- Published on 01 July 2020
6. Interstellar and circumstellar matter
Molecular globules in the Veil bubble of Orion IRAM 30 m 12CO, 13CO, and C18O (2–1) expanded maps of Orion A
Expanding bubbles in Orion A: [C II] observations of M 42, M 43, and NGC 1977
Strong winds and ultraviolet (UV) radiation from O-type stars disrupt and ionize their molecular core birthplaces, sweeping up material into parsec-sized shells. The "Veil bubble" in Orion represents a nearby example of such a shell, where the complexities of stellar feedback can be studied in detail. The Veil lies in front of the well-known M42 HII region, and it is driven by the Trapezium-cluster stars. In such a harsh environment dominated by shocks and UV radiation, little molecular emission is expected to be found. As Goicoechea et al. show, however, some pockets of molecular gas have managed to survive in the Veil, and they have been detected with the IRAM 30 m telescope as small CO globules. These globules have small masses and are moderately dense, and they seem to be confined by the shell's external pressure and are likely supported by magnetic fields. They are either transient objects that formed by hydrodynamic instabilities or pre-existing over-dense structures of the original molecular cloud. In a companion paper, Pabst et al. analyze [CII]158 microns observations of the Veil and other nearby bubbles in Orion, which were carried out with the upGREAT instrument on board SOFIA. The Veil bubble is found to have an expansion time of 0.2 Myr and to be driven by the mechanical energy input from the wind of the O-type star θ1 Ori C, the most massive star in the Trapezium. Whereas the nearby bubbles associated with M43 and NGC 1977 are caused by the thermal expansion of the gas ionized by their central later-type less massive stars.