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Unveiling the nitrogen-rich massive star in the metal-poor galaxy NGC 4068

We report the identification of the unusual emission-line stellar-like object in the nearby low-metallicity (Z ∼ 0.1 Z) dwarf galaxy NGC 4068. Our observations performed with long-slit spectrograph and Fabry-Perot interferometer demonstrate high velocity dispersion in H α line, presence of He ii λ46...

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Main Authors: Yarovova, Anastasiya D. (Author) , Egorov, Oleg (Author) , Moiseev, Alexei V (Author) , Maryeva, Olga V (Author)
Format: Article (Journal)
Language:English
Published: 2023
In: Monthly notices of the Royal Astronomical Society
Year: 2023, Volume: 518, Issue: 2, Pages: 2256-2272
ISSN:1365-2966
DOI:10.1093/mnras/stac2949
Online Access:Resolving-System, Volltext: https://doi.org/10.1093/mnras/stac2949
Verlag, lizenzpflichtig, Volltext: https://academic.oup.com/mnras/article/518/2/2256/6761713
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Author Notes:Anastasiya D Yarovova, Oleg V Egorov, Alexei V Moiseev and Olga V Maryeva
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Summary:We report the identification of the unusual emission-line stellar-like object in the nearby low-metallicity (Z ∼ 0.1 Z) dwarf galaxy NGC 4068. Our observations performed with long-slit spectrograph and Fabry-Perot interferometer demonstrate high velocity dispersion in H α line, presence of He ii λ4686Å line and peculiarly low [S ii]/[N ii] fluxes ratio for this object. From observational data, we derived that the object represents a single star of high bolometric luminosity (L* ∼ 1.5 × 106 L⊙) surrounded by an expanding nebula with kinematical age of t ∼ 0.5 Myr. The nebula exhibits significant nitrogen overabundance [log (N/O) ∼ −0.05, that is by ∼1.4 dex higher than expected for low-metallicity galaxies]. We suggested that this is a massive blue supergiant (BSG) or Wolf-Rayet (WR) star surrounded by its ejecta interacting with the interstellar medium. We calculated the models of the nebula using cloudy photoionization code, applying cmfgen-modelled BSG and WR stars as ionization sources. We found a best agreement between the modelled and observed spectra for the model assuming ionization by low-metallicity WR star of mass M* ≈ 80 M, ionizing the nebula through the strong wind and enriching the interstellar medium with nitrogen.
Item Description:Online veröffentlicht am 16. Oktober 2022
Gesehen am 08.02.2023
Physical Description:Online Resource
ISSN:1365-2966
DOI:10.1093/mnras/stac2949

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