383 research outputs found
The effects of four types of anthropogenic disturbances on composition and abundance of terrestrial isopods (Isopoda: Oniscidea)
The Brazilian Atlantic Forest is currently reduced to about 12% of its original range. Among the components that make up its great diversity, there are species with the potential to be bioindicators, which can be very important for conservation-oriented studies. This study compares the species composition, abundance and sex ratio of terrestrial isopods in sites that show different anthropogenic disturbance histories and are located within four reserves in the Atlantic Forest of southwestern Brazil. Our study explores these crustaceans as indicators of anthropogenic disturbance. The influence of one of the following factors was explored in each protected area: 1) history of vegetation harvesting, 2) trail management, 3) Eucalyptus planting, and 4) edge effect. A total of 2,217 individuals of six species (Atlantoscia sp., Benthana werneri Lemos de Castro, 1958, Pseudodiploexochus tabularis (Barnard, 1932), Pudeoniscus obscures Lemos de Castro, 1973, Styloniscus spinosus (Patience, 1907), and Trichorhina sp.) were captured in pitfall traps. The composition of isopod species was different between most of the contrasting sites within reserves, and was similar among the less disturbed sites of different reserves. The total number of isopod individuals and the sex ratio were not different between the contrasting sites within most of the reserves and only the sex ratio of Atlantoscia sp. differed between contrasting sites of one protected area. Upon an individual analysis of each species, S. spinosus (an exotic species) was most abundant in more disturbed sites. The distributions of B. werneri and Atlantoscia sp. over time were relatively synchronous, except where S. spinosus was abundant. Our results also indicate that the exotic species S. spinosus may benefit from the vegetation mosaic produced by disturbance, so differences in abundance of this species may be useful for bioindication. A change in the spatial and temporal structure of Oniscidea communities caused by anthropogenic disturbance may have a cascade effect on ecological cycles because terrestrial isopods play a fundamental role in nutrient cycling.637
The effects of four types of anthropogenic disturbances on composition and abundance of terrestrial isopods (Isopoda: Oniscidea)
The Gaia-ESO Survey: Separating disk chemical substructures with cluster models
(Abridged) Recent spectroscopic surveys have begun to explore the Galactic
disk system outside the solar neighborhood on the basis of large data samples.
In this way, they provide valuable information for testing spatial and temporal
variations of disk structure kinematics and chemical evolution. We used a
Gaussian mixture model algorithm, as a rigurous mathematical approach, to
separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample from the
Gaia-ESO survey internal data release 2. We find that the sample is separated
into five groups associated with major Galactic components; the metal-rich end
of the halo, the thick disk, and three subgroups for the thin disk sequence.
This is confirmed with a sample of red clump stars from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) survey. The two
metal-intermediate and metal-rich groups of the thin disk decomposition
([Fe/H]>-0.25 dex) highlight a change in the slope at solar metallicity. This
holds true at different radial regions. The distribution of Galactocentric
radial distances of the metal-poor part of the thin disk ([Fe/H]<-0.25 dex) is
shifted to larger distances than those of the more metal-rich parts. Moreover,
the metal-poor part of the thin disk presents indications of a scale height
intermediate between those of the thick and the rest of the thin disk, and it
displays higher azimuthal velocities than the latter. These stars might have
formed and evolved in parallel and/or dissociated from the inside-out formation
taking place in the internal thin disk. Their enhancement levels might be due
to their origin from gas pre-enriched by outflows from the thick disk or the
inner halo. The smooth trends of their properties (their spatial distribution
with respect to the plane, in particular) with [Fe/H] and [Mg/Fe] suggested by
the data indicates a quiet dynamical evolution, with no relevant merger events
A Mechanism for the Oxygen and Iron Bimodal Radial Distribution Formation in the Disc of our Galaxy
Recently it has been proposed that there are two types of SN Ia progenitors
-- short-lived and long-lived. On the basis of this idea, we develope a theory
of a unified mechanism for the formation of the bimodal radial distribution of
iron and oxygen in the Galactic disc. The underlying cause for the formation of
the fine structure of the radial abundance pattern is the influence of spiral
arms, specifically, the combined effect of the corotation resonance and
turbulent diffusion. From our modelling we conclude that to explain the bimodal
radial distributions simultaneously for oxygen and iron and to obtain
approximately equal total iron output from different types of supernovae, the
mean ejected iron mass per supernova event should be the same as quoted in
literature if maximum mass of stars, that eject heavy elements, is . For the upper mass limit of the production of iron
by a supernova II explosion should be increased by about 1.5 times.Comment: 7 pages, 6 figures, MNRAS submitte
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
Atomic and Molecular Gas Components in Spiral Galaxies of the Virgo Cluster
Based on two models, we investigate the molecular-to-atomic gas ratio in
Virgo cluster galaxies in comparison with field galaxies. We show that the
enhanced metallicity for cluster members and the ram pressure stripping of
atomic gas from the disk periphery cannot fully explain the observed gas
component ratios. The additional environmental factors affecting the
interstellar medium and leading to an increase in the molecular gas fraction
should be taken into account for cluster galaxies.Comment: 11 pages, 4 figure
NGC 300 X-1 is a Wolf-Rayet/Black-Hole binary
We present VLT/FORS2 time-series spectroscopy of the Wolf-Rayet star #41 in
the Sculptor group galaxy NGC 300. We confirm a physical association with NGC
300 X-1, since radial velocity variations of the HeII 4686 line indicate an
orbital period of 32.3 +/- 0.2 hr which agrees at the 2 sigma level with the
X-ray period from Carpano et al. We measure a radial velocity semi-amplitude of
267 +/- 8 km/s, from which a mass function of 2.6 +/- 0.3 Msun is obtained. A
revised spectroscopic mass for the WN-type companion of 26+7-5 Msun yields a
black hole mass of 20 +/- 4 Msun for a preferred inclination of 60-75 deg. If
the WR star provides half of the measured visual continuum flux, a reduced WR
(black hole) mass of 15 +4 -2.5 Msun (14.5 +3 -2.5 Msun) would be inferred. As
such, #41/NGC 300 X-1 represents only the second extragalactic Wolf-Rayet plus
black-hole binary system, after IC 10 X-1. In addition, the compact object
responsible for NGC 300 X-1 is the second highest stellar-mass black hole known
to date, exceeded only by IC 10 X-1.Comment: 5 pages, 6 figures, MNRAS Letters in press. Images and animations
available from http://www.eso.org/public/news/eso1004/ at 11am GMT on 27 Jan
1
Polycyclic aromatic hydrocarbons in the dwarf galaxy IC 10
Infrared observations from the Spitzer Space Telescope archive are used to
study the dust component of the interstellar medium in the IC~10 irregular
galaxy. Dust distribution in the galaxy is compared to the distributions of
H and [SII] emission, neutral hydrogen and CO clouds, and ionizing
radiation sources. The distribution of polycyclic aromatic hydrocarbons (PAH)
in the galaxy is shown to be highly non-uniform with the mass fraction of these
particles in the total dust mass reaching 4%. PAHs tend to avoid bright HII
regions and correlate well with atomic and molecular gas. This pattern suggests
that PAHs form in the dense interstellar gas. We propose that the significant
decrease of the PAH abundance at low metallicity is observed not only globally
(at the level of entire galaxies), but also locally (at least, at the level of
individual HII regions). We compare the distribution of the PAH mass fraction
to the distribution of high-velocity features, that we have detected earlier in
wings of H and SII lines, over the entire available galaxy area. No
conclusive evidence for shock destruction of PAHs in the IC~10 galaxy could be
found.Comment: Accepted for publication in Astronomy Report
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