Old Main-Sequence Turnoff Photometry in the Small Magellanic Cloud. I. Constraints on the Star Formation History in Different Fields

We present ground-based B and R-band color-magnitude diagrams (CMDs), reaching the oldest main-sequence turnoffs with good photometric accuracy for twelve fields in the Small Magellanic Cloud (SMC). Our fields, located between ~1 and ~4 degrees from the center of the galaxy, are situated in different parts of the SMC such as the "Wing'' area, and towards the West and South. In this paper we perform a first analysis of the stellar content in our SMC fields through comparison with theoretical isochrones and color functions (CFs). We find that the underlying spheroidally distributed population is composed of both intermediate-age and old stars and that its age composition does not show strong galacto-centric gradients. The three fields situated toward the east, in the Wing region, show very active current star formation. However, only in the eastern field closest to the center do we find an enhancement of recent star formation with respect to a constant SFR(t). The fields corresponding to the western side of the SMC present a much less populated young MS, and the CF analysis indicates that the SFR(t) greatly diminished around 2 Gyr ago in these parts. Field smc0057, the closest to the center of the galaxy and located in the southern part, shows recent star formation, while the rest of the southern fields present few bright MS stars. The structure of the red clump in all the CMDs is consistent with the large amount of intermediate-age stars inferred from the CMDs and color functions. None of the SMC fields presented here are dominated by old stellar populations, a fact that is in agreement with the lack of a conspicuous horizontal branch in all these SMC CMDs. This could indicate that a disk population is ruling over a possible old halo in all the observed fields.Comment: To appear in A

The effects of rising food prices on poverty in Mexico

We evaluate the impact of the rise in food prices during 2006-2008 on the poverty and extreme poverty rates in Mexico. We concentrate on the poor’s consumption of staple foods, and analyze the change in their consumption brought about by changed prices. We also allow households receiving income from the farming and livestock sector to benefit from increases in prices of food products. We find a modest increase in poverty using 2006-2007 prices, however, there is a daunting effect on the poor once the 2008 prices are taken into account. After considering the positive effects of public policies announced in 2008, such as reduced taxes and tariffs on food products and greater subsidies to the extremely poor, the poverty rate measured through consumption increases from 25% to 33.5%, and the extreme poverty rate from 10.58% to 16%, given the increase in food prices. Further analysis using the theory of optimal taxes suggests policies oriented towards relieving the food price pressure on the Mexican poor should aim at lowering the prices of eggs, vegetable oil, milk, and chicken

El alza de la pobreza nutricional en México

RESUMEN En este estudio analizamos la pobreza, con base en si los hogares cumplen con los requerimientos mínimos calóricos y proteínicos diarios. Se estudió el costo de estos nutrientes y se separaron los hogares por nivel de ingreso, para entender la relación entre la pobreza nutricional y la de ingresos. ABSTRACT We analyze poverty by estimating if households meet the minimum daily calorie and protein requirements, studying the cost of these nutrients, and separating households by income level to understand the relationship between nutritional and monetary poverty

Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs

The optical integrated spectra of three LMC young stellar clusters (NGC 1984, NGC 1994 and NGC 2011) exhibit concave continua and prominent molecular bands which deviate significantly from the predictions of single stellar population (SSP) models. In order to understand the appearance of these spectra, we create a set of young stellar population (MILES) models, which we make available to the community. We use archival International Ultraviolet Explorer integrated UV spectra to independently constrain the cluster masses and extinction, and rule out strong stochastic effects in the optical spectra. In addition, we also analyze deep colour-magnitude diagrams of the clusters to provide independent age determinations based on isochrone fitting. We explore hypotheses including age-spreads in the clusters, a top-heavy initial mass function, different SSP models and the role of red supergiant stars (RSG). We find that the strong molecular features in the optical spectra can only be reproduced by modeling an increased fraction of about 20 per cent by luminosity of RSG above what is predicted by canonical stellar evolution models. Given the uncertainties in stellar evolution at Myr ages, we cannot presently rule-out the presence of Myr age-spreads in these clusters. Our work combines different wavelengths as well as different approaches (resolved data as well as integrated spectra for the same sample) in order to reveal the complete picture. We show that each approach provides important information but in combination can we better understand the cluster stellar populations.Comment: Accepted for publication in MNRA

Revealing the tidal scars of the Small Magellanic Cloud

Due to their close proximity, the Large and Small Magellanic Clouds (SMC/LMC) provide natural laboratories for understanding how galaxies form and evolve. With the goal of determining the structure and dynamical state of the SMC, we present new spectroscopic data for $\sim$ 3000 SMC red giant branch stars observed using the AAOmega spectrograph at the Anglo-Australian Telescope. We complement our data with further spectroscopic measurements from previous studies that used the same instrumental configuration and proper motions from the \textit{Gaia} Data Release 2 catalogue. Analysing the photometric and stellar kinematic data, we find that the SMC centre of mass presents a conspicuous offset from the velocity centre of its associated \mbox{H\,{\sc i}} gas, suggesting that the SMC gas is likely to be far from dynamical equilibrium. Furthermore, we find evidence that the SMC is currently undergoing tidal disruption by the LMC within 2\,kpc of the centre of the SMC, and possibly all the way in to the very core. This is evidenced by a net outward motion of stars from the SMC centre along the direction towards the LMC and apparent tangential anisotropy at all radii. The latter is expected if the SMC is undergoing significiant tidal stripping, as we demonstrate using a suite of $N$-body simulations of the SMC/LMC system disrupting around the Milky Way. These results suggest that dynamical models for the SMC that assume a steady state will need to be revisited.Comment: Revised version submitted to MNRAS after referee report, 18 pages, 18 figure

The Star Formation History in a SMC field: IAC-star/IAC-pop at work

We present a progress report of a project to study the quantitative star formation history (SFH) in different parts of the Small Magellanic Cloud (SMC). We use the information in [(B-R), R] color-magnitude diagrams (CMDs), which reach down to the oldest main-sequence turnoffs and allow us to retrieve the SFH in detail. We show the first results of the SFH in a SMC field located in the Southern direction (at $\thicksim$1 kpc from the SMC center). This field is particularly interesting because in spite of being located in a place in which the HI column density is very low, it still presents a recent enhancement of star formation.Comment: Poster presented at: Stellar Populations as Building Blocks of Galaxies, Proceedings IAU Symposium No. 241, 200

Nano-hydroxyapatite for use in bone tissue repair

Bone can be considered as a biological hybrid material composed of organic and inorganic components: collagen and rod-shaped hydroxyapatite (HAP) of 20–50 nm lengths. The synthetic hydroxyapatite (Ca10(PO4)6(OH)2) has been extensively used as a bone substitute material due to its chemical and structural similarities with natural mineral bone. One way to obtain HAP nanoparticles is by using self-assembled amphiphilic molecules as structure directors. This study involves different hexadecyltrimethylammonium bromide (CTAB) micellar-block copolymer organized networks. Inorganic precursors were added in sequence to the CTAB-polymer solution, followed by a hydrothermal treatment. The final product was separated from the suspension by filtration and then dried. The X-ray diffraction and infrared spectroscopy pattern of the materials synthesized corresponds to the HAP pattern. Transmission and scanning electron microscopy microphotographs show a fiber network composed by 37 nm length HAP nanorods. After treatment with simulated body fluid (SBF) a layer of HAP nanocrystals grew on the material surface; that is related to the bioactivity of the material. To confirm the samples' biocompatibility, calvarial osteoblasts obtained from neonatal rats were exposed to the material and then, viability and cell adhesion were evaluated. A new method of HAP nanocrystals with similar shape, morphology and chemical characteristics of bone were developed. After SBF immersion, material revealed a spherulitic-like HAP layer that implies a positive physiological response and good bond ability to the host tissue. Therefore, nanomaterials obtained by the proposed synthesis could have a wide range of biomedical applications.Fil: D'elía, Noelia Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Gravina, Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Laiuppa, Juan Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Santillán, Graciela Edith. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Messina, Paula Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentin