Type Ia supernova explosions in binary systems: The impact on the secondary star and its consequences

Abstract

One method of discriminating between the many Type Ia progenitor scenarios is searching for contaminating hydrogen stripped from the companion star. However, this requires understanding the effect of the impact on different companion stars to predict the amount of hydrogen stripped and its distribution in velocity and solid angle for the types of binary scenarios have been proposed as progenitor models. We present several 2-D numerical simulations of the impact of a Type Ia supernova explosion with low-mass main sequence, subgiant, and red giant companions. The binary parameters were chosen to represent several classes of single-degenerate, hydrogen-rich Type Ia progenitor models that have been suggested in the literature. We find that the main sequence and subgiant companions lose ∼15% of their mass as a result of the impact of the supernova shell. The red giant companions lose 96%-98% of their envelopes. The main sequence companion receives a kick of 86 km s⁻¹, the subgiant 49 km s⁻¹. In all cases, the kick received by the remnant is smaller than the original orbital velocity. Because it is too small to intercept more than a negligible amount of momentum, the red giant core will not receive a kick. The characteristic velocity of the stripped hydrogen is less than 10³ km s⁻¹ for all the scenarios: 420-590 km s⁻¹ for the red giant companions (depending on the scenario), 850 km s⁻¹ for the main sequence companion, and 900 km s⁻¹ for the subgiant companion. The stripped hydrogen contaminates a wide solid angle behind the companion: 115° from the downstream axis for the red giant, 66° for the main sequence star, and 72° for the subgiant. We find that the bulk of the stripped hydrogen is embedded within the low-velocity iron of the supernova ejecta and may be visible as narrow emission lines months after maximum light. However, to make any definitive predictions requires non-LTE radiative transfer calculations using the low-velocity distribution of the stripped hydrogen to determine the effect of hydrogen contamination on the late-time supernova spectrum.