Hiding its age: the case for a younger bulge

The determination of the age of the bulge has led to two contradictory results. On the one side, the color-magnitude diagrams in different bulge fields seem to indicate a uniformly old ($>$10 Gyr) population. On the other side, individual ages derived from dwarfs observed through microlensing events seem to indicate a large spread, from $\sim$ 2 to $\sim$ 13 Gyr. Because the bulge is now recognised as being mainly a boxy peanut-shaped bar, it is suggested that disk stars are one of its main constituents, and therefore also stars with ages significantly younger than 10 Gyr. Other arguments as well point to the fact that the bulge cannot be exclusively old, and in particular cannot be a burst population, as it is usually expected if the bulge was the fossil remnant of a merger phase in the early Galaxy. In the present study, we show that given the range of metallicities observed in the bulge, a uniformly old population would be reflected into a significant spread in color at the turn-off which is not observed. Inversely, we demonstrate that the correlation between age and metallicity expected to hold for the inner disk would conspire to form a color-magnitude diagram with a remarkably small spread in color, thus mimicking the color-magnitude diagram of a uniformly old population. If stars younger than 10 Gyr are part of the bulge, as must be the case if the bulge has been mainly formed through dynamical instabilities in the disk, then a very small spread at the turn-off is expected, as seen in the observations.Comment: 11 pages, 11 figures. Accepted for publication in A&

Quantifying stellar radial migration in an N-body simulation: blurring, churning, and the outer regions of galaxy discs

Radial stellar migration in galactic discs has received much attention in studies of galactic dynamics and chemical evolution, but remains a dynamical phenomenon that needs to be fully quantified. In this work, using a Tree-SPH simulation of an Sb-type disc galaxy, we quantify the effects of blurring (epicyclic excursions) and churning (change of guiding radius). We quantify migration (either blurring or churning) both in terms of flux (the number of migrators passing at a given radius), and by estimating the population of migrators at a given radius at the end of the simulation compared to non-migrators, but also by giving the distance over which the migration is effective at all radii. We confirm that the corotation of the bar is the main source of migrators by churning in a bar-dominated galaxy, its intensity being directly linked to the episode of a strong bar, in the first 1-3 Gyr of the simulation. We show that within the outer Lindblad resonance (OLR), migration is strongly dominated by churning, while blurring gains progressively more importance towards the outer disc and at later times. Most importantly, we show that the OLR limits the exchange of angular momentum, separating the disc in two distinct parts with minimal or null exchange, except in the transition zone, which is delimited by the position of the OLR at the epoch of the formation of the bar, and at the final epoch. We discuss the consequences of these findings for our understanding of the structure of the Milky Way disc. Because the Sun is situated slightly outside the OLR, we suggest that the solar vicinity may have experienced very limited churning from the inner disc.Comment: Accepted for publication in Astronomy and Astrophysics (acceptance date: 27/04/15), 24 pages, 24 figure

Revisiting two local constraints of the Galactic chemical evolution

I review the uncertainties in two observational constraints of the Galactic disc chemical evolution: the metallicity distribution (MD) of long-lived dwarfs and the age-metallicity relation (AMR). It is shown first that the observed MD, designed with standard methods, is more fit to a closed-box model than to the infall MD. We argue that this is due to the specific contribution of the thick disc population, which has been overlooked both in the derivation of the observed MD and in the standard chemical evolution models. Although this agreement disqualifies the MD as the best supportive evidence for infall, we argue that the evolution must be more complex than described by either the closed-box or the standard infall models. A new age-metallicity distribution is obtained, where particularities of the previous recent determinations are phased out. The new AMR shows a mean increase limited to about a factor of 2 in Z over the disc age. It is shown that below 3 Gyrs, the dispersion in metallicity is about 0.1 dex, which, (given the observational uncertainties), is compatible with the small cosmic dispersion measured on the interstellar medium and meteoritic pre-solar dust grains. A population that is progressively older and more metal rich arises at a metallicity greater than that of the Hyades, to reach [Fe/H] ~ +0.5 dex at ages > 5 Gyr. We suggest that this is best explained by radial migration. A symmetrical widening towards lower metallicities is seen at about the same age. Finally, the new derived ages are sufficiently consistent that an AMR within the thick disc is confirmed. These new features altogether draw a picture of the chemical evolution where dynamical effects and complexity in the AMR dominate, rather than a generalized high dispersion at all ages. (abridged)Comment: 19 pages, 13 figures. Accepted for publication in MNRA

Juan de Torres's Poetics of Vision : "Oiosqueyanovesque"

In this article, I examine Juan de Torres's poetics of the visual through a reading of his Cancionero de Palacio dealing with the visual sphere. I argue that his poetry demonstrates familiarity with medieval scholastic psychology, particularly in relation to sight and memory. The visual sphere can be understood as both the external, phenomenological and somatic world of experience and intersubject interaction, and as the interior world of the psyche and the affect. Lacanian and Jamesonian reading strategies are deployed to approach latent psychological and socio-political content in Torres's representation of the psychic disarray of the lover. The visual sphere is the medium by and through which desire is apprehended and the subject inscribes itself in the symbolic order, seeks the desire of the Other and is subject to the surveying gaze of power hierarchies. Torres's work shows great skill and wit, and stands as a particularly good example of the way in which a highly abstract poetic corpus deals directly with the visual understood as power and hierarchy.El presente artículo examina una gama de obras de Juan de Torres del Cancionero de Palacio en que el vate trata un temario que engloba el campo visual. En las obras bajo consideración Torres recurre a la teoría de las facultades o potencias del alma según la psicología escolástica, sobre todo en su relación con el sentido de la vista y la memoria. El campo visual abarca tanto el mundo externo, fenomenológico y somático de interacciones intersubjetivas como el interno del ánimo y los sentimientos. Uso las ópticas lacaniana y jamesoniana para explicar el contenido psicológico latente y socio-político de la representación de la confusión anímica del yo-lírico. El campo visual es el medio por el cual se percibe el deseo y el sujeto se inscribe en el orden simbólico, busca el deseo del Otro y es sujeto a la vigilancia del poder. La poética de Torres manifiesta con gran destreza y cierto tono humorístico la manera en que una poesía con alto grado de abstracción trata directamente con el campo visual como registro de poder y jerarquía

When the Milky Way turned off the lights: APOGEE provides evidence of star formation quenching in our Galaxy

Quenching, the cessation of star formation, is one of the most significant events in the life cycle of galaxies. We show here the first evidence that the Milky Way experienced a generalised quenching of its star formation at the end of its thick disk formation $\sim$9 Gyr ago. Elemental abundances of stars studied as part of the APOGEE survey reveal indeed that in less than $\sim$2 Gyr the star formation rate in our Galaxy dropped by an order-of-magnitude. Because of the tight correlation between age and alpha abundance, this event reflects in the dearth of stars along the inner disk sequence in the [Fe/H]-[$\alpha$/Fe] plane. Before this phase, which lasted about 1.5 Gyr, the Milky Way was actively forming stars. Afterwards, the star formation resumed at a much lower level to form the thin disk. These events are very well matched by the latest observation of MW-type progenitors at high redshifts. In late type galaxies, quenching is believed to be related to a long and secular exhaustion of gas. In our Galaxy, it occurred on a much shorter time scale, while the chemical continuity before and after the quenching indicates that it was not due to the exhaustion of the gas. While quenching is generally associated with spheroids, our results show that it also occurs in galaxies like the Milky Way, possibly when they are undergoing a morphological transition from thick to thin disks. Given the demographics of late type galaxies in the local universe, in which classical bulges are rare, we suggest further that this may hold true generally in galaxies with mass lower than or approximately $M^*$, where quenching could be directly a consequence of thick disk formation. We emphasize that the quenching phase in the Milky Way could be contemporaneous with, and related to, the formation of the bar. We sketch a scenario on how a strong bar may inhibit star formation.Comment: 17 pages, 8 figures. Published versio

Composting paper and grass clippings with anaerobically treated palm oil mill effluent

Purpose The purpose of this study is to investigate the composting performance of anaerobically treated palm oil mill effluent (AnPOME) mixed with paper and grass clippings. Methods Composting was conducted using a laboratory scale system for 40 days. Several parameters were determined: temperature, mass reduction, pH, electrical conductivity, colour, zeta potential, phytotoxicity and final compost nutrients. Results The moisture content and compost mass were reduced by 24 and 18 %, respectively. Both final compost pH value and electrical conductivity were found to increase in value. Colour (measured as PtCo) was not suitable as a maturity indicator. The negative zeta potential values decreased from −12.25 to −21.80 mV. The phytotoxicity of the compost mixture was found to decrease in value during the process and the final nutrient value of the compost indicates its suitability as a soil conditioner. Conclusions From this study, we conclude that the addition of paper and grass clippings can be a potential substrate to be composted with anaerobically treated palm oil mill effluent (AnPOME). The final compost produced is suitable for soil conditioner

Signatures of radial migration in barred galaxies: Azimuthal variations in the metallicity distribution of old stars

By means of N-body simulations, we show that radial migration in galaxy disks, induced by bar and spiral arms, leads to significant azimuthal variations in the metallicity distribution of old stars at a given distance from the galaxy center. Metals do not show an axisymmetric distribution during phases of strong migration. Azimuthal variations are visible during the whole phase of strong bar phase, and tend to disappear as the effect of radial migration diminishes, together with a reduction in the bar strength. These results suggest that the presence of inhomogeneities in the metallicity distribution of old stars in a galaxy disk can be a probe of ongoing strong migration. Such signatures may be detected in the Milky Way by Gaia (and complementary spectroscopic data), as well as in external galaxies, by IFU surveys like CALIFA and ATLAS3D. Mixing - defined as the tendency toward a homogeneous, azimuthally symmetric, stellar distribution in the disk - and migration turns out to be two distinct processes, the effects of mixing starting to be visible when strong migration is over.Comment: 8 pages, 10 figures, accepted for publication on Astronomy and Astrophysic

On the kinematic detection of accreted streams in the Gaia era: a cautionary tale

The $\Lambda$CDM cosmological scenario predicts that our Galaxy should contain hundreds of stellar streams at the solar vicinity, fossil relics of the merging history of the Milky Way and more generally of the hierarchical growth of galaxies. Because of the mixing time scales in the inner Galaxy, it has been claimed that these streams should be difficult to detect in configuration space but can still be identifiable in kinematic-related spaces like the energy/angular momenta spaces, E-Lz and Lperp-Lz, or spaces of orbital/velocity parameters. By means of high-resolution, dissipationless N-body simulations, containing between 25$\times10^6$ and 35$\times10^6$ particles, we model the accretion of a series of up to four 1:10 mass ratio satellites then up to eight 1:100 satellites and we search systematically for the signature of these accretions in these spaces. In all spaces considered (1) each satellite gives origin to several independent overdensities; (2) overdensities of multiple satellites overlap; (3) satellites of different masses can produce similar substructures; (4) the overlap between the in-situ and the accreted population is considerable everywhere; (5) in-situ stars also form substructures in response to the satellite(s) accretion. These points are valid even if the search is restricted to kinematically-selected halo stars only. As we are now entering the 'Gaia era', our results warn that an extreme caution must be employed before interpreting overdensities in any of those spaces as evidence of relics of accreted satellites. Reconstructing the accretion history of our Galaxy will require a substantial amount of accurate spectroscopic data, that, complemented by the kinematic information, will possibly allow us to (chemically) identify accreted streams and measure their orbital properties. (abridged)Comment: Accepted on A&A. A high-resolution version of the paper is available at http://aramis.obspm.fr/~paola/ELZ/Elz.pd

A rotor-mounted digital instrumentation system for helicopter blade flight research measurements

A rotor mounted flight instrumentation system developed for helicopter rotor blade research is described. The system utilizes high speed digital techniques to acquire research data from miniature pressure transducers on advanced rotor airfoils which are flight tested on an AH-1G helicopter. The system employs microelectronic pulse code modulation (PCM) multiplexer digitizer stations located remotely on the blade and in a hub mounted metal canister. As many as 25 sensors can be remotely digitized by a 2.5 mm thick electronics package mounted on the blade near the tip to reduce blade wiring. The electronics contained in the canister digitizes up to 16 sensors, formats these data with serial PCM data from the remote stations, and transmits the data from the canister which is above the plane of the rotor. Data are transmitted over an RF link to the ground for real time monitoring and to the helicopter fuselage for tape recording. The complete system is powered by batteries located in the canister and requires no slip rings on the rotor shaft