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arXiv · 2306.12264

Near infrared view on the photodissociation regions S255, S257, NGC7538 and S140

M. S. Kirsanova·A. M. Tatarnikov·P. A. Boley·D. S. Wiebe·N. A. Maslennikova·A. A. Tatarnikov
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Abstract

We performed photometric observations of the S255, S257, S140, NGC7358 and the Orion~Bar photo-dissociation regions (PDRs) at 2 micron using narrow-band filters centered on the Br-gamma, H2 and [FeII] lines, as well as the narrow-band Kcont and the broad-band H filters for continuum subtraction. The observations were done with the 2.5-m telescope of the SAI Caucasian Mountain Observatory and the near-infrared camera and spectrograph ASTRONIRCAM. We find several high-density arc-like structures in the Br-gamma and [FeII] images of the ionized gas in NGC7538 and extended shells and arcs visible through the H2 emission. The H ionization front and H2 dissociation front are merged in NGC7538. In S255 and S257 we detected only Br-gamma emission from the HII regions and bright H2 emission from the PDRs. The projected distance between the H ionization and H2 dissociation fronts are approx. 0.3-0.4 pc, which cannot be explained using models of a uniform medium. Most probably, the ionized and neutral gas in these PDRs is clumpy. The H-to-H2 transitions in the NGC7538, S255, S257 and S140 PDRs are gradual with no sharp borders. This conclusion also confirms the suggestion of a clumpy medium.

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M. S. Kirsanova, A. M. Tatarnikov, P. A. Boley, D. S. Wiebe, N. A. Maslennikova, A. A. Tatarnikov. 2023-06-21. Near infrared view on the photodissociation regions S255, S257, NGC7538 and S140. https://doi.org/10.1134/s199034132360014x

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