7,404 research outputs found
Exploring the alpha-enhancement of metal-poor planet-hosting stars. The Kepler and HARPS samples
Recent studies showed that at low metallicities Doppler-detected
planet-hosting stars have preferably high alpha-content and belong to the thick
disk. We used the reconnaissance spectra of 87 Kepler planet candidates and
data available from the HARPS planet search survey to explore this phenomena.
Using the traditional spectroscopic abundance analysis methods we derived Ti,
Ca, and Cr abundances for the Kepler stars. In the metallicity region -0.65 <
[Fe/H] < -0.3 dex the fraction of Ti-enhanced thick-disk HARPS planet harboring
stars is 12.3 +/- 4.1 % and for their thin-disk counterparts this fraction is
2.2 +/- 1.3 %. The binomial statistics gives a probability of 0.008 that this
could have occurred by chance. Combining the two samples (HARPS + Kepler)
reinforces the significance of this result (P ~ 99.97 %). Since most of these
stars are harboring small-mass/size planets we can assume that, although
terrestrial planets can be found at low-iron regime, they are mostly enhanced
by alpha-elements. This implies that early formation of rocky planets could get
started in the Galactic thick disk, where the chemical conditions for their
formation were more favorable.Comment: 5 pages, 3 figure
Experimental analysis of drainage and water storage of litter layers
International audienceMany hydrological studies of forested ecosystems focus on the study of the forest canopy and have partitioned gross precipitation into throughfall and stemflow. However, the presence of forest litter can alter the quantities of water available for soil infiltration and runoff. Little information exists regarding the value of storage and drainage parameters for litter layers. Vegetation parameters of this kind are required in physically-based and lumped conceptual models to quatify the availabilty and distribution of water. Using a rainfall simulator and laboratory conditions two main objectives were investigated using layers of recently seneced poplar leaves, fresh grass or woodchips: 1) Effect of rain intensity on storage. With this respect we found that: maximum storage (Cmax), defined as the detention of water immediately before rainfall cessation, increased with rainfall intensity. The magnitude of the increment was up to 0.5 mm kg?1 m?2 between the lowest (9.8 mm h?1) and highest (70.9 mm h?1) rainfall intensities for poplar leaves. Minimum storage (Cmin), defined as the detention of water after drainage ceased, was not influenced by rainfall intensity. Repeated wetting-draining cycles or layer thickness have no effect on Cmax or Cmin. 2) The evaluation of drainage coefficient for the Rutter model. This model was found accurate to predict storage and drainage in the case of poplar leaves, was less accurate for fresh grass and resulted in overestimations for woodchips. Additionally, the effect of an underlaying soil matrix on lateral movement of water and storage of poplar leaves was studied. Results indicated that the soil matrix have no effect on Cmax or Cmin of the litter layer. Lateral movement of water in the poplar layer was observed at intermediate rainfall intensities (30.2 and 40.4 mm h?1), but not a the lowest or highest rates
Desarrollo experimental de controladores Fuzzy para procesos térmicos y neumáticos
In this project, a Fuzzy control system is proposed in an industrial process training module with two independent systems between them, one thermal and the other pneumatic. The control algorithm is developed in Python language v3.6 executed by a Raspberry Pi B+, both controllers depend on the error and change in error that are updated in times of 2 s and 1 s, for temperature and pressure respectively, communication with the plants uses A/D and D/A converters, the thermal Fuzzy was analyzed with three temperature references [50,100 and 150]°C, with a rise time of 191 s, 360 s and 505 s; steady state error of 5.5%, 0.7% y 0.7%, in the pneumatic system the speed of change between references is evaluated from 10 psi to 15 psi varying the activation of the compressor at the beginning of the experiments, the settling times obtained are 111 s and 106 s, with the compressor off the result is 116 s and 88 s, besides a maximum excess of 13% with inherent oscillations to the type system that are in an acceptable range. En este proyecto, se propone un sistema de control Fuzzy en un módulo de entrenamiento de procesos industriales con dos sistemas independientes entre sÃ, uno térmico y otro neumático, el algoritmo de control se desarrolla en lenguaje Python v3.6 ejecutado por una Raspberry Pi B+, ambos controladores dependen del error y cambio en el error que se actualizan en tiempos de 2 s y 1 s, para temperatura y presión respectivamente, la comunicación con las plantas emplea conversores A/D y D/A, el Fuzzy térmico se analizo con tres referencias de temperatura [50,100 y 150]°C, con un tiempo de subida de 191 s, 360 s y 505 s; error de estado estacionario de 5.5 %, 0.7% y 0.7 %, en el sistema neumático se evalúo la velocidad de cambio entre referencias de 10 psi a 15 psi variando la activación del compresor al inicio de los experimentos, los tiempos de asentamiento que se obtienen son 111 s y 106 s, con el compresor apagado el resultado es de 116 s y 88 s, además de un sobrepaso máximo de 13% con oscilaciones inherentes al tipo sistema que se encuentran en un rango aceptable. 
Abundance trend with condensation temperature for stars with different Galactic birth places
During the past decade, several studies reported a correlation between
chemical abundances of stars and condensation temperature (also known as Tc
trend). However, the real astrophysical nature of this correlation is still
debated. The main goal of this work is to explore the possible dependence of
the Tc trend on stellar Galactocentric distances, Rmean. We used high-quality
spectra of about 40 stars observed with the HARPS and UVES spectrographs to
derive precise stellar parameters, chemical abundances, and stellar ages. A
differential line-by-line analysis was applied to achieve the highest possible
precision in the chemical abundances. We confirm previous results that [X/Fe]
abundance ratios depend on stellar age and that for a given age, some elements
also show a dependence on Rmean. When using the whole sample of stars, we
observe a weak hint that the Tc trend depends on Rmean. The observed dependence
is very complex and disappears when only stars with similar ages are
considered. To conclude on the possible dependence of the Tc trend on the
formation place of stars, a larger sample of stars with very similar
atmospheric parameters and stellar ages observed at different Galactocentric
distances is neededComment: Accepted by A&
Twentieth century warming of the tropical Atlantic captured by Sr-U paleothermometry
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 32 (2017): 146–160, doi:10.1002/2016PA002976.Coral skeletons are valuable archives of past ocean conditions. However, interpretation of coral paleotemperature records is confounded by uncertainties associated with single-element ratio thermometers, including Sr/Ca. A new approach, Sr-U, uses U/Ca to constrain the influence of Rayleigh fractionation on Sr/Ca. Here we build on the initial Pacific Porites Sr-U calibration to include multiple Atlantic and Pacific coral genera from multiple coral reef locations spanning a temperature range of 23.15–30.12°C. Accounting for the wintertime growth cessation of one Bermuda coral, we show that Sr-U is strongly correlated with the average water temperature at each location (r2 = 0.91, P < 0.001, n = 19). We applied the multispecies spatial calibration between Sr-U and temperature to reconstruct a 96 year long temperature record at Mona Island, Puerto Rico, using a coral not included in the calibration. Average Sr-U derived temperature for the period 1900–1996 is within 0.12°C of the average instrumental temperature at this site and captures the twentieth century warming trend of 0.06°C per decade. Sr-U also captures the timing of multiyear variability but with higher amplitude than implied by the instrumental data. Mean Sr-U temperatures and patterns of multiyear variability were replicated in a second coral in the same grid box. Conversely, Sr/Ca records from the same two corals were inconsistent with each other and failed to capture absolute sea temperatures, timing of multiyear variability, or the twentieth century warming trend. Our results suggest that coral Sr-U paleothermometry is a promising new tool for reconstruction of past ocean temperatures.NSF Graduate Research Fellowships Grant Numbers: NSF-OCE-1338320, NSF-OCE-1031971, NSF-OCE-0926986;
WHOI Access to the Sea Grant Numbers: 27500056, 0734826;
NSF HRD;
UPR Central Administration to EAHD through the Center for Applied Tropical Ecology and Conservation of UPR2017-08-1
Kinematics and chemical properties of the Galactic stellar populations. The HARPS FGK dwarfs sample
(Abridged) We analyze chemical and kinematical properties of about 850 FGK
solar neighborhood long-lived dwarfs observed with the HARPS high-resolution
spectrograph. The stars in the sample have logg > 4 dex, 5000 < Teff < 6500 K,
and -1.39 < [Fe/H] < 0.55 dex. We apply a purely chemical analysis approach
based on the [alpha/Fe] vs. [Fe/H] plot to separate Galactic stellar
populations into the thin disk, thick disk and high-alpha metal-rich (hamr).
Our analysis shows a negative gradient of the rotational velocity of the thin
disk stars with [Fe/H] (-17 km s^-1 dex^-1), and a steep positive gradient for
both the thick disk and hamr stars with the same magnitude of about +42 km s^-1
dex^-1. For the thin disk stars we observed no correlation between orbital
eccentricities and metallicity, but observed a steep negative gradient for the
thick disk and hamr stars with practically the same magnitude (about -0.18
dex^-1). Our results suggest that radial migration played an important role in
the formation and evolution of the thin disk. For the thick disk stars it is
not possible to reach a firm conclusion about their origin. Based on the
eccentricity distribution of the thick disk stars only their accretion origin
can be ruled out, and the heating and migration scenario could explain the
positive steep gradient of V_phi with [Fe/H]. Analyzing the hamr stellar
population we found that they share properties of both the thin and thick disk
population. A comparison of the properties of the hamr stars with that of the
subsample of stars from the N-body/SPH simulation using radial migration
suggest that they may have originated from the inner Galaxy. Further detailed
investigations would help to clarify their exact nature and origin.Comment: 9 pages, 6 figures, and 2 tables. Accepted for publication in A&
The Gaia-ESO Survey: metallicity of the Chamaeleon I star forming region
Context. Recent metallicity determinations in young open clusters and
star-forming regions suggest that the latter may be characterized by a slightly
lower metallicity than the Sun and older clusters in the solar vicinity.
However, these results are based on small statistics and inhomogeneous
analyses. The Gaia-ESO Survey is observing and homogeneously analyzing large
samples of stars in several young clusters and star-forming regions, hence
allowing us to further investigate this issue.
Aims. We present a new metallicity determination of the Chamaeleon I
star-forming region, based on the products distributed in the first internal
release of the Gaia-ESO Survey.
Methods. 48 candidate members of Chamaeleon I have been observed with the
high-resolution spectrograph UVES. We use the surface gravity, lithium line
equivalent width and position in the Hertzsprung-Russell diagram to confirm the
cluster members and we use the iron abundance to derive the mean metallicity of
the region.
Results. Out of the 48 targets, we confirm 15 high probability members.
Considering the metallicity measurements for 9 of them, we find that the iron
abundance of Chamaeleon I is slightly subsolar with a mean value
[Fe/H]=-0.08+/-0.04 dex. This result is in agreement with the metallicity
determination of other nearby star-forming regions and suggests that the
chemical pattern of the youngest stars in the solar neighborhood is indeed more
metal-poor than the Sun. We argue that this evidence may be related to the
chemical distribution of the Gould Belt that contains most of the nearby
star-forming regions and young clusters.Comment: 13 pages, 11 figures, 3 tables, Accepted for publication in Astronomy
& Astrophysic
Non-circular motion evidences in the circumnuclear region of M100 (NGC 4321)
We analyse new integral field spectroscopy of the inner region (central 2.5
kpc) of the spiral galaxy NGC 4321 to study the peculiar kinematics of this
region. Fourier analysis of the velocity residuals obtained by subtracting an
axisymmetric rotation model from the velocity field, indicates
that the distortions are {\em global} features generated by an
perturbation of the gravitational potential which can be explained by the
nuclear bar. This bar has been previously observed in the near-infrared but not
in the optical continuum dominated by star formation. We detect the optical
counterpart of this bar in the 2D distribution of the old stellar population
(inferred from the equivalent width map of the stellar absorption lines). We
apply the Tremaine--Weinberg method to the stellar velocity field to calculate
the pattern speed of the inner bar, obtaining a value of
=160. This value is considerably la
rger than the one obtained when a simple bar model is considered. However the
uncertainties in the pattern speed determination prevent us to give support to
alternative scenarios.Comment: 11 pages, 11 figures, accepted for publication in MNRA
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