Hubble space telescope and United Kingdom infrared telescope observations of the center of the Trifid Nebula: Evidence for the photoevaporation of a proplyd and a protostellar condensation

The Trifid Nebula (M20) is a well-known prominent optical H II region trisected by bands of obscuring dust lanes and excited by an O7.5 star, HD 164492A. Previous near-IR, mid-IR, and radio continuum observations of the cluster of stars at the center of the Trifid Nebula indicated the presence of circumstellar disks associated with hot stars with envelopes that are photoionized externally by the UV radiation from the hot central star, HD 164492A. Using the WFPC2 on the Hubble Space Telescope, we present evidence of a resolved proplyd in Hα and [S II] line emission from a stellar source emitting cool dust emission. Using the United Kingdom Infrared Telescope, an infrared observation of the stellar source with a proplyd indicates a late F to mid-G spectral type. We also note a remarkable complex of filamentary and sheetlike structures that appear to arise from the edge of a protostellar condensation. These observations are consistent with a picture in which the bright massive star HD 164492A is responsible for the photoevaporation of protoplanetary disks of other less massive members of the cluster, as well as the closest protostellar condensation facing the central cluster. Using the evidence for a proplyd, we argue that the massive and intermediate-mass members of the cluster, HD 164492C (B6 star) and HD 164492 (Herbig Be star), have disks associated with them.