Keck near-infrared observations of the Orion proplyds: Initial results

The Hubble Space Telescope (HST) has produced dramatic images of proto-planetary disks ("proplyds") surrounding young (< 10 ⁶ year old) stars embedded in the Orion Nebula. The intense UV radiation field of the high-mass Trapezium stars heats the disk surfaces, drives mass-loss, and produces bright ionization fronts. Many disks are seen in silhouette against the nebular background of the Orion Nebula, or against the proplyd's own ionization front. The sub-arcsecond resolution and light gathering power of the Keck telescopes in the near-IR provide a unique opportunity to study the earliest phases of planetary disk evolution and disk destruction under intense UV radiation fields. We present initial results from observations of a handful of proplyds using KCAM and NIRSPEC, with and without the adaptive optics (AO) system, on Keck II. These data clearly resolve, both spatially and spectrally, ionization fronts, disks, and a microjet. The data are used to constrain mass-loss rates due to photoevaporation, disk surface wind velocity, and grain size distribution.