The cosmic carbon footprint of massive stars stripped in binary systems
  The cosmic origin of carbon, a fundamental building block of life, is still
uncertain. Yield predictions for massive stars are almost exclusively based on
single star models, even though a large fraction interact with a binary
companion. Using the MESA stellar evolution code, we predict the carbon ejected
in the winds and supernovae of single and binary-stripped stars at solar
metallicity. We find that binary-stripped stars are twice as efficient at
producing carbon (1.5-2.6 times, depending on choices on the slope of the
initial mass function and black hole formation). We confirm that this is
because the convective helium core recedes in stars that have lost their
hydrogen envelope, as noted previously. The shrinking of the core disconnects
the outermost carbon-rich layers created during the early phase of helium
burning from the more central burning regions. The same effect prevents carbon
destruction, even when the supernova shock wave passes. The yields are
sensitive to the treatment of mixing at convective boundaries, specifically
during carbon-shell burning (variations up to 40%) and improving upon this
should be a central priority for more reliable yield predictions. The yields
are robust (variations less than 0.5%) across our range of explosion
assumptions. Black hole formation assumptions are also important, implying that
the stellar graveyard now explored by gravitational-wave detections may yield
clues to better understand the cosmic carbon production. Our findings also
highlight the importance of accounting for binary-stripped stars in chemical
yield predictions and motivates further studies of other products of binary
interactions.
