Sliding along the Eddington Limit—Heavy-Weight Central Stars of Planetary Nebulae

Löbling, Lisa

doi:10.3390/galaxies6020065

Cited by 4 publications

(8 citation statements)

References 17 publications

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“…Another problem is the strong line broadening observed in its spectrum. This is consistent with a rotational velocity of 75 km/s (Löbling 2018) but could also be of different origin. While Abell 43 and NGC 7094 also show broadened lines, some PG 1159 stars, e.g.…”

Section: Selected Results and Their Discussionsupporting

confidence: 87%

(Pre)-white dwarf stars as measuring tools for yields of AGB nucleosynthesis

Löbling

2019

Proc. IAU

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In the helium-rich intershell region of asymptotic giant branch (AGB) stars, slow neutron-capture nucleosynthesis produces heavy elements beyond iron. If the stars experience a final-flash of the He-burning shell, a pulse-driven convection zone establishes, the stars become hydrogen-deficient and exhibit former intershell material at their surfaces. In their subsequent evolution towards the white-dwarf cooling sequence, but still at constant luminosity, a strong stellar wind prevents diffusion to wipe out the information about AGB yields. We present and interpret the analysis results of hydrogen-rich and -deficient post-AGB stars, discuss difficulties in their analysis and review the implications on the understanding of post-AGB evolution.

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Section: Selected Results and Their Discussionsupporting

confidence: 87%

(Pre)-white dwarf stars as measuring tools for yields of AGB nucleosynthesis

Löbling

2019

Proc. IAU

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“…The Fe deficiency of 0.4 and 0.8 dex for WD 1751+106 and WD 2134+125, respectively, does not include solar values within the error ranges. Löbling (2018) discuss the speculation of Herwig et al (2003) that this underabundance can be caused by neutron capture during the former AGB phase leading to a transformation of Fe into Ni and heavier elements. Probably the low Fe abun-dances determined in WD 1751+106 and WD 2134+125 are just a consequence of a low initial metal content for these objects.…”

Section: Comparison To Abell 30 and Abell 78mentioning

confidence: 82%

“…Also the element abundances of C -Ne, Si, P, and S were determined and agree with the values of Friederich (2010). Löbling (2018) found T eff = 115 000 ± 5000 K for both stars and log g = 5.4 ± 0.1 and log g = 5.5 ± 0.1 for WD 2134+125 and WD 1751+106, respectively. She considered 31 elements in her analysis and determined abundances in individual lineformation calculations.…”

Section: Introductionmentioning

confidence: 87%

“…Model atmospheres grids (∆T eff = 5000 K and ∆log g = 0.1) were calculated around the literature values of Löbling (2018). These models consider opacities of 31 elements from H to Ba for which the ionization fractions of the considered ions are shown in Fig.…”

Section: Effective Temperature and Surface Gravitymentioning

confidence: 99%

“…A4). The lower surface gravity values of Löbling (2018) were based on model atmospheres assuming the abundances found by Friederich (2010). Using new models with a revised He/H ratio and including opacities of more elements, these previous values appear too low.…”

Section: Effective Temperature and Surface Gravitymentioning

confidence: 99%

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Spectral analysis of the hybrid PG 1159-type central stars of the planetary nebulae Abell 43 and NGC 7094

Löbling

Rauch

Bertolami

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Stellar post asymptotic giant branch (post-AGB) evolution can be completely altered by a final thermal pulse (FTP) which may occur when the star is still leaving the AGB (AFTP), at the departure from the AGB at still constant luminosity (late TP, LTP) or after the entry to the white-dwarf cooling sequence (very late TP, VLTP). Then convection mixes the He-rich material with the H-rich envelope. According to stellar evolution models the result is a star with a surface composition of H ≈ 20 % by mass (AFTP), ≈ 1 % (LTP), or (almost) no H (VLTP). Since FTP stars exhibit intershell material at their surface, spectral analyses establish constraints for AGB nucleosynthesis and stellar evolution. We performed a spectral analysis of the socalled hybrid PG 1159-type central stars (CS) of the planetary nebulae Abell 43 and NGC 7094 by means of non-local thermodynamical equilibrium models. We confirm the previously determined effective temperatures of T eff = 115 000 ± 5 000 K and determine surface gravities of log(g / cm/s 2 ) = 5.6 ± 0.1 for both. From a comparison with AFTP evolutionary tracks, we derive stellar masses of 0.57 +0.07 −0.04 M ⊙ and determine the abundances of H, He, and metals up to Xe. Both CS are likely AFTP stars with a surface H mass fraction of 0.25 ± 0.03 and 0.15 ± 0.03, respectively, and a Fe deficiency indicating subsolar initial metallicities. The light metals show typical PG 1159-type abundances and the elemental composition is in good agreement with predictions from AFTP evolutionary models. However, the expansion ages do not agree with evolution timescales expected from the AFTP scenario and alternatives should be explored.

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Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS

Calcaferro,

Sowicka,

Uzundag

et al. 2024

A&A

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Significant advances have been achieved through the latest improvements in the photometric observations accomplished by the recent space missions, which substantially boost the study of pulsating stars via asteroseismology. The TESS mission has already proven to be of particular relevance for pulsating white dwarf and pre-white dwarf stars. We report a detailed asteroseismic analysis of the pulsating PG 1159 star NGC\,246 (TIC\,3905338), which is the central star of the planetary nebula NGC 246, based on high-precision photometric data gathered by the TESS space mission. We reduced TESS observations of NGC\,246 and performed a detailed asteroseismic analysis using fully evolutionary PG 1159 models computed accounting for the complete prior evolution of their progenitors. We constrained the mass of this star by comparing the measured mean period spacing with the average of the computed period spacings of the models, and we also employed the observed individual periods to search for a seismic stellar model. We extracted a total of $17$ periodicities from the TESS light curves from the two sectors where NGC\,246 was observed. All the oscillation frequencies are associated with $g$-mode pulsations, with periods spanning from $ 1460$ to $ 1823\ $s. We found a constant period spacing of $ 12.9\ $s, which allowed us to deduce that the stellar mass is higher than $ odot $ if the period spacing is assumed to be associated with $ 1$ modes, and that the stellar mass is $ odot $ if it is associated with $ 2$ modes. The less massive models are more consistent with the distance constraint from Gaia parallax. Although we were not able to find a unique asteroseismic model for this star, the period-to-period fit analyses suggest a high stellar mass ($ odot $) when the observed periods are associated with modes with $ 1$ only, and both a high and an intermediate stellar mass ($ odot $ and $ odot $, respectively) when the observed periods are associated with modes with a mixture of $

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Sliding along the Eddington Limit—Heavy-Weight Central Stars of Planetary Nebulae

Cited by 4 publications

References 17 publications

(Pre)-white dwarf stars as measuring tools for yields of AGB nucleosynthesis

(Pre)-white dwarf stars as measuring tools for yields of AGB nucleosynthesis

Spectral analysis of the hybrid PG 1159-type central stars of the planetary nebulae Abell 43 and NGC 7094

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS

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