3D hydrodynamic simulations of white dwarf–main-sequence star collisions – I. Head-on collisions

ABSTRACT Recently inaugurated telescopes, such as the MeerKAT radio telescope and the upcoming Rubin Observatory Legacy Survey of Space and Time, will be able to detect millions of transient events in the night sky. Stellar collisions between white dwarfs (WDs) and main-sequence (MS) stars may be detectable among such transients. Simulations will play a key role in characterizing these events and selecting targets for follow-up. We present 3D smoothed particle hydrodynamics models of dynamical interactions between a $0.6\ {\rm M}_{\odot }$ WD and 0.3, 0.6, and $1.2\ {\rm M}_{\odot }$ MS stars within globular cluster environments. Utilizing a 34-isotope nuclear network, we investigate the energetics, gas morphologies, and mass-loss properties of these collisions for different stellar mass ratios. Our models predict an overabundance of $^{13}$C, $^{15}$N, and $^{17}$O isotopes relative to solar abundances. Moreover, we find that the time-scale of the collisions is too short and maximum temperatures too low for any significant hydrogen burning or triple-alpha reactions to occur. This combined with a negligible production of elements heavier than neon may be key signatures in distinguishing these events from other transient events with similar peak bolometric luminosities ($\sim\!\! 10^{38}\!\!-\!\!10^{41}$ erg s$^{-1}$).