| 1. |
- Güsten, R., et al.
(author)
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APEX - The Atacama Pathfinder Experiment
- 2006
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6267 I
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Conference paper (peer-reviewed)abstract
- APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.
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| 2. |
- Taussig, Michael J., et al.
(author)
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ProteomeBinders : planning a European resource of affinity reagents for analysis of the human proteome
- 2007
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In: Nature Methods. - : Springer Science and Business Media LLC. - 1548-7091 .- 1548-7105. ; 4:1, s. 13-17
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Journal article (peer-reviewed)abstract
- ProteomeBinders is a new European consortium aiming to establish a comprehensive resource of well-characterized affinity reagents, including but not limited to antibodies, for analysis of the human proteome. Given the huge diversity of the proteome, the scale of the project is potentially immense but nevertheless feasible in the context of a pan-European or even worldwide coordination.
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| 3. |
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| 4. |
- Perez, A. E. Garcia, et al.
(author)
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A new sample of extremely/ultra metal-poor stars
- 2008
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In: Physica Scripta. - 0031-8949 .- 1402-4896. ; T133, s. 014036-
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Journal article (peer-reviewed)abstract
- A sample of 30 very metal-poor stars from the Hamburg-European Southern Observatory (ESO) objective-prism survey have been observed at high spectral resolution at the Very Large Telescope (VLT) using the Ultraviolet and Visual Echelle Spectrograph (UVES). Two of the observed stars are very interesting not only because of their very low iron content, approximately four orders of magnitude lower than the solar value, but also because we detected the neutral lithium resonance line at 670.8 nm. Hydrogen lines suggest that the two observed stars have effective temperatures around 6000-6250K and according to isochrones, they are either on the main-sequence or on the subgiant branch, in which case they would probably be the most metal-poor dwarfs or warm subgiants with lithium detections known. These detections would allow to determine more accurately the slope of the trend of the lithium abundance with [Fe/H] than was possible with samples of unevolved stars restricted to higher metallicities.
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| 5. |
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| 6. |
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| 7. |
- Düringer, Caroline, et al.
(author)
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Agonist-specific patterns of beta(2)-adrenoceptor responses in human airway cells during prolonged exposure.
- 2009
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In: British Journal of Pharmacology. - : Wiley. - 1476-5381 .- 0007-1188. ; 158, s. 169-179
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Journal article (peer-reviewed)abstract
- Background and purpose: beta(2)-Adrenoceptor agonists (beta(2)-agonists) are important bronchodilators used in the treatment of asthma and chronic obstructive pulmonary disease. At the molecular level, beta(2)-adrenergic agonist stimulation induces desensitization of the beta(2)-adrenoceptor. In this study, we have examined the relationships between initial effect and subsequent reduction of responsiveness to restimulation for a panel of beta(2)-agonists in cellular and in vitro tissue models. Experimental approach: beta(2)-Adrenoceptor-induced responses and subsequent loss of receptor responsiveness were studied in primary human airway smooth muscle cells and bronchial epithelial cells by measuring cAMP production. Receptor responsiveness was compared at equi-effective concentrations, either after continuous incubation for 24 h or after a 1 h pulse exposure followed by a 23 h washout. Key findings were confirmed in guinea pig tracheal preparations in vitro. Key results: There were differences in the reduction of receptor responsiveness in human airway cells and in vitro guinea pig trachea by a panel of beta(2)-agonists. When restimulation occurred immediately after continuous incubation, loss of responsiveness correlated with initial effect for all agonists. After the 1 h pulse exposure, differences between agonists emerged, for example isoprenaline and formoterol induced the least reduction of responsiveness. High lipophilicity was, to some extent, predictive of loss of responsiveness, but other factors appeared to be involved in determining the relationships between effect and subsequent loss of responsiveness for individual agonists. Conclusions and implications: There were clear differences in the ability of different beta(2) agonists to induce loss of receptor responsiveness at equi-effective concentrations.
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| 8. |
- Gehren, Thomas, et al.
(author)
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Na, Mg and Al abundances as a population discriminant for nearby metal-poor stars
- 2006
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; :451, s. 1065-1079
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Journal article (pop. science, debate, etc.)abstract
- Aims. Parameters for 55 nearby metal-poor stars are determined using high-resolution spectroscopy. Together with similar data takenfrom a recent analysis, they are used to show trends of their Galactic evolution with stellar [Fe/H] or [Mg/H] abundances. Theseparation of abundance ratios between disk and halo stars is used as a basic criterion for population membership.Methods. After careful selection of a clean subsample free of suspected or known binaries and peculiar stars, abundances of Mg, Na and Al are based on NLTE kinetic equilibrium calculations applied to spectrum synthesis methods.Results. The relation between [Na/Mg] and [Fe/H] is a continuous enrichment through all three Galactic populations spanning a rangeof values between a metal-poor plateau at [Na/Mg] = −0.7 and solar values. [Al/Mg] displays a step-like difference between starsof the Galactic halo with [Al/Mg] ∼ −0.45 and the two disk populations with [Al/Mg] ∼ +0.10. [Al/Mg] ratios, together with the[Mg/Fe] ratios, asymmetric drift velocities V, and stellar evolutionary ages, make possible the individual discrimination between stars of the thick disk and the halo. At present, this evidence is limited by the small number of stars, and by the theoretical and empirical uncertainties of stellar age determinations, but it achieves a high significance.Conclusions. While the stellar sample is not complete with respect to space volume, the resulting abundances indicate the necessityto revise current models of chemical evolution to allow for an adequate production of Al in early stellar generations.
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| 9. |
- Hayek, W, et al.
(author)
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The Hamburg/ESO R-process enhanced star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312
- 2009
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 504:2, s. 511-524
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Journal article (peer-reviewed)abstract
- We report on a detailed abundance analysis of two strongly r-process enhanced, very metal-poor stars newly discovered in the HERES project, CS 29491-069 ([Fe/H] = -2.51, [r/Fe] = +1.1) and HE 1219-0312 ([Fe/H] = -2.96, [r/Fe] = +1.5). The analysis is based on high-quality VLT/UVES spectra and MARCS model atmospheres. We detect lines of 15 heavy elements in the spectrum of CS 29491-069, and 18 in HE 1219-0312; in both cases including the Th II 4019 angstrom line. The heavy-element abundance patterns of these two stars are mostly well-matched to scaled solar residual abundances not formed by the s-process. We also compare the observed pattern with recent high-entropy wind (HEW) calculations, which assume core-collapse supernovae of massive stars as the astrophysical environment for the r-process, and find good agreement for most lanthanides. The abundance ratios of the lighter elements strontium, yttrium, and zirconium, which are presumably not formed by the main r-process, are reproduced well by the model. Radioactive dating for CS 29491-069 with the observed thorium and rare-earth element abundance pairs results in an average age of 9.5 Gyr, when based on solar r-process residuals, and 17.6 Gyr, when using HEW model predictions. Chronometry seems to fail in the case of HE 1219-0312, resulting in a negative age due to its high thorium abundance. HE 1219-0312 could therefore exhibit an overabundance of the heaviest elements, which is sometimes called an "actinide boost".
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| 10. |
- Korn, A. J., et al.
(author)
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HE 1327-2326, AN UNEVOLVED STAR WITH [Fe/H] <-5.0. III. DOES ITS ATMOSPHERE REFLECT ITS NATAL COMPOSITION?
- 2009
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 698:1, s. 410-416
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Journal article (peer-reviewed)abstract
- Based on spectroscopic constraints derived from nonlocal thermodynamic equilibrium line formation, we explore the likely range of stellar parameters (T-eff and log g) for the hyper-metal-poor (HMP) star HE 1327-2326. Combining the constraints from Balmer line profiles and the Ca I/II ionization equilibrium, a subgiant stage of evolution is indicated. This result is further supported by spectrophotometric observations of the Balmer jump. If a higher T-eff value was used (as favored by some photometric calibrations), the spectroscopic analysis would indicate a turnoff-point stage of evolution. Using a stellar-structure code that treats the effects of atomic diffusion throughout the star in detail, we evolve a low-mass model star to reach the Hertzsprung-Russell-diagram position of HE 1327-2326 after roughly 13 Gyr. While the surface abundances are modified significantly (by more than 1 dex for the case of uninhibited diffusion), such corrections cannot resolve the discrepancy between the abundance inferred from the nondetection of the Li I resonance line at 6707 angstrom and the Wilkinson Microwave Anisotropy Probe based primordial lithium abundance. As there are numerous processes that can destroy lithium, any cosmological interpretation of a lower-than-expected lithium abundance at the lowest metallicities will have to await sample sizes of unevolved HMP stars that are 1 order of magnitude larger. The situation remains equally inconclusive concerning atomic-diffusion corrections. Here, attempts have to be made to better constrain internal mixing processes, both observationally and by means of sophisticated modeling. With constraints on additional mixing processes taken from a recent globular-cluster study, the likeliest scenario is that HE 1327-2326's surface abundances have undergone mild depletion (of order 0.2 dex).
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| 11. |
- Korn, Andreas J., et al.
(author)
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New Abundances for Old Stars – Atomic Diffusion at Work in NGC 6397
- 2006
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In: The Messenger. - 0722-6691. ; 125, s. 6-10
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Research review (pop. science, debate, etc.)abstract
- A homogeneous spectroscopic analysis of unevolved and evolved stars in the metal-poor globular cluster NGC 6397 with FLAMES-UVES reveals systematic trends of stellar surface abundances that are likely caused by atomic diffu-sion. This finding helps to understand, among other issues, why the lithium abundances of old halo stars are sig-nificantly lower than the abundance found to be produced shortly after the Big Bang.
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| 12. |
- Korn, Andreas J., et al.
(author)
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The sensitivity of Lick indices to abundance variations
- 2005
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 438, s. 685-704
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Journal article (pop. science, debate, etc.)abstract
- We present results of model atmosphere/line formation calculations which quantitatively test how the 21 classical and four higher-order Balmer-line Lick/IDS indices (Worthey et al. 1994, ApJS, 94, 687; Worthey & Ottaviani 1997, ApJS, 111, 377) depend on individual elemental abundances (of carbon, nitrogen, oxygen, magnesium, iron, calcium, sodium, silicon, chromium, titanium) and overall metallicity in various stellar evolutionary stages and at various metallicities. At low metallicities the effects of an overall enhancement of α-elements are also investigated. The general results obtained by Tripicco & Bell (1995, ApJ, 110, 3035) at solar metallicity are confirmed, while details do differ. Tables are given detailing to which element every index reacts significantly, as a function of evolutionary stage and composition.This work validates a number of assumptions implicitly made in the stellar population models of Thomas et al. (2003a, MNRAS, 339, 897), which utilized the results of Tripicco & Bell (1995) to include the effects of element abundance ratios variations. In particular, these computations confirm that fractional changes to index strengths computed at solar metallicity (and solar age) can be applied over a wide range of abundances and ages, also to model old stellar populations with non-solar abundance ratios. The use of metallicity-dependent response functions not only leads to a higher degree of self-consistency in the stellar population models, but is even required for the proper modelling of the Balmer-line indices. We find that the latter become increasingly sensitive to element abundances with increasing metallicity and decreasing wavelength. While Hβ still responds only moderately to abundance ratio variations, the higher-order Balmer-line indices Hγ and Hδ display very strong dependencies at high metallicities. As shown in Thomas et al. (2004, MNRAS, 351, L19), this result allows to remove systematic effects in age determinations based on different Balmer-line indices.
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| 13. |
- Lind, K., et al.
(author)
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Atomic diffusion and mixing in old stars II. Observations of stars in the globular cluster NGC 6397 with VLT/FLAMES-GIRAFFE
- 2008
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 490:2, s. 777-U82
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Journal article (peer-reviewed)abstract
- Context. Evolutionary trends in the surface abundances of heavier elements have recently been identified in the globular cluster NGC 6397 ([Fe/H] = -2), indicating the operation of atomic diffusion in these stars. Such trends constitute important constraints for the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. Aims. We perform an independent check of the reality and size of abundance variations within this metal-poor globular cluster. Methods. Observational data covering a large stellar sample, located between the cluster turn-off point and the base of the red giant branch, are homogeneously analysed. The spectroscopic data were obtained with the medium-high resolution spectrograph FLAMES/GIRAFFE on VLT-UT2 (R similar to 27 000). We derive independent effective-temperature scales from profile fitting of Balmer lines and by applying colour-T-eff calibrations to Stromgren uvby and broad-band BVI photometry. An automated spectral analysis code is used together with a grid of MARCS model atmospheres to derive stellar surface abundances of Mg, Ca, Ti, and Fe. Results. We identify systematically higher iron abundances for more evolved stars. The turn-off point stars are found to have 0.13 dex lower surface abundances of iron compared to the coolest, most evolved stars in our sample. There is a strong indication of a similar trend in magnesium, whereas calcium and titanium abundances are more homogeneous. Within reasonable error limits, the obtained abundance trends are in agreement with the predictions of stellar structure models
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| 14. |
- Norris, John E., et al.
(author)
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HE 0557-4840 : Ultra-metal-poor and carbon-rich
- 2007
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 670:1, s. 774-788
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Journal article (peer-reviewed)abstract
- We report the discovery and high-resolution, high-S/N spectroscopic analysis of the ultra-metal-poor red giant HE 0557-4840, which is the third most heavy-element-deficient star currently known. Its atmospheric parameters are Teff=4900 K, logg=2.2, and [Fe/H]=-4.75. This brings the number of stars with [Fe/H]<-4.0 to three, and the discovery of HE 0557-4840 suggests that the metallicity distribution function of the Galactic halo does not have a ``gap'' between [Fe/H]=-4.0, where several stars are known, and the two most metal-poor stars, at [Fe/H]~-5.3. HE 0557-4840 is carbon rich ([C/Fe]=+1.6), a property shared by all three objects with [Fe/H]<-4.0, suggesting that the well-known increase of carbon relative to iron with decreasing [Fe/H] reaches its logical conclusion (ubiquitous carbon richness) at lowest abundance. We also present abundances (nine) and limits (nine) for a further 18 elements. For species having well-measured abundances or strong upper limits, HE 0557-4840 is ``normal'' in comparison with the bulk of the stellar population at [Fe/H]~-4.0, with the possible exception of Co. We discuss the implications of these results for chemical enrichment at the earliest times, in the context of single- (``mixing and fallback'') and two-component enrichment models. While neither offers a clear solution, the latter appears closer to the mark. Further data are required to determine the oxygen abundance and improve that of Co, and hence more strongly constrain the origin of this object. Based on observations collected at ANU's 2.3 m telescope on Siding Spring Mountain, Australia, and European Southern Observatory, Paranal, Chile (proposal 276.D-5041).
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