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Metal abundances of CSPNe are not well known although they provide important constraints on AGB nucleosynthesis. We aim to determine metal abundances of two hot, hydrogen-rich CSPNe (namely of A35 and NGC3587, the latter also known as M97 or the Owl Nebula) and to derive Teff and log g precisely from high-resolution, high-S/N (far-) ultraviolet observations obtained with FUSE and HST/STIS. For this purpose, we utilize NLTE model atmospheres calculated with TMAP, the Tübingen Model Atmosphere Package. Due to strong line absorption of the ISM, simultaneous modeling of interstellar features has become a standard tool in our analyses. We present preliminary results, demonstrating the importance of combining stellar and interstellar models, in order to clearly identify and measure the strengths of strategic photospheric lines. [ABSTRACT FROM AUTHOR]

We present results of model-atmosphere analyses of soft X-ray spectra of three hot WDs. These are the relatively iron-rich DA GD246, the surprisingly metal-poor DA LB1919, and the H-deficient PG1159-type star PG1520+525. The two DAs are modeled with chemically stratified and with homogeneous NLTE models in order to constrain metal abundances. FUSE and HST spectra are also employed. For the PG1159 star the effective temperature can be constrained to a precision that is not attained with optical and UV spectroscopy alone. [ABSTRACT FROM AUTHOR]

In support of the final archive of the Far Ultraviolet Spectroscopic Explorer, we have reprocessed the entire FUSE data set using CalFUSE v3.2, the latest version of the FUSE data-reduction software. Recent improvements to CalFUSE include effective-area and background files for the final two years of the mission; software modifications that increase the exposure time included in some observation-level data products; and new data products that facilitate the analysis of FUSE airglow observations. CalFUSE users will benefit from modifications that allow the pipeline to be compiled on additional Fortran compilers (f77, f90, g77, gfortran) and operating systems (Solaris 10, Linux, Mac OS X), including machines with 64-bit architectures. Finally, we have conducted an assessment of the archival data quality, including analyses of the remaining systematic errors in the effective-area and wavelength calibrations. [ABSTRACT FROM AUTHOR]

One of the most puzzling phenomena observed at the surface of sdB stars is their abundance anomalies. For instance, high-resolution optical spectroscopy shows that the C abundance is lower than the solar abundance by about a factor of ten on average. A few stars, however, show a solar abundance or an abundance higher than solar. Although optical spectroscopy allows the measurement of relatively high C abundance, it fails to provide stringent upper limits when no C lines are detected. The Far Ultraviolet Spectroscopic Explorer (FUSE) comes to the rescue when no C lines are detected in the optical, because it is 1,000 times more sensitive than the VLT for the purpose of measuring very small amounts of C in the atmospheres of sdB stars. We measure the C abundance in the FUSE spectra of 30 stars. We confirm the C abundance trend reported in previous studies, but report the disappearance of C in five stars. The upper limits that we measure for these stars are about four orders of magnitude lower than the solar abundance. The observation of very low C abundance suggests that the normal equilibrium between gravitation and radiative levitation has been disrupted, perhaps by a weak stellar wind. [ABSTRACT FROM AUTHOR]

LB 3459 is an eclipsing, close, post common-envelope binary consisting of a sdOB-type post-EHB primary star (M1 = 0.45M⊙) and a low-mass M dwarf secondary star (M2 = 0.076M⊙). A NLTE spectral analysis of FUSE observations has shown that the rotation of the primary is bound with 35±10 km/sec. Phosphorus and sulfur are newly identified in the FUSE observations. The abundances are solar and 0.01 times solar, respectively. [ABSTRACT FROM AUTHOR]

Spectral analyses of H-deficient post-AGB stars have shown that a small group of four extremely hot objects exists which have almost pure He absorption-line spectra in the optical. These are classified as O(He) stars. For their origin there are two scenarios: They could be the long-sought hot successors of RCrB stars, which have not been identified up to now. If this turns out to be true, then a third post-AGB evolutionary sequence is revealed, which is probably the result of a double-degenerate merging process. An alternative explanation might be that O(He) stars are post early-AGB stars. These depart from the AGB just before they experience their first thermal pulse (TP) which will then occur as a late thermal pulse (LTP). This would be a link to the low-mass He-enriched sdO stars and low-mass, particularly He-rich PG 1159 stars. We present results of a spectral analysis of FUSE observations of the O(He) stars by means of NLTE model-atmosphere techniques and summarize our present picture of their evolutionary scenario. [ABSTRACT FROM AUTHOR]

State-of-the-art non-LTE spectral analysis requires high-resolution and high-S/N observations of strategic metal lines in order to achieve reliable photospheric parameters like, e.g., effective temperature, surface gravity, and element abundances. Hot stars with effective temperatures higher than about 40 000 K exhibit their metal-line spectrum arising from highly ionized species predominantly in the (far) ultraviolet wavelength range. FUSE observations of hot, compact stars provided the necessary data. With these, it has been, e.g., possible to identify fluorine for the first time in observations of post-AGB stars. The evaluation of ionization equilibria of highly ionized neon, phosphorus, sulfur, and argon provides a new sensitive tool to determine effective temperatures of the hottest stars precisely. Moreover, abundance determinations have put constraints on stellar evolutionary models which, in turn, have improved greatly our picture of post-AGB evolution. [ABSTRACT FROM AUTHOR]

With the end of FUSE operations at Johns Hopkins, the long time FUSE project web presence is being transferred to an expanded archival web site hosted at the Multi-mission Archive at Space Telescope (MAST). MAST and FUSE project personnel are working together to permanently preserve the historical, technical, and scientifically important FUSE information within MAST, as well as provide access to the nearly 6,000 FUSE observations which have been fully reprocessed with CalFUSE 3.2. The MAST/FUSE web site will serve archival users, technical users, educators and the general public. The official web site transition from JHU to MAST occurred in January 2009. The MAST/FUSE web page can be accessed at the URL http://archive.stsci.edu/fuse. [ABSTRACT FROM AUTHOR]

With its unprecedented sensitivity and spectral resolution, FUSE has been a source of important data that have helped us further our knowledge and understanding of white dwarf stars. In order to illustrate the crucial contribution of FUSE to the study of white dwarfs, we present an abundance analysis of Si based on FUSE observations of 83 hydrogen-rich (DA) white dwarfs. Studying the Si abundances in the atmospheres of white dwarfs is important for understanding the mechanisms that counteract the downward diffusion of elements heavier than hydrogen. The FUSE observations show that Si is present in about 25% of white dwarfs. The Si abundances show a large scatter that is difficult to interpret in terms of a strict equilibrium between the gravitation and the radiative levitation. [ABSTRACT FROM AUTHOR]