Interaction between the ejecta, the accretion disk, and the secondary star in the recurrent nova system U Sco

TL;DR

This work addresses how post-outburst nova ejecta interact with the accretion disk and secondary in the recurrent nova U Sco, using 3D SPH simulations that include rotation about the binary center of mass. By mapping SHIVA-derived ejecta into a GADGET-2 framework and exploring variations in $M_{ m ejecta}$, $V_{ m ejecta}^{\max}$, ejecta density, $M_{ m disk}$, and disk geometry (flared vs V-shaped), the study shows that disk disruption is likely when $M_{ m ejecta}/M_{ m disk}\ge 1$ for flared disks, while certain disk geometries and higher disk masses can partially preserve the disk. Higher ejecta velocities shift material out of the system and reduce mass capture by the white dwarf, with only minor chemical contamination of the secondary predicted in U Sco-like configurations. Rotation plays a modest role in global mass loss but can reduce the fraction of secondary material captured by the WD; overall, the results underscore the sensitivity of long-term binary evolution to ejecta properties and disk structure in recurrent novae. These insights help interpret disk reformation times, mass transfer, and potential white dwarf mass growth in such systems.

Abstract

Most efforts in the modeling of recurrent novae have centered on the initial phases of the explosion and ejection, overlooking the subsequent interaction of the ejecta, first with the accretion disk orbiting the white dwarf and ultimately with the secondary star. To address this gap, a series of 3D smoothed-particle hydrodynamics simulations was conducted. These simulations explored the dynamic interactions between the nova ejecta, accretion disk, and stellar companion within the framework of the recurrent nova system U Sco. Notably, the simulations incorporate rotation around the system's center of mass. The primary goal of these simulations was to qualitatively examine the impact of various model parameters, including ejecta mass, velocity, and density, as well as the mass and geometry of the accretion disk. Simulations reveal complete disruption and sweeping of the accretion disk orbiting the white dwarf star for models with flared disks and Mejecta/Mdisk larger than 1. In contrast, V-shaped disks with a (constant) high initial density and Mejecta/Mdisk < 1 partially survive the impact with the nova ejecta. A very minor chemical contamination of the secondary star is anticipated in the U Sco case based on the limited impact of nova ejecta particles on the subgiant in all simulations. Minor mass ejection from the subgiant's outer layers is observed during the late-stage collision with ejecta and disk material, with some particles ejected from the binary system and some accreted by the white dwarf.

Figures (7)

• Figure 1: Density profile for the outer layers of the subgiant secondary star, after relaxation.
• Figure 2: Radius (upper left panel), velocity (upper right), density (lower left), and temperature profiles (lower right) of the ejecta as computed with the 1D code SHIVA. The mass coordinate is evaluated as q = 1 - m$_{int}$/M$_{wd}$.
• Figure 3: Different geometries for the mass-accretion disk: a V-shaped disk (left panel) and a flared disk (right panel).
• Figure 4: Initial density profile for the mass-accretion disk.
• Figure 5: Cross-sectional slices showing the density distribution within the binary orbital plane (XY) in Model A at various stages of the interaction between the nova ejecta and the mass-accretion disk, followed by a collision with the subgiant stellar companion. A movie showcasing the time evolution of this model is available online. Both the snapshots and the movie were generated using the visualization software SPLASH (Price 2007).