3,410 research outputs found
Estacionalidad de las larvas de crustáceos decápodos en las aguas subtropicales de la isla de Gran Canaria, Atlántico NE
A monitoring programme was established to collect plankton samples and information of environmental variables over the shelf off the island of Gran Canaria during 2005 and 2006. It produced a detailed snapshot of the composition and seasonal assemblages of the decapod larvae community in this locality, in the subtropical waters of the Canary Islands (NE Atlantic), where information about crustacean phenology has been poorly studied. The larval community was mainly composed of benthic taxa, but the contribution of pelagic taxa was also significant. Infraorders Anomura (33.4%) and Caridea (32.8%) accounted for more than half the total collected larvae. High diversity, relatively low larval abundance throughout the year and weak seasonality characterized the annual cycle. However, in relation to the temporal dynamics of temperature, two distinct larval assemblages (cold and warm) were identified that correspond to periods of mixing and stratification of the water column. The results also indicate that larval release times and durations in the subtropical waters are earlier and longer than at other higher latitudes in the NE Atlantic. We detected the presence of larvae of six species that have not yet been reported from the Canary Islands (Pandalina brevirostris, Processa edulis, Necallianasa truncata, Parapenaeus longirostris, Crangon crangon, Nematopagurus longicornis). Finally, this study provides a baseline for future comparisons with respect to fishery pressure and climate variability in this subtropical region.Durante 2005 y 2006 se estableció un monitoreo para recolectar muestras de plancton e información de las variables ambientales sobre la plataforma insular de Gran Canaria. Esto produjo una instantánea detallada de la composición y estacionalidad de las asociaciones de la comunidad de larvas de decápodos en las aguas subtropicales de esta localidad de las Islas Canarias (Atlántico NE), donde la información sobre la fenología de crustáceos está pobremente estudiada. La comunidad de larvas estuvo principalmente compuesta por taxones bentónicos, pero con una contribución significativa de taxones pelágicos. Los infraórdenes Anomura (33.4%) y Caridea (32.8%) representaron más de la mitad del total de las larvas recolectadas. Alta diversidad, relativamente baja abundancia de larvas a lo largo de todo el año, y débil estacionalidad caracterizaron el ciclo anual. Sin embargo, y relacionado con la dinámica temporal de la temperatura, dos asociaciones larvarias distintas (fría y cálida) fueron identificadas que correspondieron con periodos de mezcla y estratificación de la columna de agua. Los resultados también indican que la duración y periodos de liberación de larvas en las aguas subtropicales son más tempranos y largos en el tiempo en comparación con otras latitudes más altas en el Atlántico NE. Además, se detecta la presencia de larvas de seis especies que no han sido citadas con anterioridad para las Islas Canarias (Pandalina brevirostris, Processa edulis, Necallianasa truncata, Parapenaeus longirostris, Crangon crangon, Nematopagurus longicornis). Finalmente, este estudio supone un punto de referencia para futuras comparaciones en relación con la presión pesquera y la variabilidad climática en esta región subtropical
Accurate Atmospheric Parameters at Moderate Resolution Using Spectral Indices: Preliminary Application to the MARVELS Survey
Studies of Galactic chemical and dynamical evolution in the solar
neighborhood depend on the availability of precise atmospheric parameters
(Teff, [Fe/H] and log g) for solar-type stars. Many large-scale spectroscopic
surveys operate at low to moderate spectral resolution for efficiency in
observing large samples, which makes the stellar characterization difficult due
to the high degree of blending of spectral features. While most surveys use
spectral synthesis, in this work we employ an alternative method based on
spectral indices to determine the atmospheric parameters of a sample of nearby
FGK dwarfs and subgiants observed by the MARVELS survey at moderate resolving
power (R~12,000). We have developed three codes to automatically normalize the
observed spectra, measure the equivalent widths of the indices and, through the
comparison of those with values calculated with pre-determined calibrations,
derive the atmospheric parameters of the stars. The calibrations were built
using a sample of 309 stars with precise stellar parameters obtained from the
analysis of high-resolution FEROS spectra. A validation test of the method was
conducted with a sample of 30 MARVELS targets that also have reliable
atmospheric parameters from high-resolution spectroscopic analysis. Our
approach was able to recover the parameters within 80 K for Teff, 0.05 dex for
[Fe/H] and 0.15 dex for log g, values that are lower or equal to the typical
external uncertainties found between different high-resolution analyzes. An
additional test was performed with a subsample of 138 stars from the ELODIE
stellar library and the literature atmospheric parameters were recovered within
125 K for Teff, 0.10 dex for [Fe/H] and 0.29 dex for log g. These results show
that the spectral indices are a competitive tool to characterize stars with the
intermediate resolution spectra.Comment: Accepted for publication in AJ. Abstract edited to comply with arXiv
standards regarding the number of character
Very Low Mass Stellar and Substellar Companions to Solar-Like Stars From MARVELS V: A Low Eccentricity Brown Dwarf from the Driest Part of the Desert, MARVELS-6b
We describe the discovery of a likely brown dwarf (BD) companion with a
minimum mass of 31.7 +/- 2.0 M_Jup to GSC 03546-01452 from the MARVELS radial
velocity survey, which we designate as MARVELS-6b. For reasonable priors, our
analysis gives a probability of 72% that MARVELS-6b has a mass below the
hydrogen-burning limit of 0.072 M_Sun, and thus it is a high-confidence BD
companion. It has a moderately long orbital period of 47.8929 +0.0063/-0.0062
days with a low eccentricty of 0.1442 +0.0078/-0.0073, and a semi-amplitude of
1644 +12/-13 m/s. Moderate resolution spectroscopy of the host star has
determined the following parameters: T_eff = 5598 +/- 63, log g = 4.44 +/-
0.17, and [Fe/H] = +0.40 +/- 0.09. Based upon these measurements, GSC
03546-01452 has a probable mass and radius of M_star = 1.11 +/- 0.11 M_Sun and
R_star = 1.06 +/- 0.23 R_Sun with an age consistent with less than ~6 Gyr at a
distance of 219 +/- 21 pc from the Sun. Although MARVELS-6b is not observed to
transit, we cannot definitively rule out a transiting configuration based on
our observations. There is a visual companion detected with Lucky Imaging at
7.7 arcsec from the host star, but our analysis shows that it is not bound to
this system. The minimum mass of MARVELS-6b exists at the minimum of the mass
functions for both stars and planets, making this a rare object even compared
to other BDs.Comment: 15 pages, 15 figures, 5 tables. Accepted for publication in The
Astronomical Journa
Predicting understory maximum shrubs cover using altitude and overstory basal area in different Mediterranean forests
In some areas of the Mediterranean basin where the understory stratum represents a critical fire hazard, managing the canopy cover to control the understory shrubby vegetation is an ecological alternative to the current mechanical management techniques. In this study, we determine the relationship between the overstory basal area and the cover of the understory shrubby vegetation for different dominant canopy species (Pinaceae and Fagaceae species) along a wide altitudinal gradient in the province of Catalonia (Spain). Analyses were conducted using data from the Spanish National Forest Inventory. At the regional scale, when all stands are analysed together, a strong negative relationship between mean shrub cover and site elevation was found. Among the Pinaceae species, we found fairly good relationships between stand basal area and the maximum development of the shrub stratum for species located at intermediate elevations (Pinus nigra, Pinus sylvestris). However, at the extremes of the elevationclimatic gradient (Pinus halepensis and Pinus uncinata stands), stand basal area explained very little of the shrub cover variation probably because microsite and topographic factors override its effect. Among the Fagaceae species, a negative relationship between basal area and the maximum development of the shrub stratum was found in Quercus humilis and Fagus sylvatica dominated stands but not in Quercus ilex. This can be due to the particular canopy structure and management history of Q. ilex stands. In conclusion, our study revealed a marked effect of the tree layer composition and the environment on the relationship between the development of the understory and overstory tree structure. More fine-grained studies are needed to provide forest managers with more detailed information about the relationship between these two forest strata
Strong Ultraviolet Pulse From a Newborn Type Ia Supernova
Type Ia supernovae are destructive explosions of carbon oxygen white dwarfs.
Although they are used empirically to measure cosmological distances, the
nature of their progenitors remains mysterious, One of the leading progenitor
models, called the single degenerate channel, hypothesizes that a white dwarf
accretes matter from a companion star and the resulting increase in its central
pressure and temperature ignites thermonuclear explosion. Here we report
observations of strong but declining ultraviolet emission from a Type Ia
supernova within four days of its explosion. This emission is consistent with
theoretical expectations of collision between material ejected by the supernova
and a companion star, and therefore provides evidence that some Type Ia
supernovae arise from the single degenerate channel.Comment: Accepted for publication on the 21 May 2015 issue of Natur
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Weak Polygyny in California Sea Lions and the Potential for Alternative Mating Tactics
Female aggregation and male territoriality are considered to be hallmarks of polygynous mating systems. The development of genetic parentage assignment has called into question the accuracy of behavioral traits in predicting true mating systems. In this study we use 14 microsatellite markers to explore the mating system of one of the most behaviorally polygynous species, the California sea lion (Zalophus californianus). We sampled a total of 158 female-pup pairs and 99 territorial males across two breeding rookeries (San Jorge and Los Islotes) in the Gulf of California, Mexico. Fathers could be identified for 30% of pups sampled at San Jorge across three breeding seasons and 15% of sampled pups at Los Islotes across two breeding seasons. Analysis of paternal relatedness between the pups for which no fathers were identified (sampled over four breeding seasons at San Jorge and two at Los Islotes) revealed that few pups were likely to share a father. Thirty-one percent of the sampled males on San Jorge and 15% of the sampled males on Los Islotes were assigned at least one paternity. With one exception, no male was identified as the father of more than two pups. Furthermore, at Los Islotes rookery there were significantly fewer pups assigned paternity than expected given the pool of sampled males (p<0.0001). Overall, we found considerably lower variation in male reproductive success than expected in a species that exhibits behavior associated with strongly polygynous mating. Low variation in male reproductive success may result from heightened mobility among receptive females in the Gulf of California, which reduces the ability of males to monopolize groups of females. Our results raise important questions regarding the adaptive role of territoriality and the potential for alternative mating tactics in this species
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from
submitted version
An extremely primitive halo star
The early Universe had a chemical composition consisting of hydrogen, helium
and traces of lithium1, almost all other elements were created in stars and
supernovae. The mass fraction, Z, of elements more massive than helium, is
called "metallicity". A number of very metal poor stars have been found some of
which, while having a low iron abundance, are rich in carbon, nitrogen and
oxygen. For theoretical reasons and because of an observed absence of stars
with metallicities lower than Z=1.5E-5, it has been suggested that low mass
stars (M<0.8M\odot, the ones that survive to the present day) cannot form until
the interstellar medium has been enriched above a critical value, estimated to
lie in the range 1.5E-8\leqZ\leq1.5E-6, although competing theories claiming
the contrary do exist. Here we report the chemical composition of a star with a
very low Z\leq6.9E-7 (4.5E-5 of that of the Sun) and a chemical pattern typical
of classical extremely metal poor stars, meaning without the enrichment of
carbon, nitrogen and oxygen. This shows that low mass stars can be formed at
very low metallicity. Lithium is not detected, suggesting a low metallicity
extension of the previously observed trend in lithium depletion. Lithium
depletion implies that the stellar material must have experienced temperatures
above two million K in its history, which points to rather particular formation
condition or internal mixing process, for low Z stars.Comment: Published on Nature, 2011 Volume 477, Issue 7362, pp. 67-6
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