A search for massive UCDs in the Centaurus Galaxy Cluster

We recently initiated a search for ultra-compact dwarf galaxies (UCDs) in the Centaurus galaxy cluster (Mieske et al. 2007), resulting in the discovery of 27 compact objects with -12.2<M_V<-10.9 mag. Our overall survey completeness was 15-20% within 120 kpc projected clustercentric distance. In order to better constrain the luminosity distribution of the brightest UCDs in Centaurus, we continue our search by substantially improving our survey completeness specifically in the regime M_V<-12 mag (V_0<21.3 mag). Using VIMOS at the VLT, we obtain low-resolution spectra of 400 compact objects with 19.3<V_0<21.3 mag (-14<M_V<-12 mag at the Centaurus distance) in the central 25' of the Centaurus cluster, which corresponds to a projected radius of ~150 kpc. Our survey yields complete area coverage within ~120 kpc. For 94% of the sources included in the masks we successfully measure a redshift. Due to incompleteness in the slit assignment, our final completeness in the area surveyed is 52%. Among our targets we find three new UCDs in the magnitude range -12.2<M_V<-12 mag, hence at the faint limit of our survey. One of them is covered by archival HST WFPC2 imaging, yielding a size estimate of r_h <= 8-9 pc. At 95% confidence we can reject the hypothesis that in the area surveyed there are more than 2 massive UCDs with M_V<-12.2 mag and r_eff <=70 pc. Our survey hence confirms the extreme rareness of massive UCDs. We find that the radial distributions of Centaurus and Fornax UCDs with respect to their host clusters' centers agree within the 2 sigma level.Comment: 9 pages, 7 figures, accepted as Research Note for A&

Orientations and detachments of graphs with prescribed degrees and connectivity

We give a necessary and sufficient condition for a graph to have an orientation that has k edge-disjoint arborescences rooted at a designated vertex s subject to lower and upper bounds on the in-degree at each vertex. The result is used to derive a characterization of graphs having a detachment that contains k edge-disjoint spanning trees. Efficient algorithms for finding those orientations and detachments are also described. In particular, the paper provides an algorithm for finding a connected (loopless) detachment in O(nm) time, improving on the previous best running time bound, where n and m denote the numbers of vertices and edges, respectively. © 2014 Elsevier B.V. All rights reserved

Dynamical Formation of Millisecond Pulsars in Globular Clusters

The cumulative luminosity distribution functions (CLFs) of radio millisecond pulsars (MSPs) in globular clusters (GCs) and in the Galactic field at a frequency of 1.4 GHz have been examined. Assuming a functional form, $N \propto L^q$ where $N$ is the number of MSPs and $L$ is the luminosity at 1.4 GHz, it is found that the CLFs significantly differ with a steeper slope, $q=-0.83 \pm 0.05$, in GCs than in the Galactic field ($q=-0.48 \pm 0.04$), suggesting a different formation or evolutionary history of MSPs in these two regions of the Galaxy. To probe the production mechanism of MSPs in clusters, a search of the possible relationships between the MSP population and cluster properties was carried out. The results of an investigation of 9 GCs indicate positive correlations between the MSP population and the stellar encounter rate and metallicity. This provides additional evidence suggesting that stellar dynamical interactions are important in the formation of the MSP population in GCs.Comment: 18 pages, 3 figures, 4 tables, accepted for publication in Ap

A search for ultra-compact dwarf galaxies in the Centaurus galaxy cluster

Aim: To extend the investigations of ultra-compact dwarf galaxies (UCDs) beyond the well studied Fornax and Virgo clusters. Methods: We measured spectroscopic redshifts of about 400 compact object candidates with 19.2 < V < 22.4 mag in the central region of the Centaurus galaxy cluster (d=43Mpc), using VIMOS@VLT. The luminosity range of the candidates covers that of bright globular clusters (GCs) and of UCDs in Fornax and Virgo. Results: We confirm the cluster membership of 27 compact objects, covering an absolute magnitude range -12.2 < M_V < -10.9 mag. We do not find counterparts to the two very large and bright UCDs in Fornax and Virgo with M_V=-13.5 mag, possibly due to survey incompleteness. The compact objects' distribution in magnitude and space is consistent with that of the GC population. Their kinematics and spatial distribution associate them to the central galaxies rather than to the overall cluster potential. The compact objects have a mean metallicity consistent with that of the metal-rich globular cluster sub-population. Compact objects with high S/N spectra exhibit solar [alpha/Fe] abundances, consistent with typical dwarf elliptical galaxy values and unlike galactic bulge globular clusters. HST based size estimates for a sub-sample of eight compact objects reveal the existence of one very large object with half-light radius r_h around 30 pc, having M_V=-11.6 mag (~10^7 M_sun). This source shows super-solar [alpha/Fe] abundances. Seven further sources are only marginally larger than typical GCs with r_h in the range 4 to 10 pc. Conclusions: We consider the largest compact object found to be the only bona-fide UCD detected in our study. In order to improve our understanding of UCDs in Centaurus, a significant increase of our survey completeness is necessary.Comment: 11 pages, 12 figures, accepted for publication in A&

On the efficiency of field star capture by star clusters

An exciting recent finding regarding scaling relations among globular clusters is the so-called 'blue tilt': clusters of the blue sub-population follow a trend of redder colour with increasing luminosity. In this paper we evaluate to which extent field star capture over a Hubble time may explain the 'blue tilt'. We perform collisional N-body simulations to quantify the amount of field star capture occuring over a Hubble time to star clusters with 10^3 to 10^6 stars. In the simulations we follow the orbits of field stars passing through a star cluster and calculate the energy change that the field stars experience due to gravitational interaction with cluster stars during one passage through the cluster. The capture condition is that their total energy after the passage is smaller than the gravitational potential at the cluster's tidal radius. By folding this with the fly-by rates of field stars with an assumed space density as in the solar neighbourhood and a range of velocity dispersions, we derive estimates on the mass fraction of captured field stars as a function of environment. We find that integrated over a Hubble time, the ratio between captured field stars and total number of clusters stars is very low (<~ 10^(-4)), even for the smallest considered field star velocity dispersion sigma=15 km/s. This holds for star clusters in the mass range of both open clusters and globular clusters. We furthermore show that tidal friction has a negligible effect on the energy distribution of field stars after interaction with the cluster. We conclude that field star capture is not a probable mechanism for creating the colour-magnitude trend of metal-poor globular clusters.Comment: 8 pages, 5 figures, accepted for publication in A&

Discrete fuzzy system orbits as a portfolio selection method

[EN] The purpose of this work is to approach the portfolio selection problem from a particular System Theory framework. The System will be formed by the set of public companies in the portfolio and a set of fuzzy relations on those companies. Starting with an equally split portfolio represented by a fuzzy set B, the orbit of B is computed for a particular period obtaining a portfolio to invest in the next period. We present an example ¿nding nine portfolios to invest in 9 months and we compare them with some optimal portfolios in the ef¿cient frontier given by the Modern Portfolio Theory and with some random generated portfolios. We ¿nd a better performance in returns for the portfolio based on the systemic method.Perez-Gonzaga, S.; Jordán Núñez, J.; Miró Martínez, P. (2017). Discrete fuzzy system orbits as a portfolio selection method. Operational Research (Online). doi:10.1007/s12351-017-0361-2SAgliardi E, Agliardi R (2011) Bond pricing under imprecise information. Oper Res 11(3):299–309Esteve-Calvo P, Lloret-Climent M (2006) Coverage, invariability and orbits by structural functions. Kybernetes 35(7/8):1236–1240Jegadeesh N, Titman S (1993) Returns to buying winners and selling losers: implications for stock market efficiency. J Finance 48(1):65–91Klement EP, Mesiar R, Pap E (2013) Triangular norms, vol 8. Springer, New YorkLloret-Climent M, Villacampa-Esteve Y, Us-Domenech JL (1998) System-linkage: structural functions and hierarchies. Cybern Syst 29(1):35–46Ma YH, Lin Y (1987) Some properties of linked time systems. Int J Gen Syst 13(2):125–134Markowitz H (1952) Portfolio selection. J Finance 7(1):77–91Perez-Gonzaga S, Lloret-Climent M, Nescolarde-Selva JA (2015) Invariability, orbits and fuzzy attractors. Int J Gen Syst 45(1):29–40Tiryaki F, Ahlatcioglu B (2009) Fuzzy portfolio selection using fuzzy analytic hierarchy process. Inf Sci 179(1):53–69Von Bertalanffy L (1968) General system theory: foundations, development, applications. George Braziller, New York, pp 40Zadeh LA (1962) From circuit theory to system theory. Proc IRE 50(5):856–86

Globular cluster systems in fossil groups: NGC6482, NGC1132 and ESO306-017

We study the globular cluster (GC) systems in three representative fossil group galaxies: the nearest (NGC6482), the prototype (NGC1132) and the most massive known to date (ESO306-017). This is the first systematic study of GC systems in fossil groups. Using data obtained with the Hubble Space Telescope Advanced Camera for Surveys in the F475W and F850LP filters, we determine the GC color and magnitude distributions, surface number density profiles, and specific frequencies. In all three systems, the GC color distribution is bimodal, the GCs are spatially more extended than the starlight, and the red population is more concentrated than the blue. The specific frequencies seem to scale with the optical luminosities of the central galaxy and span a range similar to that of the normal bright elliptical galaxies in rich environments. We also analyze the galaxy surface brightness distributions to look for deviations from the best-fit S\'ersic profiles; we find evidence of recent dynamical interaction in all three fossil group galaxies. Using X-ray data from the literature, we find that luminosity and metallicity appear to correlate with the number of GCs and their mean color, respectively. Interestingly, although NGC6482 has the lowest mass and luminosity in our sample, its GC system has the reddest mean color, and the surrounding X-ray gas has the highest metallicity.Comment: 16 pages, 13 figures. Accepted for publication in A&

K2-113b: A dense hot-Jupiter transiting a solar analogue

We present the discovery of K2-113b, a dense hot-Jupiter discovered using photometry from Campaign 8 of the Kepler-2 (K2) mission and high-resolution spectroscopic follow up obtained with the FEROS spectrograph. The planet orbits a $V=13.68$ solar analogue in a $P=5.81760^{+0.00003}_{-0.00003}$ day orbit, has a radius of $0.93^{+0.10}_{-0.07}R_J$ and a mass of $1.29^{+0.13}_{-0.14}M_J$. With a density of $1.97^{+0.60}_{-0.53}$ gr/cm$^3$, the planet is among the densest systems known having masses below 2 $M_J$ and $T_{eq} > 1000$, and is just above the temperature limit at which inflation mechanisms are believed to start being important. Based on its mass and radius, we estimate that K2-113b should have a heavy element content on the order of $\sim$ 110 $M_{\oplus}$ or greater.Comment: 8 pages, 7 figures. Accepted to MNRAS; added new photometry from newest version of EVEREST, which allows for a constrain on the secondary eclipse dept

Decision making and skill development In youth football players

Este artículo presenta como se desarrolla la toma de decisiones y la habilidad técnica en jugadores con alto nivel de pericia desde los 6-7 a 13-14 años. El marco teórico está basado en la perspectiva de los sistemas dinámicos y la enseñanza comprensiva de los deportes. Se tomó como muestra a 57 jugadores del primer equipo de cada categoría de edad del Albacete Balompié: prebenjamín, benjamín, alevín e infantil. El instrumento usado fue la Herramienta de Evaluación del Rendimiento de Juego (HERJ), que mide la toma de decisiones y la ejecución, incluyendo el análisis ecológico atendiendo a principios tácticos (Bayer, 1992), comparando la situación en el juego con la decisión aplicada. Los resultados se basan en el análisis inferencial y correlacional. La evolución del rendimiento de juego se orienta desde el ataque hasta la defensa. Se han encontrado diferencias significativas en las variables entre las cuatro categorías de formación estudiadas, especialmente en el principio táctico de progresar hacia la portería contraria y en el desmarque, así como en el marcaje y la ayuda en defensa.This paper presents how decision-making and skills are developed in high level of expertise players from 6-7 to 13-14 years. The framework is based on the dynamical systems and teaching games for understanding approaches. Participants were 57 first team players of each age (n = 13 to 16) of Albacete Balompié: U-8, U-10, U-12 and U-14. The Game Performance Assessment Tool (GPET) was the instrument used for assessment, which measures decision-making and execution from an ecological view in relation to tactical principles (Bayer, 1992), comparing the game situation with the decision applied. The results are based on inferential and correlation analysis. The evolution of knowledge evolves attack to defensive. We have found significant differences in variables between the four age categories studied. These differences have been shown in attack: the progress toward goal tactical principle and shake off; on defence: marking and cover (off-ball defenders)