Astro Seminar: Mathieu Renzo

Speaker : Mathieu Renzo (University of Arizona)

Title : Widowed massive stars

Abstract: Massive stars live predominantly in multiple systems, where mass-transfer can modify their appearance and final fate. Even apparently single stars can be binary products, e.g., mergers or accreting secondary stars ejected from binaries at the companion's explosive death. These ejected "widowed" stars might constitute a significant fraction of the field population of O-type stars (up to ~10%) -- however they are typically slow-moving walkaways hard to find kinematically only. Understanding the structural and evolutionary impact of binary mass transfer onto a mid-main-sequence massive star is important not only to help distinguish binary products from genuine single stars, but also to characterize potential long-GRB progenitors (at low Z) as well as up to ~15% of H-rich supernovae. I will present self-consistent binary evolution models of the accretor star pinned onto the nearest O-type star on Earth, \zeta Ophiuchi. This fast runaway star has long been recognized as a binary product, and indeed our model match observational constraints more easily than single stars. Our accretors have important structural differences compared to single (rotating) massive stars, in terms of angular momentum profile, surface chemistry, and density profile above the helium core. In cases when the binary is not broken at the donor's explosion, these differences might have implication on isolated binary evolution paths towards a GW mergers and/or Thorne-Zytkow  object formation. Asteroseismology may offer direct constraints on the differences between accretors and stars evolving alone.