Chemical abundances in Orion protoplanetary discs: integral field spectroscopy and photoevaporation models of HST 10∗

Photoevaporating protoplanetary discs (proplyds) in the vicinity of hot massive stars, such as those found in Orion, are important objects of study for the fields of star formation, early disc evolution, planetary formation, and H ii region astrophysics. Their element abundances are largely unknown, unlike those of the main-sequence stars or the host Orion nebula. We present a spectroscopic analysis of the Orion proplyd HST 10, based on integral field observations with the Very Large Telescope/FLAMES fibre array with 0.31′ ′ × 0.31′ ′ spatial pixels. The proplyd and its vicinity are imaged in a variety of emission lines across a 6.8′ ′ × 4.3′ ′ area. The reddening, electron density and temperature are mapped out from various line diagnostics. The abundances of helium, and eight heavy elements are measured relative to hydrogen using the direct method based on the [O iii] electron temperature. The abundance ratios of O/H and S/H are derived without resort to ionization correction factors. We construct dynamic photoevaporation models of HST 10 with the Cloudy microphysics code that validate the oxygen and sulfur abundances. With the exception of [O i] λ6300 and [S ii] λ4069, the model fit is satisfactory for all spectral lines arising from the proplyd. The models show tha