The close environment of AFGL 490 in radio-interferometric observations = Die nahe Umgebung von AFGL 490 in radiointerferometrischen Beobachtungen

摘要

The formation of high-mass stars in a scaled-up version of the low-mass star formation scenario has gained confidence in recent years, but open questions remain regarding details like the structure of circumstellar disks and interaction between accretion and outflows. Advances in spatial resolution and sensitivity of (sub)millimeter instruments as ALMA open the possibility to study high-mass star formation in detail, which is challengig due to large distances, embedding in gas and dust during the whole formation phase and complex environments. This work focuses on AFGL490, an isolated nearby object at the border between intermediate and high-mass (8-10 solar masses), and one of the few known more massive objects with spatially resolved observations of a circumstellar disk. Interferometric millimeter observations of C34S, CS and CH3OH were analyzed and show two distinct emission regions in the close environment of AFGL490: an innermost region containing the earlier detected circumstellar disk, and a wider region tracing the densest parts of the outflow wall, while the region between both appears to be devoid of (emitting) dense gas. Modelled emission from flared and partially shadowed disk models plus a line radiative transfer was compared with the observed emission in the uv-plane in an attempt to better characterize the circumstellar disk properties. Spatial resolution and sensitivity of the analyzed observations do not allow for strong constraints, but provide evidence for a C34S distribution more centrally condensed than that of C17O, a possible hint for a chemical structure of the disk. In the wider environment, inverse P-Cygni line profiles hint at ongoing gas infall from the outer envelope; the strongest emission features could represent a region where the infalling envelope gas strikes the dense outflow walls close to the plane of the innermost disk. Uncertainties of the disk-outflow-system's inclination angle could not be resovled.