2013MNRAS.430.3406T

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 Hii 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 x 0.31 arcsec2 spatial pixels. The proplyd and its vicinity are imaged in a variety of emission lines across a 6.8x4.3arcsec2 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 [Oiii] 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 sulphur abundances. With the exception of [Oi] λ6300 and [Sii] λ4069, the model fit is satisfactory for all spectral lines arising from the proplyd. The models show that the classic ionization correction factor for neon significantly underestimates (0.4 dex) this element's abundance in the low ionization conditions of HST 10. Apart from iron, whose gas-phase abundance is ∼ 0.3 dex lower than in the local Orion nebula, most other elements in the proplyd do not show substantially different gas-phase abundances from the nebula. The abundances of carbon, oxygen and neon in HST 10 are practically the same as those in B-type stars in Orion.