Mergers of equal-mass binaries with compact object companions from mass transfer in triple star systems

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>In this paper, we consider triple systems composed of main-sequence (MS) stars, and their internal evolution due to stellar and binary evolution. Our focus is on triples that produce white dwarfs (WDs), where Roche lobe overflow of an evolving tertiary triggers accretion on to the inner binary via a circumbinary disc (CBD) driving it towards a mass ratio of unity. We present a combination of analytic- and population synthesis-based calculations performed using the SeBa code to constrain the expected frequency of such systems, given a realistic initial population of MS triples, and provide the predicted distributions of orbital periods. We identify the parameter space for triples that can accommodate a CBD, to inform future numerical simulations of suitable initial conditions. We find that ≳10 per cent of all MS triples should be able to accommodate a CBD around the inner binary, and compute lower limits for the production rates. This scenario broadly predicts mergers of near equal-mass binaries, producing blue stragglers (BSs), Type Ia supernovae, gamma-ray bursts and gravitational wave-induced mergers, along with the presence of an outer WD tertiary companion. We compare our predicted distributions to a sample of field BS binaries, and argue that our proposed mechanism explains the observed range of orbital periods. Finally, the mechanism considered here could produce hypervelocity MS stars, WDs, and even millisecond pulsars with masses close to the Chandrasekhar mass limit, and be used to constrain the maximum remnant masses at the time of any supernova explosion.</jats:p>

Accretion induced merger leading to core collapse supernovae in old stellar populations

“…They claim that triple-star systems where one star suffers Roche lobe overflow (RLOF) to a tight (inner) binary system amount to 1% of triple-star systems. However, in a newer paper Leigh et al (2020) find that > 10% of all triple star systems might have circumbinary disk around the inner binary. de Vries et al ( 2014) also find that under their assumptions for the cases they studied the accreted mass does not form an accretion disk around neither of the stars in the inner binary system, nor around the binary (a circumbinary disk).…”

A statistical view on stable and unstable Roche lobe overflow of a tertiary star onto the inner binary in triple systems

“…Stable triple mass transfer is also poorly understood, with only few detailed simulations having been carried out (in the stellar context; de Vries et al 2014;Leigh et al 2020). Our results relied on simplified prescriptions based on the simulations of de Vries et al (2014).…”

“…These aspects include the frequency of triple RLOF, and its outcomes. Some statistical aspects of triple RLOF were considered by Leigh et al (2020), who focused on the production of nearly equal-mass binaries through stable triple mass transfer (motivated by the detailed simulations of Portegies Zwart & Leigh 2019). Leigh et al (2020) focused on specific aspects of stable triple RLOF, and, by using a binary population synthesis code, did not take into account any coupling of the evolution between the inner binary and tertiary star until the onset of triple RLOF.…”

“…Some statistical aspects of triple RLOF were considered by Leigh et al (2020), who focused on the production of nearly equal-mass binaries through stable triple mass transfer (motivated by the detailed simulations of Portegies Zwart & Leigh 2019). Leigh et al (2020) focused on specific aspects of stable triple RLOF, and, by using a binary population synthesis code, did not take into account any coupling of the evolution between the inner binary and tertiary star until the onset of triple RLOF. Here, we carry out a more self-consistent study in which we use the population synthesis code MSE (Hamers et al 2021b), which allows us to simultaneously take into account stellar evolution, binary interactions such as tidal evolution, mass transfer and CE evolution (in both inner and outer orbits), and gravitational dynamics (including secular evolution and hence ZLK eccentricity excitation).…”

A speckle-imaging search for close triple companions of cataclysmic binaries

“…Closer in triple companions could have stayed at ∼ the same separation, or even moved closer in if they, too, were engulfed by the expanding atmosphere of the red giant. Theoretical considerations (Leigh et al 2020) and numerical simulations of the complex evolution of triple stars (Hamers et al 2021) make it clear that post common envelope binaries (PCEB) and CVs' triple companions of all masses (less than the initially most massive star in the triple system) and separations are possible.…”