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Abundances of disk and bulge giants from high-resolution optical spectra
摘要： An error occurred during the production process. The subtitle of the article in the published version was "II. O, Mg, Co, and Ti in the bulge sample". Here, we correct this to "II. O, Mg, Ca, and Ti in the bulge sample".
关键词： Galaxy: evolution,Galaxy: bulge,errata, addenda,stars: abundances
更新于2025-09-19 17:15:36
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Stellar laboratories
摘要： Context. To analyze spectra of hot stars, advanced non-local thermodynamic equilibrium (NLTE) model-atmosphere techniques are mandatory. Reliable atomic data is crucial for the calculation of such model atmospheres. Aims. We aim to calculate new Sr iv–vii oscillator strengths to identify for the ?rst time Sr spectral lines in hot white dwarf (WD) stars and to determine the photospheric Sr abundances. To measure the abundances of Se, Te, and I in hot WDs, we aim to compute new Se v, Te vi, and I vi oscillator strengths. Methods. To consider radiative and collisional bound-bound transitions of Se v, Sr iv - vii, Te vi, and I vi in our NLTE atmosphere models, we calculated oscillator strengths for these ions. Results. We newly identi?ed four Se v, 23 Sr v, 1 Te vi, and three I vi lines in the ultraviolet (UV) spectrum of RE 0503?289. We measured a photospheric Sr abundance of 6.5+3.8 ?2.4 × 10?4 (mass fraction, 9500–23 800 times solar). We determined the abundances of Se (1.6+0.9 ?0.9 × 10?4, 11 000–28 000), and I (1.4+0.8 ?0.6 × 10?3, 8000–20 000), Te (2.5+1.5 ?0.5 × 10?5, 2700–6700). No Se, Sr, Te, and I line was found in the UV spectra of G191?B2B and we could determine only upper abundance limits of approximately 100 times solar. Conclusions. All identi?ed Se v, Sr v, Te vi, and I vi lines in the UV spectrum of RE 0503?289 were simultaneously well reproduced with our newly calculated oscillator strengths.
关键词： virtual observatory tools,atomic data,stars: abundances,line: identification,stars: individual: G191-B2B,stars: individual: RE 0503-289
更新于2025-09-04 15:30:14
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A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars
摘要： Aims. Hot subdwarf stars represent a poorly understood late phase of stellar evolution. While binary evolution plays an important role for the formation of B-type subdwarfs (sdB), the origin of the helium dominated subclass of O-type subdwarfs (He-sdO) is still unknown. We search for chemical signatures of their genesis by means of quantitative spectral analyses of high-quality visual and ultraviolet spectra. Methods. Four prototypical He-sdO stars, one belonging to the nitrogen-rich and three to the C-rich subclass, were selected for which archival far-ultraviolet spectra from the FUSE satellite as well as high-resolution visual and UVA spectra taken with the ESO-UVES/FEROS spectrographs are available. Using Tlusty200/Synspec49 to compute line blanketed- non-local thermodynamic equilibrium (NLTE) model atmospheres and synthetic spectra, atmospheric parameters and the abundances patterns have been derived. The ?nal models included H, He, C, N, O, Ne, Mg, Al, Si, P, S, Fe, and Ni represented by the most detailed model atoms available. Because of the enrichment of either nitrogen or carbon, it turned out, that models including these elements at the appropriate high abundance provide su?ciently accurate approximations to the temperature strati?cation of full models. Results. No indications for binarity were found, neither radial velocity variations nor photometric evidence for the presence of a companion could be detected. All stars have helium-dominated atmospheres almost free of hydrogen and temperatures between 42 000 K and 47 000 K while their surface gravities lie between log g = 5.4 and 5.7. The abundance pattern of CD–31?4800 displays the signatures of CNO burning, while heavier elements are subsolar by about 0.4 dex, except for Ne and Si which are close to solar. The abundance patterns of the C-rich He-sdOs are more complex. A slightly subsolar metallicity is accompanied by N-enrichment and O-de?ciency, less pronounced than in CD–31?4800. Neon is mildly to strongly enriched, up to a factor of ten with respect to the sun in LS IV +10? 9. The nickel-to-iron ratio is signi?cantly super-solar. Using spectral energy distributions and Gaia parallaxes the masses of the stars were determined. They are found to scatter around the canonical mass for the core helium ?ash, although the uncertainties are large. Conclusions. The abundance pattern observed for CD–31?4800 is consistent with predictions of models for slow (cold) mergers of pairs of equal mass helium WDs except for the low oxygen abundance observed. Models for composite mergers were considered for the C-rich stars, but predict abundance pattern dissimilar to those determined. [CW83] 0904?02, though, may be a candidate for a composite He-WD merger, as it rotates and appears to be more massive than the other program stars. New evolutionary models for the hot ?asher scenario predict abundance patterns similar to those determined for the C-rich stars. Hence, C-rich He-sdO may well result from late He ?ashes with deep-mixing episodes.
关键词： stars: evolution,subdwarfs,stars: atmospheres,stars: abundances
更新于2025-09-04 15:30:14
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A VLT/FORS2 spectroscopic survey of individual stars in a transforming dwarf galaxy
摘要： Understanding the properties of dwarf galaxies is important not only to put them in their proper cosmological context, but also to understand the formation and evolution of the most common type of galaxies. Dwarf galaxies are divided into two main classes, dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs), which differ from each other mainly because the former are gas-rich objects currently forming stars, while the latter are gas-deficient with no on-going star formation. Transition types (dT) are thought to represent dIs in the process of losing their gas, and can therefore shed light into the possible process of dwarf irregulars (dIrrs) becoming gas-deficient, passively evolving galaxies. Here we present preliminary results from our wide-area VLT/FORS2 MXU spectroscopic survey of the Phoenix dT, from which we obtained line-of-sight velocities and metallicities from the nIR Ca II triplet lines for a large sample of individual Red Giant Branch stars.
关键词： techniques: spectroscopic,stars: abundances,galaxies: evolution,galaxies: dwarf,Local Group
更新于2025-09-04 15:30:14