Low-metallicity massive single stars with rotation

  • Context. Metal-poor massive stars are assumed to be progenitors of certain supernovae, gamma-ray bursts, and compact object mergers that might contribute to the early epochs of the Universe with their strong ionizing radiation. However, this assumption remains mainly theoretical because individual spectroscopic observations of such objects have rarely been carried out below the metallicity of the Small Magellanic Cloud. Aims. Here we explore the predictions of the state-of-the-art theories of stellar evolution combined with those of stellar atmospheres about a certain type of metal-poor (0.02 Z(circle dot)) hot massive stars, the chemically homogeneously evolving stars that we call Transparent Wind Ultraviolet INtense (TWUIN) stars. Methods. We computed synthetic spectra corresponding to a broad range in masses (20 130 M-circle dot) and covering several evolutionary phases from the zero-age main-sequence up to the core helium-burning stage. We investigated the influence of mass loss and wind clumping on spectral appearance andContext. Metal-poor massive stars are assumed to be progenitors of certain supernovae, gamma-ray bursts, and compact object mergers that might contribute to the early epochs of the Universe with their strong ionizing radiation. However, this assumption remains mainly theoretical because individual spectroscopic observations of such objects have rarely been carried out below the metallicity of the Small Magellanic Cloud. Aims. Here we explore the predictions of the state-of-the-art theories of stellar evolution combined with those of stellar atmospheres about a certain type of metal-poor (0.02 Z(circle dot)) hot massive stars, the chemically homogeneously evolving stars that we call Transparent Wind Ultraviolet INtense (TWUIN) stars. Methods. We computed synthetic spectra corresponding to a broad range in masses (20 130 M-circle dot) and covering several evolutionary phases from the zero-age main-sequence up to the core helium-burning stage. We investigated the influence of mass loss and wind clumping on spectral appearance and classified the spectra according to the Morgan-Keenan (MK) system. Results. We find that TWUIN stars show almost no emission lines during most of their core hydrogen-burning lifetimes. Most metal lines are completely absent, including nitrogen. During their core helium-burning stage, lines switch to emission, and even some metal lines (oxygen and carbon, but still almost no nitrogen) are detected. Mass loss and clumping play a significant role in line formation in later evolutionary phases, particularly during core helium-burning. Most of our spectra are classified as an early-O type giant or supergiant, and we find Wolf-Rayet stars of type WO in the core helium-burning phase. Conclusions. An extremely hot, early-O type star observed in a low-metallicity galaxy could be the result of chemically homogeneous evolution and might therefore be the progenitor of a long-duration gamma-ray burst or a type Ic supernova. TWUIN stars may play an important role in reionizing the Universe because they are hot without showing prominent emission lines during most of their lifetime.show moreshow less

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Author details:Brankica Kubatova, D. Szecsi, Andreas Alexander Christoph SanderORCiDGND, J. Kubat, F. Tramper, J. Krticka, C. Kehrig, Wolf-Rainer HamannORCiDGND, Rainer HainichGND, Tomer ShenarORCiDGND
DOI:https://doi.org/10.1051/0004-6361/201834360
ISSN:1432-0746
ISSN:0004-6361
Title of parent work (English):Astronomy and astrophysics : an international weekly journal
Subtitle (English):II. Predicting spectra and spectral classes of chemically homogeneously evolving stars
Publisher:EDP Sciences
Place of publishing:Les Ulis
Publication type:Article
Language:English
Date of first publication:2019/02/25
Completion year:2019
Release date:2021/04/06
Tag:galaxies: dwarf; radiative transfer; stars: massive; stars: rotation; stars: winds, outflows
Volume:623
Page number:32
Funding institution:GACRGrant Agency of the Czech Republic [16-01116S]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [HA 1455/26]; STFCScience & Technology Facilities Council (STFC) [ST/R000565/1]; European Research Council (ERC) under the European UnionEuropean Research Council (ERC) [DLV-772225-MULTIPLES]; [RVO: 67985815]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
DDC classification:5 Naturwissenschaften und Mathematik / 52 Astronomie / 520 Astronomie und zugeordnete Wissenschaften
Peer review:Referiert
Publishing method:Open Access / Bronze Open-Access