Mid-infrared imaging of the massive young star AFGL 2591: Probing the circumstellar environment of an outflow source

摘要

Most, if not all, stars are now believed to produce energetic outflows duringtheir formation. Yet, almost 20 years after the discovery of bipolar outflowsfrom young stars, the origins of this violent phenomenon are not wellunderstood. One of the difficulties of probing the outflow process,particularly in the case of massive embedded stars, is a deficit of highspatial resolution observations. Here, we present sub-arcsecond-resolutionmid-infrared images of one massive young stellar object, AFGL 2591, and itsimmediate surroundings. Our images, at 11.7, 12.5 and 18.0 microns, reveal aknot of emission ~6'' SW of the star, which may be evidence for a recentejection event or an embedded companion star. This knot is roughly coincidentwith a previously seen near-infrared reflection nebula and a radio source, andlies within the known large-scale CO outflow. We also find a new faint NWsource which may be another embedded lower-luminosity star. The IRASmid-infrared spectrum of AFGL 2591 shows a large silicate absorption feature at10 microns, implying that the primary source is surrounded by an opticallythick dusty envelope. We discuss the interrelationship of these phenomena andsuggest that mid-infrared imaging and spectroscopy provide powerful tools forprobing massive star birth.