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Article: Electron temperatures and densities of planetary nebulae determined from the nebular hydrogen recombination spectrum and temperature and density variations

TitleElectron temperatures and densities of planetary nebulae determined from the nebular hydrogen recombination spectrum and temperature and density variations
Authors
KeywordsAtomic Processes
Ism: Abundances
Planetary Nebulae: General
Issue Date2004
PublisherBlackwell Publishing Ltd. The Journal's web site is located at http://www.blackwellpublishing.com/journals/MNR
Citation
Monthly Notices Of The Royal Astronomical Society, 2004, v. 351 n. 3, p. 935-955 How to Cite?
AbstractA method is presented to derive electron temperatures and densities of planetary nebulae (PNe) simultaneously, using the observed hydrogen recombination spectrum, which includes continuum and line emission. By matching theoretical spectra to observed spectra around the Balmer jump at about 3646 Å, we determine electron temperatures and densities for 48 Galactic PNe. The electron temperatures based on this method - hereafter T e(Bal) - are found to be systematically lower than those derived from [O III] λ4959/λ4363 and [O III] (88 μm + 52 μm)/λ4959 ratios - hereafter T e([O III] na) and T e([O III] fn). The electron densities based on this method are found to be systematically higher than those derived from [O II] λ3729/λ3726, [S II] λ6731/λ6716, [Cl III] λ5537/λ5517, [Ar IV] λ4740/λ4711 and [O III] 88 μm/52 μm ratios. These results suggest that temperature and density fluctuations are generally present within nebulae. The comparison of T e([O III] na) and T e(Bal) suggests that the fractional mean-square temperature variation (t 2) has a representative value of 0.031. A majority of temperatures derived from the T e([O III] fn) ratio are found to be higher than those of T e([O III] na), which is attributed to the existence of dense clumps in nebulae - those [O III] infrared fine-structure lines are suppressed by collisional de-excitation in the clumps. By comparing T e([O III] fn), T e([O III] na) and T e(Bal) and assuming a simple two-density- component model, we find that the filling factor of dense clumps has a representative value of 7 × 10 -5. The discrepancies between T e([O III] na) and T e(Bal) are found to be anticorrelated with electron densities derived from various density indicators; high-density nebulae have the smallest temperature discrepancies. This suggests that temperature discrepancy is related to nebular evolution. In addition, He/H abundances of PNe are found to be positively correlated with the difference between T e([O III] na) and T e(Bal), suggesting that He/H abundances might have been overestimated generally because of the possible existence of H-deficient knots. Electron temperatures and densities deduced from spectra around the Paschen jump regions at 8250 Å are also obtained for four PNe: NGC 7027, NGC 6153, M 1-42 and NGC 7009. Electron densities derived from spectra around the Paschen jump regions are in good agreement with the corresponding values derived from spectra around the Balmer jump, whereas temperatures deduced from the spectra around the Paschen jump are found to be lower than the corresponding values derived from spectra around the Balmer jump for all the four cases. The reason remains unclear.
Persistent Identifierhttp://hdl.handle.net/10722/174987
ISSN
2015 Impact Factor: 4.952
2015 SCImago Journal Rankings: 2.806
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorZhang, Yen_US
dc.contributor.authorLiu, XWen_US
dc.contributor.authorWesson, Ren_US
dc.contributor.authorStorey, PJen_US
dc.contributor.authorLiu, Yen_US
dc.contributor.authorDanziger, IJen_US
dc.date.accessioned2012-11-26T08:48:39Z-
dc.date.available2012-11-26T08:48:39Z-
dc.date.issued2004en_US
dc.identifier.citationMonthly Notices Of The Royal Astronomical Society, 2004, v. 351 n. 3, p. 935-955en_US
dc.identifier.issn0035-8711en_US
dc.identifier.urihttp://hdl.handle.net/10722/174987-
dc.description.abstractA method is presented to derive electron temperatures and densities of planetary nebulae (PNe) simultaneously, using the observed hydrogen recombination spectrum, which includes continuum and line emission. By matching theoretical spectra to observed spectra around the Balmer jump at about 3646 Å, we determine electron temperatures and densities for 48 Galactic PNe. The electron temperatures based on this method - hereafter T e(Bal) - are found to be systematically lower than those derived from [O III] λ4959/λ4363 and [O III] (88 μm + 52 μm)/λ4959 ratios - hereafter T e([O III] na) and T e([O III] fn). The electron densities based on this method are found to be systematically higher than those derived from [O II] λ3729/λ3726, [S II] λ6731/λ6716, [Cl III] λ5537/λ5517, [Ar IV] λ4740/λ4711 and [O III] 88 μm/52 μm ratios. These results suggest that temperature and density fluctuations are generally present within nebulae. The comparison of T e([O III] na) and T e(Bal) suggests that the fractional mean-square temperature variation (t 2) has a representative value of 0.031. A majority of temperatures derived from the T e([O III] fn) ratio are found to be higher than those of T e([O III] na), which is attributed to the existence of dense clumps in nebulae - those [O III] infrared fine-structure lines are suppressed by collisional de-excitation in the clumps. By comparing T e([O III] fn), T e([O III] na) and T e(Bal) and assuming a simple two-density- component model, we find that the filling factor of dense clumps has a representative value of 7 × 10 -5. The discrepancies between T e([O III] na) and T e(Bal) are found to be anticorrelated with electron densities derived from various density indicators; high-density nebulae have the smallest temperature discrepancies. This suggests that temperature discrepancy is related to nebular evolution. In addition, He/H abundances of PNe are found to be positively correlated with the difference between T e([O III] na) and T e(Bal), suggesting that He/H abundances might have been overestimated generally because of the possible existence of H-deficient knots. Electron temperatures and densities deduced from spectra around the Paschen jump regions at 8250 Å are also obtained for four PNe: NGC 7027, NGC 6153, M 1-42 and NGC 7009. Electron densities derived from spectra around the Paschen jump regions are in good agreement with the corresponding values derived from spectra around the Balmer jump, whereas temperatures deduced from the spectra around the Paschen jump are found to be lower than the corresponding values derived from spectra around the Balmer jump for all the four cases. The reason remains unclear.en_US
dc.languageengen_US
dc.publisherBlackwell Publishing Ltd. The Journal's web site is located at http://www.blackwellpublishing.com/journals/MNRen_US
dc.relation.ispartofMonthly Notices of the Royal Astronomical Societyen_US
dc.subjectAtomic Processesen_US
dc.subjectIsm: Abundancesen_US
dc.subjectPlanetary Nebulae: Generalen_US
dc.titleElectron temperatures and densities of planetary nebulae determined from the nebular hydrogen recombination spectrum and temperature and density variationsen_US
dc.typeArticleen_US
dc.identifier.emailZhang, Y: zhangy96@hku.hken_US
dc.identifier.authorityZhang, Y=rp00841en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1111/j.1365-2966.2004.07838.xen_US
dc.identifier.scopuseid_2-s2.0-3042776467en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-3042776467&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume351en_US
dc.identifier.issue3en_US
dc.identifier.spage935en_US
dc.identifier.epage955en_US
dc.identifier.isiWOS:000222261500020-
dc.publisher.placeUnited Kingdomen_US
dc.identifier.scopusauthoridZhang, Y=23768446500en_US
dc.identifier.scopusauthoridLiu, XW=7409287288en_US
dc.identifier.scopusauthoridWesson, R=7003586236en_US
dc.identifier.scopusauthoridStorey, PJ=7005203247en_US
dc.identifier.scopusauthoridLiu, Y=36064406700en_US
dc.identifier.scopusauthoridDanziger, IJ=7004368453en_US

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