Investigating the Nature of the Dust Emission around Massive Protostar NGC 7538 IRS 1: Circumstellar Disk and Outflow?

Abstract

We have obtained high resolution mid-infrared images of the high mass protostar NGC 7538 IRS 1 using Michelle on Gemini North and find that the circumstellar dust associated with this source is extended on both large and small scales. The large-scale mid-infrared emission is asymmetric about the peak of IRS 1, being more extended to the northwest than the southeast. The position angle of the mid-infrared emission is similar to the position angle of the linearly distributed methanol masers at this location which are thought to trace a circumstellar disk. However, this position angle is also very similar to that of the CO outflow in this region which appears to be centered on IRS 1. We suggest that the large-scale extended mid-infrared emission is coming from dust heated on the walls of the outflow cavities near the source. IRS 1 is also elongated in the mid-infrared on a smaller scale, and this elongation is near PERPENDICULAR to the axis of the CO outflow (and the linearly distributed methanol masers). Because of its orientation with respect to the outflow and its estimated size (R_disk~450AU at 11.7um), we propose that the small-scale elongation seen in the mid-infrared is a circumstellar disk that may be collimating the outflow from IRS 1.