Abundances in bulge stars from high-resolution, near-IR spectra I. The CNO elements observed during the science verification of CRIRES at VLT

The formation and evolution of the Milky Way bulge is not yet well understood and its classification is ambiguous. Constraints can, however, be obtained by studying the abundances of key elements in bulge stars. The aim of this study is to determine the chemical evolution of CNO, and a few other elements in stars in the Galactic bulge, and to discuss the sensitivities of the derived abundances from molecular lines. High-resolution, near-IR spectra in the H band were recorded using VLT/CRIRES. Due to the high and variable visual extinction in the line-of-sight towards the bulge, an analysis in the near-IR is preferred. The CNO abundances can all be determined simultaneously from the numerous molecular lines in the wavelength range observed. The three giant stars in Baade's window presented here are the first bulge stars observed with CRIRES. We have especially determined the CNO abundances, with uncertainties of less than 0.20 dex, from CO, CN, and OH lines. Since the systematic uncertainties in the derived CNO abundances due to uncertainties in the stellar fundamental parameters, notably Teff, are significant, a detailed discussion of the sensitivities of the derived abundances is included. We find good agreement between near-IR and optically determined O, Ti, Fe, and Si abundances. Two of our stars show a solar [C+N/Fe], suggesting that these giants have experienced the first dredge-up and that the oxygen abundance should reflect the original abundance of the giants. The two giants fit into the picture, in which there is no significant difference between the O abundance in bulge and thick-disk stars. Our determination of the S abundances is the first for bulge stars. The high [S/Fe] values for all the stars indicate a high star-formation rate in an early phase of the bulge evolution.Comment: Accepted by A&

Particle transfer and fusion cross-section for Super-heavy nuclei in dinuclear system

Within the dinuclear system (DNS) conception, instead of solving Fokker-Planck Equation (FPE) analytically, the Master equation is solved numerically to calculate the fusion probability of super-heavy nuclei, so that the harmonic oscillator approximation to the potential energy of the DNS is avoided. The relative motion concerning the energy, the angular momentum, and the fragment deformation relaxations is explicitly treated to couple with the diffusion process, so that the nucleon transition probabilities, which are derived microscopically, are time-dependent. Comparing with the analytical solution of FPE, our results preserve more dynamical effects. The calculated evaporation residue cross sections for one-neutron emission channel of Pb-based reactions are basically in agreement with the known experimental data within one order of magnitude.Comment: 19 pages, plus 6 figures, submitted to Phys. Rev.

A combined computational and experimental investigation of the [2Fe–2S] cluster in biotin synthase

Biotin synthase was the first example of what is now regarded as a distinctive enzyme class within the radical S-adenosylmethionine superfamily, the members of which use Fe/S clusters as the sulphur source in radical sulphur insertion reactions. The crystal structure showed that this enzyme contains a [2Fe–2S] cluster with a highly unusual arginine ligand, besides three normal cysteine ligands. However, the crystal structure is at such a low resolution that neither the exact coordination mode nor the role of this exceptional ligand has been elucidated yet, although it has been shown that it is not essential for enzyme activity. We have used quantum refinement of the crystal structure and combined quantum mechanical and molecular mechanical calculations to explore possible coordination modes and their influences on cluster properties. The investigations show that the protonation state of the arginine ligand has little influence on cluster geometry, so even a positively charged guanidinium moiety would be in close proximity to the iron atom. Nevertheless, the crystallised enzyme most probably contains a deprotonated (neutral) arginine coordinating via the NH group. Furthermore, the Fe···Fe distance seems to be independent of the coordination mode and is in perfect agreement with distances in other structurally characterised [2Fe–2S] clusters. The exceptionally large Fe···Fe distance found in the crystal structure could not be reproduced

GRB Simulations in GLAST

The Gamma-ray Large Area Space Telescope (GLAST), scheduled to be launched in fall of 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT) is a pair conversion telescope built with a high precision silicon tracker, a segmented CsI electromagnetic calorimeter and a plastic anticoincidence shield. The LAT will survey the sky in the energy range between 20 MeV to more than 300 GeV, shedding light on many issues left open by its highly successful predecessor EGRET. LAT will observe Gamma-Ray Bursts (GRB) in an energy range never explored before; to tie these frontier observations to the better-known properties at lower energies, a second instrument, the GLAST Burst Monitor (GBM) will provide important spectra and timing in the 10 keV to 30 MeV range. We briefly present the instruments onboard the GLAST satellite, their synergy in the GRB observations and the work done so far by the collaboration in simulation, analysis, and GRB sensitivity estimation

Light from the Cosmic Frontier: Gamma-Ray Bursts

Gamma-Ray Bursts (GRBs) are the most powerful cosmic explosions since the Big Bang, and thus act as signposts throughout the distant Universe. Over the last 2 decades, these ultra-luminous cosmological explosions have been transformed from a mere curiosity to essential tools for the study of high-redshift stars and galaxies, early structure formation and the evolution of chemical elements. In the future, GRBs will likely provide a powerful probe of the epoch of reionisation of the Universe, constrain the properties of the first generation of stars, and play an important role in the revolution of multi-messenger astronomy by associating neutrinos or gravitational wave (GW) signals with GRBs. Here, we describe the next steps needed to advance the GRB field, as well as the potential of GRBs for studying the Early Universe and their role in the up-coming multi-messenger revolution.Comment: White paper submitted to ESA as a contribution to the deliberations on the science themes for the L2 and L3 mission opportunitie

Circumstellar water vapour in M-type AGB stars: Constraints from H2O(1_10 - 1_01) lines obtained with Odin

Aims: Spectrally resolved circumstellar H2O(1_10 - 1_01) lines have been obtained towards three M-type AGB stars using the Odin satellite. This provides additional strong constrains on the properties of circumstellar H2O and the circumstellar envelope. Methods: ISO and Odin satellite H2O line data are used as constraints for radiative transfer models. Special consideration is taken to the spectrally resolved Odin line profiles, and the effect of excitation to the first excited vibrational states of the stretching modes (nu1=1 and nu3=1) on the derived abundances is estimated. A non-local, radiative transfer code based on the ALI formalism is used. Results: The H2O abundance estimates are in agreement with previous estimates. The inclusion of the Odin data sets stronger constraints on the size of the H2O envelope. The H2O(1_10 - 1_01) line profiles require a significant reduction in expansion velocity compared to the terminal gas expansion velocity determined in models of CO radio line emission, indicating that the H2O emission lines probe a region where the wind is still being accelerated. Including the nu3=1 state significantly lowers the estimated abundances for the low-mass-loss-rate objects. This shows the importance of detailed modelling, in particular the details of the infrared spectrum in the range 3 to 6 micron, to estimate accurate circumstellar H2O abundances. Conclusions: Spectrally resolved circumstellar H2O emission lines are important probes of the physics and chemistry in the inner regions of circumstellar envelopes around asymptotic giant branch stars. Predictions for H2O emission lines in the spectral range of the upcoming Herschel/HIFI mission indicate that these observations will be very important in this context.Comment: accepted in A&A, 10 pages, 8 figure

MARCS model atmospheres

In this review presented at the Symposium A stellar journey in Uppsala, June 2008, I give my account of the historical development of the MARCS code from the first version published in 1975 and its premises to the 2008 grid. It is shown that the primary driver for the development team is the science that can be done with the models, and that they constantly strive to include the best possible physical data. A few preliminary comparisons of M star model spectra to spectrophotometric observations are presented. Particular results related to opacity effects are discussed. The size of errors in the spectral energy distribution (SED) and model thermal stratification are estimated for different densities of the wavelength sampling. The number of points used in the MARCS 2008 grid (108000) is large enough to ensure errors of only a few K in all models of the grid, except the optically very thin layers of metal-poor stars. Errors in SEDs may reach about 10% locally in the UV. The published sampled SEDs are thus appropriate to compute synthetic broad-band photometry, but higher resolution spectra will be computed in the near future and published as well on the MARCS site (marcs.astro.uu.se). Test model calculations with TiO line opacity accounted for in scattering show an important cooling of the upper atmospheric layers of red giants. Rough estimates of radiative and collisional time scales for electronic transitions of TiO indicate that scattering may well be the dominant mechanism in these lines. However models constructed with this hypothesis are incompatible with optical observations of TiO (Arcturus) or IR observations of OH (Betelgeuse), although they may succeed in explaining H2O line observations. More work is needed in that direction.Comment: Review talk at the conference "A stellar journey" held in Uppsala, June 2008. In press in Physica Scripta, eds. Paul Barklem, Andreas Korn, and Bertrand Ple

Reorganization Energy for Internal Electron Transfer in Multicopper Oxidases.

We have calculated the reorganization energy for the intramolecular electron transfer between the reduced type 1 copper site and the peroxy intermediate of the trinuclear cluster in the multicopper oxidase CueO. The calculations are performed at the combined quantum mechanics and molecular mechanics (QM/MM) level, based on molecular dynamics simulations with tailored potentials for the two copper sites. We obtain a reorganization energy of 91-133 kJ/mol, depending on the theoretical treatment. The two Cu sites contribute by 12 and 22 kJ/mol to this energy, whereas the solvent contribution is 34 kJ/mol. The rest comes from the protein, involving small contributions from many residues. We have also estimated the energy difference between the two electron-transfer states and show that the reduction of the peroxy intermediate is exergonic by 43-87 kJ/mol, depending on the theoretical method. Both the solvent and the protein contribute to this energy difference, especially charged residues close to the two Cu sites. We compare these estimates with energies obtained from QM/MM optimizations and QM calculations in a vacuum and discuss differences between the results obtained at various levels of theory