The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418

The 9.7-micron silicate absorption profile in the interstellar medium provides important information on the physical and chemical composition of interstellar dust grains. Measurements in the Milky Way have shown that the profile in the diffuse interstellar medium is very similar to the amorphous silicate profiles found in circumstellar dust shells around late M stars, and narrower than the silicate profile in denser star-forming regions. Here, we investigate the silicate absorption profile towards the very heavily obscured nucleus of NGC 4418, the galaxy with the deepest known silicate absorption feature, and compare it to the profiles seen in the Milky Way. Comparison between the 8-13 micron spectrum obtained with TReCS on Gemini and the larger aperture spectrum obtained from the Spitzer archive indicates that the former isolates the nuclear emission, while Spitzer detects low surface brightness circumnuclear diffuse emission in addition. The silicate absorption profile towards the nucleus is very similar to that in the diffuse ISM in the Milky Way with no evidence of spectral structure from crystalline silicates or silicon carbide grains.Comment: 7 Pages, 3 figures. MNRAS in pres

Structural changes at the semiconductor-insulator phase transition in the single layered La0.5Sr1.5MnO4 perovskite

The semiconductor-insulator phase transition of the single-layer manganite La0.5Sr1.5MnO4 has been studied by means of high resolution synchrotron x-ray powder diffraction and resonant x-ray scattering at the Mn K edge. We conclude that a concomitant structural transition from tetragonal I4/mmm to orthorhombic Cmcm phases drives this electronic transition. A detailed symmetry-mode analysis reveals that condensation of three soft modes -Delta_2(B2u), X1+(B2u) and X1+(A)- acting on the oxygen atoms accounts for the structural transformation. The Delta_2 mode leads to a pseudo Jahn-Teller distortion (in the orthorhombic bc-plane only) on one Mn site (Mn1) whereas the two X1+ modes produce an overall contraction of the other Mn site (Mn2) and expansion of the Mn1 one. The X1+ modes are responsible for the tetragonal superlattice (1/2,1/2,0)-type reflections in agreement with a checkerboard ordering of two different Mn sites. A strong enhancement of the scattered intensity has been observed for these superlattice reflections close to the Mn K edge, which could be ascribed to some degree of charge disproportion between the two Mn sites of about 0.15 electrons. We also found that the local geometrical anisotropy of the Mn1 atoms and its ordering originated by the condensed Delta_2 mode alone perfectly explains the resonant scattering of forbidden (1/4,1/4,0)-type reflections without invoking any orbital ordering.Comment: 3 tables and 10 figures; accepted in Phys. Rev.

Ground state and excitation spectra of a strongly correlated lattice by the coupled cluster method

We apply Coupled Cluster Method to a strongly correlated lattice and develop the Spectral Coupled Cluster equations by finding an approximation to the resolvent operator, that gives the spectral response for an certain class of probe operators. We apply the method to a $MnO_2$ plane model with a parameters choice which corresponds to previous experimental works and which gives a non-nominal symmetry ground state. We show that this state can be observed using our Spectral Coupled Cluster Method by probing the Coupled Cluster solution obtained from the nominal reference state. In this case one observes a negative energy resonance which corresponds to the true ground state

An X-ray Study of Local Infrared Bright Galaxies

We are carrying out detailed study of the X-ray and infrared (IR) properties of a sample of local (d < 70 Mpc) luminous infrared galaxies (LIRGs) using XMM-Newton and Spitzer (imaging and spectroscopy). The main goal is to study the extreme processes of star formation and/or active galactic nuclei (AGN) taking place in this cosmologically important class of galaxies. In this proceedings we present the preliminary results obtained from the analysis of the XMM-Newton X-ray images and the X-ray spectral modeling.Comment: 5 pages, to appear in Highlights of Spanish Astrophysics VI, Proceedings of the IX Scientific Meeting of the Spanish Astronomical Society held on September 13-17, 2010, in Madrid, Spai

Graphic study and geovisualization of the old windmills of La Mancha (Spain)

In Spain, one can find geographical diversity and unique sites of great significance and cultural heritage. Many of the nation’s treasured places, however, have deteriorated or have even disappeared. What is left, then, should be studied and documented both graphically and infographically. It is important to preserve and document Spain’s unique locations, especially those related to vernacular heritage, to transhumance and visual impact assessment in many national infrastructures projects. Windmills are important examples of agro-industrial heritage and are sometimes found in the beds of streams and rivers but can also be found high in the hills. Their presence is constant throughout the Iberian Peninsula. These mills are no longer in use due to technological advances and the emergence of new grinding systems. The aim of this study was to present a specific methodology for the documentation of windmills, to create a graphical representation using computer graphics, as well as to disseminate knowledge of this agro-industrial heritage. This research has integrated graphic materials, including freehand sketches, photographs, digital orthophotos, computer graphics and multimedia in the creation of a specific methodology based on cutting-edge technology such as a digital photogrammetric workstation (DPW), global navigation satellite systems (GNSS), computer-aided design (CAD) and computer animation

A Multiwavelength Study of the Starburst Galaxy NGC 7771

We present a multiwavelength study of the interacting starburst galaxy NGC 7771, including new optical and ultra-violet spectra and a previously unpublished soft X-ray ROSAT image and spectrum. The far-infrared, radio, and X-ray fluxes suggest that a massive burst of star-formation is currently in progress but the small equivalent width of the Balmer emission lines (equivalent width H(alpha approximately equals 100 A), the weak UV flux, the low abundance of ionised oxygen, and the shape of the optical spectrum lead us to conclude that there are few 0 stars. This might normally suggest that star-formation has ceased but the galaxy's barred gravitational potential and large gas reserves imply that this should not be so, and we therefore consider other explanations. We argue that the observations cannot be due to effects of geometry, density bounded nebulae, or dust within the nebulae, and conclude that a truncated IMF is required. The dwarf galaxy NGC 7770 appears to be in the initial stages of a merger with NGC 7771, and the resulting tidal perturbations may have induced the apparent two-armed spiral pattern, and driven a substantial fraction of the disk gas inwards. The presence of a bulge in NGC 7771 may be moderating the starburst so that, while still occuring on a large scale with a supernova rate of 0.8-1/yr, it is less violent and the IMF has a relatively low upper mass limit. We find that there is a cluster of stars obscuring part of the starburst region, and we offer an explanation of its origin

Techniques de bas niveau en traitement d'images pour la télédétection des milieux non homogènes

La télédétection vise à acquérir l'information sur des cibles en étudiant leur réponse aux ondes électromagnétiques. Et partout nous rencontrons des milieux non homogènes et des composites. Connaître comment ces milieux non homogènes répondent a la sonde de télédétection est de la plus grande importance pour la praticabilité même de la télédétection. Le comportement macroscopique d'un composite peut séxprimer en fonction des caractéristiques macroscopiques de ses constituants, mais d'une manière complexe incluant la géométrie de leur arrangement. Si nous pouvons obtenir le tenseur diélectrique efficace d'un composé, nous pouvons modéliser sa réponse au champ électromagnétique, et donc sa réponse comme cible de télédétection. La nécessité pour inclure la géométrie détaillée du système d'une façon efficace dans des méthodes numériques, ainsi qu'une équivalence entre les images numériques et les modèles de treillis des composites, suggère le recours aux techniques de bas niveau de traitement d'images numériques. Le cadre de cette thèse est le traitement numérique d'un problème général de télédétection fondée sur le problème électromagnétique d'homogénéisation dans des microstructures. Dans ce contexte, deux techniques de traitement d'images de bas niveau sont présentées, à savoir, une nouvelle méthode pour l'étiquetage des composantes connexes, présentant des améliorations significatives par rapport aux méthodes existantes, et une méthode de codage des configurations locales avec plusieurs caractéristiques la rendant appropriée pour des applications variées. Leurs avantages sont discutés, et des exemples d'application sont fournis au-delà du domaine spécifique étant à leur origine, comme la vision artificielle, le codage d'image, ou encore la synthèse d'image.The aim of remote sensing is obtaining information about targets by studying their response to electromagnetic waves. And everywhere we found non homogeneous media. Knowing how these non homogeneous media respond to the remote sensing probe is of great importance for the very feasibility of remote sensing. The macroscopic behaviour of a composite can be expressed as a function of the macroscopic characteristics of its constituents, but usually in a complex way which includes the geometry of their arrangement. If we are able to obtain the effective permittivity tensor of any given composite, we can model its macroscale response to the electromagnetic field, and therefore its response as a remote sensing target. The necessity of including the detailed geometry of the system in an efficient way in the numerical methods, together with an equivalence between grid models and digital images, suggest the recourse to low level image processing techniques. The framework of this thesis is the numerical treatment of a general problem in remote sensing based on the electromagnetic problem of homogenization of microstructures. In this context, two low level image processing techniques are presented, a new method for the labelling of connected components, with significant advantages over the classical methods, and a local configuration encoding scheme with characteristics which render it useful for different applications. Their advantages and applicability are discussed, together with some examples of application in fields out of the scope of the specific problem which originated them, namely computer vision, image coding, and image synthesis