1,647 research outputs found
Spectroscopic versus Photometric Metallicities: Milky Way Dwarf Spheroidal Companions as a Test Case
Aims. The method of deriving photometric metallicities using red giant branch
stars is applied to resolved stellar populations under the common assumption
that they mainly consist of single-age old stellar populations. We explore the
effect of the presence of mixed-age stellar populations on deriving photometric
metallicities. Methods. We use photometric data sets for the five Galactic
dwarf spheroidals Sculptor, Sextans, Carina, Fornax, and Leo II in order to
derive their photometric metallicity distribution functions from their resolved
red giant branches using isochrones of the Dartmouth Stellar Evolutionary
Database. We compare the photometric metallicities with published spectroscopic
metallicities based on the analysis of the near-infrared Ca triplet (Ca T),
both on the metallicity scale of Carretta & Gratton and on the scale defined by
the Dartmouth isochrones. In addition, we compare the photometric metallicities
with published spectroscopic metallicities based on spectral synthesis and
medium-resolution spectroscopy, and on high resolution spectra where available.
Results. The mean properties of the spectroscopic and photometric metallicity
samples are comparable within the intrinsic scatter of each method although the
mean metallicities of dSphs with pronounced intermediate-age population
fractions may be underestimated by the photometric method by up to a few tenths
of dex in [Fe/H]. The star-by-star differences of the spectroscopic minus the
photometric metallicities show a wide range of values along the fiducial
spectroscopic metallicity range, with the tendency to have systematically lower
photometric metallicities for those dwarf spheroidals with a higher fraction of
intermediate-age populations. Such discrepancies persist even in the case of
the purely old Sculptor dSph, where one would na\"ively expect a very good
match when comparing with medium or low resolution metallicity measurements.
Overall, the agreement between Ca T metallicities and photometric metallicities
is very good in the metallicity range from ~ -2 dex to ~ -1.5 dex. We find that
the photometric method is reliable in galaxies that contain small (less than
15%) intermediate-age stellar fractions. Therefore, in the presence of
mixed-age stellar populations, one needs to quantify the fraction of the
intermediate-age stars in order to assess their effect on determining
metallicities from photometry alone. Finally, we note that the comparison of
spectroscopic metallicities of the same stars obtained with different methods
reveals similarly large discrepancies as the comparison with photometric
metallicities.Comment: 17 pages, 12 figures; A&A accepte
In Silico Mining for Antimalarial Structure-Activity Knowledge and Discovery of Novel Antimalarial Curcuminoids.
Malaria is a parasitic tropical disease that kills around 600,000 patients every year. The emergence of resistant Plasmodium falciparum parasites to artemisinin-based combination therapies (ACTs) represents a significant public health threat, indicating the urgent need for new effective compounds to reverse ACT resistance and cure the disease. For this, extensive curation and homogenization of experimental anti-Plasmodium screening data from both in-house and ChEMBL sources were conducted. As a result, a coherent strategy was established that allowed compiling coherent training sets that associate compound structures to the respective antimalarial activity measurements. Seventeen of these training sets led to the successful generation of classification models discriminating whether a compound has a significant probability to be active under the specific conditions of the antimalarial test associated with each set. These models were used in consensus prediction of the most likely active from a series of curcuminoids available in-house. Positive predictions together with a few predicted as inactive were then submitted to experimental in vitro antimalarial testing. A large majority from predicted compounds showed antimalarial activity, but not those predicted as inactive, thus experimentally validating the in silico screening approach. The herein proposed consensus machine learning approach showed its potential to reduce the cost and duration of antimalarial drug discovery
Chemical evolution of the Small Magellanic Cloud based on planetary nebulae
We investigate the chemical evolution of the Small Magellanic Cloud (SMC)
based on abundance data of planetary nebulae (PNe). The main goal is to
investigate the time evolution of the oxygen abundance in this galaxy by
deriving an age-metallicity relation. Such a relation is of fundamental
importance as an observational constraint of chemical evolution models of the
SMC. We have used high quality PNe data in order to derive the properties of
the progenitor stars, so that the stellar ages could be estimated. We collected
a large number of measured spectral fluxes for each nebula, and derived
accurate physical parameters and nebular abundances. New spectral data for a
sample of SMC PNe obtained between 1999 and 2002 are also presented. These data
are used together with data available in the literature to improve the accuracy
of the fluxes for each spectral line. We obtained accurate chemical abundances
for PNe in the Small Magellanic Cloud, which can be useful as tools in the
study of the chemical evolution of this galaxy and of Local Group galaxies. We
present the resulting oxygen versus age diagram and a similar relation
involving the [Fe/H] metallicity based on a correlation with stellar data. We
discuss the implications of the derived age-metallicity relation for the SMC
formation, in particular by suggesting a star formation burst in the last 2-3
Gyr.Comment: 11 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
A close look at the Centaurus A group of galaxies: I. Metallicity distribution functions and population gradients in early-type dwarfs
We study dwarf galaxies in the Centaurus A group to investigate their
metallicity and possible environmental effects. The Centaurus A group (at ~4
Mpc from the Milky Way) contains about 50 known dwarf companions of different
morphologies and stellar contents, thus making it a very interesting target to
study how these galaxies evolve. Here we present results for the early-type
dwarf galaxy population in this group. We use archival HST/ACS data to study
the resolved stellar content of 6 galaxies, together with isochrones from the
Dartmouth stellar evolutionary models. We derive photometric metallicity
distribution functions of stars on the upper red giant branch via isochrone
interpolation. The 6 galaxies are moderately metal-poor (=-1.56 to
-1.08), and metallicity spreads are observed (internal dispersions of
sigma_[Fe/H]=0.10 to 0.41 dex). We also investigate the possible presence of
intermediate-age stars, and discuss how these affect our results. The dwarfs
exhibit flat to weak radial metallicity gradients. For the two most luminous,
most metal-rich galaxies, we find statistically significant evidence for at
least two stellar subpopulations: the more metal-rich stars are found in the
center of the galaxies, while the metal-poor ones are more broadly distributed
within the galaxies. We find no clear trend of the derived physical properties
as a function of (present-day) galaxy position in the group, which may be due
to the small sample we investigate. We compare our results to the early-type
dwarf population of the Local Group, and find no outstanding differences,
despite the fact that the Centaurus A group is a denser environment that is
possibly in a more advanced dynamical stage.Comment: 21 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
Carbon enrichment of the evolved stars in the Sagittarius dwarf spheroidal
We present spectra of 1142 colour-selected stars in the direction of the
Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy, of which 1058 were taken with
VLT/FLAMES multi-object spectrograph and 84 were taken with the SAAO Radcliffe
1.9-m telescope grating spectrograph. Spectroscopic membership is confirmed (at
>99% confidence) for 592 stars on the basis of their radial velocity, and
spectral types are given. Very slow rotation is marginally detected around the
galaxy's major axis. We identify five S stars and 23 carbon stars, of which all
but four carbon stars are newly-determined and all but one (PQ Sgr) are likely
Sgr dSph members. We examine the onset of carbon-richness in this metal-poor
galaxy in the context of stellar models. We compare the stellar death rate (one
star per 1000-1700 years) to known planetary nebula dynamical ages and find
that the bulk population produce the observed (carbon-rich) planetary nebulae.
We compute average lifetimes of S and carbon stars as 60-250 and 130-500 kyr,
compared to a total thermal-pulsing asymptotic giant branch lifetime of
530-1330 kyr. We conclude by discussing the return of carbon-rich material to
the ISM.Comment: 14 pages, 10 figures, accepted MNRA
Characterization of volatile compounds of Daucus crinitus Desf. Headspace Solid Phase Microextraction as alternative technique to Hydrodistillation
<p>Abstract</p> <p>Background</p> <p>Traditionally, the essential oil of aromatic herbs is obtained using hydrodistillation (HD). Because the emitted volatile fraction plays a fundamental role in a plant's life, various novel techniques have been developed for its extraction from plants. Among these, headspace solid phase microextraction (HS-SPME) can be used to obtain a rapid fingerprint of a plant's headspace. <it>Daucus crinitus </it>Desf. is a wild plant that grows along the west coast of Algeria. Only a single study has dealt with the chemical composition of the aerial part oils of Algerian <it>D. crinitus</it>, in which isochavicol isobutyrate (39.0%), octyl acetate (12.3%), and β-caryophyllene (5.4%) were identified. Using GC-RI and GC-MS analysis, the essential oils and the volatiles extracted from separated organs of <it>D. crinitus </it>Desf. were studied using HS-SPME.</p> <p>Results</p> <p>GC-RI and GC-MS analysis identified 72 and 79 components in oils extracted using HD and in the volatile fractions extracted using SPME, respectively. Two types of essential oils were produced by the plant: the root oils had aliphatic compounds as the main component (87.0%-90.1%), and the aerial part oils had phenylpropanoids as the main component (43.1%-88.6%). HS-SPME analysis showed a more precise distribution of compounds in the organs studied: oxygenated aliphatic compounds were well represented in the roots (44.3%-84.0%), hydrocarbon aliphatic compounds were in the leaves and stems (22.2%-87.9%), and phenylpropanoids were in the flowers and umbels (47.9%-64.2%). Moreover, HS-SPME allowed the occurrence of isochavicol (29.6 - 34.7%) as main component in <it>D. crinitus </it>leaves, but it was not detected in the oils, probably because of its solubility in water.</p> <p>Conclusions</p> <p>This study demonstrates that HD and HS-SPME modes could be complimentary extraction techniques in order to obtain the complete characterization of plant volatiles.</p
Search for CP violation in D+→ϕπ+ and D+s→K0Sπ+ decays
A search for CP violation in D + → ϕπ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb−1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (−0.04 ± 0.14 ± 0.14)% for candidates with K − K + mass within 20 MeV/c 2 of the ϕ meson mass. A search for a CP -violating asymmetry that varies across the ϕ mass region of the D + → K − K + π + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+s→K0Sπ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%
Study of decays to the final state and evidence for the decay
A study of decays is performed for the first time
using data corresponding to an integrated luminosity of 3.0
collected by the LHCb experiment in collisions at centre-of-mass energies
of and TeV. Evidence for the decay
is reported with a significance of 4.0 standard deviations, resulting in the
measurement of
to
be .
Here denotes a branching fraction while and
are the production cross-sections for and mesons.
An indication of weak annihilation is found for the region
, with a significance of
2.4 standard deviations.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-022.html,
link to supplemental material inserted in the reference
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
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