Modelización geoquímica de los procesos de fusión parcial

18 páginas, 6 figuras, 1 apendice.[ES] Durante la fusión, los elementos traza y los isótopos estables sufren fraccionación mientras que los isótopos radiogénicos no varían. Como la distribución de los primeros entre las fases que intervienen sigue las leyes de las soluciones diluidas, se pueden establecer ecuaciones relativamente sencillas, que posibilitan la modelización del proceso. A su vez, el comportamiento de los isótopos radiogénicos hace que los magmas hereden la signatura del sólido del que derivar, lo que facilita la identificación del mismo. Las ecuaciones propuestas para los diferentes tipos de fusión indican que en la fusión en equilibrio la abundancia en el fundido de elementos traza altamente incompatibles alcanza valores muy elevados al comienzo del proceso y disminuye progresivamente al aumentar el grado de fusión, mientras que la concentración de los elementos compatibles crece lentamente al aumentar el porcentaje de fusión y bruscamente cuando éste alcanza valores muy altos. En la fusión fraccionada el primero de los líquidos que se genera removiliza casi completamente a todos los elementos altamente incompatibles del sistema, y los sucesivos líquidos producidos tienen muy baja concentración en dichos elementos. En la fusión incongruente se generan líquidos ricos en aquellos elementos traza que tienen altos coeficientes de reparto para las fases que funden y bajos para las de nueva formación, mientras que están empobrecidos en los elementos que entran en estas últimas fases. Si la fusión tiene lugar en presencia de una fase fluida el líquido está empobrecido, en relación al generado cuando dicha fase está ausente, en aquellos elementos que tienen coeficientes de reparto líquido-fluido aproximadamente iguales a la unidad, ya que una parte de los mismos se concentra en el fluido. Finalmente, en la fusión en desequilibrio o no difusión a la primera fracción de líquido que aparece tiene una concentración en elementos incompatibles superior y en elementos compatibles inferior a la del sólido del que deriva, con lo que la interfase sólido-líquido se empobrece y se enriquece, respectivamente. Sin embargo, al final del proceso la concentración de los elementos en el líquido se iguala a la que tenía la parte de sólido que ha fundido. Para modelizar la fusión parcid en equilibrio se pueden seguir dos vías diferentes, según se disponga o no de los coefcientes de reparto mineral-líquido y se conozcan o no los porcentajes en los que intervienen dichas fases. Si se dispone de dichos parámetros, se puede intentar duplicar las concentraciones elementales observadas en los líquidos primarios, previa selección de unas constantes razonables. Por el contrario, si no se conocen aquellos parámetros la mJdelización se puede llevar a cabo de forma distinta, según se disponga de la composición de los líquidos generados o del residuo. Si se conoce la composición de los líquidos generados, se utilizan las variaciones en las concentraciones elementales que presentan las rocas, mediante un ajuste simultáneo de todas ellas por resolución de un sistema de ecuaciones formado por las expresiones que describen el proceso, para un número suficiente de elementos, o bien independientemente para cada parámetro y elemento. A su vez, si se conoce la composición química de los residuos hay que suponer la composición del protolito y a partir del elemento más residual fijar los dos parámetros que quedan por conocer: el coeficiente de partición global residuofundido para los distintos elementos y el grado de fusión que ha sufrido cada restita, asumiendo, según proceda, el grado de fusión, el coeficiente de reparto global de uno de los elementos o la concentración del mismo.[EN] During melting processes both stable isotopes and trace elements fractionate, whereas radiogenic isotopes do not change. The distribution of the former between the phases that participate, follows diluted solutions laws in such a way that it is possible to establish relatively simple equations to model these processes. Additionally, the radiogenic isotopes behaviour implies that the magmas retain the source signature thus allowing its identification. In the case of equilibrium melting, the highly incompatible elements abundance is very high in the liquid at the beginning of the process and decreases progressively as the melting degree increases. On the contrary, the concentration in compatible elements grows very slowly during the first steps to increase sharply for the highest F values. During fractional melting, the first liquid generated removes almost all the incompatible elements thus producing a relative depletion in those elements in the successive liquids. In the case of incongruent melting, the magmas are enriched in the trace elements with high distribution coefficients for the phases that melt and low for the newly generated phases, and are impoverished in the elements that constitute the new phases. If melting is produced in the presence of a fluid phase, the liquid will be depleted in those elements with fluid/liquid distribution coefficients close to 1, rdative to the same liquid generated without a fluid phase. Finally, during disequilibrium or nondiffusive melting, the first liquid fraction has a concentration in incompatible dements higher and in compatible elements lower than that in the source, so the solid-liquid interface is depleted and enriched, respectively. However, at the end of the process the concentration of elements in the liquid is equated to the abundance in the solid that melted. To model equilibrium me1ting two diferent approaches can be followed, depending on the availability of the mineral-liquid distribution coefficients and the percentages in which the mineral phases have participated. When these parameters are known, it is possible to duplicate the concentrations observed in the primary liquids by selecting reasonable constants. On the contrary, when these parameters are unknown the approach to follow will depend on the knowledge of the cbmposition of the liquids or that of the residue. In the first case, the element concentrations of tbe rocks are used to obtain a simultaneous best-fit solution of a system constituted by tile equations that describe the process, either for a number of elements, or individually for each parameter and element. If the composition of the residue is known, it is necessary to guess the composition of the protolith. Then, from the most residual element the two remaining parameters (the residue- melt bulk distribution coefficient and the degree of melting of each restite) are defined, either assuming the degree of melting, the elements bulk distribution coefficient, or their concentration.Este trabajo se ha realizado dentro del Proyecto de Investigación PB92-lOS «Magmatismo intraplaca relacionado con puntos calientes en la Península Ibérica», financiado por la Dirección General de Investigación Científica y Técnica.Peer reviewe

A young stellar environment for the superluminous supernova PTF12dam

The progenitors of super luminous supernovae (SLSNe) are still a mystery. Hydrogen-poor SLSN hosts are often highly star-forming dwarf galaxies and the majority belongs to the class of extreme emission line galaxies hosting young and highly star-forming stellar populations. Here we present a resolved long-slit study of the host of the hydrogen-poor SLSN PTF12dam probing the kpc environment of the SN site to determine the age of the progenitor. The galaxy is a "tadpole" with uniform properties and the SN occurred in a star-forming region in the head of the tadpole. The galaxy experienced a recent star-burst superimposed on an underlying old stellar population. We measure a very young stellar population at the SN site with an age of ~3 Myr and a metallicity of 12+log(O/H)=8.0 at the SN site but do not observe any WR features. The progenitor of PTF12dam must have been a massive star of at least 60 M_solar and one of the first stars exploding as a SN in this extremely young starburst.Comment: submitted to MNRAS letters. 5 pages, 3 figures, supplementary material: 2 figures, 2 table

On the absence of acylated anthocyanins in some wild grapevine accessions

Our current research is focused on the anthocyanin composition of female grape accessions, mostly Spanish, preserved at El Encín Germplasm Bank. In 2008, berries of 126 accessions were taken at maturity. After the extraction from grape skins, total anthocyans were determined by spectrophotometry, and the anthocyanin fingerprint of grapes by HPLC, considering the relative amount of 15 anthocyanins. Among those 126 accessions, 23 genotypes (18.25 %) did not present acylated anthocyanins. Thus, those 23 genotypes presented a characteristic anthocyanin fingerprint, similar at a certain extent to that presented by some Rhine basin and Italian grape cultivars, e.g., 'Pinot Noir' and 'Gaglioppo'. Nevertheless, the absence of acylated anthocyanins has not been described in any Spanish grape cultivar. The examination of the anthocyanin fingerprint of wild grapes without acylated anthocyanins reveals that the regulation of the anthocyanin biosynthesis may differ in various wild grape accessions.

The cosmic evolution of the spatially-resolved star formation rate and stellar mass of the CALIFA survey

We investigate the cosmic evolution of the absolute and specific star formation rate (SFR, sSFR) of galaxies as derived from a spatially-resolved study of the stellar populations in a set of 366 nearby galaxies from the CALIFA survey. The analysis combines GALEX and SDSS images with the 4000 break, H_beta, and [MgFe] indices measured from the datacubes, to constrain parametric models for the SFH, which are then used to study the cosmic evolution of the star formation rate density (SFRD), the sSFR, the main sequence of star formation (MSSF), and the stellar mass density (SMD). A delayed-tau model, provides the best results, in good agreement with those obtained from cosmological surveys. Our main results from this model are: a) The time since the onset of the star formation is larger in the inner regions than in the outer ones, while tau is similar or smaller in the inner than in the outer regions. b) The sSFR declines rapidly as the Universe evolves, and faster for early than for late type galaxies, and for the inner than for the outer regions of galaxies. c) SFRD and SMD agree well with results from cosmological surveys. At z< 0.5, most star formation takes place in the outer regions of late spiral galaxies, while at z>2 the inner regions of the progenitors of the current E and S0 are the major contributors to SFRD. d) The inner regions of galaxies are the major contributor to SMD at z> 0.5, growing their mass faster than the outer regions, with a lookback time at 50% SMD of 9 and 6 Gyr for the inner and outer regions. e) The MSSF follows a power-law at high redshift, with the slope evolving with time, but always being sub-linear. f) In agreement with galaxy surveys at different redshifts, the average SFH of CALIFA galaxies indicates that galaxies grow their mass mainly in a mode that is well represented by a delayed-tau model, with the peak at z~2 and an e-folding time of 3.9 Gyr.Comment: 23 pages, 16 figures, 6 tables, accepted for publication in Astronomy & Astrophysics. *Abridged abstract

The spatially resolved star formation history of CALIFA galaxies: Cosmic time scales

This paper presents the mass assembly time scales of nearby galaxies observed by CALIFA at the 3.5m telescope in Calar Alto. We apply the fossil record method of the stellar populations to the complete sample of the 3rd CALIFA data release, with a total of 661 galaxies, covering stellar masses from 10$^{8.4}$ to 10$^{12}$ M$_{\odot}$ and a wide range of Hubble types. We apply spectral synthesis techniques to the datacubes and process the results to produce the mass growth time scales and mass weighted ages, from which we obtain temporal and spatially resolved information in seven bins of galaxy morphology and six bins of stellar mass (M$_{\star}$) and stellar mass surface density ($\Sigma_{\star}$). We use three different tracers of the spatially resolved star formation history (mass assembly curves, ratio of half mass to half light radii, and mass-weighted age gradients) to test if galaxies grow inside-out, and its dependence with galaxy stellar mass, $\Sigma_{\star}$, and morphology. Our main results are as follows: (a) The innermost regions of galaxies assemble their mass at an earlier time than regions located in the outer parts; this happens at any given M$_{\star}$, $\Sigma_{\star}$, or Hubble type, including the lowest mass systems. (b) Galaxies present a significant diversity in their characteristic formation epochs for lower-mass systems. This diversity shows a strong dependence of the mass assembly time scales on $\Sigma_{\star}$ and Hubble type in the lower-mass range (10$^{8.4}$ to 10$^{10.4}$), but a very mild dependence in higher-mass bins. (c) All galaxies show negative $\langle$log age$\rangle_{M}$ gradients in the inner 1 HLR. The profile flattens with increasing values of $\Sigma_{\star}$. There is no significant dependence on M$_{\star}$ within a particular $\Sigma_{\star}$ bin, except for the lowest bin, where the gradients becomes steeper.Comment: 15 pages, 13 figures, 3 tables, accepted for publication in Astronomy & Astrophysics. *Abridged abstract

Solvent-Induced Acceleration of the Rate of Activation of a Molecular Reaction

An increase in the rates of activated processes with the coupling to the solvent has long been predicted through the phenomenological Langevin equation in the weak coupling regime. However, its direct observation in particle-based models has been elusive because the coupling typically places the processes in the spacial-diffusion limited regime wherein rates decrease with increasing friction. In this work, the forward and backward reaction rates of the LiNC Ð LiCN isomerization reaction in a bath of argon atoms at various densities have been calculated directly using molecular dynamics trajectories. The so-called Kramers turnover in the rate with microscopic friction is clearly visible, thus providing direct and unambiguous evidence for the energy-diffusion regime in which rates increase with friction

Modelling the scope to conserve an endemic-rich mountain butterfly taxon in a changing climate

Taxa restricted to mountains may be vulnerable to global warming, unless local-scale topographic variation and conservation actions can protect them against expected changes to the climate. We tested how climate change will affect the 19 mountain-restricted Erebia species of the Iberian Peninsula, of which 7 are endemic. To examine the scope for local topographic variation to protect against warming, we applied species distribution models (HadGEM2 and MPI) at two spatial scales (10 × 10 and 1 × 1 km) for two representative concentration pathways (RCP4.5 and RCP8.5) in 2050 and 2070. We also superimposed current and future ranges on the protected area (PA) network to identify priority areas for adapting Erebia conservation to climate change. In 10 × 10 km HadGEM2 models, climatically suitable areas for all species decreased in 2050 and 2070 (average −95.7%). Modelled decreases at 1 × 1 km were marginally less drastic (−95.3%), and 14 out of 19 species were still expected to lose their entire climatically favourable range by 2070. The PA network is well located to conserve the species that are expected to retain some climatically suitable areas in 2070. However, we identify 25 separate 10 × 10 km squares where new PAs would help to adapt the network to expected range shifts or contractions by Erebia. Based on our results, adapting the conservation of range-restricted mountain taxa to projected climate change will require the implementation of complementary in situ and ex situ measures alongside urgent climate change mitigationBiology Department from Universidad Autonoma de Madrid, Grant/Award Number: SBPLY/17/180501/000492; European Regional Development Fund; MCIU/AEI/ FEDER, UE, Grant/Award Number: RTI2018-096739-B-C21; NexTdive project, Grant/Award Number: PID2021-124187NBI00; Spanish Ministry of Science and Innovatio