2020ApJ...900..157M -
Astrophys. J., 900, 157-157 (2020/September-2)
Phase-modulated X-ray emission from Cepheids due to pulsation-driven shocks.
MOSCHOU S.-P., VLAHAKIS N., DRAKE J.J., EVANS N.R., NEILSON H.R., GUZIK J.A. and ZUHONE J.
Abstract (from CDS):
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 x 10–13 M☉ yr–1 to 3 x 10–8 M☉ yr–1, and peak X-ray luminosities, 5 x 10–17 erg cm–2 s–1 to 1.4 x 10–12 erg cm–2 s–1. 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.
Abstract Copyright:
© 2020. The American Astronomical Society. All rights reserved.
Journal keyword(s):
Pulsating variable stars - Delta Cepheid variable stars - Stellar flares - Late-type stars - Stellar atmospheres - Stellar coronae - Magnetohydrodynamical simulations - Plasma astrophysics - High energy astrophysics - Shocks - Stellar physics
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