Expanding shells around young clusters -- S 171/Be 59

Abstract

Some HII regions that surround young stellar clusters are bordered by molecular shells that appear to expand at a rate inconsistent with our current model simulations. In this study we focus on the dynamics of Sharpless 171 (including NGC 7822), which surrounds the cluster Berkeley 59. We aim to compare the velocity pattern over the molecular shell with the mean radial velocity of the cluster for estimates of the expansion velocities of different shell structures, and to match the observed properties with model simulations. Optical spectra of 27 stars located in Berkeley 59 were collected at the Nordic Optical Telescope, and a number of molecular structures scattered over the entire region were mapped in ${}^{13}$CO(1-0) at Onsala Space Observatory. We obtained radial velocities and MK classes for the cluster's stars. At least four of the O stars are found to be spectroscopic binaries, in addition to one triplet system. From these data we obtain the mean radial velocity of the cluster. From the ${}^{13}$CO spectra we identify three shell structures, expanding relative to the cluster at moderate velocity (4 km/s), high velocity (12 km/s), and in between. The high-velocity cloudlets extend over a larger radius and are less massive than the low-velocity cloudlets. We performed a model simulation to understand the evolution of this complex. Our simulation of the Sharpless 171 complex and Berkeley 59 cluster demonstrates that the individual components can be explained as a shell driven by stellar winds from the massive cluster members. However, our relatively simple model produces a single component. Modelling of the propagation of shell fragments through a uniform interstellar medium demonstrates that dense cloudlets detached from the shell are decelerated less efficiently than the shell itself. They can reach greater distances and retain higher velocities than the shell.

27 pages, 14 figures, 8 tables, 3 appendices. Accepted for publication in Astronomy & Astrophysics

References in corpus (13)

• Array Programming with NumPy
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Before the first supernova: combined effects of HII regions and winds on molecular clouds
• A catalog of newly identified star clusters in GAIA DR2
• Efficiently Cooled Stellar Wind Bubbles in Turbulent Clouds I. Fractal Theory and Application to Star-Forming Clouds
• Efficiently Cooled Stellar Wind Bubbles in Turbulent Clouds II. Validation of Theory with Hydrodynamic Simulations
• MONOS: Multiplicity Of Northern O-type Spectroscopic systems. I. Project description and spectral classifications and visual multiplicity of previously known objects
• Stellar contents and star formation in the young star cluster Be 59
• Young cluster Berkeley 59 : Properties, evolution and star formation
• MONOS.II. Orbit review and analysis for 35 single-lined spectroscopic binary systems and candidates
• Simulating stellar winds in AMUSE
• Testing Models of Triggered Star Formation with Young Stellar Objects in Cepheus OB4
• Expanding shells around young clusters -- S 171/Be 59

Cited by in corpus (2)

• Expanding shells around young clusters -- S 171/Be 59
• Internal dynamics and structure of Cepheus OB4. The asymmetric expansion of Berkeley 59