34 research outputs found
Probing the LMC age gap at intermediate cluster masses
The LMC has a rich star cluster system spanning a wide range of ages and
masses. One striking feature of the LMC cluster system is the existence of an
age gap between 3-10 Gyrs. But this feature is not as clearly seen among field
stars. Three LMC fields containing relatively poor and sparse clusters whose
integrated colours are consistent with those of intermediate age simple stellar
populations have been imaged in BVI with the Optical Imager (SOI) at the
Southern Telescope for Astrophysical Research (SOAR). A total of 6 clusters, 5
of them with estimated initial masses M < 10^4M_sun, were studied in these
fields. Photometry was performed and Colour-Magnitude Diagrams (CMD) were built
using standard point spread function fitting methods. The faintest stars
measured reach V ~ 23. The CMD was cleaned from field contamination by making
use of the three-dimensional colour and magnitude space available in order to
select stars in excess relative to the field. A statistical CMD comparison
method was developed for this purpose. The subtraction method has proven to be
successful, yielding cleaned CMDs consistent with a simple stellar population.
The intermediate age candidates were found to be the oldest in our sample, with
ages between 1-2 Gyrs. The remaining clusters found in the SOAR/SOI have ages
ranging from 100 to 200 Myrs. Our analysis has conclusively shown that none of
the relatively low-mass clusters studied by us belongs to the LMC age-gap.Comment: 9 pages, 8 figures. Accepted to MNRA
Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Bulge studies
We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to
measure extinction values in the complete area of the Galactic bulge covered by
the survey at high resolution. We derive reddening values using the method
described in Paper I. This is based on measuring the mean (J-Ks) color of red
clump giants in small subfields of 2' to 6' in the following bulge area:
-10.3<b<+5.1 and -10<l<+10.4. To determine the reddening values E(J-Ks) for
each region, we measure the RC color and compare it to the (J-Ks) color of RC
stars measured in Baade's window, for which we adopt E(B-V)=0.55. This allows
us to construct a reddening map sensitive to small scale variations minimizing
the problems arising from differential extinction. The significant reddening
variations are clearly observed on spatial scales as small as 2'. We find a
good agreement between our extinction measurements and Schlegel maps in the
outer bulge, but, as already stated in the literature the Schlegel maps are not
reliable for regions within |b| < 6. In the inner regions we compare our
results with maps derived from DENIS and Spitzer surveys. While we find good
agreement with other studies in the corresponding overlapping regions, our
extinction map has better quality due to both higher resolution and a more
complete spatial coverage in the Bulge. We investigate the importance of
differential reddening and demonstrate the need for high resolution extinction
maps for detailed studies of Bulge stellar populations and structure. The
extinction variations on scales of up to 2'-6', must be taken into account when
analysing the stellar populations of the Bulge.Comment: Accepted for publication in A&
The puzzling dredge-up pattern in NGC 1978
Low-mass stars are element factories that efficiently release their products
in the final stages of their evolution by means of stellar winds. Since they
are large in number, they contribute significantly to the cosmic matter cycle.
To assess this contribution quantitatively, it is crucial to obtain a detailed
picture of the stellar interior, particularly with regard to nucleosynthesis
and mixing mechanisms. We seek to benchmark stellar evolutionary models of
low-mass stars. In particular, we measure the surface abundance of ^{12}C in
thermally pulsing AGB stars with well-known mass and metallicity, which can be
used to infer information about the onset and efficiency of the third
dredge-up. We recorded high-resolution near-infrared spectra of AGB stars in
the LMC cluster NGC 1978. The sample comprised both oxygen-rich and carbon-rich
stars, and is well-constrained in terms of the stellar mass, metallicity, and
age. We derived the C/O and ^{12}C/^{13}C ratio from the target spectra by a
comparison to synthetic spectra. Then, we compared the outcomes of stellar
evolutionary models with our measurements. The M stars in NGC 1978 show values
of C/O and ^{12}C/^{13}C that can best be explained with moderate extra-mixing
on the RGB coupled to a moderate oxygen enhancement in the chemical
composition. These oxygen-rich stars do not seem to have undergone third
dredge-up episodes (yet). The C stars show carbon-to-oxygen and carbon isotopic
ratios consistent with the occurrence of the third dredge-up. We did not find S
stars in this cluster. None of the theoretical schemes that we considered was
able to reproduce the observations appropriately. Instead, we discuss some
non-standard scenarios to explain the puzzling abundance pattern in NGC 1978.Comment: 16 pages, 9 figures, 4 tables, accepted for publication in A&A,
language revise
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201
Evidence for a deficit of young and old stars in the Milky Way inner in-plane disc
We give independent proof of the deficit of stars in the in-plane central
disc with respect to the predictions of a pure exponential density
distribution. We use three different methods: 1) the inversion of the red clump
giant distribution in near-infrared colour-magnitude diagrams to obtain the
star density along the line of sight; 2) the determination of the density
distribution of 1612 MHz sources by means of the distance determination of
OH/IR sources from their kinematical information; 3) an analysis of near and
mid-infrared star counts and comparison with models. All the tests give the
same result: a defect of stars in the inner disc with respect to an exponential
disc (either with constant scaleheight or extrapolated from the outer disc),
but only in near plane regions. This deficit might be interpreted as a flare in
the vertical distribution. The in-plane density is almost independent of R and
not an exponential law. Further away from the plane, however, the density
increases towards the centre due to the increase of the scaleheight. Tests also
show that this result cannot be due to extinction. The deficit affects both the
young and the old populations, so it is probably a rather stable feature of the
disc, and might be due to the existence of an in-plane bar sweeping the
near-plane stars.Comment: 17 pages with 27 postscript figures, to be published in A&
Reddening and metallicity maps of the Milky Way Bulge from VVV and 2MASS. I.The method and minor axis maps
We present a method to obtain reddening maps and to trace structure and
metallicity gradients of the bulge using data from the recently started ESO
public survey Vista Variables in the Via Lactea (VVV). We derive the mean J-Ks
color of the red clump (RC) giants in 1835 subfields in the Bulge region with
-8<b<-0.4 and 0.2<l<1.7, and compare it to the color of RC stars in Baade's
Window for which we adopt E(B-V)=0.55. This allows us to derive the reddening
map on a small enough scale to minimize the problems arising from differential
extinction. The dereddened magnitudes are then used to build the bulge
luminosity function in regions of 0.4 x 0.4 deg to obtain the mean RC
magnitudes. These are used as distance indicator in order to trace the bulge
structure. Finally, for each subfield we derive photometric metallicities
through interpolation of red giant branch colors on a set of empirical ridge
lines. The photometric metallicity distributions are compared to metallicity
distributions obtained from high resolution spectroscopy in the same regions.
The reddening determination is sensitive to small scale variations which are
clearly visible in our maps. The luminosity function clearly shows the double
RC recently discovered in 2MASS and OGLE III datasets, hence allowing to trace
the X-shape morphology of the bulge. Finally, the mean of the derived
photometric metallicity distributions are in remarkable agreement with those
obtained from spectroscopy. The VVV survey presents a unique tool to map the
bulge properties by means of the consistent method presented here. The
remarkable agreement between our results and those presented in literature for
the minor axis allows us to safely extend our method to the whole region
covered by the survey.Comment: Accepted for publication in A&
Revealing the cold dust in low-metallicity environments: I. Photometry analysis of the Dwarf Galaxy Survey with Herschel
Context. We present new photometric data from our Herschel Guaranteed Time Key Programme, the Dwarf
Galaxy Survey (DGS),
dedicated to the observation of the gas and dust in low-metallicity environments. A total of 48
dwarf galaxies were observed with the PACS and SPIRE instruments onboard the Herschel Space
Observatory at 70, 100, 160, 250, 350, and 500 µm.
Aims. The goal of this paper is to provide reliable far infrared (FIR) photometry for the DGS
sample and to analyse the FIR/submillimetre (submm) behaviour of the DGS galaxies. We focus on a
systematic comparison of the derived FIR properties (FIR luminosity, LFIR, dust mass, Mdust , dust
temperature, T, emissivity index, β) with more metal-rich galaxies and investigate the detection of
a potential submm excess.
Methods. The data reduction method is adapted for each galaxy in order to derive the most reliable
photometry from the final maps. The derived PACS flux densities are compared with the Spitzer MIPS
70 and 160 µm bands. We use colour-colour diagrams to analyse the FIR/submm behaviour of the DGS
galaxies and modified blackbody fitting procedures to determine their dust properties. To study the
variation in these dust properties with metallicity, we also include galaxies from the Herschel
KINGFISH sample, which contains more metal-rich environments, totalling 109 galaxies.
Results. The location of the DGS galaxies on Herschel colour-colour diagrams highlights the
differences in dust grain properties and/or global environments of low-metallicity dwarf galaxies.
The dust in DGS galaxies is generally warmer than in KINGFISH galaxies (TDGS ∼ 32 K and TKINGFIS H
∼ 23 K). The emissivity index, β, is ∼ 1.7 in the DGS, however metallicity does not make
a strong effect on β. The proportion of dust mass relative to stellar mass is lower in
low-metallicity galaxies: Mdust /Mstar ∼ 0.02%
for the DGS versus 0.1% for KINGFISH. However, per unit dust mass, dwarf galaxies emit about six
times more in the FIR/submm
than higher metallicity galaxies. Out of the 22 DGS galaxies detected at 500 µm, about 41% present
an excess in the submm beyond the explanation of our dust SED model, and this excess can go up to
150% above the prediction from the model. The excess mainly appears in lower metallicity galaxies
(12+log(O/H) ;S 8.3), and the strongest excesses are detected in the most metal-poor galaxies.
However, we so stress the need for observations longwards of the Herschel wavelengths to detect any
submm excess appearing beyond 500 .Norwegian Lis
Need for recovery amongst emergency physicians in the UK and Ireland: A cross-sectional survey
OBJECTIVES: To determine the need for recovery (NFR) among emergency physicians and to identify demographic and occupational characteristics associated with higher NFR scores. DESIGN: Cross-sectional electronic survey. SETTING: Emergency departments (EDs) (n=112) in the UK and Ireland. PARTICIPANTS: Emergency physicians, defined as any registered physician working principally within the ED, responding between June and July 2019. MAIN OUTCOME MEASURE: NFR Scale, an 11-item self-administered questionnaire that assesses how work demands affect intershift recovery. RESULTS: The median NFR Score for all 4247 eligible, consented participants with a valid NFR Score was 70.0 (95% CI: 65.5 to 74.5), with an IQR of 45.5-90.0. A linear regression model indicated statistically significant associations between gender, health conditions, type of ED, clinical grade, access to annual and study leave, and time spent working out-of-hours. Groups including male physicians, consultants, general practitioners (GPs) within the ED, those working in paediatric EDs and those with no long-term health condition or disability had a lower NFR Score. After adjusting for these characteristics, the NFR Score increased by 3.7 (95% CI: 0.3 to 7.1) and 6.43 (95% CI: 2.0 to 10.8) for those with difficulty accessing annual and study leave, respectively. Increased percentage of out-of-hours work increased NFR Score almost linearly: 26%-50% out-of-hours work=5.7 (95% CI: 3.1 to 8.4); 51%-75% out-of-hours work=10.3 (95% CI: 7.6 to 13.0); 76%-100% out-of-hours work=14.5 (95% CI: 11.0 to 17.9). CONCLUSION: Higher NFR scores were observed among emergency physicians than reported in any other profession or population to date. While out-of-hours working is unavoidable, the linear relationship observed suggests that any reduction may result in NFR improvement. Evidence-based strategies to improve well-being such as proportional out-of-hours working and improved access to annual and study leave should be carefully considered and implemented where feasible
Strong Interaction Physics at the Luminosity Frontier with 22 GeV Electrons at Jefferson Lab
This document presents the initial scientific case for upgrading the
Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab)
to 22 GeV. It is the result of a community effort, incorporating insights from
a series of workshops conducted between March 2022 and April 2023. With a track
record of over 25 years in delivering the world's most intense and precise
multi-GeV electron beams, CEBAF's potential for a higher energy upgrade
presents a unique opportunity for an innovative nuclear physics program, which
seamlessly integrates a rich historical background with a promising future. The
proposed physics program encompass a diverse range of investigations centered
around the nonperturbative dynamics inherent in hadron structure and the
exploration of strongly interacting systems. It builds upon the exceptional
capabilities of CEBAF in high-luminosity operations, the availability of
existing or planned Hall equipment, and recent advancements in accelerator
technology. The proposed program cover various scientific topics, including
Hadron Spectroscopy, Partonic Structure and Spin, Hadronization and Transverse
Momentum, Spatial Structure, Mechanical Properties, Form Factors and Emergent
Hadron Mass, Hadron-Quark Transition, and Nuclear Dynamics at Extreme
Conditions, as well as QCD Confinement and Fundamental Symmetries. Each topic
highlights the key measurements achievable at a 22 GeV CEBAF accelerator.
Furthermore, this document outlines the significant physics outcomes and unique
aspects of these programs that distinguish them from other existing or planned
facilities. In summary, this document provides an exciting rationale for the
energy upgrade of CEBAF to 22 GeV, outlining the transformative scientific
potential that lies within reach, and the remarkable opportunities it offers
for advancing our understanding of hadron physics and related fundamental
phenomena.Comment: Updates to the list of authors; Preprint number changed from theory
to experiment; Updates to sections 4 and 6, including additional figure
Artificial neural network modelling of generalised parton distributions
International audienceWe discuss the use of machine learning techniques in effectively nonparametric modelling of generalised parton distributions (GPDs) in view of their future extraction from experimental data. Current parameterisations of GPDs suffer from model dependency that lessens their impact on phenomenology and brings unknown systematics to the estimation of quantities like Mellin moments. The new strategy presented in this study allows to describe GPDs in a way fulfilling theory-driven constraints, keeping model dependency to a minimum. Getting a better grip on the control of systematic effects, our work will help the GPD phenomenology to achieve its maturity in the precision era commenced by the new generation of experiments