Liu, X-W;
Barlow, MJ;
Zhang, Y;
Bastin, RJ;
Storey, PJ;
(2006)
Chemical abundances for Hf 2-2, a planetary nebula with the strongest-known heavy-element recombination lines.
Monthly Notices of the Royal Astronomical Society
, 368
(4)
pp. 1959-1970.
10.1111/j.1365-2966.2006.10283.x.
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Abstract
We present high-quality optical spectroscopic observations of the planetary nebula (PN) Hf 2-2. The spectrum exhibits many prominent optical recombination lines (ORLs) from heavy-element ions. Analysis of the H I and He I recombination spectrum yields an electron temperature of ∼900 K, a factor of 10 lower than given by the collisionally excited [O III] forbidden lines. The ionic abundances of heavy elements relative to hydrogen derived from ORLs are about a factor of 70 higher than those deduced from collisionally excited lines (CELs) from the same ions, the largest abundance discrepancy factor (adf) ever measured for a PN. By comparing the observed O IIλ4089/λ4649 ORL ratio to theoretical value as a function of electron temperature, we show that the O II ORLs arise from ionized regions with an electron temperature of only ∼630 K. The current observations thus provide the strongest evidence that the nebula contains another previously unknown component of cold, high-metallicity gas, which is too cool to excite any significant optical or ultraviolet CELs and is thus invisible via such lines. The existence of such a plasma component in PNe provides a natural solution to the long-standing dichotomy between nebular plasma diagnostics and abundance determinations using CELs on the one hand and ORLs on the other.
| Type: | Article |
|---|---|
| Title: | Chemical abundances for Hf 2-2, a planetary nebula with the strongest-known heavy-element recombination lines |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1111/j.1365-2966.2006.10283.x |
| Publisher version: | https://doi.org/10.1111/j.1365-2966.2006.10283.x |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | ISM: abundances, planetary nebulae: individual: Hf 2-2 |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10095566 |
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