Binary progenitor models of type IIb supernovae

Abstract

Massive stars that lose their hydrogen-rich envelope down to a few tenths of a solar mass explode as extended type IIb supernovae, an intriguing subtype that links the hydrogen-rich type II supernovae with the hydrogen-poor type Ib and Ic. The progenitors may be very massive single stars that lose their envelope due to their stellar wind, but mass stripping due to interaction with a companion star in a binary system is currently considered to be the dominant formation channel. Anticipating the upcoming automated transient surveys, we computed an extensive grid of binary models with the Eggleton binary evolution code. We identify the limited range of initial orbital periods and mass ratios required to produce type IIb binary progenitors. The rate we predict from our standard models, which assume conservative mass transfer, is about six times smaller than the current rate indicated by observations. It is larger but still comparable to the rate expected from massive single stars. We evaluate extensively the effect of various assumptions such as the adopted accretion efficiency, the binary fraction and distributions for the initial binary parameters. To recover the observed rate we must generously allow for uncertainties and consider low accretion efficiencies in combination with limited angular momentum loss from the system. Motivated by the claims of detection and non-detection of companions for a few IIb supernovae, we investigate the properties of the secondary star at the moment of explosion. We identify three cases: (1) the companion is predicted to appear as a hot O star in about 90% of the cases, as a result of mass accretion during its main sequence evolution, (2) the companion becomes an over-luminous B star in about 3% of the cases, if mass accretion occurred while crossing the Hertzsprung gap or (3) in systems with very similar initial masses the companion will appear as a K supergiant. The second case, which applies to the well-studied case of SN 1993J and possibly to SN 2001ig, is the least common case and requires that the companion very efficiently accretes the transferred material -in contrast to what is required to recover the overall IIb rate. We note that relative rates quoted above depend on the assumed efficiency of semi-convective mixing: for inefficient semi-convection the presence of blue supergiant companions is expected to be more common, occurring in up to about 40% of the cases. Our study demonstrates that type IIb supernovae have the potential to teach us about the physics of binary interaction and about stellar processes such as internal mixing and possibly stellar-wind mass loss. The fast increasing number of type IIb detections from automated surveys may lead to more solid constraints on these model uncertainties in the near future.

Late-time spectral line formation in Type IIb supernovae, with application to SN 1993J, SN 2008ax, and SN 2011dh

“…Binary stellar evolution codes can explain the progenitor structures by Roche lobe overflow (e.g. Benvenuto et al 2013), although attempts to reproduce the observed rates have so far not been successful (Claeys et al 2011). The search for a binary companion to SN 2011dh will provide a crucial test for the binary progenitor hypothesis, as it did for SN 1993J (Maund et al 2004).…”

PTF12os and iPTF13bvn

“…Simulations of binary evolution show that the final amount of stripping of the exploding star depends mainly on the initial masses of the two stars in the binary system, the spatial configuration of the system, and the metallicity of the stars. Within the parameter space explored by Yoon et al (2010) and others, both SNe IIb and Ib are produced in a bimodal fashion, but not at the observed rates (e.g., Li et al 2011; see also Claeys et al 2011).…”

“…Two main mechanisms have been suggested to produce SE SNe: either binary mass transfer (e.g., Iben & Tutukov 1985;Yoon et al 2010;Claeys et al 2011;Dessart et al 2012;Yoon 2015) or strong line-driven winds from massive Wolf-Rayet (WR) stars (e.g., Conti 1976;Smith 2014).…”

“…Further, the progenitor of the wellobserved Type IIb SN 2011dh has been shown by Ergon et al (2014Ergon et al ( , 2015 to most likely be a composite of a nearly completely stripped compact He core with a mass of 3.3-4.0 M surrounded by a thin H-rich envelope extending out to 200-300 R . Binary evolution modeling can readily reproduce these properties at the time of explosion, while single-star models encounter difficulties in reproducing the relatively low ejecta mass in combination with the observed H shell (Claeys et al 2011;Benvenuto et al 2013). Recently, Folatelli et al (2014a) have also claimed that the remaining flux in Hubble Space Telescope (HST) imaging obtained ∼ 1160 d past the explosion is consistent with a suitable binary companion to SN 2011dh; however, Maund et al (2015) disagree with this conclusion.…”

Inferring supernova IIb/Ib/Ic ejecta properties from light curves and spectra: correlations from radiative-transfer models

“…While the close-binary evolution scenario offers an attractive solution to both core-collapse SN statistics (see, e.g., Podsiadlowski et al 1992;Eldridge et al 2008;Smith et al 2011) and inferred ejecta properties (Ensman & Woosley 1988;Woosley et al 1995), it is not clear today what fraction arises from the explosion of stars that evolve in isolation. The diversity of massive close binaries can qualitatively explain the observed diversity of SNe IIb (Claeys et al 2011), but for moderate main-sequence masses, the binary channel seems to favour the production of SNe ‹ email: Luc.Dessart@oca.eu Ib (Yoon et al 2010). The distinction between SNe Ib and Ic, which is observational (Wheeler & Levreault 1985;Harkness et al 1987;Filippenko et al 1990;Wheeler et al 1987), is challenged by the presence of broad lines, causing blending/overlap, and the difficulty of exciting He I (Lucy 1991).…”