<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Moschou, Sofia-Paraskevi</style></author><author><style face="normal" font="default" size="100%">Vlahakis, Nektarios</style></author><author><style face="normal" font="default" size="100%">Drake, Jeremy J.</style></author><author><style face="normal" font="default" size="100%">Evans, Nancy Remage</style></author><author><style face="normal" font="default" size="100%">Neilson, Hilding R.</style></author><author><style face="normal" font="default" size="100%">Guzik, Joyce Ann</style></author><author><style face="normal" font="default" size="100%">ZuHone, John</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Phase-modulated X-Ray Emission from Cepheids due to Pulsation-driven Shocks</style></title><short-title><style face="normal" font="default" size="100%">The Astrophysical Journal</style></short-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">1261</style></keyword><keyword><style  face="normal" font="default" size="100%">1307</style></keyword><keyword><style  face="normal" font="default" size="100%">1584</style></keyword><keyword><style  face="normal" font="default" size="100%">1603</style></keyword><keyword><style  face="normal" font="default" size="100%">1621</style></keyword><keyword><style  face="normal" font="default" size="100%">1966</style></keyword><keyword><style  face="normal" font="default" size="100%">2086</style></keyword><keyword><style  face="normal" font="default" size="100%">305</style></keyword><keyword><style  face="normal" font="default" size="100%">368</style></keyword><keyword><style  face="normal" font="default" size="100%">739</style></keyword><keyword><style  face="normal" font="default" size="100%">909</style></keyword><keyword><style  face="normal" font="default" size="100%">Astrophysics - High Energy Astrophysical Phenomena</style></keyword><keyword><style  face="normal" font="default" size="100%">Astrophysics - Solar and Stellar Astrophysics</style></keyword><keyword><style  face="normal" font="default" size="100%">Delta Cepheid variable stars</style></keyword><keyword><style  face="normal" font="default" size="100%">High energy astrophysics</style></keyword><keyword><style  face="normal" font="default" size="100%">Late-type stars</style></keyword><keyword><style  face="normal" font="default" size="100%">Magnetohydrodynamical simulations</style></keyword><keyword><style  face="normal" font="default" size="100%">Plasma astrophysics</style></keyword><keyword><style  face="normal" font="default" size="100%">Pulsating variable stars</style></keyword><keyword><style  face="normal" font="default" size="100%">Shocks</style></keyword><keyword><style  face="normal" font="default" size="100%">Stellar atmospheres</style></keyword><keyword><style  face="normal" font="default" size="100%">Stellar coronae</style></keyword><keyword><style  face="normal" font="default" size="100%">Stellar flares</style></keyword><keyword><style  face="normal" font="default" size="100%">Stellar physics</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2020</style></year><pub-dates><date><style  face="normal" font="default" size="100%">2020/09/1</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://ui.adsabs.harvard.edu/abs/2020ApJ...900..157M</style></url></web-urls></urls><publisher><style face="normal" font="default" size="100%">IOP</style></publisher><volume><style face="normal" font="default" size="100%">900</style></volume><pages><style face="normal" font="default" size="100%">157</style></pages><isbn><style face="normal" font="default" size="100%">0004-637X</style></isbn><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">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 × 10&lt;SUP&gt;-13&lt;/SUP&gt; M&lt;SUB&gt;⊙&lt;/SUB&gt; yr&lt;SUP&gt;-1&lt;/SUP&gt; to 3 × 10&lt;SUP&gt;-8&lt;/SUP&gt; M&lt;SUB&gt;⊙&lt;/SUB&gt; yr&lt;SUP&gt;-1&lt;/SUP&gt;, and peak X-ray luminosities, 5 × 10&lt;SUP&gt;-17&lt;/SUP&gt; erg cm&lt;SUP&gt;-2&lt;/SUP&gt; s&lt;SUP&gt;-1&lt;/SUP&gt; to 1.4 × 10&lt;SUP&gt;-12&lt;/SUP&gt; erg cm&lt;SUP&gt;-2&lt;/SUP&gt; s&lt;SUP&gt;-1&lt;/SUP&gt;. 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.</style></abstract></record></records></xml>