Sur quelques Cystoidées cités par les Drs. J. Almera et M.Faura dans l'Ordovicien de Barcelone

Con motivo de la elaboración del Mapa Geológico de Cataluña a escala 1:40.000, subvencionado por la Excma. Diputación Provincial de Barcelona, a partir de 1886, dirigida por el Dr. J. Almera con la colaboración del Dr. M. Faura i Sans, fueron recogidos numerosos fósiles paleozoicos en la Provincia de Barcelona, entre los cuales figuraban algunos ejemplares de Cystoideos que fueron clasificados como Echinosphaerites cf. balticus EICHW., por Barrois (1891), procedentes de las localidades de Montcada, El Papiol, Gracia y Aiguafreda, actualmente inaccesibles en su mayor parte. Estos ejemplares estuvieron depositados en el Museo Geológico del Seminano Conciliar de Barcelona hasta 1918, en que fueron trasladados al Museo Geológico Municipal en el Parque de la Ciudadela.Dentro de nuestro plan de estudio y revisión de los Cystoideos de España hemos considerado necesario proceder a la revisión de estos fósiles, estudiados hace más de 70 años y que últimamente hemos podido localizar en las colecciones de los dos Museos mencionados, pues todo parecía indicar que su clasificación no era correcta, ya que últimamente se ha podido comprobar que la especie Heliocrinites (Echinosphaerites) balticus (EIcHw.), no existe en nuestra Peninsula.Todos los ejemplares revisados son placas aisladas de Cystoideos, conservadas como moldes externos sobre pizarras, por haberse disuelto las placas posteriormente a su fosilización.Uno de los ejemplares pertenece a las colecciones del Seminario Conciliar, procede de Montcada, ya fue determinado por Almera como Echinosphaerites sp; posteriormente como Oocystis? por el Dr. Via Boada, y se trata realmente del molde externo de una placa de Caryocrinites (=Oocystis) aff. europaeus QUENSTEDT.Los demás ejemplares proceden de las colecciones del Museo Municipal de Barcelona, y son también Caryocrinites, aunque aparecían en las etiquetas como Echinosphaerites aff. balticus. Probablemente corresponden al Caryocrinites rugatus (FORBES).Por lo que se refiere al nivel estratigráfico en que fueron recogidos los ejemplares, parece ser más bien Ashgill en vez de Caradoc

Chemical similarities between Galactic bulge and local thick disk red giant stars

The evolution of the Milky Way bulge and its relationship with the other Galactic populations is still poorly understood. The bulge has been suggested to be either a merger-driven classical bulge or the product of a dynamical instability of the inner disk. To probe the star formation history, the initial mass function and stellar nucleosynthesis of the bulge, we performed an elemental abundance analysis of bulge red giant stars. We also completed an identical study of local thin disk, thick disk and halo giants to establish the chemical differences and similarities between the various populations. High-resolution infrared spectra of 19 bulge giants and 49 comparison giants in the solar neighborhood were acquired with Gemini/Phoenix. All stars have similar stellar parameters but cover a broad range in metallicity. A standard 1D local thermodynamic equilibrium analysis yielded the abundances of C, N, O and Fe. A homogeneous and differential analysis of the bulge, halo, thin disk and thick disk stars ensured that systematic errors were minimized. We confirm the well-established differences for [O/Fe] (at a given metallicity) between the local thin and thick disks. For the elements investigated, we find no chemical distinction between the bulge and the local thick disk, which is in contrast to previous studies relying on literature values for disk dwarf stars in the solar neighborhood. Our findings suggest that the bulge and local thick disk experienced similar, but not necessarily shared, chemical evolution histories. We argue that their formation timescales, star formation rates and initial mass functions were similar.Comment: Accepted for publication in A&A, 5 page

Is the solar spectrum latitude dependent? An investigation with SST/TRIPPEL

Context: In studies of the solar spectrum relative to spectra of solar twin stars, it has been found that the chemical composition of the Sun seems to depart systematically from those of the twins. One possible explanation is that the effect is due to the special aspect angle of the Sun when observed from Earth, as compared with the aspect angles of the twins. Thus, a latitude dependence of the solar spectrum, even with the heliocentric angle constant, could lead to effects of the type observed. Aim: We explore a possible variation in the strength of certain spectral lines, used in the comparisons between the composition of the Sun and the twins, at loci on the solar disk with different latitudes but at constant heliocentric angle. Methods: We use the TRIPPEL spectrograph at the Swedish 1-m Solar Telescope on La Palma to record spectra in five spectral regions in order to compare different locations on the solar disk at a heliocentric angle of 45 deg. Equivalent widths and other parameters are measured for fifteen different lines representing nine atomic species. Results: The relative variations in equivalent widths at the equator and at solar latitude 45 deg are found to be less than 1.5 % for all spectral lines studied. Translated to elemental abundances as they would be measured from a terrestrial and a hypothetical pole-on observer, the difference is estimated to be within 0.005 dex in all cases. Conclusion: It is very unlikely that latitude effects could cause the reported abundance difference between the Sun and the solar twins. The accuracy obtainable in measurements of small differences in spectral line strengths between different solar disk positions is very high.Comment: 9 pages, 10 figures, accepted by Astronomy & Astrophysic

New Indicators for AGN Power: The Correlation Between [O IV] lambda 25.89 micron and Hard X-ray Luminosity for Nearby Seyfert Galaxies

We have studied the relationship between the [O IV] lambda 25.89 micron emission line luminosities, obtained from Spitzer spectra, the X-ray continua in the 2-10 keV band, primarily from ASCA, and the 14-195 keV band obtained with the SWIFT/Burst Alert Telescope (BAT), for a sample of nearby (z < 0.08) Seyfert galaxies. For comparison, we have examined the relationship between the [O III] 5007, the 2-10 keV and the 14-195 keV luminosities for the same set of objects. We find that both the [O IV] and [O III] luminosities are well-correlated with the BAT luminosities. On the other hand, the [O III] luminosities are better-correlated with 2-10 keV luminosities than are those of [O IV]. When comparing [O IV] and [O III] luminosities for the different types of galaxies, we find that the Seyfert 2's have significantly lower [O III] to [O IV] ratios than the Seyfert 1's. We suggest that this is due to more reddening of the narrow line region (NLR) of the Seyfert 2's. Assuming Galactic dust to gas ratios, the average amount of extra reddening corresponds to a hydrogen column density of ~ few times 10^21 cm^-2, which is a small fraction of the X-ray absorbing columns in the Seyfert 2's. The combined effects of reddening and the X-ray absorption are the probable reason why the [O III] versus 2-10 keV correlation is better than the [O IV] versus 2-10 keV, since the [O IV] emission line is much less affected by extinction. Overall, we find the [O IV] to be an accurate and truly isotropic indicator of the power of the AGN. This suggests that it can be useful in deconvolving the contribution of the AGN and starburst to the spectrum of Compton-thick and/or X-ray weak sources.Comment: Accepted for publication in the Astrophysical Journal. 31 pages, 6 figures, 4 table

The Mid-Infrared Continua of Seyfert Galaxies

An analysis of archival mid-infrared (mid-IR) spectra of Seyfert galaxies from the Spitzer Space Telescope observations is presented. We characterize the nature of the mid-IR active nuclear continuum by subtracting a template starburst spectrum from the Seyfert spectra. The long wavelength part of the spectrum contains a strong contribution from the starburst-heated cool dust; this is used to effectively separate starburst-dominated Seyferts from those dominated by the active nuclear continuum. Within the latter category, the strength of the active nuclear continuum drops rapidly beyond ~ 20 micron. On average, type 2 Seyferts have weaker short-wavelength active nuclear continua as compared to type 1 Seyferts. Type 2 Seyferts can be divided into two types, those with strong poly-cyclic aromatic hydrocarbon (PAH) bands and those without. The latter type show polarized broad emission lines in their optical spectra. The PAH-dominated type 2 Seyferts and Seyfert 1.8/1.9s show very similar mid-IR spectra. However, after the subtraction of the starburst component, there is a striking similarity in the active nuclear continuum of all Seyfert optical types. PAH-dominated Seyfert 2s and Seyfert 1.8/1.9s tend to show weak active nuclear continua in general. A few type 2 Seyferts with weak/absent PAH bands show a bump in the spectrum between 15 and 20 micron. We suggest that this bump is the peak of a warm (~200 K) blackbody dust emission, which becomes clearly visible when the short-wavelength continuum is weaker. This warm blackbody emission is also observed in other Seyfert optical subtypes, suggesting a common origin in these active galactic nuclei.Comment: 25 pages, 3 tables, 11 figures; Accepted for Publication in Nov. 2009 ApJ issue

VLT-UVES abundance analysis of four giants in NGC 6553

Metal-rich globular clusters trace the formation of bulges. Abundance ratios in the metal-rich globular clusters such as NGC 6553 can constrain the formation timescale of the Galactic bulge. The purpose of this study is determine the metallicity and elemental ratios in individual stars of the metal-rich bulge globular cluster NGC 6553. A detailed abundance analysis of four giants in NGC 6553 is carried out, based on optical high-resolution echelle spectra obtained with UVES at the ESO VLT-UT2 Kueyen telescope. A metallicity [Fe/H]= -0.20 dex is derived, together with $\alpha$-element enhancement of Mg and Si ([Mg/Fe]=+0.28, [Si/Fe]=+0.21), solar Ca and Ti ([Ca/Fe]=+0.05, [Ti/Fe]=-0.01), and a mild enhancement of the r-process element Eu with [Eu/Fe] = +0.10. A mean heliocentric radial velocity of -1.86 km s$^{-1}$ is measured. We compare our results with previous investigations of the cluster.Comment: 15 pages, 8 figures, A&A, in pres

Uncovering the Spectral Energy Distribution in Active Galaxies Using High Ionization Mid-infrared Emission Lines

The shape of the spectral energy distribution of active galaxies in the EUV--soft X-ray band (13.6 eV to 1 keV) is uncertain because obscuration by dust and gas can hamper our view of the continuum. To investigate the shape of the spectral energy distribution in this energy band, we have generated a set of photoionization models which reproduce the small dispersion found in correlations between high-ionization mid-infrared emission lines in a sample of hard X-ray selected AGN. Our calculations show that a broken power-law continuum model is sufficient to reproduce the [Ne V]14.32 mm/[NeIII], [Ne V]24.32mm/[O IV]25.89mm and [O IV] 25.89mm/[Ne III] ratios, and does not require the addition of a "big bump" EUV model component. We constrain the EUV--soft X-ray slope, alpha_i, to be between 1.5 -- 2.0 and derive a best fit of alpha_i ~ 1.9 for Seyfert 1 galaxies, consistent with previous studies of intermediate redshift quasars. If we assume a blue bump model, most sources in our sample have derived temperatures between T_{BB}=10^{5.18} K to 10^{5.7} K, suggesting that the peak of this component spans a large range of energies extending from ~ lambda 600A to lambda 1900A. In this case, the best fitting peak energy that matches the mid-infrared line ratios of Seyfert 1 galaxies occurs between ~ lambda 700--1000A. Despite the fact that our results do not rule out the presence of an EUV bump, we conclude that our power-law model produces enough photons with energies > 4 Ry to generate the observed amount of mid-infrared emission in our sample of BAT AGN.Comment: Accepted for publication in The Astrophysical Journal. 11 Figure

M67-1194, an unusually Sun-like solar twin in M67

The rich open cluster M67 is known to have a chemical composition close to solar, and an age around 4Gyr. It thus offers the opportunity to check our understanding of the physics and the evolution of solar-type stars in a cluster environment. We present the first spectroscopic study at high resolution, R~50,000, of the potentially best solar twin, M67-1194, identified among solar-like stars in M67. Based on a pre-selection of solar-twin candidates performed at medium resolution by Pasquini et al. (2008), we explore the chemical-abundance similarities and differences between M67-1194 and the Sun, using VLT/FLAMES-UVES. Working with a solar twin in the framework of a differential analysis, we minimize systematic model errors in the abundance analysis compared to previous studies which utilized more evolved stars to determine the metallicity of M67. We find M67-1194 to have stellar parameters indistinguishable from the solar values, with the exception of the overall metallicity which is slightly super-solar ([Fe/H]=0.023 +/- 0.015). An age determination based on evolutionary tracks yields 4.2 +/- 1.6Gyr. Most surprisingly, we find the chemical abundance pattern to closely resemble the solar one, in contrast to most known solar twins in the solar neighbourhood. We confirm the solar-twin nature of M67-1194, the first solar twin known to belong to a stellar association. This fact allows us to put some constraints on the physical reasons for the seemingly systematic departure of M67-1194 and the Sun from most known solar twins regarding chemical composition. We find that radiative dust cleansing by nearby luminous stars may be the explanation for the peculiar composition of both the Sun and M67-1194, but alternative explanations are also possible. The chemical similarity between the Sun and M67-1194 also suggests that the Sun once formed in a cluster like M67