744 research outputs found
The Gaia-ESO Survey: Tracing interstellar extinction
Large spectroscopic surveys have enabled in the recent years the computation
of three-dimensional interstellar extinction maps thanks to accurate stellar
atmospheric parameters and line-of-sight distances. Such maps are complementary
to 3D maps extracted from photometry, allowing a more thorough study of the
dust properties. Our goal is to use the high-resolution spectroscopic survey
Gaia-ESO in order to obtain with a good distance resolution the interstellar
extinction and its dependency as a function of the environment and the
Galactocentric position. We use the stellar atmospheric parameters of more than
5000 stars, obtained from the Gaia-ESO survey second internal data release, and
combine them with optical (SDSS) and near-infrared (VISTA) photometry as well
as different sets of theoretical stellar isochrones, in order to calculate
line-of-sight extinction and distances. The extinction coefficients are then
compared with the literature to discuss their dependancy on the stellar
parameters and position in the Galaxy. Within the errors of our method, our
work does not show that there is any dependence of the interstellar extinction
coefficient on the atmospheric parameters of the stars. We do not find any
evidence of the variation of E(J-H)/E(J-K) with the angle from the Galactic
centre nor with Galactocentric distance. This suggests that we are dealing with
a uniform extinction law in the SDSS ugriz bands and the near-IR JHKs bands.
Therefore, extinction maps using mean colour-excesses and assuming a constant
extinction coefficient can be used without introducing any systematic errors.Comment: 13 pages, 14 figures, 1 Appendix accepted for publication in
Astronomy&Astrophysic
Is hospital based MMR vaccination for children with egg allergy here to stay?
Egg allergy is incorrectly considered to constitute a contraindication to MMR in the community, despite a long history of its safe administration to egg allergic children. The product insert perpetuates this misinformation but the Irish guidelines from the RCPI are unequivocal. We reviewed all paediatric cases vaccinated in our hospital in 2007-2008. Forty seven of 91 children receiving vaccinations in hospital, had been referred for MMR due to concerns regarding egg allergy. In 32% (n=15), GP referral for vaccination was made despite correspondence from the clinic advising routine vaccination in the community. Nineteen were second MMR immunisations, which should all have occurred in the community. Unnecessary hospital referral for MMR vaccination is an extra burden on hospital resources, and causes unwarranted anxiety amongst parents of children with egg allergy. A change in practice seems difficult to achieve, as many referrals happen despite individualised correspondence to GPs and other referring clinicians outlining the current guidelines
The Gaia-ESO Survey: Separating disk chemical substructures with cluster models
(Abridged) Recent spectroscopic surveys have begun to explore the Galactic
disk system outside the solar neighborhood on the basis of large data samples.
In this way, they provide valuable information for testing spatial and temporal
variations of disk structure kinematics and chemical evolution. We used a
Gaussian mixture model algorithm, as a rigurous mathematical approach, to
separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample from the
Gaia-ESO survey internal data release 2. We find that the sample is separated
into five groups associated with major Galactic components; the metal-rich end
of the halo, the thick disk, and three subgroups for the thin disk sequence.
This is confirmed with a sample of red clump stars from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) survey. The two
metal-intermediate and metal-rich groups of the thin disk decomposition
([Fe/H]>-0.25 dex) highlight a change in the slope at solar metallicity. This
holds true at different radial regions. The distribution of Galactocentric
radial distances of the metal-poor part of the thin disk ([Fe/H]<-0.25 dex) is
shifted to larger distances than those of the more metal-rich parts. Moreover,
the metal-poor part of the thin disk presents indications of a scale height
intermediate between those of the thick and the rest of the thin disk, and it
displays higher azimuthal velocities than the latter. These stars might have
formed and evolved in parallel and/or dissociated from the inside-out formation
taking place in the internal thin disk. Their enhancement levels might be due
to their origin from gas pre-enriched by outflows from the thick disk or the
inner halo. The smooth trends of their properties (their spatial distribution
with respect to the plane, in particular) with [Fe/H] and [Mg/Fe] suggested by
the data indicates a quiet dynamical evolution, with no relevant merger events
The Gaia-ESO Survey: N-body modelling of the Gamma Velorum cluster
The Gaia-ESO Survey has recently unveiled the complex kinematic signature of
the Gamma Velorum cluster: this cluster is composed of two kinematically
distinct populations (hereafter, population A and B), showing two different
velocity dispersions and a relative ~2 km s^-1 radial velocity (RV) shift. In
this paper, we propose that the two populations of the Gamma Velorum cluster
originate from two different sub-clusters, born from the same parent molecular
cloud. We investigate this possibility by means of direct-summation N-body
simulations. Our scenario is able to reproduce not only the RV shift and the
different velocity dispersions, but also the different centroid (~0.5 pc), the
different spatial concentration and the different line-of-sight distance (~5
pc) of the two populations. The observed 1-2 Myr age difference between the two
populations is also naturally explained by our scenario, in which the two
sub-clusters formed in two slightly different star formation episodes. Our
simulations suggest that population B is strongly supervirial, while population
A is close to virial equilibrium. We discuss the implications of our models for
the formation of young star clusters and OB associations in the Milky Way.Comment: 12 pages, 7 figures, 2 tables, Astronomy and Astrophysics, in pres
The Gaia-ESO Survey: the selection function of the Milky Way field stars
The Gaia-ESO Survey was designed to target all major Galactic components
(i.e., bulge, thin and thick discs, halo and clusters), with the goal of
constraining the chemical and dynamical evolution of the Milky Way. This paper
presents the methodology and considerations that drive the selection of the
targeted, allocated and successfully observed Milky Way field stars. The
detailed understanding of the survey construction, specifically the influence
of target selection criteria on observed Milky Way field stars is required in
order to analyse and interpret the survey data correctly. We present the target
selection process for the Milky Way field stars observed with VLT/FLAMES and
provide the weights that characterise the survey target selection. The weights
can be used to account for the selection effects in the Gaia-ESO Survey data
for scientific studies. We provide a couple of simple examples to highlight the
necessity of including such information in studies of the stellar populations
in the Milky Way.Comment: 18 pages, 19 figures, Accepted for publication in MNRAS (April 25,
2016
The Gaia-ESO Survey: Detailed Abundances in the Metal-poor Globular Cluster NGC 4372
We present the abundance analysis for a sample of 7 red giant branch stars in
the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part
of the Gaia-ESO Survey. This is the first extensive study of this cluster from
high resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca,
Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19
0.03 and find no evidence for a metallicity spread. This metallicity
makes NGC 4372 one of the most metal-poor galactic globular clusters. We also
find an {\alpha}-enhancement typical of halo globular clusters at this
metallicity. Significant spreads are observed in the abundances of light
elements. In particular we find a Na-O anti-correlation. Abundances of O are
relatively high compared with other globular clusters. This could indicate that
NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al
spread is also present which spans a range of more than 0.5 dex in Al
abundances. Na is correlated with Al and Mg abundances at a lower significance
level. This pattern suggests that the Mg-Al burning cycle is active. This
behavior can also be seen in giant stars of other massive, metal-poor clusters.
A relation between light and heavy s-process elements has been identified.Comment: 14 pages, 14 figures, accepted for publication in A&
The Gaia-ESO Survey: the chemical structure of the Galactic discs from the first internal data release
Most high-resolution spectroscopic studies of the Galactic discs were mostly
confined to objects in the solar vicinity. Here we aim at enlarging the volume
in which individual chemical abundances are used to characterise both discs,
using the first internal data release of the Gaia-ESO survey. We derive and
discuss the abundances of eight elements (Mg, Al, Si, Ca, Ti, Fe, Cr, Ni, and
Y). The trends of these elemental abundances with iron are very similar to
those in the solar neighbourhood. We find a natural division between alpha-rich
and alpha-poor stars, best seen in the bimodality of the [Mg/M] distributions
in bins of metallicity, which we attribute to thick- and thin-disc sequences,
respectively. With the possible exception of Al, the observed dispersion around
the trends is well described by the expected errors, leaving little room for
astrophysical dispersion. Using previously derived distances from Recio-Blanco
et al. (2014b), we further find that the thick-disc is more extended vertically
and is more centrally concentrated towards the inner Galaxy than the thin-disc,
which indicates a shorter scale-length. We derive the radial and vertical
gradients in metallicity, iron, four alpha-element abundances, and Al for the
two populations, taking into account the identified correlation between R_GC
and |Z|. Radial metallicity gradient is found in the thin disc. The positive
radial individual [alpha/M] gradients found are at variance from the gradients
observed in the RAVE survey. The thin disc also hosts a negative vertical
metallicity gradient, accompanied by positive individual [alpha/M] and [Al/M]
gradients. The thick-disc, presents no radial metallicity gradient, a shallower
vertical metallicity gradient than the thin-disc, an alpha-elements-to-iron
radial gradient in the opposite sense than that of the thin disc, and positive
vertical individual [alpha/M] and [Al/M] gradients.Comment: 24 pages, 10 figure
The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc
According to our current cosmological model, galaxies like the Milky Way are
expected to experience many mergers over their lifetimes. The most massive of
the merging galaxies will be dragged towards the disc-plane, depositing stars
and dark matter into an accreted disc structure. In this work, we utilize the
chemo-dynamical template developed in Ruchti et al. to hunt for accreted stars.
We apply the template to a sample of 4,675 stars in the third internal data
release from the Gaia-ESO Spectroscopic Survey. We find a significant component
of accreted halo stars, but find no evidence of an accreted disc component.
This suggests that the Milky Way has had a rather quiescent merger history
since its disc formed some 8-10 billion years ago and therefore possesses no
significant dark matter disc.Comment: 15 pages, 11 figures, accepted for publication in MNRA
The Gaia-ESO Survey: the most metal-poor stars in the Galactic bulge
We present the first results of the EMBLA survey (Extremely Metal-poor BuLge
stars with AAOmega), aimed at finding metal-poor stars in the Milky Way bulge,
where the oldest stars should now preferentially reside. EMBLA utilises
SkyMapper photometry to pre-select metal-poor candidates, which are
subsequently confirmed using AAOmega spectroscopy. We describe the discovery
and analysis of four bulge giants with -2.72<=[Fe/H]<=-2.48, the lowest
metallicity bulge stars studied with high-resolution spectroscopy to date.
Using FLAMES/UVES spectra through the Gaia-ESO Survey we have derived
abundances of twelve elements. Given the uncertainties, we find a chemical
similarity between these bulge stars and halo stars of the same metallicity,
although the abundance scatter may be larger, with some of the stars showing
unusual [{\alpha}/Fe] ratios.Comment: 7 pages, 5 figures. Accepted for publication by MNRA
Gaia FGK Benchmark stars: Opening the black box of stellar element abundance determination
Gaia and its complementary spectroscopic surveys combined will yield the most comprehensive database of kinematic and chemical information of stars in the Milky Way. The Gaia FGK benchmark stars play a central role in this matter as they are calibration pillars for the atmospheric parameters and chemical abundances for various surveys. The spectroscopic analyses of the benchmark stars are done by combining different methods, and the results will be affected by the systematic uncertainties inherent in each method. In this paper, we explore some of these systematic uncertainties. We determined line abundances of Ca, Cr, Mn and Co for four benchmark stars using six different methods. We changed the default input parameters of the different codes in a systematic way and found, in some cases, significant differences between the results. Since there is no consensus on the correct values for many of these default parameters, we urge the community to raise discussions towards standard input parameters that could alleviate the difference in abundances obtained by different methods. In this work, we provide quantitative estimates of uncertainties in elemental abundances due to the effect of differing technical assumptions in spectrum modelling
- âŠ