67 research outputs found
Evolutionary synthesis of galaxies at high spectral resolution with the code PEGASE-HR
We present PEGASE-HR, a new stellar population synthesis program generating
high resolution spectra (R=10 000) over the optical range lambda=400--680 nm.
It links the spectro-photometric model of galaxy evolution PEGASE.2 (Fioc &
Rocca-Volmerange 1997) to an updated version of the ELODIE library of stellar
spectra observed with the 193 cm telescope at the Observatoire de
Haute-Provence (Prugniel & Soubiran 2001a). The ELODIE star set gives a fairly
complete coverage of the Hertzprung-Russell (HR) diagram and makes it possible
to synthesize populations in the range [Fe/H]=-2 to +0.4. This code is an
exceptional tool for exploring signatures of metallicity, age, and kinematics.
We focus on a detailed study of the sensitivity to age and metallicity of the
high-resolution stellar absorption lines and of the classical metallic indices
proposed until now to solve the age-metallicity degeneracy. Validity tests on
several stellar lines are performed by comparing our predictions for Lick
indices to the models of other groups. The comparison with the lower resolution
library BaSeL (Lejeune et al. 1997) confirms the quality of the ELODIE library
when used for simple stellar populations (SSPs) from 10 Myr to 20 Gyr.
Predictions for the evolved populations of globular clusters and elliptical
galaxies are given and compared to observational data. Two new high-resolution
indices are proposed around the Hgamma line. They should prove useful in the
analysis of spectra from the new generation of telescopes and spectrographs.Comment: 18 pages, 18 figures. Astronomy & Astrophysics, in press. The models
are available at http://www.iap.fr/pegase
Nature vs. nurture in the low-density environment: structure and evolution of early-type dwarf galaxies in poor groups
We present the stellar population properties of 13 dwarf galaxies residing in
poor groups (low-density environment, LDE) observed with VIMOS@VLT. Ages,
metallicities, and [alpha/Fe] ratios were derived from the Lick indices Hbeta,
Mgb, Fe5270 and Fe5335 through comparison with our simple stellar population
(SSP) models accounting for variable [alpha/Fe] ratios. For a fiducial
subsample of 10 early-type dwarfs we derive median values and scatters around
the medians of 5.7 \pm 4.4 Gyr, -0.26 \pm 0.28, and -0.04 \pm 0.33 for age, log
Z/Zsun, and [alpha/Fe], respectively. For a selection of bright early-type
galaxies (ETGs) from the Annibali et al.2007 sample residing in comparable
environment we derive median values of 9.8 \pm 4.1 Gyr, 0.06 \pm 0.16, and 0.18
\pm 0.13 for the same stellar population parameters. It follows that dwarfs are
on average younger, less metal rich, and less enhanced in the alpha-elements
than giants, in agreement with the extrapolation to the low mass regime of the
scaling relations derived for giant ETGs. From the total (dwarf + giant) sample
we derive that age \propto sigma^{0.39 \pm 0.22}, Z \propto sigma^{0.80 \pm
0.16}, and alpha/Fe \propto sigma^{0.42 \pm 0.22}. We also find correlations
with morphology, in the sense that the metallicity and the [alpha/Fe] ratio
increase with the Sersic index n or with the bulge-to-total light fraction B/T.
The presence of a strong morphology-[alpha/Fe] relation appears to be in
contradiction to the possible evolution along the Hubble sequence from low B/T
(low n) to high B/T (high n) galaxies. We also investigate the role played by
environment comparing the properties of our LDE dwarfs with those of Coma red
passive dwarfs from the literature. We find possible evidence that LDE dwarfs
experienced more prolonged star formations than Coma dwarfs, however larger
data samples are needed to draw more firm conclusions.Comment: Accepted for publication on A&
Coude-feed stellar spectral library - atmospheric parameters
Context: Empirical libraries of stellar spectra play an important role in
different fields. For example, they are used as reference for the automatic
determination of atmospheric parameters, or for building synthetic stellar
populations to study galaxies. The CFLIB (Coude-feed library, Indo-US) database
is at present one of the most complete libraries, in terms of its coverage of
the atmospheric parameters space (Teff, log g and [Fe/H]) and wavelength
coverage 3460 - 9464 A at a resolution of 1 A FWHM. Although the atmospheric
parameters of most of the stars were determined from detailed analyses of
high-resolution spectra, for nearly 300 of the 1273 stars of the library at
least one of the three parameters is missing. For the others, the measurements,
compiled from the literature, are inhomogeneous.
Aims: In this paper, we re-determine the atmospheric parameters, directly
using the CFLIB spectra, and compare them to the previous studies.
Methods: We use the ULySS program to derive the atmospheric parameters, using
the ELODIE library as a reference.
Results: Based on comparisons with several previous studies we conclude that
our determinations are unbiased. For the 958 F,G, and K type stars the
precision on Teff, log g, and [Fe/H] is respectively 43 K, 0.13 dex and 0.05
dex. For the 53 M stars they are 82 K, 0.22 dex and 0.28 dex. And, for the 260
OBA type stars the relative precision on Teff is 5.1%, and on log g, and [Fe/H]
the precision is respectively 0.19 dex and 0.16 dex. These parameters will be
used to re-calibrate the CFLIB fluxes and to produce synthetic spectra of
stellar populations.Comment: 51 pages, accepted for publication in Astronomy and Astrophysic
Pyoderma gangrenosum – a review
Pyoderma gangrenosum (PG) is a rare noninfectious neutrophilic dermatosis. Clinically it starts with sterile pustules that rapidly progress and turn into painful ulcers of variable depth and size with undermined violaceous borders. The legs are most commonly affected but other parts of the skin and mucous membranes may also be involved. Course can be mild or malignant, chronic or relapsing with remarkable morbidity. In many cases PG is associated with an underlying disease, most commonly inflammatory bowel disease, rheumatic or haematological disease and malignancy. Diagnosis of PG is based on history of an underlying disease, typical clinical presentation, histopathology, and exclusion of other diseases that would lead to a similar appearance. The peak of incidence occurs between the ages of 20 to 50 years with women being more often affected than men. Aetiology has not been clearly determined yet. The treatment of PG is a challenge. Randomized, double-blinded prospective multicenter trials for PG are not available. The best documented treatments are systemic corticosteroids and ciclosporin A. Combinations of steroids with cytotoxic drugs are used in resistant cases. The combination of steroids with sulfa drugs or immunosuppressants has been used as steroid-sparing modalities. Anti-tumor necrosis alpha therapy in Crohn's disease showed a rapid response of PG. Skin transplants and the application of bioengineered skin is useful in selected cases as a complement to the immunosuppressive treatment. Topical therapy with modern wound dressings is useful to minimize pain and the risk of secondary infections. Despite recent advances in therapy, the prognosis of PG remains unpredictable
SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems
Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II),
SDSS-III is a program of four spectroscopic surveys on three scientific themes:
dark energy and cosmological parameters, the history and structure of the Milky
Way, and the population of giant planets around other stars. In keeping with
SDSS tradition, SDSS-III will provide regular public releases of all its data,
beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an
overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5
million massive galaxies and Lya forest spectra of 150,000 quasars, using the
BAO feature of large scale structure to obtain percent-level determinations of
the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2,
which is now completed, measured medium-resolution (R=1800) optical spectra of
118,000 stars in a variety of target categories, probing chemical evolution,
stellar kinematics and substructure, and the mass profile of the dark matter
halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain
high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution
element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars,
measuring separate abundances for ~15 elements per star and creating the first
high-precision spectroscopic survey of all Galactic stellar populations (bulge,
bar, disks, halo) with a uniform set of stellar tracers and spectral
diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars
with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to
detect giant planets with periods up to two years, providing an unprecedented
data set for understanding the formation and dynamical evolution of giant
planet systems. (Abridged)Comment: Revised to version published in The Astronomical Journa
Developmental dyscalculia: a dysconnection syndrome?
Numerical understanding is important for everyday life. For children with developmental dyscalculia (DD), numbers and magnitudes present profound problems which are thought to be based upon neuronal impairments of key regions for numerical understanding. The aim of the present study was to investigate possible differences in white matter fibre integrity between children with DD and controls using diffusion tensor imaging. White matter integrity and behavioural measures were evaluated in 15 children with developmental dyscalculia aged around 10Â years and 15 matched controls. The main finding, obtained by a whole brain group comparison, revealed reduced fractional anisotropy in the superior longitudinal fasciculus in children with developmental dyscalculia. In addition, a region of interest analysis exhibited prominent deficits in fibres of the superior longitudinal fasciculus adjacent to the intraparietal sulcus, which is thought to be the core region for number processing. To conclude, our results outline deficient fibre projection between parietal, temporal and frontal regions in children with developmental dyscalculia, and therefore raise the question of whether dyscalculia can be seen as a dysconnection syndrome. Since the superior longitudinal fasciculus is involved in the integration and control of distributed brain processes, the present results highlight the importance of considering broader domain-general mechanisms in the diagnosis and therapy of dyscalculia
Neurochemistry Predicts Convergence of Written and Spoken Language: A Proton Magnetic Resonance Spectroscopy Study of Cross-Modal Language Integration
mapThis .kmz file contains a georeferenced sheet overlay from the Sanborn Fire Insurance Maps for Ogden, 1950. The downloaded .kmz file is accessible for viewing in Google Earth and other GIS software systems. Multiple .kmz files can be loaded into a GIS software system in order to view a continuous set of sheet overlays
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