The Role of Binary Configuration in Shaping Nova Evolution via Wind Accretion in Symbiotic Systems

Abstract

We investigate the impact of the Bondi--Hoyle--Lyttleton (BHL) accretion mechanism on the evolution of nova eruptions in symbiotic systems by systematically varying three key input parameters: the initial donor (asymptotic giant branch; AGB) mass, the initial white dwarf (WD) mass, and the initial binary separation ($a$). We explore models with AGB masses in the range $1.5$--$3.5\,{\rm M_{\odot}}$, WD masses in the range $0.7$--$1.25\,{\rm M_{\odot}}$, and separations in the range $1$--$8\,{\rm kR_{\odot}}$. We find that all models exhibit a significant long-term orbital increase. This trend is primarily driven by the fact that approximately $99\%$ of the AGB mass is lost from the system, either directly via a wind that is not accreted by the WD, or accreted onto the WD and subsequently ejected during nova eruptions. As a result, the secular orbital response to mass loss or mass transfer dominates over angular-momentum-loss sinks that could otherwise shrink the orbit, producing a consistent orbital widening. Consequently, all WD masses gradually decrease with time. More massive WDs achieve higher mass-transfer efficiencies and accretion rates, leading to slightly higher mass-retention efficiencies per nova. However, because higher accretion rates also produce more frequent eruptions, the total WD mass lost over the AGB lifetime is larger in these systems. We conclude that symbiotic systems transferring mass via the BHL mechanism are unlikely to be viable progenitors of Type Ia supernovae.

Figures (19)

• Figure 1: AGB mass ($M_{\rm AGB}$), its radius ($R_{\rm AGB}$) and its wind rate ($\dot{M_{\rm w}}$), the mass transfer efficiency ($\dot{M}_{\rm acc}/\dot{M}_{\rm w}$), the change in WD mass ($\Delta M_{\rm WD}$), the binary separation ($a$), and the orbital period ($P_{\rm orb}$), for an initial 1.0$M_\odot$ WD with an initial 8000$\rm{R_\odot}$ binary separation, and three different initial AGB masses: 1.42 (blue), 2.49 (red) and 3.49${M_\odot}$ (green). The final AGB masses are 0.58, 0.62 and 0.71$M_\odot$ respectively. The WD shows an overall mass loss regardless of the choice of initial AGB mass, and the orbital separation and period increase for all three models, as most of the matter is lost from the system.
• Figure 2: Mass retention efficiency ($\eta$), average accretion rate ($\dot{M}_{av,acc}$), maximum temperature ($T_{\rm max}$), core temperature ($T_{\rm c}$) and mass fractions of hydrogen ($X_{\rm ej}$), helium ($Y_{\rm ej}$), and heavy elements ($Z_{\rm ej}$) in the ejecta per cycle. Models with higher accretion rates exhibit greater WD mass retention and shorter core cooling times. This leads to a higher hydrogen fraction and helium content, and lower fraction of heavier elements in the ejecta.
• Figure 3: Description as in Figure \ref{['Fig1']}, for an initial $M_{\rm WD} = 1.0M_\odot$ and $M_{\rm AGB} = 1.42M_\odot$, with three initial separations of $a_{\rm ini}$ = 1000 (dotted blue), 4000 (solid sky-blue) and 8000$\rm{R_\odot}$(solid blue). The panel showing ${\dot{M}_{\rm acc}/\dot{M}_{\rm w}}$ has two y-axes: the left y-axis corresponds to $a_{\rm ini} = 4000$ and $8000\rm{R_\odot}$, and the right y-axis corresponds to $a_{\rm ini} = 1000\rm{R_\odot}$. The same applies to the panel of $\Delta M_{\rm WD}$. The model with an initial separation of $a_{\mathrm{ini}} = 1000\rm{R_\odot}$ shows an increase in WD mass due to a higher accretion rate, resulting in reduced mass ejection during nova eruptions. The separation and orbital period continue to increase as most of the mass is lost from the system.
• Figure 4: Description as in Figure \ref{['Fig2']}, for an initial $M_{\rm WD} = 1.0M_\odot$ and $M_{\rm AGB} = 1.42M_\odot$, with three initial separations of $a_{\rm ini}$ = 1000, 4000, 8000$\rm{R_\odot}$.
• Figure 5: Description as in Figure \ref{['Fig1']}, for an initial $M_{\rm AGB} = 1.42\rm{M_{\odot}}$ and an initial separation of $a_{\rm ini} = 8000 \rm{R_\odot}$, with three different WD masses: $M_{\rm WD} = 1.25$ (dash-dotted teal), $1.0$ (solid blue), and $0.7 \rm{M_\odot}$ (dashed navy-blue). Models with more massive WDs lose more mass due to higher accretion rates and a higher number of eruptions, causing increased mass loss from the system. The orbital separation and period follow the general trend of increasing values.