light for habitable worlds. Overall, we determine that rapid stellar rotation has important consequences for the overall habitability of a system and must be accounted for both when modeling exoplanet environments and in observation of planets around high-mass stars.

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