Low-metallicity massive single stars with rotation. Evolutionary models applicable to I Zwicky 18
Abstract
Context. Low-metallicity environments such as the early Universe and compact star-forming dwarf galaxies contain many massive stars. These stars influence their surroundings through intense UV radiation, strong winds and explosive deaths. A good understanding of low-metallicity environments requires a detailed theoretical comprehension of the evolution of their massive stars.
Aims: We aim to investigate the role of metallicity and rotation in shaping the evolutionary paths of massive stars and to provide theoretical predictions that can be tested by observations of metal-poor environments.
Methods: Massive rotating single stars with an initial metal composition appropriate for the dwarf galaxy
Results: Even moderately fast rotators, which may be abundant at this metallicity, are found to undergo efficient mixing induced by rotation resulting in quasi chemically-homogeneous evolution. These homogeneously-evolving models reach effective temperatures of up to 90 kK during core hydrogen burning. This, together with their moderate mass-loss rates, make them transparent wind ultraviolet intense stars (TWUIN star), and their expected numbers might explain the observed He II ionising photon flux in I Zw 18 and other low-metallicity He II galaxies. Our slowly rotating stars above ~80 M⊙ evolve into late B- to M-type supergiants during core hydrogen burning, with visual magnitudes up to 19m at the distance of I Zw 18. Both types of stars, TWUIN stars and luminous late-type supergiants, are only predicted at low metallicity.
Conclusions: Massive star evolution at low metallicity is shown to differ qualitatively from that in metal-rich environments. Our grid can be used to interpret observations of local star-forming dwarf galaxies and high-redshift galaxies, as well as the metal-poor components of our Milky Way and its globular clusters.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 2015
- DOI:
- 10.1051/0004-6361/201526617
- arXiv:
- arXiv:1506.09132
- Bibcode:
- 2015A&A...581A..15S
- Keywords:
-
- stars: massive;
- galaxies: dwarf;
- stars: rotation;
- stars: evolution;
- supergiants;
- ultraviolet: stars;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- accepted for publication in A\&