A new library of theoretical stellar spectra with scaled-solar and alpha-enhanced mixtures

Theoretical stellar libraries have been increasingly used to overcome limitations of empirical libraries, e.g. by exploring atmospheric parameter spaces not well represented in the latter. This work presents a new theoretical library which covers 3000 $\leq$ Teff $\leq$ 25000\,K, -0.5 $\leq$ log g $\leq$ 5.5, and 12 chemical mixtures covering 0.0017 $\leq$ Z $\leq$ 0.049 at both scaled-solar and $\alpha$-enhanced compositions. This library complements previous ones by providing: (i) homogeneous computations of opacity distribution functions, models atmospheres, statistical surface fluxes and high resolution spectra; (ii) high resolution spectra with continua slopes corrected by the effect of predicted lines, and; (iii) two families of $\alpha$-enhanced mixtures for each scaled-solar iron abundance, to allow studies of the $\alpha$-enhancement both at `fixed iron' and `fixed Z' cases. Comparisons to observed spectra were performed and confirm that the synthetic spectra reproduce well the observations, although there are wavelength regions which should be still improved. The atmospheric parameter scale of the model library was compared to one derived from a widely used empirical library, and no systematic difference between the scales was found. This is particularly reassuring for methods which use synthetic spectra for deriving atmospheric parameters of stars in spectroscopic surveys

A grid of Synthetic Spectra for Hot DA White Dwarfs and Its Application in Stellar Population Synthesis

In this work we present a grid of LTE and non-LTE synthetic spectra of hot DA white dwarfs (WDs). In addition to its usefulness for the determination of fundamental stellar parameters of isolated WDs and in binaries, this grid will be of interest for the construction of theoretical libraries for stellar studies from integrated light. The spectral grid covers both a wide temperature and gravity range, with 17,000 K <= T_eff <= 100,000 K and 7.0 <= log(g) <= 9.5. The stellar models are built for pure hydrogen and the spectra cover a wavelength range from 900 A to 2.5 microns. Additionally, we derive synthetic HST/ACS, HST/WFC3, Bessel UBVRI and SDSS magnitudes. The grid was also used to model integrated spectral energy distributions of simple stellar populations and our modeling suggests that DAs might be detectable in ultraviolet bands for populations older than ~8 Gyr.Comment: to be published in The Astrophysical Journal Supplement Serie

Abundance patterns in early-type galaxies: is there a 'knee' in the [Fe/H] vs. [alpha/Fe] relation?

Early-type galaxies (ETGs) are known to be enhanced in alpha elements, in accordance with their old ages and short formation timescales. In this contribution we aim to resolve the enrichment histories of ETGs. This means we study the abundance of Fe ([Fe/H]) and the alpha-element groups ([alpha/Fe]) separately for stars older than 9.5 Gyr ([Fe/H]o, [alpha/Fe]o) and for stars between 1.5 and 9.5 Gyr ([Fe/H]i, [alpha/Fe]i). Through extensive simulation we show that we can indeed recover the enrichment history per galaxy. We then analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS selected to be ETGs. We separate out those galaxies for which the abundance of iron in stars grows throughout the lifetime of the galaxy, i.e. in which [Fe/H]o < [Fe/H]i. We confirm earlier work where the [Fe/H] and [alpha/Fe] parameters are correlated with the mass and velocity dispersion of ETGs. We emphasize that the strongest relation is between [alpha/Fe] and age. This relation falls into two regimes, one with a steep slope for old galaxies and one with a shallow slope for younger ETGs. The vast majority of ETGs in our sample do not show the 'knee' in the plot of [Fe/H] vs. [alpha/Fe] commonly observed in local group galaxies. This implies that for the vast majority of ETGs, the stars younger than 9.5 Gyrs are likely to have been accreted or formed from accreted gas. The properties of the intermediate-age stars in accretion-dominated ETGs indicate that mass growth through late (minor) mergers in ETGs is dominated by galaxies with low [Fe/H] and low [alpha/Fe]. The method of reconstructing the stellar enrichment histories of ETGs introduced in this paper promises to constrain the star formation and mass assembly histories of large samples of galaxies in a unique way.Comment: 22 pages, 25 figures, accepted for publication by A&

Full spectral fitting of Milky Way and M31 globular clusters: ages and metallicities

Context: The formation and evolution of disk galaxies are long standing questions in Astronomy. Understanding the properties of globular cluster systems can lead to important insights on the evolution of its host galaxy. Aims: We aim to obtain the stellar population parameters - age and metallicity - of a sample of M31 and Galactic globular clusters. Studying their globular cluster systems is an important step towards understanding their formation and evolution in a complete way. Methods: Our analysis employs a modern pixel-to-pixel spectral fitting technique to fit observed integrated spectra to updated stellar population models. By comparing observations to models we obtain the ages and metallicities of their stellar populations. We apply this technique to a sample of 38 globular clusters in M31 and to 41 Galactic globular clusters, used as a control sample. Results: Our sample of M31 globular clusters spans ages from 150 Myr to the age of the Universe. Metallicities [Fe/H] range from -2.2 dex to the solar value. The age-metallicity relation obtained can be described as having two components: an old population with a flat age-[Fe/H] relation, possibly associated with the halo and/or bulge, and a second one with a roughly linear relation between age and metallicity, higher metallicities corresponding to younger ages, possibly associated with the M31 disk. While we recover the very well known Galactic GC metallicity bimodality, our own analysis of M31's metallicity distribution function (MDF) suggests that both GC systems cover basically the same [Fe/H] range yet M31's MDF is not clearly bimodal. These results suggest that both galaxies experienced different star formation and accretion histories.Comment: A&A, in pres

Theoretical study on the bond performance of CFRP-to-steel single-lap shear tests with multiple debonding defects

The amount of research on the external bonding of Carbon Fiber Reinforced Polymers (CFRP) to degraded structures has increased recently. The adhesive is the weakest element of the joint and the bonding of the adherends is critical for the efficiency of the joint. Therefore, the influence of multiple debonding defects on CFRP-to-steel joints has still not been correctly quantified nor fully understood. For this reason, the current work proposes a new numerical strategy that allows for studying the influence of multiple debonding defects when a brittle and ductile adhesive is used. A new nonlinear bond-slip relationship is used and four different ratios between the debonded and the bonded area (η) are assumed: 0%, 25%, 50%, and 75%. The proposed model is based on the Finite Difference Method (FDM) and validation is carried out with a commercial Finite Element Method (FEM) package. The load-slip curves allowed for observing that the proposed FDM and the FEM are consistent and both revealed degradation of the load capacity of the joints with the increase of η. Moreover, by adopting a displacement control at the CFRP-free end, a snap-through and snap-back phenomenon are observed in the specimens with a localized debonding defect

Gene identification for the cblD defect of vitamin B12 metabolism

Background Vitamin B12 (cobalamin) is an essential cofactor in several metabolic pathways. Intracellular conversion of cobalamin to its two coenzymes, adenosylcobalamin in mitochondria and methylcobalamin in the cytoplasm, is necessary for the homeostasis of methylmalonic acid and homocysteine. Nine defects of intracellular cobalamin metabolism have been defined by means of somatic complementation analysis. One of these defects, the cblD defect, can cause isolated methylmalonic aciduria, isolated homocystinuria, or both. Affected persons present with multisystem clinical abnormalities, including developmental, hematologic, neurologic, and metabolic findings. The gene responsible for the cblD defect has not been identified. Methods We studied seven patients with the cblD defect, and skin fibroblasts from each were investigated in cell culture. Microcell-mediated chromosome transfer and refined genetic mapping were used to localize the responsible gene. This gene was transfected into cblD fibroblasts to test for the rescue of adenosylcobalamin and methylcobalamin synthesis. Results The cblD gene was localized to human chromosome 2q23.2, and a candidate gene, designated MMADHC (methylmalonic aciduria, cblD type, and homocystinuria), was identified in this region. Transfection of wild-type MMADHC rescued the cellular phenotype, and the functional importance of mutant alleles was shown by means of transfection with mutant constructs. The predicted MMADHC protein has sequence homology with a bacterial ATP-binding cassette transporter and contains a putative cobalamin binding motif and a putative mitochondrial targeting sequence. Conclusions Mutations in a gene we designated MMADHC are responsible for the cblD defect in vitamin B12 metabolism. Various mutations are associated with each of the three biochemical phenotypes of the disorder

Uniformidade de distribuição de água e ions em diferentes profundidades do solo com bananeira fertirrigada.

A uniformidade de distribuição (CUD), de água e nutrientes via fertirrigação por microaspersão em bananeira tem sido avaliada em condições de solo nu, entretanto, é necessário avaliar com o solo sob cobertura morta, o que altera as propriedades físicas do solo nessa condição. Esse trabalho teve como objetivo avaliar a uniformidade de distribuição de água, da Condutividade elétrica aparente (CEa), dos íons potássio e nitrato no entorno do microaspersor após uma fertirrigação em um pomar de bananeira (BRS Princesa). O experimento seguiu o delineamento de blocos casualizados em esquemas de parcelas subdivididas, com os tratamentos T1: com cobertura e T2: sem cobertura na parcela, profundidade de 0,20 0,40 e 0,60 m na sub parcela. As avaliações foram feitas 1 e 24 horas após a fertirrigação. A avaliação foi feita com sondas de TDR instaladas a 0,20; 0,40 e 0,60 m, próximo de coletores de água dispostos em uma malha de 0,50 x 0,50 m com o microaspersor de vazão 53Lh-¹ instalado entre quatro plantas. O tratamento com cobertura morta apresentou maior coeficiente de uniformidade de distribuição (CUD) em todas as profundidades comparado ao tratamento sem cobertura enquanto a condutividade elétrica teve comportamento inverso onde o CUD foi superior no tratamento sem cobertura,. Após a fertirrigação a umidade do solo com cobertura foi estatisticamente superior a do sem cobertura, entretanto esses valores se aproximaram 24 horas após

Nuclear magnetic resonance measurements reveal the origin of the Debye process in monohydroxy alcohols

Monohydroxy alcohols show a structural relaxation and at longer time scales a Debye-type dielectric peak. From spin-lattice relaxation experiments using different nuclear probes an intermediate, slower-than-structural dynamics is identified for n-butanol. Based on these findings and on diffusion measurements, a model of self-restructuring, transient chains is proposed. The model is demonstrated to explain consistently the so far puzzling observations made for this class of hydrogen-bonded glass forming liquids.Comment: 4 pages, 4 figure