Journal Article

Chemical abundances in the protoplanetary disc LV 2 (Orion): clues to the causes of the abundance anomaly in H <span class="smallCaps">ii</span> regions

Y. G. Tsamis, J. R. Walsh, J. M. Vílchez and D. Péquignot

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 2, pages 1367-1380
Published in print April 2011 | ISSN: 0035-8711
Published online March 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17991.x
Chemical abundances in the protoplanetary disc LV 2 (Orion): clues to the causes of the abundance anomaly in H ii regions

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Optical integral field spectroscopy of the archetype protoplanetary disc LV 2 in the Orion nebula is presented, taken with the Very Large Telescope (VLT) FLAMES/Argus fibre array. The detection of recombination lines (RLs) of C ii and O ii from this class of objects is reported, and the lines are utilized as abundance diagnostics. The study is complemented with the analysis of Hubble Space Telescope (HST) Faint Object Spectrograph ultraviolet and optical spectra of the target contained within the Argus field of view. By subtracting the local nebula background the intrinsic spectrum of the proplyd is obtained and its elemental composition is derived for the first time. The proplyd is found to be overabundant in carbon, oxygen and neon compared to the Orion nebula and the Sun.

The simultaneous coverage over LV 2 of the C iii]λ1908 and [O iii]λ5007 collisionally excited lines (CELs) and C ii and O ii RLs has enabled us to measure the abundances of C2 + and O2 + for LV 2 with both sets of lines. The two methods yield consistent results for the intrinsic proplyd spectrum, but not for the proplyd spectrum contaminated by the generic nebula spectrum, thus providing one example where the long-standing abundance anomaly plaguing metallicity studies of H ii regions has been resolved. These results would indicate that the standard forbidden-line methods used in the derivation of light metal abundances in H ii regions in our own and other galaxies underestimate the true gas metallicity.

Keywords: planets and satellites: general; protoplanetary discs; stars: pre-main-sequence; stars: protostars; ISM: abundances; H ii regions; ISM: individual objects: LV2; ISM: individual objects: 167−317; ISM: individual objects: Orion nebula

Journal Article.  9711 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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