35 research outputs found
Spectroscopic study of the elusive globular cluster ESO452-SC11 and its surroundings
Globular clusters (GCs) are amongst the oldest objects in the Galaxy and play
a pivotal role in deciphering its early history. We present the first
spectroscopic study of the GC ESO452-SC11 using the AAOmega spectrograph at
medium resolution. Given the sparsity of this object and high degree of
foreground contamination due to its location toward the bulge, few details are
known for this cluster: there is no consensus of its age, metallicity, or its
association with the disk or bulge. We identify 5 members based on radial
velocity, metallicity, and position within the GC. Using spectral synthesis,
accurate abundances of Fe and several -, Fe-peak, neutron-capture
elements (Si,Ca,Ti,Cr,Co,Ni,Sr,Eu) were measured. Two of the 5 cluster
candidates are likely non-members, as they have deviant Fe abundances and
[/Fe] ratios. The mean radial velocity is 192 km s with a
low dispersion of 2.83.4 km s, in line with its low mass. The mean
Fe-abundance from spectral fitting is , with a spread driven by
observational errors. The -elements of the GC candidates are marginally
lower than expected for the bulge at similar metallicities. As spectra of
hundreds of stars were collected in a 2 degree field around ESO452-SC11,
detailed abundances in the surrounding field were measured. Most non-members
have higher [/Fe] ratios, typical of the nearby bulge population. Stars
with measured Fe-peak abundances show a large scatter around Solar values,
though with large uncertainties. Our study provides the first systematic
measurement of Sr in a Galactic bulge GC. The Eu and Sr abundances of the GC
candidates are consistent with a disk or bulge association. Our calculations
place ESO452 on an elliptical orbit in the central 3 kpc of the bulge. We find
no evidence of extratidal stars in our data. (Abridged)Comment: 10 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Understanding the astrophysical origin of silver, palladium and other neutron-capture elements
A high-precision abundance analysis of the nuclear benchmark star HD 20
We present our chemical abundance investigation of the metal-poor
([Fe/H]=-1.60 dex), r-process-enriched ([Eu/Fe]=0.73 dex) halo star HD 20 using
novel and archival high-resolution spectra at outstanding signal-to-noise
ratios. By combining one of the first asteroseismic gravity measurements in the
metal-poor regime from a TESS light curve with non-LTE analyses of iron lines,
we derive a set of highly accurate and precise stellar parameters. These allow
us to delineate a chemical pattern comprised of solid detections of 48
elements, including 28 neutron-capture elements, which establishes HD 20 among
the few benchmark stars that have almost complete patterns with low systematic
dependencies on the stellar parameters. Our light-element (Z<30) abundances are
representative of other, similarly metal-poor stars in the Galactic halo with
contributions from core-collapse supernovae of type II. A comparison to the
scaled solar r-pattern shows that the lighter neutron-capture elements
(37<Z<60) are poorly matched. In particular, we find imprints of the weak
r-process acting at low metallicities. Nonetheless, by comparing our detailed
abundances to the observed metal-poor star BD +17 3248, we find a persistent
residual pattern that is indicative of enrichment contributions from the
s-process. We show that mixing with material from predicted yields of massive,
rotating AGB stars at low metallicity considerably improves the fit. Based on a
solar ratio of heavy- to light-s elements -- at odds with model predictions for
the i-process -- and a missing clear residual pattern with respect to other
stars with claimed contributions from this process, we refute (strong)
contributions from such astrophysical sites providing intermediate neutron
densities. Finally, nuclear cosmochronology is used to tie our detection of the
radioactive element Th to an age estimate for HD 20 of Gyr.
[abridged]Comment: 23 pages (+10 pages appendix), 27 figures, 8 tables, revised version
resubmitted to A&
The Gaia-ESO survey: 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing at the origin of chemical abundance variations
Atomic diffusion and mixing processes in stellar interiors influence the
structure and the surface composition of stars. Some of these processes cannot
yet be modelled from the first principles. This limits their applicability in
stellar models used for studies of stellar populations and Galactic evolution.
Our main goal is to put constrains on the stellar structure and evolution
models using new refined measurements of chemical composition in stars of
Galactic open cluster. We use medium-resolution, 19 200 <= R <= 21 500, optical
spectra of the stars in the open cluster NGC 2420 obtained within the Gaia-ESO
survey. The sample covers all evolutionary stages from the main-sequence to red
giant branch. Stellar parameters are derived using a combined Bayesian analysis
of spectra, 2MASS photometry, and astrometric data from Gaia DR2. The
abundances of Mg, Ca, Fe, and Li are determined from non-local thermodynamic
equilibrium (NLTE) synthetic spectra, computed using one-dimensional (1D) and
averaged three-dimensional (3D) model atmospheres. We compare our results with
a grid of Code d'Evolution Stellaire Adaptatif et Modulaire (CESTAM) stellar
evolution models, which include atomic diffusion, turbulent and rotational
mixing. We find prominent evolutionary trends in the abundances of Fe, Ca, Mg,
and Li with the mass of the stars in the cluster. Fe, Mg, and Ca show a
depletion at the cluster turn-off, but the abundances gradually increase and
flatten near the base of the RGB. The abundance trend for Li displays a
signature of rotational mixing on the main-sequence and abrupt depletion on the
subgiant branch, which is caused by advection of Li-poor material to the
surface. The analysis of abundances combined with the CESTAM model predictions
allows us to place limits on the parameter space of the models and to constrain
the zone in the stellar interior where turbulent mixing takes place.Comment: accepted for publication in A&
Effects of the peripherally acting μ-opioid receptor antagonist methylnaltrexone on acute pancreatitis severity:study protocol for a multicentre double-blind randomised placebo-controlled interventional trial, the PAMORA-AP trial
BACKGROUND: Moderate to severe acute pancreatitis (AP) is associated with a high rate of complications and increased mortality, yet no targeted pharmacologic treatment currently exists. As pain is a dominant symptom in AP, patients are exposed to excess levels of both endo- and exogenous opioids, which may have harmful effects on the course of AP. This trial investigates the effects of the peripherally acting μ-opioid receptor antagonist (PAMORA) methylnaltrexone on disease severity and clinical outcomes in patients with moderate to severe AP. METHODS: PAMORA-AP is a multicentre, investigator-initiated, double-blind, randomised, placebo-controlled, interventional trial, which will be conducted at four referral centres for acute pancreatitis in Denmark. Ninety patients with early-onset AP (pain onset within 48 h) as well as predicted moderate to severe disease (two or more systemic inflammatory response syndrome criteria upon admission) will be prospectively included. Subsequently, participants will be randomised (1:1) to intravenous treatment with either methylnaltrexone or matching placebo (Ringer’s lactate) during 5 days of admission. The primary endpoint will be the group difference in disease severity as defined and measured by the Pancreatitis Activity Scoring System (PASS) score 48 h after randomisation. Secondary endpoints include daily PASS scores; disease severity according to the Atlanta classification; quantification of need for analgesics, nutritional support, intravenous fluid resuscitation and antibiotics; duration of hospital admissions, readmission rates and mortality. Pain intensity and gut function will be self-reported using validated questionnaires. Exploratory endpoints include circulating levels of pro-and anti-inflammatory markers, polyethylene glycol recovery from the urine, circulating levels of blood markers of intestinal permeability, the prevalence of pancreatic complications on computed tomography (CT) scans, and colon transit time assessed using a CT-based radiopaque marker method. DISCUSSION: This trial aims to evaluate the PAMORA methylnaltrexone as a novel targeted pharmacotherapy in patients with moderate to severe AP with the potential benefit of improved patient outcomes. TRIAL REGISTRATION: ClinicalTrials.govNCT04743570. Registered on 28 January 2021. EudraCT 2020-002313-18
The discovery space of ELT-ANDES. Stars and stellar populations
The ArmazoNes high Dispersion Echelle Spectrograph (ANDES) is the optical and
near-infrared high-resolution echelle spectrograph envisioned for the European
Extremely Large Telescope (ELT). We present a selection of science cases,
supported by new calculations and simulations, where ANDES could enable major
advances in the fields of stars and stellar populations. We focus on three key
areas, including the physics of stellar atmospheres, structure, and evolution;
stars of the Milky Way, Local Group, and beyond; and the star-planet
connection. The key features of ANDES are its wide wavelength coverage at high
spectral resolution and its access to the large collecting area of the ELT.
These features position ANDES to address the most compelling and potentially
transformative science questions in stellar astrophysics of the decades ahead,
including questions which cannot be anticipated today.Comment: 46 pages, 8 figures; submitted to Experimental Astronomy on behalf of
the ANDES Science Tea
A low-gluten diet induces changes in the intestinal microbiome of healthy Danish adults
\ua9 2018, The Author(s). Adherence to a low-gluten diet has become increasingly common in parts of the general population. However, the effects of reducing gluten-rich food items including wheat, barley and rye cereals in healthy adults are unclear. Here, we undertook a randomised, controlled, cross-over trial involving 60 middle-aged Danish adults without known disorders with two 8-week interventions comparing a low-gluten diet (2 g gluten per day) and a high-gluten diet (18 g gluten per day), separated by a washout period of at least six weeks with habitual diet (12 g gluten per day). We find that, in comparison with a high-gluten diet, a low-gluten diet induces moderate changes in the intestinal microbiome, reduces fasting and postprandial hydrogen exhalation, and leads to improvements in self-reported bloating. These observations suggest that most of the effects of a low-gluten diet in non-coeliac adults may be driven by qualitative changes in dietary fibres
CUBES : the Cassegrain U-band Efficient Spectrograph
In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (> 40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R >20, 000 (with a lower-resolution, sky-limited mode of R ~7, 000). With the design focusing on maximizing the instrument throughput (ensuring a Signal to Noise Ratio (SNR) ~20 per high-resolution element at 313 nm for U ~18.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the detailed design and construction phase. First science operations are planned for 2028