Identification and Characterization of Faint Emission Lines in the Spectrum of the Planetary Nebula IC 418

Sharpee, B. D.; Baldwin, J. A.; Williams, Robert E.

doi:10.1086/424035

Cited by 30 publications

(58 citation statements)

References 52 publications

(137 reference statements)

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“…The data for all four PNe were reduced using standard procedures with IRAF-based reduction packages in the same manner that has been described in detail in our discussion of comparable spectra of the PN IC 418 that we obtained previously with the Cerro Tololo Inter-American Observatory 4 m echelle spectrograph (Sharpee et al 2004). A correction was made for the presence of Rowland ghosts near strong lines (Baldwin et al 2000).…”

Section: Observations and Data Reductionmentioning

confidence: 99%

s‐Process Abundances in Planetary Nebulae

Sharpee

Zhang

Williams

et al. 2007

ApJ

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112

229

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The s-process should occur in all but the lower mass progenitor stars of planetary nebulae, and this should be reflected in the chemical composition of the gas that is expelled to create the current planetary nebula shell. Weak forbidden emission lines are expected from several s-process elements in these shells and have been searched for and in some cases detected in previous investigations. Here we extend these studies by combining very high signal-to-noise ratio echelle spectra of a sample of PNe with a critical analysis of the identification of the emission lines of Z > 30 ions. Emission lines of Br, Kr, Xe, Rb, Ba, and Pb are detected with a reasonable degree of certainty in at least some of the objects studied here, and we also tentatively identify lines from Te and I, each in one object. The strengths of these lines indicate enhancement of s-process elements in the central star progenitors, and we determine the abundances of Br, Kr, and Xe, elements for which atomic data relevant for abundance determination have recently become available. As representative elements of the ''light'' and ''heavy''s-process peaks, Kr and Xe exhibit similar enhancements over solar values, suggesting that PN progenitors experience substantial neutron exposure.

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Section: Observations and Data Reductionmentioning

confidence: 99%

s‐Process Abundances in Planetary Nebulae

Sharpee

Zhang

Williams

et al. 2007

ApJ

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112

229

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“…NGC 7009 is an evolved medium‐excitation PN exhibiting an extraordinarily rich and prominent ORL spectrum of heavy element ions that is hardly rivalled by any other bright PNe of similar excitation class. Hitherto, fairly complete emission line identifications covering the whole optical wavelength range have been carried out for a few bright objects, including the high‐excitation class PN NGC 7027 (Zhang et al 2005a) and the low‐excitation class PN IC 418 (Sharpee et al 2003; Sharpee et al 2004), amongst others. For NGC 7027, a total of 1174 identified emission lines have been tabulated, including 739 isolated features and more than 200 blended ones without individual flux estimates.…”

Section: Emission Line Identificationmentioning

confidence: 99%

Very deep spectroscopy of the bright Saturn nebula NGC 7009 - I. Observations and plasma diagnostics

Fang

Liu

2011

Monthly Notices of the Royal Astronomical Society

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We present very deep CCD spectrum of the bright, medium‐excitation planetary nebula NGC 7009, with a wavelength coverage from 3040 to 11 000 Å. Traditional emission line identification is carried out to identify all the emission features in the spectra, based on the available laboratory atomic transition data. Since the spectra are of medium resolution, we use multi‐Gaussian line profile fitting to deblend faint blended lines, most of which are optical recombination lines (ORLs) emitted by singly ionized ions of abundant second‐row elements such as C, N, O and Ne. Computer‐aided emission‐line identification, using the code emili developed by Sharpee et al., is then employed to further identify all the emission lines thus obtained. In total about 1200 emission features are identified, with the faintest ones down to fluxes 10−4 of Hβ. The flux errors for all emission lines, estimated from multi‐Gaussian fitting, are presented. Plots of the whole optical spectrum, with identified emission lines labelled, are presented along with the results of multi‐Gaussian fits. Of all the properly identified emission lines, permitted lines contribute 81 per cent to the total line number. More than 200 O ii permitted lines are presented, as well as many others from N ii and Ne ii. Due to its relatively simple atomic structure, C ii presents few lines. Within the flux range 10−2–10−4 Hβ where most permitted lines of C ii, N ii, O ii and Ne ii fall, the average flux measurement uncertainties are about 10–20 per cent. Comparison is also made of the number of emission lines identified in the current work of NGC 7009 and those of several other planetary nebulae (PNe) that have been extensively studied in the recent literature, and it shows that our line‐deblending procedure increases the total line number significantly, especially for emission lines with fluxes lower than 10−3 of Hβ. Higher resolution is still needed to obtain more reliable fluxes for those extremely faint emission lines, lines of fluxes of the order of 10−5–10−6 of Hβ. Plasma diagnostics using optical forbidden line ratios give an average electron temperature of 10 020 K, which agrees well with previous results of the same object. The average electron density of NGC 7009 derived from optical forbidden line ratios is 4290 cm−3. The [O iii] λ4959/λ4363 nebular‐to‐auroral line ratio yields an electron temperature of 9800 K. The ratio of the nebular continuum Balmer discontinuity at 3646 Å to H ii reveals an electron temperature of 6500 K, about 600 K lower than the measurements published in the literature. The Balmer decrement reveals a density of about 3000 cm−3. Also derived are electron temperatures from the He i line ratios, and a value of 5100 K from the λ7281/λ6678 ratio is adopted. Utilizing the effective recombination coefficients newly available, we find an electron temperature around 1000 K from the O ii ORL spectrum. Thus the general pattern of electron temperatures, Te([O iii]) ≳Te(H i BJ) ≳Te(He i) ≳Te(O ii), which is seen in many PNe, is repeated ...

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“…Figure 10 displays Figure 10 demonstrates that our model provides a reasonable match to the O i λ5513, but is unable to explain the profiles of O i λ7773 and N i λ8223, whose widths appear to be broader that those of the predicted lines. As pointed out by Sharpee et al (2004), fluorescence excitation may contribute substantially to the intensity of these lines, and the radiation of the lines may originate predominantly in the outer neutral regions.…”

Section: Emission Line Profiles Of Ic 418mentioning

confidence: 95%

“…The analysis of a larger number of PNe will appear in a separate paper. Highresolution echelle spectra of the PN IC 418 were obtained in 2001 with the 4 m Blanco telescope at Cerro Tololo InterAmerican Observatory (Sharpee et al 2004), covering a wavelength range from 3500 to 9865 Å. IC 418 is a low-excitation…”

Section: Emission Line Profiles Of Ic 418mentioning

confidence: 99%

Emission line profiles as a probe of physical conditions in planetary nebulae

Zhang

2008

A&A

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Aims. We present an analysis of physical conditions in planetary nebulae (PNe) in terms of collisionally-excited line (CEL) and optical-recombination line (ORL) profiles. We aim to investigate whether line profiles could be used to study the long-standing CEL/ORL abundance-discrepancy problem in nebular astrophysics. Methods. Using 1D photoionization models and their assumed velocity fields, we simulate the line profiles of various ionic species. We attempt to use our model to account for the observed CEL and ORL profiles. As a case study we present a detailed study of line profiles of the low-excitation planetary nebula (PN) IC 418.Results. Our results show that the profiles of classical temperature and density diagnostic lines, such as [O iii] λλ4363, 5007, [S ii] λλ6716, 6731, and [Ar iv] λλ4711, 4740, provide a powerful tool to study nebular temperature and density variations. The method enables the CEL/ORL abundance-discrepancy problem to be studied more rigorously than before. A pure photoionization model of a chemically-homogeneous nebula seems to explain the observed disagreements in the profiles for the [O iii] λ4363 and the λ5007 lines, but cannot account for the differences between the [O iii] CELs and the O ii ORLs. We also investigate the temperature and density variations in the velocity space of a sample of PNe, which are found to be insignificant.

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Identification and Characterization of Faint Emission Lines in the Spectrum of the Planetary Nebula IC 418

Cited by 30 publications

References 52 publications

s‐Process Abundances in Planetary Nebulae

s‐Process Abundances in Planetary Nebulae

Very deep spectroscopy of the bright Saturn nebula NGC 7009 - I. Observations and plasma diagnostics

Emission line profiles as a probe of physical conditions in planetary nebulae

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