15,011 research outputs found
Bridge over troubled gas: clusters and associations under the SMC and LMC tidal stresses
We obtained SOAR telescope B and V photometry of 14 star clusters and 2
associations in the Bridge tidal structure connecting the LMC and SMC. These
objects are used to study the formation and evolution of star clusters and
associations under tidal stresses from the Clouds. Typical star clusters in the
Bridge are not richly populated and have in general relatively large diameters
(~30-35 pc), being larger than Galactic counterparts of similar age. Ages and
other fundamental parameters are determined with field-star decontaminated
photometry. A self-consistent approach is used to derive parameters for the
most-populated sample cluster NGC 796 and two young CMD templates built with
the remaining Bridge clusters. We find that the clusters are not coeval in the
Bridge. They range from approximately a few Myr (still related to optical HII
regions and WISE and Spitzer dust emission measurements) to about 100-200 Myr.
The derived distance moduli for the Bridge objects suggests that the Bridge is
a structure connecting the LMC far-side in the East to the foreground of the
SMC to the West. Most of the present clusters are part of the tidal dwarf
candidate D 1, which is associated with an H I overdensity. We find further
evidence that the studied part of the Bridge is evolving into a tidal dwarf
galaxy, decoupling from the Bridge.Comment: 15 pages, 15 figures, MNRAS, Accepted 2015 July 2
Scaling limit for a drainage network model
We consider the two dimensional version of a drainage network model
introduced by Gangopadhyay, Roy and Sarkar, and show that the appropriately
rescaled family of its paths converges in distribution to the Brownian web. We
do so by verifying the convergence criteria proposed by Fontes, Isopi, Newman
and Ravishankar.Comment: 15 page
A Multi-Membership Catalogue for 1876 Open Clusters using UCAC4 data
The main objective of this work is to determine the cluster members of 1876
open clusters, using positions and proper motions of the astrometric catalogue
UCAC4. For this purpose we apply three different methods, all them based on a
Bayesian approach, but with different formulations: a purely parametric method,
another completely non-parametric algorithm, and a third, recently developed by
Sampedro & Alfaro, using both formulations at different steps of the whole
process. The first and second statistical moments of the members phase-space
subspace, obtained after applying the three methods, are compared for every
cluster. Although, on average, the three methods yield similar results,
specific differences between them, as well as for some particular clusters, are
also present. The comparison with other published catalogues shows good
agreement. We have also estimated for the first time the mean proper motion for
a sample of 18 clusters. The results are organized in a single catalogue formed
by two main files, one with the most relevant information for each cluster,
partially including that in UCAC4, and the other showing the individual
membership probabilities for each star in the cluster area. The final
catalogue, with an interface design that enables an easy interaction with the
user, is available in electronic format at SSG-IAA
(http://ssg.iaa.es/en/content/sampedro-cluster-catalog) website.Comment: Accepted for publication in MNRAS. 9 pages, 3 figures, 6 table
Metallic magnetism at finite temperatures studied by relativistic disordered moment description: Theory and applications
We develop a self-consistent relativistic disordered local moment (RDLM)
scheme aimed at describing finite temperature magnetism of itinerant metals
from first principles. Our implementation in terms of the
Korringa--Kohn--Rostoker multiple scattering theory and the coherent potential
approximation allows to relate the orientational distribution of the spins to
the electronic structure, thus a self-consistent treatment of the distribution
is possible. We present applications for bulk bcc Fe, L1-FePt and FeRh
ordered in the CsCl structure. The calculations for Fe show significant
variation of the local moments with temperature, whereas according to the mean
field treatment of the spin fluctuations the Curie temperature is
overestimated. The magnetic anisotropy of FePt alloys is found to depend
strongly on intermixing between nominally Fe and Pt layers, and it shows a
power-law behavior as a function of magnetization for a broad range of chemical
disorder. In case of FeRh we construct a lattice constant vs. temperature phase
diagram and determine the phaseline of metamagnetic transitions based on
self-consistent RDLM free energy curves.Comment: 11 pages, 8 figure
An embedded formulation with conforming
Use of strong discontinuities with satisfaction of compatibilit
Electronic Phase Separation Transition as the Origin of the Superconductivity and the Pseudogap Phase of Cuprates
We propose a new phase of matter, an electronic phase separation transition
that starts near the upper pseudogap and segregates the holes into high and low
density domains. The Cahn-Hilliard approach is used to follow quantitatively
this second order transition. The resulting grain boundary potential confines
the charge in domains and favors the development of intragrain superconducting
amplitudes. The zero resistivity transition arises only when the intergrain
Josephson coupling is of the order of the thermal energy and phase
locking among the superconducting grains takes place. We show that this
approach explains the pseudogap and superconducting phases in a natural way and
reproduces some recent scanning tunneling microscopy dataComment: 4 pages and 5 eps fig
- …