5,026 research outputs found
Unprecedented layered coordination polymers of dithiolene group 10 metals: Magnetic and electrical properties
One-pot reactions between Ni(ii), Pd(ii) or Pt(ii) salts and 3,6-dichloro-1,2-benzenedithiol (HSC6H2Cl2SH) in KOH medium under argon lead to a series of bis-dithiolene coordination polymers. X-ray analysis shows the presence of a common square planar complex [M(SC6H2Cl2S)2]2- linked to potassium cations forming either a two-dimensional coordination polymer network for {[K2(μ-H2O)2(μ-thf)(thf)2][M(SC6H2Cl2S)2]}n [M = Ni (1) and Pd (2)] or a one-dimensional coordination polymer for {[K2(μ-H2O)2(thf)6][Pt(SC6H2Cl2S)2]}n (3). In 3 the coordination environment of the potassium ions may slightly change leading to the two-dimensional coordination polymer {[K2(μ-H2O)(μ-thf)2][Pt(SC6H2Cl2S)2]}n (4) that crystallizes together with 3. The physical characterization of compounds 1-3 show similar trends, they are diamagnetic and behave as semiconductorsWe thank financial support from MICINN (MAT2013-46753-C2-1-P, CTQ2014-52758-P and MAT2014-56143-R) and Generalitat Valenciana (PrometeoII/2014/076
Les recherches de Leibniz au sujet de la langue basque
La mentalité puissante de Leibniz, quoique connue pour ses écrits philosophiques et mathématiques, a embrassé presque tous les domaines de la connaissance, dont la linguistique. Dans le domaine de ses études linguistiques, en particulier, dans celui de sa recherche sur les diverses langues historiques et naturelles, Leibniz a porté un intérêt exclusif à connaître la nature et les caractéristiques de la langue basque. Suivant la logique de sa thèse de l'"harmonie préétablie", Leibniz faisait la recherche au sujet de l'harmonie parmi les diverses langues du monde, où il a trouvé un intérêt spécial à essayer de pénétrer les mystères du vieil euscarien (basque) qui s'avérait si différent du reste des langues européennes
A young double stellar cluster in a HII region, emerging from its parent molecular cloud
We report the properties of a new young double stellar cluster in the region
towards IRAS 07141-0920 contained in the HII region Sh2-294. High-resolution
optical UBVRI and Halpha images, near-infrared JHKs and H2 filter images were
used to make photometric and morphological studies of the point sources and the
nebula seen towards Sh2-294. The optical images reveal an emission nebula with
very rich morphological details, composed mainly of UV scattered light and of
Halpha emission. Contrasting with the bright parts of the nebula, opaque,
elongated patches are seen. Our optical photometry confirms that the
illuminator of the nebula is likely to be a B0.5V star located at a distance of
about 3.2 kpc. Our near-IR images reveal an embedded cluster, extending for
about 2 pc and exhibiting sub-clustering: a denser, more condensed, sub-cluster
surrounding the optical high-mass B0.5V illuminator star; and a more embedded,
optically invisible, sub-cluster located towards the eastern, dark part of the
nebula and including the luminous MSX source G224.1880+01.2407, a massive
protostellar candidate that could be the origin of jets and extended features
seen at 2.12 micron. The double cluster appears to be clearing the remaining
molecular material of the parent cloud, creating patches of lower extinction
and allowing some of the least reddened members to be detected in the optical
images. We find 12 MS and 143 PMS members using 3 different methods: comparison
with isochrones in optical colour-magnitude diagrams, detection of near-IR
excess, and presence of Halpha emission. The most massive star fits a 4 Myr
post-MS isochrone. The age of the optically selected PMS population is
estimated to be 7-8 Myr. The IR-excess population shows sub-clustering on
scales as small as 0.23 pc and is probably much younger.Comment: 15 pages, 16 figure
Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu
To understand the formation and evolution of the different stellar
populations within our Galaxy it is essential to combine detailed kinematical
and chemical information for large samples of stars. We derive chemical
abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu for a large sample of more
than 1000 FGK dwarf stars with high-resolution (\,115000) and
high-quality spectra from the HARPS-GTO program. The abundances are derived by
a standard Local Thermodinamyc Equilibrium (LTE) analysis using measured
Equivalent Widths (EWs) injected to the code MOOG and a grid of Kurucz ATLAS9
atmospheres. We find that thick disk stars are chemically disjunct for Zn and
Eu and also show on average higher Zr but lower Ba and Y when compared to the
thin disk stars. We also discovered that the previously identified
high- metal-rich population is also enhanced in Cu, Zn, Nd and Eu with
respect to the thin disk but presents Ba and Y abundances lower on average,
following the trend of thick disk stars towards higher metallities and further
supporting the different chemical composition of this population. The ratio of
heavy-s to light-s elements of thin disk stars presents the expected behaviour
(increasing towards lower metallicities) and can be explained by a major
contribution of low-mass AGB stars for s-process production at disk
metallicities. However, the opposite trend found for thick disk stars suggests
that intermediate-mass AGB stars played an important role in the enrichment of
the gas from where these stars formed. Previous works in the literature also
point to a possible primary production of light-s elements at low metallicities
to explain this trend. Finally, we also find an enhancement of light-s elements
in the thin disk at super solar metallicities which could be caused by the
contribution of metal-rich AGB stars. (short version)Comment: 20 pages, 19 figures, accepted by A&
Searching for the signatures of terrestrial planets in F-, G-type main-sequence stars
We have studied the volatile-to-refractory abundance ratios to investigate
their possible relation with the low-mass planetary formation. We present a
fully differential chemical abundance analysis using high-quality HARPS and
UVES spectra of 61 late F- and early G-type main-sequence stars, 29 are planet
hosts and 32 are stars without detected planets. As the previous sample of
solar analogs, these stars slightly hotter than the Sun also provide very
accurate Galactic chemical abundance trends in the metallicity range . Stars with and without planets show similar mean abundance
ratios. Moreover, when removing the Galactic chemical evolution effects, these
mean abundance ratios, , versus condensation
temperature tend to exhibit less steep trends with nearly null or slightly
negative slopes. We have also analyzed a sub-sample of 26 metal-rich stars, 13
with and 13 without known planets and find the similar, although not equal,
abundance pattern with negative slopes for both samples of stars with and
without planets. Using stars at S/N provides equally steep abundance
trends with negative slopes for both stars with and without planets. We revisit
the sample of solar analogs to study the abundance patterns of these stars, in
particular, 8 stars hosting super-Earth-like planets. Among these stars having
very low-mass planets, only four of them reveal clear increasing abundance
trends versus condensation temperature. Finally, we have compared these
observed slopes with those predicted using a simple model which enables us to
compute the mass of rocks which have formed terrestrial planets in each
planetary system. We do not find any evidence supporting the conclusion that
the volatile-to-refractory abundance ratio is related to the presence of rocky
planets.Comment: Accepted for publication in A&
Massive Open Online Courses: Combining Methodologies and Architecture for a Success Learning
Massive Open Online Courses: Combining Methodologies and Architecture for a Success Learnin
CNO behaviour in planet-harbouring stars. II. Carbon abundances in stars with and without planets using the CH band
Context. Carbon, oxygen and nitrogen (CNO) are key elements in stellar
formation and evolution, and their abundances should also have a significant
impact on planetary formation and evolution.
Aims. We present a detailed spectroscopic analysis of 1110 solar-type stars,
143 of which are known to have planetary companions. We have determined the
carbon abundances of these stars and investigate a possible connection between
C and the presence of planetary companions. Methods. We used the HARPS
spectrograph to obtain high-resolution optical spectra of our targets. Spectral
synthesis of the CH band at 4300\AA was performed with the spectral synthesis
codes MOOG and FITTING.
Results. We have studied carbon in several reliable spectral windows and have
obtained abundances and distributions that show that planet host stars are
carbon rich when compared to single stars, a signature caused by the known
metal-rich nature of stars with planets. We find no different behaviour when
separating the stars by the mass of the planetary companion.
Conclusions. We conclude that reliable carbon abundances can be derived for
solar-type stars from the CH band at 4300\AA. We confirm two different slope
trends for [C/Fe] with [Fe/H] because the behaviour is opposite for stars above
and below solar values. We observe a flat distribution of the [C/Fe] ratio for
all planetary masses, a finding that apparently excludes any clear connection
between the [C/Fe] abundance ratio and planetary mass.Comment: 10 pages, 10 figures. Accepted to A&
C/O vs Mg/Si ratios in solar type stars: The HARPS sample
Aims. We present a detailed study of the Mg/Si and C/O ratios and their
importance in determining the mineralogy of planetary companions. Methods.
Using 499 solar-like stars from the HARPS sample, we determine C/O and Mg/Si
elemental abundance ratios to study the nature of the possible planets formed.
We separated the planetary population in low-mass planets ( < 30 ) and high-mass planets ( > 30 ) to test for possible
relation with the mass. Results. We find a diversity of mineralogical ratios
that reveal the different kinds of planetary systems that can be formed, most
of them dissimilar to our solar system. The different values of the Mg/Si and
C/O ratios can determine different composition of planets formed. We found that
100\% of our planetary sample present C/O < 0.8. 86\% of stars with high-mass
companions present 0.8 > C/O > 0.4, while 14\% present C/O values lower than
0.4. Regarding Mg/Si, all stars with low-mass planetary companion showed values
between 1 and 2, while 85% of the high-mass companion sample does. The other
15\% showed Mg/Si values below 1. No stars with planets were found with Mg/Si >
2. Planet hosts with low-mass companions present C/O and Mg/Si ratios similar
to those found in the Sun, whereas stars with high-mass companions have lower
C/O.Comment: 9 pages, 12 figues. Accepted in A&
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