Poster abstracts

Modeling and three-dimensional representation of the magnetic field lines of a white dwarf
Alberto Mario Moros Marcillo

Within the study and analysis of the stellar magnetic fields, is the parameterization of various properties of the stars, where plays a fundamental role the evolutionary state of the same. This article will go into the physics behind white dwarfs or even neutron stars, which are the last evolutionary states of the large number of stars abounding (existing) in the known universe. In this way, this work will focus on the analysis of electromagnetic behaviors of a white dwarf, performing a simulation of the magnetic field in Matlab based on the model of Dynamo and the use of Magneto-dynamic equations, emphasizing the field intensity and magnetic flux of these stars. Therefore, this work will demonstrate how these properties evolve in time based on the geometric 3D analysis of the lines of the magnetic field of the star, having as parameters the distribution of charge of the star, the speed of rotation, the temperature and star dimensions. It will be demonstrated the construction of the lines of magnetic field of the proposed model of the star, in a 3D simulation including the toolbox of Biot-Savart in Matlab and using numerical methods from the afore mentioned parameters. It is concluded that the developed model complies with the parameters of the Magneto hydrodynamic equations, showing it at the same time of placing a test particle near the neighborhood of the simulated star, which is accelerated to the magnetic poles depending on the type of charge of the star, increasing the emission of electromagnetic blast as they are commonly found in the pulsars.

Stellar flybys in protoplanetary discs
Nicolás Cuello

Stellar flybys or encounters are expected to occur in stellar clusters. Presumably, such tidal encounters affect the surroundings of young stars, namely their protoplanetary discs. Here we present 3D hydrodynamical simulations of a circumprimary disc around a (single) star which is perturbed by a stellar flyby. We assume that the perturber is on an unbound parabolic orbit (e=1). By considering different orbital inclinations, pericentre distances, mass ratios and flyby times we study the disc response during and after the encounter. This is done for the gaseous phase and the dusty phase for grain sizes ranging from 1 $\mu$m to 1 cm. We observe a very rich structure in the disc during and after the flyby: warped rings, spirals with evolving pitch angles, increasing accretion rates and disc truncation. In addition, we compare these dynamical effects to the ones caused by an outer companion on an eccentric orbit. Finally, we discuss the implications for planet formation in such systems.

A star forming region in the Galactic plane at l=317
M. Corti, G. Baume, L. Suad

The region of the G316.8-0.1 radio source host also the IRAS 14416-5937 source and the embedded clusters DBS 89-90-91. We studied this region, identified as a star forming region, using the combination of data at different spectral ranges. They include photometric infrared (2MASS, VVV, Spitzer, Herschel) and radio (SGPS, PMN) surveys. These data were complemented with already known information for some particular objects in the area. With this information, we could carried out an analysis of the stellar populations and structures of the interstellar medium (ISM) in this direction assessing the possible relation between them. We obtained preliminary values of the main features of the clusters as their stellar densities, distances, reddenings and sizes. Additionaly, we could identify some YSO candidates. Regarding the ISM, we could estimate the electronic density, excitation parameter and mass of the HII Region.

Weak lensing analysis of Compact Groups using CS82 data
Martin Chalela, Elizabeth J. Gonzalez, Martin Makler, Diego Garcia Lambas, Ana L. O’Mill

In this work we present a lensing study of Compact Groups (CGs) using data obtained from the high quality Canada-France-Hawaii Telescope Stripe 82 Survey. Using stacking techniques we computed the average density contrast profile and analyse the lensing signal dependence on
groups surface brightness and morphological content. We obtain larger lensing signal for CGs with higher surface brightness probably due to their lower contamination by interlopers. Also, we find a strong dependence of the group lensing signal on the group concentration parameter, with the most concentrated quintile showing a significant lensing signal consistent with an isothermal sphere with $\sigma_V =289 \pm 22$ km/s and a NFW profile with $R_{200}=0.53\pm0.04$ Mpc. For this sample we obtain a dynamical mass lower than the weak lensing mass, suggesting that group dynamics may be affected by galaxy dynamical friction and interactions.

FIR/sub-mm signatures of the first galaxies
Maria Emilia De Rossi, Volker Bromm

We construct analytical models for studying dust emission from the first galaxies, exploring different grain size distributions and chemical compositions. For typical dwarf-size galaxies at redshifts z~10, the peak of dust emission occurs at an observed wavelength of ~500 micrometers. The predicted flux from these sources is below the capabilities of current and upcoming observatories, but is a target for next-generation telescopes. Our results suggest that primeval galactic systems would contribute to the observed FIR/sub-mm extragalactic background light (EBL), although their imprint is hidden in dominant foregrounds. Considering the strong dependence of our model EBL on the dust-to-metal ratio, we infer that estimates of the FIR/sub-mm EBL could provide important constraints on the amount of dust in the early Universe.

Dynamics of the large scale structures
Marcelo Lares, Heliana Luparello, Victoria Maldonado, Andrés Ruiz, Dante Paz, Diego García Lambas

The expanding complex pattern of filaments, walls and voids build the evolving cosmic web with material flowing from underdense onto high density regions. Here we explore the dynamical behaviour of voids and galaxies in void shells relative to neighboring overdense superstructures, using the Millenium Simulation and the main galaxy catalogue in Sloan Digital Sky Survey data. We define a correlation measure to estimate the tendency of voids to be located at a given distance from a superstructure. We find voids-in-clouds (S-types) preferentially located closer to superstructures than voids-in-voids (R-types) although we obtain that voids within $\sim$40 Mpc of superstructures are infalling in a similar fashion independently of void type. Galaxies residing in void shells show infall towards the closest superstructure, along with the void global motion, with a differential velocity component depending on their relative position in the shell with respect to the direction to the superstructure. This effect is produced by void expansion and therefore is stronger for R-types. We also find that galaxies in void shells facing the superstrucure flow towards the overdensities faster than galaxies elsewere at the same relative distance to the superstructure. The results obtained for the simulation are also reproduced for the SDSS data with a linearized velocity field implementation.

CaT study of Bulge Globular Clusters
M.C. Parisi, D. Geisler, R. Cohen, F. Mauro, S. Villanova, I. Saviane

It has been recognized for a long time that our Galaxy contains at least two populations of Globular Clusters: one associated with the halo and the other with Disco/Bulge of the Milky Way (BGC). Both populations strongly trace the chemical and dynamic properties of the respective Galactic components. While the Globular Clusters of the halo have been studied in great detail, the BGC have been relatively neglected, mainly due to the high interstellar reddening. The Vista Variables in the Via Lactea survey (VVV) has been an important advance for the infrared study of the Galaxy’s BGC system. However, there are two fundamental parameters of these objects that the VVV can not provide with the required precision: radial velocities (VR) and metallicities. The most efficient way to derive these important parameters is through the near infrared spectroscopic observation of the Ca II Triplet lines (CaT – 8500). In this work, we present preliminary results of a sample of BGC studied with the CaT technique, through observations obtained with the FORS2 instrument of the VLT (Chile). Our results will not only contribute to the understanding of the distribution of metallicities and VRs of the CGB system, but will also provide information on possible interesting objects for the search, by means of high dispersion spectroscopy, of multiple populations in BGC.

Extragalactic stellar photometry and blending problem
C. Feinstein, G. Baume, J. Rodriguez, M.M. Vergne

The images provided by the Advanced Camera for Surveys at the Hubble Space Telescope (ACS/HST) has the amazing spacial resolution of 0″”.05/pixel therefore, it could resolve individual stars in nearby galaxies and in particular young blue stars in associations and open clusters of the recent starburts. These data are usefulfor studies of the extragalactic young extragalactic population using color magnitud diagrams (CMD) of the stellar groups. However, even with the excellent indicated spatial resolution, the blending of several stars in crowded fields can change the shape of the CMDs. Some of the blending could be handled in the cases they produce particular features on the stellar PSF profile (e.g. abnormal sharpness, roundness, etc). But in some cases the blend could be difficult to detect, this is the case were a pair or several stars are in the same line of sight (e.g. obseved in the same pixel). In this work, we investigated the importance of the blending effect in several crowded regions, using both numerical simulations and real ACS/HST data. In particular, we evaluated the influence of this effect over the CMDs, luminosity functions (LFs) and reddening estimations obtained from the observations

Halo occupation models for accurate clustering predictions

Esteban Jim\’enez, Sergio Contreras, Nelson Padilla, Idit Zehavi, Carlton Baugh, Violeta Gonz\’alez-Perez

We obtain the two-point galaxy correlation function and halo occupation distributions (HODs) of samples ranked by stellar mass or star formation rate (SFR). We define the samples by a number density and they are taken from different Semi-Analytical Models (SAMs) outputs. Accurate measures of clustering are good to get cosmological information through the connection of correlation function with the density fluctuations. In this sense, we use the HOD to populate the dark matter haloes as accurate as possible to get a good understanding of the galaxy clustering. Thus, we develop three different populating procedures to study differences in clustering and to taking care of dispersion on halo occupation which is present principally in SFR samples. We find that there are no substantial differences in clustering predictions at large scales between the three models. Nevertheless, predictions at small scales are very sensitive to the model applied. In particular, we find that the model that uses the HOD of central and satellite galaxies separately and assumes a super-Poisson distribution for satellites is the best model. This is consistent with either stellar mass or SFR samples.


Study of newly detected binary stars in the Galactic external disk with VVV Gramajo Luciana, Palma Tali, Minniti Dante, Clari\’a Olmedo Juan Jos\’e

In this contribution we present a sample of new candidates of eclipsing binary systems detected in the NIR bands using the Vista Variables in the Via Lactea (VVV) survey. The new detections are concentrated in the external regions of the Galactic disk. The sample consists of detached, semidetached and contact eclipsing binaries. We use the new version of the Wilson and Devinney code and the Physics Of Eclipsing Binaries (PHOEBE) interactive code to model the light curves and derive their astrophysical parameters. Our results show that we find mainly contact and detached binaries with eccentricities of about 0.0001, inclinations of approximately 80 and surface temperatures ranging between 3500 K and 6000 K.