@article {39339,
	title = {Phase-modulated X-Ray Emission from Cepheids due to Pulsation-driven Shocks},
	volume = {900},
	year = {2020},
	month = {2020/09/1},
	pages = {157},
	publisher = {IOP},
	abstract = {Cepheids are pulsating variable stars with a periodic chromospheric response at UV wavelengths close to their minimum radius phase. Recently, an X-ray variable signature was captured in observations during the maximum radius phase. This X-ray emission came as a surprise and is not understood. In this work, we use the modern astrophysical code PLUTO to investigate the effects of pulsations on Cepheid X-ray emission. We run a number of hydrodynamic numerical simulations with a variety of initial and boundary conditions in order to explore the capability of shocks to produce the observed phase-dependent X-ray behavior. Finally, we use the Simulated Observations of X-ray Sources (SOXS) package to create synthetic spectra for each simulation case and link our simulations to observables. We show that, for certain conditions, we can reproduce observed X-ray fluxes at phases 0.4-0.8 when the Cepheid is at maximum radius. Our results span a wide range of mass-loss rates, 2 {\texttimes} 10<SUP>-13</SUP> M<SUB>⊙</SUB> yr<SUP>-1</SUP> to 3 {\texttimes} 10<SUP>-8</SUP> M<SUB>⊙</SUB> yr<SUP>-1</SUP>, and peak X-ray luminosities, 5 {\texttimes} 10<SUP>-17</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP> to 1.4 {\texttimes} 10<SUP>-12</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>. We conclude that Cepheids exhibit two-component emission with (a) shock waves being responsible for the phase-dependent variable emission (phases 0.2-0.6) and (b) a separate quiescent mechanism being the dominant emission mechanism for the remaining phases.},
	keywords = {1261, 1307, 1584, 1603, 1621, 1966, 2086, 305, 368, 739, 909, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics, Delta Cepheid variable stars, High energy astrophysics, Late-type stars, Magnetohydrodynamical simulations, Plasma astrophysics, Pulsating variable stars, Shocks, Stellar atmospheres, Stellar coronae, Stellar flares, Stellar physics},
	isbn = {0004-637X},
	url = {https://ui.adsabs.harvard.edu/abs/2020ApJ...900..157M},
	author = {Moschou, Sofia-Paraskevi and Vlahakis, Nektarios and Drake, Jeremy J. and Evans, Nancy Remage and Neilson, Hilding R. and Guzik, Joyce Ann and ZuHone, John}
}
