TY  - GEN
A1  - Todt, Helge Tobias
A1  - Peña, Miriam
A1  - Zühlke, Julia
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Gräfener, Götz
T1  - Weak emission line central stars of planetary nebulae
T2  - Planetary Nebulae: an Eye to the Future
N2  - To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 462 
KW  - stars: AGB and post-AGB
KW  - stars: Wolf-Rayet
KW  - stars: abundances
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413775
ER  - 
TY  - GEN
A1  - Sandin, Christer
A1  - Steffen, Matthias
A1  - Jacob, Ralf
A1  - Schönberner, Detlef
A1  - Rühling, Ute
A1  - Hamann, Wolf-Rainer
A1  - Todt, Helge Tobias
T1  - The role of heat conduction to the formation of [WC]-type planetary nebulae
T2  - Proceedings of the International Astronomical Union
N2  - X-ray observations of young Planetary Nebulæ (PNe) have revealed diffuse emission in extended regions around both H-rich and  H-deficient central stars. In order to also repro-duce physical properties of H-deficient objects, we have, at first, extended our time-dependent radiation-hydrodynamic models with heat conduction for such conditions. Here we present some of the important physical concepts, which determine how and when a hot wind-blown bubble forms. In this study we have had to consider the, largely unknown, evolution of the CSPN, the slow (AGB) wind, the fast hot-CSPN wind, and the chemical composition. The main conclusion of our work is that heat conduction is needed to explain X-ray properties of wind-blown bubbles also in H-deficient objects.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 582 
KW  - conduction
KW  - hydrodynamics
KW  - planetary nebulae: general
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413702
SN  - 1866-8372
IS  - 582
SP  - 494
EP  - 495
ER  - 
TY  - GEN
A1  - Guerrero, Martín A.
A1  - Chu, You-Hua
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
A1  - Schönberner, Detlef
A1  - Todt, Helge Tobias
A1  - Steffen, Matthias
A1  - Ruiz, Nieves
A1  - Gruendl, Robert A.
A1  - Blair, William P.
T1  - Ablation and wind mass-loading in the born-again planetary nebula A 30
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - We present XMM-Newton and Chandra observations of the born-again planetary nebula A 30. These X-ray observations reveal a bright unresolved source at the position of the central star whose X-ray luminosity exceeds by far the model expectations for photospheric emission and for shocks within the stellar wind. We suggest that a “born-again hot bubble” may be responsible for this X-ray emission. Diffuse X-ray emission associated with the petal-like features and one of the H-poor knots seen in the optical is also found. The weakened emission of carbon lines in the spectrum of the diffuse emission can be interpreted as the dilution of stellar wind by mass-loading or as the detection of material ejected during a very late thermal pulse.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 563 
KW  - planetary nebulae: individual (A 30)
KW  - X-rays: ISM
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-412341
SN  - 1866-8372
IS  - 563
ER  -