scholarly journals (F)UV spectral analysis of 15 extremely hot, hydrogen-rich central stars of planetary nebulae

2011 ◽  
Vol 7 (S283) ◽  
pp. 211-214
Author(s):  
Marc Ziegler ◽  
Thomas Rauch ◽  
Klaus Werner ◽  
Jeffrey W. Kruk
Keyword(s):  
Spectral Analysis ◽  
Planetary Nebulae ◽  
Type A ◽  
Spectral Analyses ◽  
Wide Range ◽  
Line Absorption ◽  
Central Stars

AbstractWe present results of a (F)UV spectral analysis of 15 hot, hydrogen-rich central stars of planetary nebulae (CSPNe) of DAO-type (A 7, A 31, A 35, A 39, NGC 3587, NGC 6720, NGC 6853, NGC 7293, PuWe 1, Sh 2-174) and O(H)-type (A 36, Lo 1, LSS 1362, NGC 1360, NGC 4361). The sample covers a wide range of parameters (Teff ≈ 70–130 kK, log g = 5.4–7.4). It represents different stages of post-AGB evolution. The derived stellar parameters are crucial constraints for AGB nucleosynthesis and stellar evolutionary calculations. Detailed spectral analyses using fully line-blanketed NLTE model atmospheres including 23 elements from hydrogen to nickel are performed. Additional modeling of the ISM line absorption enables to unambigiously identify nearly all observed lines and to improve both, the photospheric as well as the ISM model.

scholarly journals De-Centered Central Stars of Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 541-542 ◽  
Author(s):  
Aubrie McLean ◽  
Martín A. Guerrero ◽  
Robert A. Gruendl ◽  
You-Hua Chu
Keyword(s):  
Binary System ◽  
Mass Loss ◽  
Planetary Nebulae ◽  
Central Star ◽  
Large Sample ◽  
Preliminary Results ◽  
Wide Range ◽  
Central Stars

The origin of the wide range of morphologies observed in planetary nebulae (PNe) is not well established. The influence of a binary companion of the central star can naturally explain this variety of morphologies, but very few PNe have known binary central stars. The evolution of the binary system with mass loss may result in the displacement of the central star from the nebular center. The large sample of PNe observed by HST is being used to search for de-centered central stars. Preliminary results indicate that the occurrence of de-centered central stars is widespread among all morphological types of PNe.

scholarly journals NLTE analysis of central stars of highly excited Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 132-132
Author(s):  
T. Rauch ◽  
J. Köppen ◽  
R. Napiwotzki ◽  
K. Werner
Keyword(s):  
White Dwarfs ◽  
State Of The Art ◽  
Planetary Nebulae ◽  
Evolutionary Status ◽  
Agb Stars ◽  
Spectral Analyses ◽  
Central Stars

Very hot central stars (CSPN) of highly excited planetary nebulae (PN) display directly the formation of white dwarfs. Only a few of these CSPN have been analyzed so far due to their low brightness and thus, the interpretation of their evolutionary status is hampered by statistical incompleteness. In the last decade many spectral analyses of very hot post-AGB stars by means of state-of-the-art NLTE model atmospheres have been performed (e.g. Rauch et al. 1996; Werner & Rauch 1994; Rauch & Werner 1995) and our picture of post-AGB evolution has been improved.

scholarly journals Spectral analysis of the O(He)-type central stars of the planetary nebulae K 1-27 and LoTr 4

2011 ◽  
Vol 7 (S283) ◽  
pp. 482-483
Author(s):  
Nicole Reindl ◽  
Ellen Ringat ◽  
Thomas Rauch ◽  
Klaus Werner ◽  
Jeffrey. W. Kruk
Keyword(s):  
Spectral Analysis ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Evolutionary Sequence ◽  
Preliminary Results ◽  
Pure Helium ◽  
R Coronae Borealis Stars ◽  
Central Stars

AbstractThe four known O(He) stars are the only amongst the hottest post-AGB stars whose atmospheres are composed of almost pure helium. Thus, their evolution deviates from the hydrogen-deficient post-AGB evolutionary sequence of carbon-dominated stars like e.g. PG 1159 stars. The origin of the O(He) stars is still not explained. They might be either post-early AGB stars or the progeny of R Coronae Borealis stars. We present preliminary results of a non-LTE spectral analysis based on FUSE and HST/COS observations.

scholarly journals The H. R.-diagram of central stars of planetary nebulae

1984 ◽  
Vol 105 ◽  
pp. 209-212
Author(s):  
D. Schönberner
Keyword(s):  
Spectral Region ◽  
Planetary Nebulae ◽  
Temperature Sensitive ◽  
Spectral Analyses ◽  
Central Stars ◽  
Made In

During the last years some progress has been made in the determination of temperatures of central stars of planetary nebulae (CPN). The main reasons are the successful deployment of space crafts which made the more temperature sensitive spectral region in the UV accessible, and the application of NLTE-spectral analyses (e.g. Mendez et al., 1981). Therefore, a re-examination of the H.R.-diagram of CPN's seems to be in order.

(F)UV Spectral Analysis of Hot, Hydrogen-Rich Central Stars of Planetary Nebulae

2010 ◽  
Author(s):  
M. Ziegler ◽  
T. Rauch ◽  
K. Werner ◽  
J. W. Kruk ◽  
Klaus Werner ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Planetary Nebulae ◽  
Central Stars

scholarly journals Quantitative spectral analyses of CSPNs of early [WC]-type

1997 ◽  
Vol 180 ◽  
pp. 114-115
Author(s):  
L. Koesterke ◽  
W.-R Hamann
Keyword(s):  
Computer Technology ◽  
Planetary Nebulae ◽  
Magellanic Clouds ◽  
Spectral Analyses ◽  
Physical Conditions ◽  
The Galaxy ◽  
Central Stars ◽  
Solution Techniques

Among the Central Stars of Planetary Nebulae (CSPN) there are several stars which show Wolf-Rayet-type spectra resembling those of Pop. I Wolf-Rayet (WR) stars of the carbon sequence (WC). Due to progress in computer technology and new solution techniques it became possible ten years ago to calculate models which account for the very complex physical conditions in Wolf-Rayet atmospheres (Hillier 1989, Hamann et al. 1992). These models have been successfully applied to the vast majority of Pop. IWR stars in the Galaxy and the Magellanic Clouds (Hamann et al. 1995) and, in the last three years, to an increasing sample of CSPNs of [WC] type (Koesterke & Hamann 1996, Leuenhagen & Hamann 1996, Leuenhagen this meeting). Here we present the analyses of ten CSPNs of early [WC] type, i.e. from [WC 2] to [WC 4].

scholarly journals Analysis of hydrogen rich PG 1159 central stars of Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 103-103 ◽  
Author(s):  
S. Dreizler ◽  
K. Werner ◽  
U. Heber
Keyword(s):  
Detection Limit ◽  
Mass Loss ◽  
Small Group ◽  
Qualitative Agreement ◽  
Planetary Nebulae ◽  
Time Dependent ◽  
Spectral Analyses ◽  
Abundance Pattern ◽  
Incomplete Removal ◽  
Central Stars

The PG 1159 stars represent the hottest stage of post-AGB evolution. Quantitative spectral analyses of most known PG 1159 stars have been carried out by us from optical, UV and EUV observations (see Dreizler et al 1995 for a review). It has been shown that these stars have atmospheres dominated by C and He with a significant admixture of O. These abundances reveal the inter–shell matter of a former AGB star. The four stars, HS 2324+3944, NGC 7094, Abell 43, and Sh 2-68, define a small group of peculiar PG 1159 stars (termed hybrid PG 1159). Unlike all other PG 1159 stars hydrogen is detected in their spectra. Three of them are CSPNe. Our Non-LTE analyses (Dreizler et al 1995; Dreizler et al 1996) show that these stars have typical PG 1159 Teff, log g as well as C and He abundances (Table 1). In contrast, the O abundance is lower than in PG 1159 stars. N is probably present but near the detection limit of the currently available spectra. Hybrid PG 1159 stars tend to have lower masses/luminosities than ordinary PG 1159 stars. A reduced mass-loss in their post-AGB evolution might be responsible for the incomplete removal of the H rich envelope. However, peeling of a post-AGB star alone can not produce the observed abundance pattern. In addition, mixing is required. A first evolution calculation with time dependent mixing of Iben & MacDonald (1995) shows some qualitative agreement in the abundance pattern like the C/He ratio it is, however, not able to explain the overall abundances.

scholarly journals Spectral analysis of mid-IR excesses of central stars of planetary nebulae

2011 ◽  
Vol 7 (S283) ◽  
pp. 310-311
Author(s):  
Jana Bilikova ◽  
You-Hua Chu ◽  
Kate Y.L. Su ◽  
Robert Gruendl
Keyword(s):  
Spectral Analysis ◽  
White Dwarfs ◽  
Planetary Nebulae ◽  
Circumstellar Dust ◽  
Spectroscopic Observations ◽  
Central Stars

AbstractIn our Spitzer 24 μm survey of hot white dwarfs (WDs) we found 9 WDs with IR excesses, 7 of them are still central stars of planetary nebulae (CSPNs). We have thus carried out a Spitzer archival survey of CSPNs, and found additional objects with IR excesses. To date, a total of 13 CSPNs show IR excesses from Spitzer observations. These mid-IR excesses are indicative of the presence of circumstellar dust, which could be produced by collisions or disruption of sub-planetary objects. To further assess the nature of these IR excesses, we have obtained Spitzer IRS, Gemini NIRI and Michelle, and KPNO 4m echelle spectra of these objects. In this poster, we summarize the spectroscopic observations and discuss the nature of these IR excesses.

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

2019 ◽  
Vol 489 (1) ◽  
pp. 1054-1071 ◽  
Author(s):  
L Löbling ◽  
T Rauch ◽  
M M Miller Bertolami ◽  
H Todt ◽  
F Friederich ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Stellar Evolution ◽  
Surface Composition ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Thermodynamical Equilibrium ◽  
Non Local ◽  
Rich Material ◽  
Stellar Masses ◽  
Central Stars

Abstract 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 $\mathrm{H}\approx \, 20$ per cent by mass (AFTP), ≈ 1 per cent (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 so-called 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 $\mbox{$T_\mathrm{eff}$}\, = 115\, 000\pm 5\, 000 \, \mathrm{K}$ and determine surface gravities of $\log\,(g\,/\,(\mathrm{cm}\,\mathrm{s}^{-2} )) = 5.6\pm 0.1$ 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 an 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 time-scales expected from the AFTP scenario and alternatives should be explored.

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