Central star temperatures of optically thick planetary nebulae and a distance-independent test of dredge-up theory

Kaler, J. B.; Jacoby, George H.

doi:10.1086/167957

Cited by 106 publications

(87 citation statements)

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“…The low N/O ratio also indicates the absence of hot bottom burning (HBB), which is predicted for more massive AGB stars. From a comparison with stellar evolutionary tracks, Kaler & Jacoby (1989) deduce N/O > 0.8 as a sharp limit for N-enriched PNe, which are supposed to indicate HBB in AGB-stars with M core > 0.8 M .…”

Section: Evolutionary Statusmentioning

confidence: 87%

The central star of the planetary nebula PB 8: a Wolf-Rayet-type wind of an unusual WN/WC chemical composition

Todt

Peña

Hamann

et al. 2010

A&A

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A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. As a rule, these CSPNe exhibit a chemical composition of helium, carbon, and oxygen with the majority showing Wolf-Rayet-like emission line spectra. These stars are classified as CSPNe of a spectral type [WC]. We perform a spectral analysis of CSPN PB 8 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. The source PB 8 displays wind-broadened emission lines from strong mass loss. Most strikingly, we find that its surface composition is hydrogen-deficient, but not carbon-rich. With mass fractions of 55% helium, 40% hydrogen, 1.3% carbon, 2% nitrogen, and 1.3% oxygen, it differs greatly from the 30-50% of carbon which are typically seen in [WC]-type central stars. The atmospheric mixture in PB 8 has an analogy in the WN/WC transition type among the massive Wolf-Rayet stars. Therefore we suggest to introduce a new spectral type [WN/WC] for CSPNe, with PB 8 as its first member. The central star of PB 8 has a relatively low temperature of T * = 52 kK, as expected for central stars in their early evolutionary stages. Its surrounding nebula is less than 3000 years old, i.e. relatively young. Existing calculations for the post-AGB evolution can produce hydrogen-deficient stars of the [WC] type, but do not predict the composition found in PB 8. We discuss various scenarios that might explain the origin of this unique object.

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Section: Evolutionary Statusmentioning

confidence: 87%

The central star of the planetary nebula PB 8: a Wolf-Rayet-type wind of an unusual WN/WC chemical composition

Todt

Peña

Hamann

et al. 2010

A&A

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“…Decidedly, this is not the case of NGC 6741, which is optically thick, ionization bounded, and wrapped up in a dense cocoon of almost-neutral matter. The extinction estimates reported in the literature (mean values along the nebular slice covered by the spectrograph slit) cluster around c(Hβ) tot = 1.05 (Kaler & Lutz 1985;Kaler & Jacoby 1989;Cahn et al 1992;Hyung & Aller 1997).…”

Section: The Absorption (Interstellar + Circum-nebular)mentioning

confidence: 91%

“…Previous ground-based estimates reported in the literature are: 19.5 (Pottasch 1981), 17.6 (Tylenda et al 1989), 19.16 (Kaler & Jacoby 1989) and 19.26 (Hyung & Aller 1997) for m V , and >20.2 (Gathier & Pottasch 1988) and 18.2 (Tylenda et al 1989) for m B .…”

Section: The Central Star Parametersmentioning

confidence: 94%

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The 3-D shaping of NGC 6741: A massive, fast-evolving Planetary Nebula at the recombination-reionization edge

Sabbadin¹,

Benetti²,

Ragazzoni

et al. 2005

A&A

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Abstract. We infer the gas kinematics, diagnostics and ionic radial profiles, distance and central star parameters, nebular photo-ionization model, spatial structure and evolutionary phase of the Planetary Nebula NGC 6741 by means of long-slit ESO NTT+EMMI high-resolution spectra at nine position angles, reduced and analysed according to the tomographic and 3-D methodologies developed at the Astronomical Observatory of Padua (Italy). NGC 6741 (distance 2.0 kpc, age 1400 yr, ionized mass M ion 0.06 M ) is a dense (electron density up to 12 000 cm −3 ), high-excitation, almost-prolate ellipsoid (0.036 pc×0.020 pc×0.018 pc, major, intermediate and minor semi-axes, respectively), surrounded by a sharp low-excitation skin (the ionization front), and embedded in a spherical (radius 0.080 pc), almostneutral, high-density (n(H I) 7 × 10 3 atoms cm −3 ) halo containing a large fraction of the nebular mass (M halo ≥ 0.20 M ). The kinematics, physical conditions and ionic structure indicate that NGC 6741 is in a deep recombination phase, started about 200 years ago, and caused by the rapid luminosity drop of the massive (M * = 0.66−0.68 M ), hot (log T * 5.23) and faint (log L * /L 2.75) post-AGB star, which has exhausted the hydrogen-shell nuclear burning and is moving along the white dwarf cooling sequence. The general expansion law of the ionized gas in NGC 6741, V exp (km s −1 ) = 13 × R , fails in the innermost, highest-excitation layers, which move slower than expected. The observed deceleration is ascribable to the luminosity drop of the central star (the decreasing pressure of the hot-bubble no longer balances the pressure of the ionized gas), and appears in striking contrast to recent reports inferring that acceleration is a common property of the Planetary Nebulae innermost layers. A detailed comparative analysis proves that the "U"-shaped expansion velocity field is a spurious, incorrect result due to a combination of: (a) simplistic assumptions (spherical shell hypothesis for the nebula); (b) unfit reduction method (emission profiles integrated along the slit); and (c) inappropriate diagnostic choice (λ4686 Å of He II, i.e. a thirteen finestructure components recombination line). Some general implications for the shaping mechanisms of Planetary Nebulae are discussed.

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“…Effective temperatures (T e f ! ) of PNe progenitors were estimated from (A4686/H,B) or (A5007)/H(3) ratios (Kaler & Jacoby 1989, 1991. Progenitor luminosities (L/L0) were derived from relations of V magnitude with H,6 absolute flux, T e f f , and extinction constant from Kaler & Jacoby 1989.…”

Section: Determination Of Age-abundance Relationsmentioning

confidence: 99%

Chemical Evolution of the Small Magellanic Cloud: The Planetary Nebulae

Idiart

Costa

2003

Symp. - Int. Astron. Union

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Central star temperatures of optically thick planetary nebulae and a distance-independent test of dredge-up theory

Cited by 106 publications

References 0 publications

The central star of the planetary nebula PB 8: a Wolf-Rayet-type wind of an unusual WN/WC chemical composition

The central star of the planetary nebula PB 8: a Wolf-Rayet-type wind of an unusual WN/WC chemical composition

The 3-D shaping of NGC 6741: A massive, fast-evolving Planetary Nebula at the recombination-reionization edge

Chemical Evolution of the Small Magellanic Cloud: The Planetary Nebulae

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