The Diamond Ring in Cygnus X: Advanced stage of an expanding bubble of ionised carbon
Year: 2025
Type: article
Abstract: The ‘Diamond Ring’ within Cygnus X, south-west of the DR21 ridge, stands out as a prominent, nearly circular structure in infrared (IR) and far-infrared (FIR) emission, spanning approximately 6 pc in diameter. It is enclosed by clumpy molecular clouds seen in CO lines and contains an H II region, visible in cm emission. It resembles a classical H II region associated with an expanding bubble seen routinely in the 158 μm line of ionised carbon ([C II ]). However, our recent observations utilising the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA) under the FEEDBACK program for the spectrally resolved [C II ] line have revealed a slightly tilted ring with a mass of ~10 3 M ⊙ , advancing at a velocity of ~1.3 km s −1 . The bulk emission of the gas has a line-of-sight (LOS) velocity around −2 km s −1 . The [C II ] data revealed that the ‘Diamond’ of the Diamond Ring is an unrelated, dense gas clump at a LOS velocity of ~7 km s −1 . The driving source, which is also responsible for powering the associated H II region, is a B0.5e star, classified by our IR spectroscopy. This observation marks the first instance where we observe only a slowly expanding ring of [C II ] emission and not an expanding 3D shell. We suggest that the H II region (along with its associated [C II ] bubble), initially formed by a massive star, expanded outwards from a flat slab of molecular gas nearly in the plane of the sky. Presently, the [C II ] ring is confined by the swept-up gas of the slab, while the parts of the shell moving in the directions perpendicular to the shell along the LOS have dissipated, resulting in a notable decrease in the expansion of the remaining ring. This scenario is supported by dedicated simulations that trace the evolution of the [C II ] bubble. Our observations support the scenario of H II region evolution in ‘flat’ molecular clouds, reported earlier in the literature. In this geometry, we propose that the Diamond Ring represents the terminal phase of an expanding [C II ] bubble driven by stellar winds and thermal pressure.
Source: Astronomy and Astrophysics
Authors: Simon M. Dannhauer, Sebastian Vider, Nicola Schneider, Robert Simon, Fernando Comeron, Eduard Keilmann, Stefanie Walch, Lars Bonne, Slawa Kabanovic, Volker Ossenkopf-Okada, Daniel Seifried, Timea Csengeri, Amanda Djupvik, Yan Gong, Andreas Brunthaler, Michael Rugel, Dominik A. Riechers, Sylvain Bontemps, Netty Honingh, Urs U. Graf, Alexander G. G. M. Tielens
Institutions: University of Cologne, European Southern Observatory, European Southern Observatory, Ames Research Center, Centre National de la Recherche Scientifique, Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, Aarhus University, Nordic Optical Telescope, Chinese Academy of Sciences, Purple Mountain Observatory, Max Planck Institute for Radio Astronomy, National Radio Astronomy Observatory, Leiden University, Leiden Observatory, University of Maryland, College Park
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Awards: G1134310069, G2528670510, G8131311138
OpenAlex ID: W7083438866