Chemical abundances in the protoplanetary disc LV 2 (Orion) - II. High-dispersion VLT observations and microjet properties

Tsamis, Y. G. and Walsh, J. R. (2011). Chemical abundances in the protoplanetary disc LV 2 (Orion) - II. High-dispersion VLT observations and microjet properties. Monthly Notices of the Royal Astronomical Society, 417(3) pp. 2072–2084.



Integral field spectroscopy of the LV 2 proplyd is presented taken with the Very Large Telescope (VLT)/FLAMES Argus array at an angular resolution of 0.31 × 0.31 arcsec2 and velocity resolutions down to 2 km s-1 pixel-1. Following subtraction of the local M42 emission, the spectrum of LV 2 is isolated from the surrounding nebula. We measured the heliocentric velocities and widths of a number of lines detected in the intrinsic spectrum of the proplyd, as well as in the adjacent Orion nebula falling within a 6.6 × 4.2 arcsec2 field of view. It is found that far-ultraviolet to optical collisional lines with critical densities, Ncr, ranging from 103 to 109 cm-3 suffer collisional de-excitation near the rest velocity of the proplyd correlating tightly with their critical densities. Lines of low Ncr are suppressed the most. The bipolar jet arising from LV 2 is spectrally and spatially well detected in several emission lines. We compute the [O III] electron temperature profile across LV 2 in velocity space and measure steep temperature variations associated with the red-shifted lobe of the jet, possibly being due to a shock discontinuity. From the velocity-resolved analysis the ionized gas near the rest frame of LV 2 has Te= 9200 ± 800 K and Ne∼ 106 cm-3, while the red-shifted jet lobe has Te≈ 9000–104 K and Ne∼ 106–107 cm-3. The jet flow is highly ionized but contains dense semineutral clumps emitting neutral oxygen lines. The abundances of N+, O2+, Ne2+, Fe2+, S+and S2+ are measured for the strong red-shifted jet lobe. Iron in the core of LV 2 is depleted by 2.54 dex with respect to solar as a result of sedimentation on dust, whereas the efficient destruction of dust grains in the fast microjet raises its Fe abundance to at least 30 per cent solar. Sulphur does not show evidence of significant depletion on dust, but its abundance both in the core and the jet is only about half solar.

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