Mon. Not. R. Astron. Soc., 358, 457-467 (2005/April-1)
Helium recombination spectra as temperature diagnostics for planetary nebulae.
ZHANG Y., LIU X.-W., LIU Y. and RUBIN R.H.
Abstract (from CDS):
Electron temperatures derived from the HeI recombination line ratios, designated Te(HeI), are presented for 48 planetary nebulae (PNe). We study the effect that temperature fluctuations inside nebulae have on the Te(HeI) value. We show that a comparison between Te(HeI) and the electron temperature derived from the Balmer jump of the HI recombination spectrum, designated Te(HI), provides an opportunity to discriminate between the paradigms of a chemically homogeneous plasma with temperature and density variations, and a two-abundance nebular model with hydrogen-deficient material embedded in diffuse gas of a `normal' chemical composition (i.e. ∼solar), as the possible causes of the dichotomy between the abundances that are deduced from collisionally excited lines and those deduced from recombination lines. We find that Te(HeI) values are significantly lower than Te(HI) values, with an average difference of <Te(HI) -Te(HeI)≥ 4000 K. The result is consistent with the expectation of the two-abundance nebular model but is opposite to the prediction of the scenarios of temperature fluctuations and/or density inhomogeneities. From the observed difference between Te(HeI) and Te(HI), we estimate that the filling factor of hydrogen-deficient components has a typical value of 10–4. In spite of its small mass, the existence of hydrogen-deficient inclusions may potentially have a profound effect in enhancing the intensities of HeI recombination lines and thereby lead to apparently overestimated helium abundances for PNe.
ISM: general - planetary nebulae: general
In Ref. : Peimbert et al. 2004 : 2004ApJS.150.431P instead of 2004ApJ.150.431P.
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