The shape of gold

Having a detailed theoretical knowledge of the low-energy structure of the heavy odd-mass nucleus $^{197}$Au is of prime interest as the structure of this isotope represents an important input to theoretical simulations of collider experiments involving gold ions performed worldwide at relativistic energies. In the present article, therefore, we report on new results on the structure of $^{197}$Au obtained from state-of-the-art multi-reference energy density functional (MR-EDF) calculations. Our MR-EDF calculations were realized using the Skyrme-type pseudo-potential SLyMR1, and include beyond mean-field correlations through the mixing, in the spirit of the Generator Coordinate Method (GCM), of particle-number and angular-momentum projected triaxially deformed Bogoliubov quasi-particle states. Comparison with experimental data shows that the model gives a reasonable description of $^{197}$Au with in particular a good agreement for most of the spectroscopic properties of the $3/2_1^+$ ground state. From the collective wave function of the correlated state, we compute an average deformation $\bar{\beta}(3/2_1^+)=0.13$ and $\bar{\gamma}(3/2_1^+)=40^\circ$ for the ground state. We use this result to construct an intrinsic shape of $^{197}$Au representing a microscopically-motivated input for precision simulations of the associated collider processes. We discuss, in particular, how the triaxiality of this nucleus is expected to impact $^{197}$Au+$^{197}$Au collision experiments at ultrarelativistic energy.Comment: 16 pages, 6 figure

Structure of 128,129,130^{128,129,130}Xe through multi-reference energy density functional calculations

Recently, values for the Kumar quadrupole deformation parameters of the nucleus $^{130}$Xe have been computed from the results of a Coulomb excitation experiment, indicating that this xenon isotope has a prominent triaxial ground state. Within a different context, it was recently argued that the analysis of particle correlations in the final states of ultra-relativistic heavy-ion collisions performed at the Large Hadron Collider (LHC) points to a similar structure for the adjacent isotope, $^{129}$Xe. In the present work, we report on state-of-the-art multi-reference energy density functional calculations that combine projection on proton and neutron number as well as angular momentum with shape mixing for the three isotopes $^{128,129,130}$Xe using the Skyrme-type pseudo-potential SLyMR1. Exploring the triaxial degree of freedom, we demonstrate that the ground states of all three isotopes display a very pronounced triaxial structure. Moreover, comparison with experimental results shows that the calculations reproduce fairly well the low-energy excitation spectrum of the two even-mass isotopes. By contrast, the calculation of $^{129}$Xe reveals some deficiencies of the effective interaction.Comment: 26 pages, 17 figure

Risk of acute myocardial infarction with NSAIDs in real world use : bayesian meta-analysis of individual patient data

OBJECTIVE To characterise the determinants, time course, and risks of acute myocardial infarction associated with use of oral non-steroidal anti-inflammatory drugs (NSAIDs). DESIGN Systematic review followed by a one stage bayesian individual patient data meta-analysis. DATA SOURCES Studies from Canadian and European healthcare databases. REVIEW METHODS Eligible studies were sourced from computerised drug prescription or medical databases, conducted in the general or an elderly population, documented acute myocardial infarction as specific outcome, studied selective cyclo-oxygenase-2 inhibitors (including rofecoxib) and traditional NSAIDs, compared risk of acute myocardial infarction in NSAID users with non-users, allowed for time dependent analyses, and minimised effects of confounding and misclassification bias. EXPOSURE AND OUTCOMES Drug exposure was modelled as an indicator variable incorporating the specific NSAID, its recency, duration of use, and dose. The outcome measures were the summary adjusted odds ratios of first acute myocardial infarction after study entry for each category of NSAID use at index date (date of acute myocardial infarction for cases, matched date for controls) versus non-use in the preceding year and the posterior probability of acute myocardial infarction. RESULTS A cohort of 446 763 individuals including 61 460 with acute myocardial infarction was acquired. Taking any dose of NSAIDs for one week, one month, or more than a month was associated with an increased risk of myocardial infarction. With use for one to seven days the probability of increased myocardial infarction risk (posterior probability of odds ratio >1.0) was 92% for celecoxib, 97% for ibuprofen, and 99% for diclofenac, naproxen, and rofecoxib. The corresponding odds ratios (95% credible intervals) were 1.24 (0.91 to 1.82) for celecoxib, 1.48 (1.00 to 2.26) for ibuprofen, 1.50 (1.06 to 2.04) for diclofenac, 1.53 (1.07 to 2.33) for naproxen, and 1.58 (1.07 to 2.17) for rofecoxib. Greater risk of myocardial infarction was documented for higher dose of NSAIDs. With use for longer than one month, risks did not appear to exceed those associated with shorter durations. CONCLUSIONS All NSAIDs, including naproxen, were found to be associated with an increased risk of acute myocardial infarction. Risk of myocardial infarction with celecoxib was comparable to that of traditional NSAIDS and was lower than for rofecoxib. Risk was greatest during the first month of NSAID use and with higher doses.Peer reviewe

Massive star formation and feedback in W49A: The source of our Galaxy's most luminous water maser outflow

We present high spatial resolution mid-IR images of the ring of UCHII regions in W49A obtained at Gemini North, allowing us to identify the driving source of its powerful H2O maser outflow. These data also confirm our previous report that several radio sources in the ring are undetected in the mid-IR because they are embedded deep inside the cloud core. We locate the source of the water maser outflow at the position of the compact mid-IR peak of source G (source G:IRS1). This IR source is not coincident with any identified compact radio continuum source, but is coincident with a hot molecular core, so we propose that G:IRS1 is a hot core driving an outflow analogous to the wide-angle bipolar outflow in OMC-1. G:IRS1 is at the origin of a larger bipolar cavity and CO outflow. The water maser outflow is orthogonal to the bipolar CO cavity, so the masers probably reside near its waist in the cavity walls. Models of the IR emission require a massive protostar of 45Msun, 3e5Lsun, and an effective envelope accretion rate of 1e-3Msun/yr. Feedback from the central star could potentially drive the H2O maser outflow, but it has insufficient radiative momentum to have driven the large-scale CO outflow, requiring that this massive star had an active accretion disk over the past 10^4 yr. Combined with the spatialy resolved morphology in IR images, G:IRS1 in W49 provides compelling evidence for a massive protostar that formed by accreting from a disk, accompanied by a bipolar outflow.Comment: 14 pages, MNRAS accepte

Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy

We review the present observational knowledge on the spatial distribution and the physical state of the different (molecular, atomic and ionized) components of the interstellar gas in the innermost 3 kpc of our Galaxy -- a region which we refer to as the interstellar Galactic bulge, to distinguish it from its stellar counterpart. We try to interpret the observations in the framework of recent dynamical models of interstellar gas flows in the gravitational potential of a barred galaxy. Finally, relying on both the relevant observations and their theoretical interpretation, we propose a model for the space-averaged density of each component of the interstellar gas in the interstellar Galactic bulge.Comment: 19 pages, 11 figure

The Effect of Spiral Arms on Star Formation in the Galaxy

We have examined the ratio between the integrated luminosity of massive young stellar objects detected by the Red MSX Source (RMS) survey and the mass of molecular clouds in the Galactic Ring Survey region, as a function of Galactocentric radius. The results indicate that 60--80% of the observed increases in the star-formation rate density associated with spiral-arm features are due to source crowding within the arms. Of the remainder, most of the increase in the inner Sagittarius arm is due to an enhancement in the simple star-formation efficiency, i.e. in the number of RMS sources per unit molecular gas mass. In the inner Perseus arm, the residual increase is due to a higher than average mean source luminosity, which implies a top-heavy IMF, and this is entirely due to the presence, in the GRS region, of the W49 star-forming complex, which appears to be exceptional in its nature. The results also suggest that there is little or no increase in the star-formation efficiency on kiloparsec scales in the Scutum tangent region which includes W43. We discuss the possible role played by the spiral arms in influencing the star-formation efficiency and conclude that the most likely mechanisms are related to orbit crowding within the arms.Comment: 7 pages, 7 figures, accepted by MNRA

Spitzer Space Telescope observations of the Carina Nebula: The steady march of feedback-driven star formation

We report the first results of imaging the Carina Nebula with Spitzer/IRAC, providing a catalog of point sources and YSOs based on SED fits. We discuss several aspects of the extended emission, including dust pillars that result when a clumpy molecular cloud is shredded by massive star feedback. There are few "extended green objects" (EGOs) normally taken as signposts of outflow activity, and none of the HH jets detected optically are seen as EGOs. A population of "extended red objects" tends to be found around OB stars, some with clear bow-shocks. These are dusty shocks where stellar winds collide with flows off nearby clouds. Finally, the relative distributions of O stars and subclusters of YSOs as compared to dust pillars shows that while some YSOs are located within pillars, many more stars and YSOs reside just outside pillar heads. We suggest that pillars are transient phenomena, part of a continuous outwardly propagating wave of star formation driven by massive star feedback. As pillars are destroyed, they leave newly formed stars in their wake, which are then subsumed into the young OB association. Altogether, the current generation of YSOs shows no strong deviation from a normal IMF. The number of YSOs suggests a roughly constant star-formation rate over the past 3Myr, implying that star formation in pillars constitutes an important mechanism to construct unbound OB associations. Accelerated pillars may give birth to O-type stars that, after several Myr, could appear to have formed in isolation.Comment: 25 pages, 15 figures, MNRAS accepte

W49A: A starburst triggered by expanding shells

W49A is a giant molecular cloud which harbors some of the most luminous embedded clusters in the Galaxy. However, the explanation for this starburst-like phenomenon is still under debate. Methods. We investigated large-scale Spitzer mid-infrared images together with a Galatic Ring Survey 13CO J = 1-0 image, complemented with higher resolution (~ 11 arcsec) 13CO J = 2-1 and C18O J = 2-1 images over a ~ 15 x 13 pc^2 field obtained with the IRAM 30m telescope. Two expanding shells have been identified in the mid-infrared images, and confirmed in the position-velocity diagrams made from the 13CO J = 2-1 and C18O J = 2-1 data. The mass of the averaged expanding shell, which has an inner radius of ~ 3.3 pc and a thickness of ~ 0.41 pc, is about 1.9 x 10^4 M*. The total kinetic energy of the expanding shells is estimated to be ~ 10^49 erg which is probably provided by a few massive stars, whose radiation pressure and/or strong stellar winds drive the shells. The expanding shells are likely to have a common origin close to the two ultracompact Hii regions (source O and source N), and their expansion speed is estimated to be ~ 5 km/s, resulting in an age of ~ 3-7 x 10^5 years. In addition, on larger (~ 35 x 50 pc^2) scales, remnants of two gas ejections have been identified in the 13CO J = 1 - 0 data. Both ejections seem to have the same center as the expanding shells with a total energy of a few times 10^50 erg. The main driving mechanism for the gas ejections is unclear, but likely related to the mechanism which triggers the starburst in W49A

The Physical Properties of High-Mass Star-Forming Clumps: A Systematic Comparison of Molecular Tracers

We present observations of HCO+ and H^13CO+, N2H+, HCS+, HCN and HN^13C, SO and ^34SO, CCH, SO_2, and CH_3OH-E towards a sample of 27 high-mass clumps coincident with water maser emission. All transitions are observed with or convolved to nearly identical resolution (30"), allowing for inter-comparison of the clump properties derived from the mapped transitions. We find N2H+ emission is spatially differentiated compared to the dust and the other molecules towards a few very luminous cores (10 of 27) and the N2H+ integrated intensity does not correlate well with dust continuum flux. We calculate the effective excitation density, n_eff, the density required to excite a 1 K line in T_kin=20 K gas for each molecular tracer. The intensity of molecular tracers with larger effective excitation densities (n_eff > 10^5 cm^-3) appear to correlate more strongly with the submillimeter dust continuum intensity. The median sizes of the clumps are anti-correlated with the n_eff of the tracers (which span more than three orders of magnitude). Virial mass is not correlated with n_eff, especially where the lines are optically thick as the linewidths may be broadened significantly by non-virial motions. The median mass surface density and median volume density of the clumps is correlated with n_eff indicating the importance of understanding the excitation conditions of the molecular tracer when deriving the average properties of an ensemble of cores.Comment: 75 pages, 38 figure

Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES

We present results of deep echelle spectrophotometry of the brightest knot of the HH202 in the Orion Nebula --HH202-S-- using the ultraviolet Visual Echelle Spectrograph (UVES). The high spectral resolution has permitted to separate the component associated with the ambient gas from that associated with the gas flow. We derive electron densities and temperatures for both components, as well as the chemical abundances of several ions and elements from collisionally excited lines, including the first determinations of Ca^{+} and Cr^{+} abundances in the Orion Nebula. We also calculate the He^{+}, C^{2+}, O^{+} and O^{2+} abundances from recombination lines. The difference between the O^{2+} abundances determined from collisionally excited and recombination lines --the so-called abundance discrepancy factor-- is 0.35 dex and 0.11 dex for the shock and nebular components, respectively. Assuming that the abundance discrepancy is produced by spatial variations in the electron temperature, we derive values of the temperature fluctuation parameter, t^2, of 0.050 and 0.016, for the shock and nebular components, respectively. Interestingly, we obtain almost coincident t^2 values for both components from the analysis of the intensity ratios of He I lines. We find significant departures from case B predictions in the Balmer and Paschen flux ratios of lines of high principal quantum number n. We analyze the ionization structure of HH202-S, finding enough evidence to conclude that the flow of HH202-S has compressed the ambient gas inside the nebula trapping the ionization front. We measure a strong increase of the total abundances of nickel and iron in the shock component, the abundance pattern and the results of photoionization models for both components are consistent with the partial destruction of dust after the passage of the shock wave in HH202-S.Comment: 23 pages, 7 figures. Accepted for publication in MNRA