Stellar wind properties of the nearly complete sample of O stars in the low metallicity young star cluster NGC 346 in the SMC galaxy
<i>Context.<i/> Massive stars are among the main cosmic engines driving the evolution of star-forming galaxies. Their powerful ionising radiation and stellar winds inject a large amount of energy in the interstellar medium. Furthermore, mass-loss (<i>Ṁ<i/>) through radiative...
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| Hauptverfasser: | , , , , , , , , , , , |
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| Dokumenttyp: | Article (Journal) |
| Sprache: | Englisch |
| Veröffentlicht: |
28 October 2022
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| In: |
Astronomy and astrophysics
Year: 2022, Jahrgang: 666, Pages: 1-33 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202243281 |
| Online-Zugang: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1051/0004-6361/202243281 Verlag, lizenzpflichtig, Volltext: https://www.aanda.org/articles/aa/abs/2022/10/aa43281-22/aa43281-22.html 
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| Verfasserangaben: | M.J. Rickard, R. Hainich, W.-R. Hamann, L.M. Oskinova, R.K. Prinja, V. Ramachandran, D. Pauli, H. Todt, A.A.C. Sander, T. Shenar, Y.-H. Chu, and J.S. Gallagher III |
| Zusammenfassung: | <i>Context.<i/> Massive stars are among the main cosmic engines driving the evolution of star-forming galaxies. Their powerful ionising radiation and stellar winds inject a large amount of energy in the interstellar medium. Furthermore, mass-loss (<i>Ṁ<i/>) through radiatively driven winds plays a key role in the evolution of massive stars. Even so, the wind mass-loss prescriptions used in stellar evolution models, population synthesis, and stellar feedback models often disagree with mass-loss rates empirically measured from the UV spectra of low metallicity massive stars.<i>Aims.<i/> The most massive young star cluster in the low metallicity Small Magellanic Cloud galaxy is NGC 346. This cluster contains more than half of all O stars discovered in this galaxy so far. A similar age, metallicity (Z), and extinction, the O stars in the NGC 346 cluster are uniquely suited for a comparative study of stellar winds in O stars of different subtypes. We aim to use a sample of O stars within NGC 346 to study stellar winds at low metallicity.<i>Methods.<i/> We mapped the central 1′ of NGC 346 with the long-slit UV observations performed by the Space Telescope Imaging Spectrograph (STIS) on board of the <i>Hubble<i/> Space Telescope and complemented these new datasets with archival observations. Multi-epoch observations allowed for the detection of wind variability. The UV dataset was supplemented by optical spectroscopy and photometry. The resulting spectra were analysed using a non-local thermal equilibrium model atmosphere code (PoWR) to determine wind parameters and ionising fluxes.<i>Results.<i/> The effective mapping technique allowed us to obtain a mosaic of almost the full extent of the cluster and resolve stars in its core. Among hundreds of extracted stellar spectra, 21 belong to O stars. Nine of them are classified as O stars for the first time. We analyse, in detail, the UV spectra of 19 O stars (with a further two needing to be analysed in a later paper due to the complexity of the wind lines as a result of multiplicity). This more than triples the number of O stars in the core of NGC 346 with constrained wind properties. We show that the most commonly used theoretical mass-loss recipes for O stars over-predict mass-loss rates. We find that the empirical scaling between mass-loss rates (<i>Ṁ<i/>) and luminosity (<i>L<i/>), <i>Ṁ<i/> ∝ <i>L<i/><sup>2.4<sup/>, is steeper than theoretically expected by the most commonly used recipes. In agreement with the most recent theoretical predictions, we find within <i>Ṁ<i/> ∝ <i>Z<sup>α<sup/><i/> that <i>α<i/> is dependent upon <i>L<i/>. Only the most luminous stars dominate the ionisation feedback, while the weak stellar winds of O stars in NGC 346 and the lack of previous supernova explosions in this cluster restrict the kinetic energy input. |
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| Beschreibung: | Gesehen am 15.12.2022 |
| Beschreibung: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202243281 |