266 research outputs found
Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IV: Synthesis and the Sulfur Anomaly
We have compiled a large sample of O, Ne, S, Cl, and Ar abundances which have
been determined for 85 galactic planetary nebulae in a consistent and
homogeneous manner using spectra extending from 3600-9600 Angstroms. Sulfur
abundances have been computed using the near IR lines of [S III] 9069,9532
along with [S III] temperatures. We find average values, expressed
logarithmically with a standard deviation, of log(S/O)=-1.91(+/-.24),
log(Cl/O)=-3.52(+/-.16), and log(Ar/O)=-2.29(+/-.18), numbers consistent with
previous studies of both planetary nebulae and H II regions. We also find a
strong correlation between [O III] and [S III] temperatures among planetary
nebulae. In analyzing abundances of Ne, S, Cl, and Ar with respect to O, we
find a tight correlation for Ne-O, and loose correlations for Cl-O and Ar-O.
All three trends appear to be colinear with observed correlations for H II
regions. S and O also show a correlation but there is a definite offset from
the behavior exhibited by H II regions and stars. We suggest that this S
anomaly is most easily explained by the existence of S^+3, whose abundance must
be inferred indirectly when only optical spectra are available, in amounts in
excess of what is predicted by model-derived ionization correction factors.
Finally for the disk PNe, abundances of O, Ne, S, Cl, and Ar all show gradients
when plotted against galactocentric distance. The slopes are statistically
indistinguishable from one another, a result which is consistent with the
notion that the cosmic abundances of these elements evolve in lockstep.Comment: 43 pages, including 11 figures. Accepted for publication in the
Astronomical Journal. See also astro-ph/0106213 for Northern sample results,
astro-ph/0109161 and astro-ph/0108336 for the data and abundance information
for the Southern sample, and astro-ph/020954
Limited risk of Zika virus transmission by five Aedes albopictus populations from Spain
Background: Aedes albopictus, the Asian tiger mosquito, is an exotic invasive species in Europe. It has substantial
public health relevance due to its potential role in transmitting several human pathogens. Out of the European counâ
tries, Spain has one of the highest risk levels of autochthonous arbovirus transmission due to both the high density of
Ae. albopictus and the extensive tourist infux from vector-endemic areas. This study aims to investigate the suscepâ
tibility of fve Ae. albopictus populations from mainland Spain and the Balearic Islands to a Brazilian Zika virus (ZIKV)
strain.
Methods: The F1 generation of each Ae. albopictus population was orally challenged with a ZIKV-infected blood meal
(1.8Ă106 PFU/ml). At 7 and 14 days post-infection (dpi), mosquito bodies (thorax and abdomen) and heads were
individually analysed through RT-qPCR to determine the infection rate (IR) and dissemination rate (DR), respectively.
The saliva of infected mosquitoes was inoculated in Vero cells and the transmission rate was assessed by plaque assay
or RT-qPCR on ~33 individuals per population.
Results: The IR and DR ranged between 12â88%, and 0â60%, respectively, suggesting that ZIKV is capable of crossâ
ing the midgut barrier. Remarkably, no infectious viral particle was found in saliva samples, indicating a low ability of
ZIKV to overcome the salivary gland barrier. A subsequent assay revealed that a second non-infective blood meal 48 h
after ZIKV exposure did not infuence Ae. albopictus vector competence.
Conclusions: The oral experimental ZIKV infections performed here indicate that Ae. albopictus from Spain become
infected and disseminate the virus through the body but has a limited ability to transmit the Brazilian ZIKV strain
through biting. Therefore, the results suggest a limited risk of autochthonous ZIKV transmission in Spain by Ae.
albopictusinfo:eu-repo/semantics/publishedVersio
Nebular abundances of southern symbiotic stars
We have calculated relative elemental abundances for a sample of 43 symbiotic
stars. Helium abundances and the relative elemental abundances N/O, Ne/O, Ar/O
were derived from new spectra collected in the optical range through low
dispersion spectroscopy. The He ionic abundances were derived taking into
account self-absorption effects in Balmer lines. We found that the symbiotic
stars in the galactic bulge have heavy element abundances showing the same wide
distribution as other bulge objects. In the galactic disk, the symbiotic stars
follow the abundance gradient as derived from different kinds of objects.Comment: 12 pages, 6 figures, A&A - accepte
Chemical evolution of the Small Magellanic Cloud based on planetary nebulae
We investigate the chemical evolution of the Small Magellanic Cloud (SMC)
based on abundance data of planetary nebulae (PNe). The main goal is to
investigate the time evolution of the oxygen abundance in this galaxy by
deriving an age-metallicity relation. Such a relation is of fundamental
importance as an observational constraint of chemical evolution models of the
SMC. We have used high quality PNe data in order to derive the properties of
the progenitor stars, so that the stellar ages could be estimated. We collected
a large number of measured spectral fluxes for each nebula, and derived
accurate physical parameters and nebular abundances. New spectral data for a
sample of SMC PNe obtained between 1999 and 2002 are also presented. These data
are used together with data available in the literature to improve the accuracy
of the fluxes for each spectral line. We obtained accurate chemical abundances
for PNe in the Small Magellanic Cloud, which can be useful as tools in the
study of the chemical evolution of this galaxy and of Local Group galaxies. We
present the resulting oxygen versus age diagram and a similar relation
involving the [Fe/H] metallicity based on a correlation with stellar data. We
discuss the implications of the derived age-metallicity relation for the SMC
formation, in particular by suggesting a star formation burst in the last 2-3
Gyr.Comment: 11 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
New abundances of planetary nebulae in the Galactic Bulge
New observations and derived chemical abundances are reported for a sample of
57 bulge planetary nebulae (PN). Together with our previous results, a total of
over a hundred objects have been analyzed, which constitute one of the largest
samples of bulge nebulae studied under homogeneous conditions, including
equipment and reduction procedures. In general, our data show a good agreement
with some recent results in the literature, in the sense that the average
abundances of bulge PN are similar to those from disk objects, however showing
a larger dispersion.Comment: 12 pages, 9 figure
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