# The Evolution of Massive Helium Stars Including Mass Loss

## TL;DR

This paper models the evolution of helium stars with mass loss, revealing differences from single star evolution, implications for supernova explosions, black hole formation, and potential observational signatures.

## Contribution

It introduces a comprehensive model of helium star evolution including mass loss, highlighting differences from single stars and implications for supernovae and black hole masses.

## Key findings

- Helium stars with mass loss are less massive at death, easing supernova explosions.
- Most black holes formed are around 9 solar masses.
- Maximum black hole mass from pulsational pair-instability is 46 solar masses.

## Abstract

The evolution of helium stars with initial masses in the range 1.6 to 120 Msun is studied, including the effects of mass loss by winds. These stars are assumed to form in binary systems when their expanding hydrogenic envelopes are promptly lost just after helium ignition. Significant differences are found with single star evolution, chiefly because the helium core loses mass during helium burning rather than gaining it from hydrogen shell burning. Consequently presupernova stars for a given initial mass function have considerably smaller mass when they die and will be easier to explode. Even accounting for this difference, the helium stars with mass loss develop more centrally condensed cores that should explode more easily than their single-star counterparts. The production of low mass black holes may be diminished. Helium stars with initial masses below 3.2 Msun experience significant radius expansion after helium depletion, reaching blue supergiant proportions. This could trigger additional mass exchange or affect the light curve of the supernova. The most common black hole masses produced in binaries is estimated to be about 9 Msun. A new maximum mass for black holes derived from pulsational pair-instability supernovae is derived - 46 Msun, and a new potential gap at 10 - 12 Msun is noted. Models pertinent to SN 2014ft are presented and a library of presupernova models is generated.