Diagnostic line ratios in the IC 1805 optical gas complex
Autor: | Laurent Drissen, Gilles Joncas, Dominic Lagrois |
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Rok vydání: | 2012 |
Předmět: |
Physics
Shock wave Nebula Spectral signature Shock (fluid dynamics) 010308 nuclear & particles physics Astrophysics::High Energy Astrophysical Phenomena Astronomy and Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Astrophysics Photoionization 01 natural sciences Stars Space and Planetary Science 0103 physical sciences Astrophysics::Solar and Stellar Astrophysics Astrophysics::Earth and Planetary Astrophysics Supergiant 010303 astronomy & astrophysics Astrophysics::Galaxy Astrophysics Line (formation) |
Zdroj: | Monthly Notices of the Royal Astronomical Society. 420:2280-2299 |
ISSN: | 0035-8711 |
Popis: | Large HII regions, with angular dimensions exceeding 10 pc, usually enclose numerous massive O-stars. Stellar winds from such stars are expected to play a sizeable role in the dynamical, morphological and chemical evolution of the targeted nebula. Kinematically, stellar winds remain hardly observable i.e., the typical expansion velocities of wind-blown bubbles being often confused with other dynamical processes also regularly found HII regions. However, supersonic shock waves, developed by stellar winds, should favor shock excitation and leave a well-defined spectral signature in the ionized nebular content. In this work, the presence of stellar winds, observed through shock excitation, is investigated in the brightest portions of the Galactic IC 1805 nebula, a giant HII region encompassing at least 10 O-stars from main-sequence O9 to giant and supergiant O4. The use of the imaging Fourier transform spectrometer SpIOMM enabled the simultaneous acquisition of the spectral information associated to the Halpha6563A, [NII]6548, 6584A, and [SII]6716, 6731A ionic lines. Diagnostic diagrams, first introduced by Sabbadin and collaborators, were used to circumscribe portions of the nebula likely subject to shock excitation from other areas dominated by photoionization. The gas compression, expected from supersonic shocks, is investigated by comparing the pre- and post-shocked material's densities computed from the [SII]/[SII] line ratio. The typical [NII]/[NII] line ratio slightly exceeds the theoretical value of 3 expected in low-density regimes. To explain such behavior, a scenario based on collisional de-excitations affecting the [NII]6548A line is proposed. |
Databáze: | OpenAIRE |
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