627 research outputs found
Clues on the evolution of the Carina dwarf spheroidal galaxy from the color distribution of its red giant stars
The thin red giant branch (RGB) of the Carina dwarf spheroidal galaxy appears
at first sight quite puzzling and seemingly in contrast with the presence of
several distinct bursts of star formation. In this Letter, we provide a
measurement of the color spread of red giant stars in Carina based on new BVI
wide-field observations, and model the width of the RGB by means of synthetic
color-magnitude diagrams. The measured color spread, Sigma{V-I}=0.021 +/-
0.005, is quite naturally accounted for by the star-formation history of the
galaxy. The thin RGB appears to be essentially related to the limited age range
of its dominant stellar populations, with no need for a metallicity dispersion
at a given age. This result is relatively robust with respect to changes in the
assumed age-metallicity relation, as long as the mean metallicity over the
galaxy lifetime matches the observed value ([Fe/H] = -1.91 +/- 0.12 after
correction for the age effects). This analysis of photometric data also sets
some constraints on the chemical evolution of Carina by indicating that the
chemical abundance of the interstellar medium in Carina remained low throughout
each episode of star formation even though these episodes occurred over many
Gyr.Comment: 4 pages, 3 figures, accepted for publication in the Astrophysical
Journal Letter
Weak Galactic Halo--Fornax dSph Connection from RR Lyrae Stars
For the first time accurate pulsation properties of the ancient variable
stars of the Fornax dwarf spheroidal galaxy (dSph) are discussed in the broad
context of galaxy formation and evolution. Homogeneous multi-band optical
photometry of spanning {\it twenty} years has allowed us to identify and
characterize more than 1400 RR Lyrae stars (RRLs) in this galaxy. Roughly 70\%
are new discoveries. We investigate the period-amplitude distribution and find
that Fornax shows a lack of High Amplitude (A_V\gsim0.75 mag) Short Period
fundamental-mode RRLs (P\lsim0.48 d, HASPs). These objects occur in stellar
populations more metal-rich than [Fe/H]-1.5 and they are common in the
Galactic halo (Halo) and in globulars. This evidence suggests that old (age
older than 10 Gyr) Fornax stars are relatively metal-poor.
A detailed statistical analysis of the role of the present-day Fornax dSph in
reproducing the Halo period distribution shows that it can account for only a
few to 20\% of the Halo when combined with RRLs in massive dwarf galaxies
(Sagittarius dSph, Large Magellanic Cloud). This finding indicates that
Fornax-like systems played a minor role in building up the Halo when compared
with massive dwarfs. We also discuss the occurrence of HASPs in connection with
the luminosity and the early chemical composition of nearby dwarf galaxies. We
find that, independently of their individual star formation histories, bright
(M_V\lsim-13.5 mag) galaxies have HASPs, whereas faint ones (M_V\gsim-11
mag) do not. Interestingly enough, Fornax belongs to a luminosity range
(--11M--13.5 mag) in which the occurrence of HASPs appears to be
correlated with the early star formation and chemical enrichment of the host
galaxy.Comment: 7 pages, 5 figures, A&A, accepte
Stellar populations in the dwarf spheroidal galaxy Leo I
We present a detailed study of the color magnitude diagram (CMD) of the dwarf
spheroidal galaxy Leo I, based on archival Hubble Space Telescope data. Our
photometric analysis, confirming previous results on the brighter portion of
the CMD, allow us to obtain an accurate sampling of the stellar populations
also at the faint magnitudes corresponding to the Main Sequence. By adopting a
homogeneous and consistent theoretical scenario for both hydrogen and central
helium-burning evolutionary phases, the various features observed in the CMD
are interpreted and reliable estimations for both the distance modulus and the
age(s) for the main stellar components of Leo I are derived. More in details,
from the upper luminosity of the Red Giant Branch and the lower luminosity of
the Subgiant Branch we simultaneously constrain the galaxy distance and the age
of the oldest stellar population in Leo I. In this way we obtain a distance
modulus (m-M)_V=22.000.15 mag and an age of 10--15 Gyr or 9--13 Gyr,
adopting a metallicity Z=0.0001 and 0.0004, respectively. The reliability of
this distance modulus has been tested by comparing the observed distribution of
the Leo I anomalous Cepheids in the period-magnitude diagram with the predicted
boundaries of the instability strip, as given by convective pulsating models.Comment: 19 pages, 3 tables, 14 figures To be published in A
The Chemical Enrichment History of the Large Magellanic Cloud
Ca II triplet spectroscopy has been used to derive stellar metallicities for
individual stars in four LMC fields situated at galactocentric distances of
3\arcdeg, 5\arcdeg, 6\arcdeg\@ and 8\arcdeg\@ to the north of the Bar. Observed
metallicity distributions show a well defined peak, with a tail toward low
metallicities. The mean metallicity remains constant until 6\arcdeg\@
([Fe/H]-0.5 dex), while for the outermost field, at 8\arcdeg, the mean
metallicity is substantially lower than in the rest of the disk
([Fe/H]-0.8 dex). The combination of spectroscopy with deep CCD
photometry has allowed us to break the RGB age--metallicity degeneracy and
compute the ages for the objects observed spectroscopically. The obtained
age--metallicity relationships for our four fields are statistically
indistinguishable. We conclude that the lower mean metallicity in the outermost
field is a consequence of it having a lower fraction of intermediate-age stars,
which are more metal-rich than the older stars. The disk age--metallicity
relationship is similar to that for clusters. However, the lack of objects with
ages between 3 and 10 Gyr is not observed in the field population. Finally, we
used data from the literature to derive consistently the age--metallicity
relationship of the bar. Simple chemical evolution models have been used to
reproduce the observed age--metallicity relationships with the purpose of
investigating which mechanism has participated in the evolution of the disk and
bar. We find that while the disk age--metallicity relationship is well
reproduced by close-box models or models with a small degree of outflow, that
of the bar is only reproduced by models with combination of infall and outflow.Comment: 45 pages, 10 figures, accepted for publication in Astronomical
Journa
Sex-specific alterations in NAD+ metabolism in 3xTg Alzheimer's disease mouse brain assessed by quantitative targeted LC-MS.
Levels of nicotinamide adenine dinucleotide (NAD+) are known to decline with age and have been associated with impaired mitochondrial function leading to neurodegeneration, a key facet of Alzheimer's disease (AD). NAD+synthesis is sustained via tryptophan-kynurenine (Trp-Kyn) pathway as de novo synthesis route, and salvage pathways dependent on the availability of nicotinic acid and nicotinamide. While being currently investigated as a multifactorial disease with a strong metabolic component, AD remains without curative treatment and important sex differences were reported in relation to disease onset and progression. The aim of this study was to reveal the potential deregulation of NAD+metabolism in AD with the direct analysis of NAD+precursors in the mouse brain tissue (wild type (WT) versus triple transgenic (3xTg) AD), using a sex-balanced design. To this end, we developed a quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, which allowed for the measurement of the full spectrum of NAD+precursors and intermediates in all three pathways. In brain tissue of mice with developed AD symptoms, a decrease in kynurenine (Kyn) versus increase in kynurenic acid (KA) levels were observed in both sexes with a significantly higher increment of KA in males. These alterations in Trp-Kyn pathway might be a consequence of neuroinflammation and a compensatory production of neuroprotective kynurenic acid. In the NAD+ salvage pathway, significantly lower levels of nicotinamide mononucleotide (NMN) were measured in the AD brain of males and females. Depletion of NMN implies the deregulation of salvage pathway critical for maintaining optimal NAD+ levels and mitochondrial and neuronal function
Single-Step Extraction Coupled with Targeted HILIC-MS/MS Approach for Comprehensive Analysis of Human Plasma Lipidome and Polar Metabolome.
Expanding metabolome coverage to include complex lipids and polar metabolites is essential in the generation of well-founded hypotheses in biological assays. Traditionally, lipid extraction is performed by liquid-liquid extraction using either methyl-tert-butyl ether (MTBE) or chloroform, and polar metabolite extraction using methanol. Here, we evaluated the performance of single-step sample preparation methods for simultaneous extraction of the complex lipidome and polar metabolome from human plasma. The method performance was evaluated using high-coverage Hydrophilic Interaction Liquid Chromatography-ESI coupled to tandem mass spectrometry (HILIC-ESI-MS/MS) methodology targeting a panel of 1159 lipids and 374 polar metabolites. The criteria used for method evaluation comprised protein precipitation efficiency, and relative MS signal abundance and repeatability of detectable lipid and polar metabolites in human plasma. Among the tested methods, the isopropanol (IPA) and 1-butanol:methanol (BUME) mixtures were selected as the best compromises for the simultaneous extraction of complex lipids and polar metabolites, allowing for the detection of 584 lipid species and 116 polar metabolites. The extraction with IPA showed the greatest reproducibility with the highest number of lipid species detected with the coefficient of variation (CV) < 30%. Besides this difference, both IPA and BUME allowed for the high-throughput extraction and reproducible measurement of a large panel of complex lipids and polar metabolites, thus warranting their application in large-scale human population studies
Mechanistic insights into bacterial metabolic reprogramming from omics-integrated genome-scale models.
Understanding the adaptive responses of individual bacterial strains is crucial for microbiome engineering approaches that introduce new functionalities into complex microbiomes, such as xenobiotic compound metabolism for soil bioremediation. Adaptation requires metabolic reprogramming of the cell, which can be captured by multi-omics, but this data remains formidably challenging to interpret and predict. Here we present a new approach that combines genome-scale metabolic modeling with transcriptomics and exometabolomics, both of which are common tools for studying dynamic population behavior. As a realistic demonstration, we developed a genome-scale model of Pseudomonas veronii 1YdBTEX2, a candidate bioaugmentation agent for accelerated metabolism of mono-aromatic compounds in soil microbiomes, while simultaneously collecting experimental data of P. veronii metabolism during growth phase transitions. Predictions of the P. veronii growth rates and specific metabolic processes from the integrated model closely matched experimental observations. We conclude that integrative and network-based analysis can help build predictive models that accurately capture bacterial adaptation responses. Further development and testing of such models may considerably improve the successful establishment of bacterial inoculants in more complex systems
Variable stars in the dwarf irregular galaxy NGC 6822: the photometric catalogue
Deep B,V time-series photometry obtained with the ESO Very Large Telescope
has been used to identify variable stars in the dwarf irregular galaxy NGC
6822. We surveyed a 6.8x6.8 arcmin area of the galaxy and detected a total
number of 390 candidate variables with the optimal image subtraction technique
(Alard 2000). Light curves on a magnitude scale were obtained for 262 of these
variables. Differential flux light curves are available for the remaining
sample. In this paper we present the photometric catalogue of calibrated light
curves and time-series data, along with coordinates and classification of the
candidate variables. A detailed description is provided of the procedures used
to identify the variable stars and calibrate their differential flux light
curves on a magnitude scale.Comment: 22 pages, 19 figures only as JPEG. Revised version with corrected eq.
5. Full text with better resolution .ps figures available upon request from
the authors. Uses aa.cls (included), in press on A&A. Table 2 will only be
published at the CDS, Appendix A, Tables 4,5,6 will only be available in the
electronic edition of the Journa
The bursty star formation history of the Fornax dwarf spheroidal galaxy revealed with the HST
We present a new derivation of the star formation history (SFH) of the dSph
galaxy Fornax in two central regions, characterised by unprecedented precision
and age resolution. It reveals that star formation has proceeded in sharp
bursts separated by periods of low-level or quiescent activity. The SFH was
derived through colour-magnitude diagram (CMD) fitting of two extremely deep
Hubble Space Telescope CMDs, sampling the centre and one core radius. The
attained age resolution allowed us to single out a major star formation episode
at early times, a second strong burst Gyr ago and recent
intermittent episodes Gyr ago. Detailed testing with mock stellar
populations was used to estimate the duration of the main bursts and study the
occurrence of low-level star formation between them. The SFHs in both regions
show common features, with activity at the same epochs and similar
age-metallicity relationship. However, clear indications of a spatial gradient
were also found, with mean age increasing with radius and star formation
episodes being more prolonged in the centre. While some galaxy evolution models
predict bursty SFHs in dwarf galaxies and thus a secular origin of the observed
SFH cannot be excluded in Fornax, other evidence points to possible mergers or
interactions as the cause of its bursty SFH. In particular, we calculated the
Fornax orbit relative to the closest dwarfs and the Milky Way and observed a
correspondence between the main intermediate-age and young events and
peri-passages of Fornax around the Milky Way, possibly indicating
tidally-induced star formation.Comment: 20 pages, 12+3 figures, accepted for publication in MNRAS; corrected
error estimation (Figure 5, Sec. 3.3), added Sec. 4.3, appendices, more
references, moderate revision of text and figure
Modelling of dual-frequency ICRF heating in ASDEX Upgrade discharges relevant to the ITER baseline scenario
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