Modeling the Stellar Flux of Circumbinary Planets S. Karthik Yadavalli, Billy Quarles, Gongjie Li Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332

Introduction: In the solar system, the Earth is said A circumbinary planet orbiting a G-M binary can to be in the habitable zone (HZ) of the Sun. It is within a undergo 40% flux variations near the critical range of distances from the Sun to be able to support stability limit (e.g., Quarles et al., 2018) of the binary. liquid water on the surface. Each star, based on its spectral properties, has a uniquely defined habitable zone (Haghighipour & Kaltenegger, 2013). Just as the Earth and the other planets in the solar system orbit the Sun, the other stars in the universe host planets of their own, known as exoplanets. Although the solar system is a single-star system, binary star systems are quite common. It is estimated that half of all star systems in the universe are binaries s. As such, nearly a dozen different binary star systems are known to host at least one exoplanet (e.g., Li et al. 2016). A planet that orbits 2 stars, called a circumbinary planet, is bound to have much more interesting weather patterns. The Earth, which only orbits one star, currently gets almost constant flux of stellar radiation in a near circular orbit. On the contrary, it is possible for a circumbinary planet in a near circular orbit to have wildly varying fluxes. If a circumbinary planet is within the habitable zone and indeed hosts life, an interesting question to ask is kind of flux variations would the life on such a planet endure? Methods: We use the Rebound library in python to run N-body simulations of circumbinary orbits. The flux on the planet is measured as a function of the distance between planet and star, the angle of the star from the planet’s surface (declination), the angle between a planet’s spin and its orbit (obliquity), and latitude (Kane & Torres, 2017). These values are computer numerically at each time step and compiled into a daily average flux at a latitude as a function of orbital phase. Such a simulation for a circumbinary planet is compared to a similar simulation for an Earth- Sun system. We further this work by integrating different Figure 1: The top panel shows the fluxes on a zero-tilt, circular orbit circumbinary planet in orbit around a G-K spectral type binary star configurations of the spectral types of the central binary system as a function of latitude. The bottom panel shows the flux star. We then condense this information by finding the variation on a circumbinary planet during 1 circular orbit around a G-K average flux variation on a planet as a function of the Spectra type binary at various distances from the binary planet’s semimajor axis. We compute how this value varies with different spectral types for the binary. Results: Comparing to a circumstellar planet’s References: (earth-like) flux variation, a circumbinary’s flux Haghighipour, N. & Kaltenegger, L. (2013) apj, 777, variation has important differences. For a circumstellar 166. planet with zero obliquity (no tilt), the region of high flux Kane, S. & Torres, S. (2017) aj, 154, 204. is constant with latitude over one orbit period. For a Li, G. et al. (2016) apj, 831, 96 circumbinary planet, the flux on the planet changes Quarles, B. et al. (2018) apj, 856, 150.. throughout its orbit around the binary because the distance to the stars changes as the binary orbit progresses. We compare the flux variations on a circumbinary planet orbiting G-A, G-F, G-G, G-K, and G-M spectral type binaries. From the above, we calculate the following results: (1) The flux variations on a planet are maximized when the binary mass ratio m1/(m1+m2) is near 0.3, (2) Flux variations are not constant with latitude for zero obliquity circumbinary planets, (3)