Spectral characteristics of fast rotating metal-poor massive stars

Abstract

Low-metallicity massive stars are assumed to be progenitors of certain supernovae, gamma-ray bursts, and gravitational wave emitting mergers. These exotic phenomena contribute to their host galaxies through strong ionizing radiation and mechanical feedback. Here we investigate a certain type of very metal-poor (0.02 Zsun) hot massive single stars that rotate fast and evolve chemically homogeneously. Combining state-of-the-art theories of stellar evolution and stellar atmospheres modelling we predict synthetic spectra of these stars corresponding to different masses and evolutionary phases. The predicted spectra in early evolutionary phases is classified mainly as an early-O type giant or supergiant while in later evolutionary phases most of our model spectra are assigned to the WO-type spectral class. The Hubble Space Telescope's (HST) Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) program will enable us to compare our predicted spectra with observations of stars of similar nature (e.g., metal-poor stars in Sextant A).

Figures (2)

• Figure 1: The continuum SED of chemically-homogeneously evolving star with different M$_\mathrm{ini}$ (marked in the right-top corner of each panel), and in different evolutionary stages marked by the value Y$_\mathrm{S}$ in the top-left panel (colored lines). Models were calculated assuming nominal values of the mass-loss rate (i.e., the values used in the stellar evolutionary models) and a smooth wind (D=1). Black lines represent the SEDs of the same models but with 100 times lower mass-loss rate. H i, He i, are He ii represent ionisation stages of hydrogen and helium, respectively.
• Figure 2: Synthetic spectra of chemically-homogeneously evolving stars in the UV (left panel) and optical (right panel) regions with M$_\mathrm{ini}=59~M_{\odot}$ and in different evolutionary phases marked by the value $Y_{\mathrm{S}}$. Colored lines represent models with nominal mass-loss rates (i.e., the values used in the stellar evolutionary models) and smooth wind while the corresponding black lines represent the same models but with 100 times lower mass-loss rates.