THE ULTRACOMPACT H-II REGION G5.97-1.17 - AN EVAPORATING CIRCUMSTELLAR DISK IN M8

We present new high spatial resolution optical, infrared, and radio ob servations of G5.97-1.17, an ultracompact H II region 2 ''.17 distant from the O7 star Herschel 36 in the center of M8, the Lagoon Nebula. I nfrared imaging was obtained using the adaptive optics system ADONIS o n the ESO 3.6 m telescope and a thermal-IR camera on the Hale 5 m; opt ical images taken with the Hubble Space Telescope Wide Field Planetary Camera 2 were extracted from the ST-ECF data archive; and radio conti nuum images were made using the VLA. The narrowband optical images sho w G5.97-1.17 to be a bow shock-shaped structure with its apex pointed toward Her 36, with the H alpha flux distributed over O ''.6 and consi stent with the appearance at 2 cm. The optical continuum and near-infr ared images show a star displaced from the peak of the bow shock by 0' '.125 in the direction away from Her 36. This star exhibits a thermal- IR excess, indicating hot circumstellar dust, the presence of which ca n be reconciled with the optical visibility of the star if the dust is in a disklike (rather than spherical) distribution. Therefore, contra ry to previous hypotheses that G5.97-1.17 is an ultracompact H II regi on intrinsically ionized by an embedded BO star, our observations stro ngly suggest that it is actually a young star surrounded by a circumst ellar disk that is being photoevaporated by Her 36, similar to the so- called proplyds seen near theta(1) Ori C in the Orion Nebula. At a dis tance of 1.8 kpc, this is the most distant known proplyd. These new ob servations confirm our previous claims based on earlier adaptive optic s and deconvolved WF/PC images.