122 research outputs found
Density functional electronic spectrum of the cluster and possible local Jahn-Teller distorsions in the La-Ba-Cu-O superconductor
We present a density functional theory (DFT) calculation in the generalized
gradient approximation to study the possibility for the existence of
Jahn-Teller (JT) or pseudo Jahn-Teller (PJT) type local distortions in the
La-Ba-Cu-O superconducting system. We performed the calculation and
correspondingly group theory classification of the electronic ground state of
the CuO elongated octahedra cluster, immersed in a background
simulating the superconductor. Part of the motivation to do this study is that
the origin of the apical deformation of the CuO cluster is not
due to a pure JT effect, having therefore a non {\it a priori} condition to
remove the degeneracy of the electronic ground state of the parent regular
octahedron. We present a comparative analysis of the symmetry classified
electron spectrum with previously reported results using unrestricted
Hartree-Fock calculations (UHF). Both the DFT and UHF calculations produced a
non degenerate electronic ground state, not having therefore the necessary
condition for a pure JT effect. However, the appearance of a degenerate E
state near to the highest occupied molecular orbital in the DFT calculation,
suggests the possibility for a PJT effect responsible for a local distortion of
the oxidized CuO cluster.Comment: 12 pages, 3 figures, submitted to International Journal of Modern
Physics B (IJMPB
A stellar census in globular clusters with MUSE: The contribution of rotation to cluster dynamics studied with 200 000 stars
This is the first of a series of papers presenting the results from our survey of 25 Galactic globular clusters with the MUSE integral-field spectrograph. In combination with our dedicated algorithm for source deblending, MUSE provides unique multiplex capabilities in crowded stellar fields and allows us to acquire samples of up to 20 000 stars within the half-light radius of each cluster. The present paper focuses on the analysis of the internal dynamics of 22 out of the 25 clusters, using about 500 000 spectra of 200 000 individual stars. Thanks to the large stellar samples per cluster, we are able to perform a detailed analysis of the central rotation and dispersion fields using both radial profiles and two-dimensional maps. The velocity dispersion profiles we derive show a good general agreement with existing radial velocity studies but typically reach closer to the cluster centres. By comparison with proper motion data we derive or update the dynamical distance estimates to 14 clusters. Compared to previous dynamical distance estimates for 47 Tuc, our value is in much better agreement with other methods. We further find significant (>3sigma) rotation in the majority (13/22) of our clusters. Our analysis seems to confirm earlier findings of a link between rotation and the ellipticities of globular clusters. In addition, we find a correlation between the strengths of internal rotation and the relaxation times of the clusters, suggesting that the central rotation fields are relics of the cluster formation that are gradually dissipated via two-body relaxation
The giant planet orbiting the cataclysmic binary DP Leonis
Planets orbiting post-common envelope binaries provide fundamental
information on planet formation and evolution, especially for the yet nearly
unexplored class of circumbinary planets. We searched for such planets in \odp,
an eclipsing short-period binary, which shows long-term eclipse-time
variations. Using published, reanalysed, and new mid-eclipse times of the white
dwarf in DP\,Leo, obtained between 1979 and 2010, we find agreement with the
light-travel-time effect produced by a third body in an elliptical orbit. In
particular, the measured binary period in 2009/2010 and the implied radial
velocity coincide with the values predicted for the motion of the binary and
the third body around the common center of mass. The orbital period, semi-major
axis, and eccentricity of the third body are P_c = 28.0 +/- 2.0 yrs, a_c = 8.2
+/- 0.4 AU, and e_c = 0.39 +/- 0.13. Its mass of M_c sin(i_c) = 6.1 +/- 0.5 M_J
qualifies it as a giant planet. It formed either as a first generation object
in a protoplanetary disk around the original binary or as a second generation
object in a disk formed in the common envelope shed by the progenitor of the
white dwarf. Even a third generation origin in matter lost from the present
accreting binary can not be entirely excluded. We searched for, but found no
evidence for a fourth body.Comment: Accepted by A&
Nonbonding oxygen holes and spinless scenario of magnetic response in doped cuprates
Both theoretical considerations and experimental data point to a more
complicated nature of the valence hole states in doped cuprates than it is
predicted by Zhang-Rice model. Actually, we deal with a competition of
conventional hybrid Cu 3d-O 2p state and purely
oxygen nonbonding state with symmetry. The latter
reveals a non-quenched Ising-like orbital moment that gives rise to a novel
spinless purely oxygen scenario of the magnetic response in doped cuprates with
the oxygen localized orbital magnetic moments of the order of tenths of Bohr
magneton. We consider the mechanism of Cu-O 2p transferred orbital
hyperfine interactions due to the mixing of the oxygen O 2p orbitals with Cu 3p
semicore orbitals. Quantitative estimates point to a large magnitude of the
respective contributions both to local field and electric field gradient, and
their correlated character.Comment: 7 pages, 1 figur
An eclipsing substellar binary in a young triple system discovered by SPECULOOS
Mass, radius, and age are three of the most fundamental parameters for
celestial objects, enabling studies of the evolution and internal physics of
stars, brown dwarfs, and planets. Brown dwarfs are hydrogen-rich objects that
are unable to sustain core fusion reactions but are supported from collapse by
electron degeneracy pressure. As they age, brown dwarfs cool, reducing their
radius and luminosity. Young exoplanets follow a similar behaviour. Brown dwarf
evolutionary models are relied upon to infer the masses, radii and ages of
these objects. Similar models are used to infer the mass and radius of directly
imaged exoplanets. Unfortunately, only sparse empirical mass, radius and age
measurements are currently available, and the models remain mostly unvalidated.
Double-line eclipsing binaries provide the most direct route for the absolute
determination of the masses and radii of stars. Here, we report the SPECULOOS
discovery of 2M1510A, a nearby, eclipsing, double-line brown dwarf binary, with
a widely-separated tertiary brown dwarf companion. We also find that the system
is a member of the Myr-old moving group, Argus. The system's age
matches those of currently known directly-imaged exoplanets. 2M1510A provides
an opportunity to benchmark evolutionary models of brown dwarfs and young
planets. We find that widely-used evolutionary models do reproduce the mass,
radius and age of the binary components remarkably well, but overestimate the
luminosity by up to 0.65 magnitudes, which could result in underestimated
photometric masses for directly-imaged exoplanets and young field brown dwarfs
by 20 to 35%
Kinematic differences between multiple populations in Galactic globular clusters
Aims. The formation process of multiple populations in globular clusters is still up for debate. These populations are characterized by different light-element abundances. Kinematic differences between the populations are particularly interesting in this respect, because they allow us to distinguish between single-epoch formation scenarios and multi-epoch formation scenarios. We derive rotation and dispersion profiles for 25 globular clusters and aim to find kinematic differences between multiple populations in 21 of them to constrain the formation process.
Methods. We split red-giant branch (RGB) stars in each cluster into three populations (P1, P2, P3) for the type-II clusters and two populations (P1 and P2) otherwise using Hubble photometry. We derive the global rotation and dispersion profiles for each cluster by using all stars with radial velocity measurements obtained from MUSE spectroscopy. We also derive these profiles for the individual populations of each cluster. Based on the rotation and dispersion profiles, we calculate the rotation strength in terms of ordered-overrandom motion (v/σ)HL evaluated at the half-light radius of the cluster. We then consistently analyse all clusters for differences in the rotation strength of their populations.
Results. We detect rotation in all but four clusters. For NGC 104, NGC 1851, NGC 2808, NGC 5286, NGC 5904, NGC 6093, NGC 6388, NGC 6541, NGC 7078 and NGC 7089 we also detect rotation for P1 and/or P2 stars. For NGC 2808, NGC 6093 and NGC 7078 we find differences in (v/σ)HL between P1 and P2 that are larger than 1σ. Whereas we find that P2 rotates faster than P1 for NGC 6093 and NGC 7078, the opposite is true for NGC 2808. However, even for these three clusters the differences are still of low significance. We find that the strength of rotation of a cluster generally scales with its median relaxation time. For P1 and P2 the corresponding relation is very weak at best. We observe no correlation between the difference in rotation strength between P1 and P2 and cluster relaxation time. The stellar radial velocities derived from MUSE data that this analysis is based on are made publicly available
Magnetic resonance microscopy and correlative histopathology of the infarcted heart
Altres ajuts:The present study was supported by the EU Joint Programming Initiative 'A Healthy Diet for a Healthy Life' (JPI HDHL INTIMIC-085), Generalitat Valenciana (GV/2018/116), INCLIVA and Universitat de Valencia (program VLC-BIOCLINIC 20-nanomIRM-2016A).Delayed enhancement cardiovascular magnetic resonance (MR) is the gold-standard for non-invasive assessment after myocardial infarction (MI). MR microscopy (MRM) provides a level of detail comparable to the macro objective of light microscopy. We used MRM and correlative histopathology to identify infarct and remote tissue in contrast agent-free multi-sequence MRM in swine MI hearts. One control group (n = 3 swine) and two experimental MI groups were formed: 90 min of ischemia followed by 1 week (acute MI = 6 swine) or 1 month (chronic MI = 5 swine) reperfusion. Representative samples of each heart were analysed by contrast agent-free multi-sequence (T1-weighting, T2-weighting, T2*-weighting, T2-mapping, and T2*-mapping). MRM was performed in a 14-Tesla vertical axis imager (Bruker-AVANCE 600 system). Images from MRM and the corresponding histopathological stained samples revealed differences in signal intensities between infarct and remote areas in both MI groups (p-value < 0.001). The multivariable models allowed us to precisely classify regions of interest (acute MI: specificity 92% and sensitivity 80%; chronic MI: specificity 100% and sensitivity 98%). Probabilistic maps based on MRM images clearly delineated the infarcted regions. As a proof of concept, these results illustrate the potential of MRM with correlative histopathology as a platform for exploring novel contrast agent-free MR biomarkers after MI
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