The Outcome of Supernovae in Massive Binaries; Removed Mass, and Its Separation Dependence

Abstract

The majority of massive stars are formed in binary systems. It is hence reasonable to expect that most core-collapse supernovae (CCSNe) take place in binaries and the existence of a companion star may leave some imprints in observed features. Having this in mind, we have conducted two-dimensional hydrodynamical simulations of the collisions of CCSNe ejecta with the companion star in an almostequal-mass (∼ 10M ) binary to find out possible consequences of such events. In particular we pay attention to the amount of mass removed and its dependence on the binary separation. In contrast to the previous surmise, we find that the companion mass is stripped not by momentum transfer but by shock heating. Up to 25% of the original mass can be removed for the closest separations and the removed mass decreases as M ub ∝ a −4.3 with the binary separation a. By performing some experimental computations with artificially-modified densities of incident ejecta, we show that if the velocity of ejecta is fixed, the density of incident ejecta is the single important parameter that actually determines the removed mass as M ub ∝ ρ 1.4 ej . On the other hand, another set of simulations with modified velocities of incident ejecta demonstrate that the strength of the forward shock, which heats up the stellar material and causes the mass loss of the companion star, is actually the key parameter for the removed mass.

Effects of the Core-collapse Supernova Ejecta Impact on a Rapidly Rotating Massive Companion Star

“…The detailed structures of a red-giant companion star are very different from stars in the MS phase. Therefore, A = 0.26 and η = −4.3 are taken in Hirai et al (2014), while they are 0.143 and −2.65, respectively, in Liu et al (2015). Although we focus on MS stars, we take the value for fitting parameters (A and η) from both in Hirai et al (2014) and Liu et al (2015) to estimate the stripped masses in order to discuss the effects of M st on rotating massive stars.…”

“…Here, we must note that it is still different even when an additional heating source is introduced to simulate the shock heating due to the interaction between SN ejecta and a companion star. As shown by Pan et al (2012), Liu et al (2013) and Hirai et al (2014), the internal structures of a star are strongly affected while the shock is passing through the star. However, in our model, the internal structures of massive stars are not affected by such interaction.…”

“…According to Hirai et al (2014) and Liu et al (2015), the timescale, t st , for mass stripping during CCSN, is several hours. The distribution of angular momentum within the star may depend on the Eddintton-Sweet circulation (Zahn 1992), whose timescale is given by…”

“…In the remaining 15 HMXBs, their optical counterparts are supergiants, that is, they are sgHMXBs (Liu et al 2006;Romano et al 2014). Based on Wheeler et al (1975), Hirai et al (2014) and Liu et al (2015), these optical counterparts should be greatly affected by the ejecta of supernovae. However, to our knowledge, the effects of CCSN ejecta on the companion star are seldom considered in previous literatures on HMXBs.…”

Revealing the binary origin of Type Ic superluminous supernovae through nebular hydrogen emission

“…This 56 Ni mass is too low to explain the peak luminosity of iPTF13ehe, leading to the suggestion that two or more luminosity sources power iPTF13ehe (Y15 and Wang et al 2015 Liu et al (2015b) have recently studied the collision between SN ejecta and its companion star in core-collapse SNe with different separations, companion masses, ejecta masses, and explosion energies (see also Hirai et al 2014). They investigate how the stripping fraction f ≡ M st /M 2 (where M 2 is the companion mass before the collision) is affected by these parameters.…”