A radio-continuum and photoionization-model study of the two planetary nebulae in the Sagittarius dwarf galaxy

G. Dudziak, D. Pequignot, A.A. Zijlstra, J.R. Walsh

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Abstract

Radio continuum observations at 1.4, 4.8 and 8.6 GHz of the two Planetary Nebulae (PNe) in the Sagittarius dwarf galaxy reveal the elongated shape ofWray 16-423 and the extreme compactness of He 2-436. It is confirmed that He 2-436 is subject to local dust extinction. Photoionization models for both PNe are obtained from two different codes, allowing theoretical uncertainties to be assessed. Wray 16-423, excited by a star of effective temperature 1.07×105K, is an ellipsoidal, matterbounded nebula, except for a denser sector of solid angle 15%. He 2-436, excited by a 7×104K star, includes two radiation- bounded shells, with the very dense, lowmass, incomplete, inner shell possibly corresponding to a transitory event. The continuum jump at the He+ limit (_22.8nm) agrees with NLTE model stellar atmospheres, despite the Wolf-Rayet nature of the stars. Both stars are on the same (H-burning) evolutionary track of initial mass (1.2±0.1) M⊙ and may be twins, with the PN ejection of Wray 16-423 having occured _ 1500 years before He 2-436. The PN abundances re-inforce the common origin of the parent stars, indicating almost identical depletions with respect to solar for O, Ne, Mg, S, Cl, Ar, and K (-0.55±0.07 dex), and strong overabundances for carbon, particularly in He 2-436. He i lines consistently point to large identical overabundances for helium in both PNe. An excess nitrogen makes Wray 16-423 nearly a Type I PN. These PNe provide a means to calibrate both metallicity and age of the stellar population of Sagittarius. They confirm that the youngest, most metal-rich population has an age of 5Gyr and a metallicity of [Fe/H]= −0.55, in agreement with the slope of the red giant branch.
Original languageEnglish
Pages (from-to)717-723
Number of pages6
JournalAstronomy and Astrophysics
Volume363
Issue number2
Publication statusPublished - 2000

Fingerprint

planetary nebulae
dwarf galaxies
photoionization
shell
radio
continuums
stars
helium
extinction
metallicity
dust
atmosphere
nitrogen
metal
carbon
stellar atmospheres
wolves
void ratio
nebulae
ejection

Keywords

  • stars
  • planetary nebulae
  • galaxies
  • Sagittarius
  • radio-continuum

Cite this

Dudziak, G. ; Pequignot, D. ; Zijlstra, A.A. ; Walsh, J.R. / A radio-continuum and photoionization-model study of the two planetary nebulae in the Sagittarius dwarf galaxy. In: Astronomy and Astrophysics. 2000 ; Vol. 363, No. 2. pp. 717-723.
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abstract = "Radio continuum observations at 1.4, 4.8 and 8.6 GHz of the two Planetary Nebulae (PNe) in the Sagittarius dwarf galaxy reveal the elongated shape ofWray 16-423 and the extreme compactness of He 2-436. It is confirmed that He 2-436 is subject to local dust extinction. Photoionization models for both PNe are obtained from two different codes, allowing theoretical uncertainties to be assessed. Wray 16-423, excited by a star of effective temperature 1.07×105K, is an ellipsoidal, matterbounded nebula, except for a denser sector of solid angle 15{\%}. He 2-436, excited by a 7×104K star, includes two radiation- bounded shells, with the very dense, lowmass, incomplete, inner shell possibly corresponding to a transitory event. The continuum jump at the He+ limit (_22.8nm) agrees with NLTE model stellar atmospheres, despite the Wolf-Rayet nature of the stars. Both stars are on the same (H-burning) evolutionary track of initial mass (1.2±0.1) M⊙ and may be twins, with the PN ejection of Wray 16-423 having occured _ 1500 years before He 2-436. The PN abundances re-inforce the common origin of the parent stars, indicating almost identical depletions with respect to solar for O, Ne, Mg, S, Cl, Ar, and K (-0.55±0.07 dex), and strong overabundances for carbon, particularly in He 2-436. He i lines consistently point to large identical overabundances for helium in both PNe. An excess nitrogen makes Wray 16-423 nearly a Type I PN. These PNe provide a means to calibrate both metallicity and age of the stellar population of Sagittarius. They confirm that the youngest, most metal-rich population has an age of 5Gyr and a metallicity of [Fe/H]= −0.55, in agreement with the slope of the red giant branch.",
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Dudziak, G, Pequignot, D, Zijlstra, AA & Walsh, JR 2000, 'A radio-continuum and photoionization-model study of the two planetary nebulae in the Sagittarius dwarf galaxy', Astronomy and Astrophysics, vol. 363, no. 2, pp. 717-723.

A radio-continuum and photoionization-model study of the two planetary nebulae in the Sagittarius dwarf galaxy. / Dudziak, G.; Pequignot, D.; Zijlstra, A.A.; Walsh, J.R.

In: Astronomy and Astrophysics, Vol. 363, No. 2, 2000, p. 717-723.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A radio-continuum and photoionization-model study of the two planetary nebulae in the Sagittarius dwarf galaxy

AU - Dudziak, G.

AU - Pequignot, D.

AU - Zijlstra, A.A.

AU - Walsh, J.R.

PY - 2000

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N2 - Radio continuum observations at 1.4, 4.8 and 8.6 GHz of the two Planetary Nebulae (PNe) in the Sagittarius dwarf galaxy reveal the elongated shape ofWray 16-423 and the extreme compactness of He 2-436. It is confirmed that He 2-436 is subject to local dust extinction. Photoionization models for both PNe are obtained from two different codes, allowing theoretical uncertainties to be assessed. Wray 16-423, excited by a star of effective temperature 1.07×105K, is an ellipsoidal, matterbounded nebula, except for a denser sector of solid angle 15%. He 2-436, excited by a 7×104K star, includes two radiation- bounded shells, with the very dense, lowmass, incomplete, inner shell possibly corresponding to a transitory event. The continuum jump at the He+ limit (_22.8nm) agrees with NLTE model stellar atmospheres, despite the Wolf-Rayet nature of the stars. Both stars are on the same (H-burning) evolutionary track of initial mass (1.2±0.1) M⊙ and may be twins, with the PN ejection of Wray 16-423 having occured _ 1500 years before He 2-436. The PN abundances re-inforce the common origin of the parent stars, indicating almost identical depletions with respect to solar for O, Ne, Mg, S, Cl, Ar, and K (-0.55±0.07 dex), and strong overabundances for carbon, particularly in He 2-436. He i lines consistently point to large identical overabundances for helium in both PNe. An excess nitrogen makes Wray 16-423 nearly a Type I PN. These PNe provide a means to calibrate both metallicity and age of the stellar population of Sagittarius. They confirm that the youngest, most metal-rich population has an age of 5Gyr and a metallicity of [Fe/H]= −0.55, in agreement with the slope of the red giant branch.

AB - Radio continuum observations at 1.4, 4.8 and 8.6 GHz of the two Planetary Nebulae (PNe) in the Sagittarius dwarf galaxy reveal the elongated shape ofWray 16-423 and the extreme compactness of He 2-436. It is confirmed that He 2-436 is subject to local dust extinction. Photoionization models for both PNe are obtained from two different codes, allowing theoretical uncertainties to be assessed. Wray 16-423, excited by a star of effective temperature 1.07×105K, is an ellipsoidal, matterbounded nebula, except for a denser sector of solid angle 15%. He 2-436, excited by a 7×104K star, includes two radiation- bounded shells, with the very dense, lowmass, incomplete, inner shell possibly corresponding to a transitory event. The continuum jump at the He+ limit (_22.8nm) agrees with NLTE model stellar atmospheres, despite the Wolf-Rayet nature of the stars. Both stars are on the same (H-burning) evolutionary track of initial mass (1.2±0.1) M⊙ and may be twins, with the PN ejection of Wray 16-423 having occured _ 1500 years before He 2-436. The PN abundances re-inforce the common origin of the parent stars, indicating almost identical depletions with respect to solar for O, Ne, Mg, S, Cl, Ar, and K (-0.55±0.07 dex), and strong overabundances for carbon, particularly in He 2-436. He i lines consistently point to large identical overabundances for helium in both PNe. An excess nitrogen makes Wray 16-423 nearly a Type I PN. These PNe provide a means to calibrate both metallicity and age of the stellar population of Sagittarius. They confirm that the youngest, most metal-rich population has an age of 5Gyr and a metallicity of [Fe/H]= −0.55, in agreement with the slope of the red giant branch.

KW - stars

KW - planetary nebulae

KW - galaxies

KW - Sagittarius

KW - radio-continuum

UR - http://arxiv.org/PS_cache/astro-ph/pdf/0009/0009054v1.pdf

UR - http://arxiv.org/abs/astro-ph/0009054v1

M3 - Article

VL - 363

SP - 717

EP - 723

JO - Astronomy and Astrophysics

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ER -