13,322 research outputs found
Proper motions in the VVV Survey: Results for more than 15 million stars across NGC 6544
Context: In the last six years, the VVV survey mapped 562 sq. deg. across the
bulge and southern disk of the Galaxy. However, a detailed study of these
regions, which includes globular clusters (GCs) and thousands of open
clusters is by no means an easy challenge. High differential reddening and
severe crowding along the line of sight makes highly hamper to reliably
distinguish stars belonging to different populations and/or systems. Aims: The
aim of this study is to separate stars that likely belong to the Galactic GC
NGC 6544 from its surrounding field by means of proper motion (PM) techniques.
Methods: This work was based upon a new astrometric reduction method optimized
for images of the VVV survey. Results: Photometry over the six years baseline
of the survey allowed us to obtain a mean precision of mas/yr, in
each PM coordinate, for stars with Ks < 15 mag. In the area studied here,
cluster stars separate very well from field stars, down to the main sequence
turnoff and below, allowing us to derive for the first time the absolute PM of
NGC 6544. Isochrone fitting on the clean and differential reddening corrected
cluster color magnitude diagram yields an age of 11-13 Gyr, and
metallicity [Fe/H] = -1.5 dex, in agreement with previous studies restricted to
the cluster core. We were able to derive the cluster orbit assuming an
axisymmetric model of the Galaxy and conclude that NGC 6544 is likely a halo
GC. We have not detected tidal tail signatures associated to the cluster, but a
remarkable elongation in the galactic center direction has been found. The
precision achieved in the PM determination also allows us to separate bulge
stars from foreground disk stars, enabling the kinematical selection of bona
fide bulge stars across the whole survey area. Our results show that VVV data
is perfectly suitable for this kind of analysis.Comment: 13 pages, 12 figures, accepted in A&
Magnetized strange quark matter and magnetized strange quark stars
Strange quark matter could be found in the core of neutron stars or forming
strange quark stars. As is well known, these astrophysical objects are endowed
with strong magnetic fields which affect the microscopic properties of matter
and modify the macroscopic properties of the system. In this paper we study the
role of a strong magnetic field in the thermodynamical properties of a
magnetized degenerate strange quark gas, taking into account beta-equilibrium
and charge neutrality. Quarks and electrons interact with the magnetic field
via their electric charges and anomalous magnetic moments. In contrast to the
magnetic field value of 10^19 G, obtained when anomalous magnetic moments are
not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the
stability of the system. A phase transition could be hidden for fields greater
than this value.Comment: 9 pages, 9 figure
Criterios de clasificación y re-definición de un perfil comercial de la Agricultura Familiar Campesina, Región del Maule, Chile
Jara-Rojas, R (reprint author), Univ Talca, Fac Ciencias Agr, Dpto Econ Agr, 2 Norte 685 Talca,Casilla 747, Talca, Chile.In Chile, small-scale farmers are classified according to old approaches from 1993 that do not include changes occurred in the last two decades. Maule is the region with most rural population in Chile which represents a significant stratum for development, innovation and competitiveness. This study explores a new approach of small-scale farmers -associated with Family Farm Agriculture (AFC) - classification in Chile and it describes a commercial profile or AFC-1 for famers of the Maule Region. A Cluster analysis to determine AFC-1 farmers is used. The analysis includes four association variables: Total Assets, Farm Income, Production Costs and Management Indicators. The results suggest that 16.4% of the farmers have a commercial profile and they could stay out support provided by the National Institute for Agricultural Development (INDAP). This group of farmers would not belong to AFC in short terms. This fact could bring restriction to AFC-1 farmers such as lack of credit access, less investment incentives and technical assistance. Thus, it would expect low process of technology adoption and welfare improvement. New agrarian policies must be warranted to support this important group of famers with a commercial profile
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