2,163 research outputs found
Sulfur, Chlorine, & Argon Abundances in Planetary Nebulae. I: Observations and Abundances in a Northern Sample
This paper is the first of a series specifically studying the abundances of
sulfur, chlorine, and argon in Type II planetary nebulae (PNe) in the Galactic
disk. Ratios of S/O, Cl/O, and Ar/O constitute important tests of differential
nucleosynthesis of these elements and serve as strict constraints on massive
star yield predictions. We present new ground-based optical spectra extending
from 3600-9600 Angstroms for a sample of 19 Type II northern PNe. This range
includes the strong near infrared lines of [S III] 9069,9532, which allows us
to test extensively their effectiveness as sulfur abundance indicators. We also
introduce a new, model-tested ionization correction factor for sulfur. For the
present sample, we find average values of S/O=1.2E-2(+/- 0.71E-2),
Cl/O=3.3E-4(+/- 1.6E-4), and Ar/O=5.0E-3(+/- 1.9E-3).Comment: 44 pages, 6 figures. Accepted for publication in the Astrophysical
Journa
Resistência do tipo antibiose a ninfas de Tibraca limbativentris (Stal, 1860) (Heteroptera: Pentatomidae) em variedades de arroz.
O percevejo-do-colmo (Tibraca limbativentris Stal, 1860) é uma importante praga do arroz no Brasil. O uso de variedades resistentes a esse inseto é uma ferramenta importante para o seu controle. O experimento foi conduzido em casa de vegetação na Embrapa Arroz e Feijão. Foi avaliada resistência tipo antibiose em ninfas de T. limbativentris em 16 variedades de arroz em delineamento experimental de blocos casualizados em oito repetições. Os caracteres utilizados para detectar indícios de resistência do tipo antibiose foram: número de ninfas vivas, massa seca (mg)/ninfas, superfície corporal/mm2, índice de sobrevivência e desenvolvimento e dias de vida das ninfas. Realizaram-se três tipos de análises: a) considerando somente os dados obtidos nas repetições avaliadas aos 7, 13, 21 e 26 dias após a infestação; b) considerando somente os dados das quatro repetições avaliadas aos 35 dias após a infestação e c) considerando os dados obtidos conjuntamente nas oito repetições. Conclui-se que as variedades Arroz Comum e Desconhecido Branco, principalmente a primeira, evidenciam possuir características que lhes confere determinado grau de resistência do tipo antibiose a ninfas de T. limbativentris
Metallicity in the Galactic Center: The Arches cluster
We present a quantitative spectral analysis of five very massive stars in the
Arches cluster, located near the Galactic center, to determine stellar
parameters, stellar wind properties and, most importantly, metallicity content.
The analysis uses a new technique, presented here for the first time, and uses
line-blanketed NLTE wind/atmosphere models fit to high-resolution near-infrared
spectra of late-type nitrogen-rich Wolf-Rayet stars and OfI+ stars in the
cluster. It relies on the fact that massive stars reach a maximum nitrogen
abundance that is related to initial metallicity when they are in the WNL
phase. We determine the present-day nitrogen abundance of the WNL stars in the
Arches cluster to be 1.6% (mass fraction) and constrain the stellar metallicity
in the cluster to be solar. This result is invariant to assumptions about the
mass-luminosity relationship, the mass-loss rates, and rotation speeds. In
addition, from this analysis, we find the age of the Arches cluster to be
2-2.5Myr, assuming coeval formation
The populations of planetary nebulae in the direction of the Galactic bulge
We have observed 44 planetary nebulae (PNe) in the direction of the Galactic
bulge, and merged our data with published ones. We have distinguished, in the
merged sample of 164 PNe, those PNe most likely to prtain physically to the
Galactic bulge and those most likely to belong to the Galactic disk. We have
determined the chemical composition of all the 164 objects in a coherent way.
We looked for stellar emission features and discovered 14 new [WR] stars and 15
new weak emission line central stars.
The analyzed data led us to the following conclusions: (1) The spectral type
distribution of [WR] stars is very different in the bulge and in the disk of
the Galaxy. However, the observed distributions are strongly dependent on
selection effects. (2) The proportion of [WR] PNe is significantly larger in
the bulge than in the disk. (3) The oxygen abundances in [WR] stars do no
appear to be significantly affected by nucleosynthesis and mixing in the
progenitors. (4) The O/H gradient of the Galactic disk PNe population flattens
in the most internal parts of the Galaxy. (5) The median oxygen abundance in
the bulge PN population is larger by 0.2 dex than in the disk population seen
in the direction of the bulge. (6) Bulge PNe with smaller O/H tend to have
smaller radial velocities. (7) The oxygen abundance distribution of bulge PNe
is similar in shape to that of the metallicity distribution of bulge giants,
but significantly narrower. (8) The location of SB 32 (PN G 349.7-09.1) in the
(V_lsr, l_II) diagram and its low oxygen abundance argues that it probably
belongs to the halo population.Comment: 14 pages, 16 figures. Accepted for publication in A&
Stellar Iron Abundances at the Galactic Center
We present measurements of [Fe/H] for six M supergiant stars and three giant
stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star
within 30 pc of the GC. The results are based on high-resolution (lambda /
Delta lambda =40,000) K-band spectra, taken with CSHELL at the NASA Infrared
Telescope Facility.We determine the iron abundance by detailed abundance
analysis,performed with the spectral synthesis program MOOG.The mean [Fe/H] of
the GC stars is determined to be near solar,[Fe/H] = +0.12 0.22. Our
analysis is a differential analysis, as we have observed and applied the same
analysis technique to eleven cool, luminous stars in the solar neighborhood
with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of
the solar neighborhood comparison stars, [Fe/H] = +0.03 0.16, is similar
to that of the GC stars. The width of the GC [Fe/H] distribution is found to be
narrower than the width of the [Fe/H] distribution of Baade's Window in the
bulge but consistent with the width of the [Fe/H] distribution of giant and
supergiant stars in the solar neighborhood.Comment: 41 pages, 9 figures, ApJ, in pres
Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating
We model the photoelectric emission from and charging of interstellar dust
and obtain photoelectric gas heating efficiencies as a function of grain size
and the relevant ambient conditions. Using realistic grain size distributions,
we evaluate the net gas heating rate for various interstellar environments, and
find less heating for dense regions characterized by R_V=5.5 than for diffuse
regions with R_V=3.1. We provide fitting functions which reproduce our
numerical results for photoelectric heating and recombination cooling for a
wide range of interstellar conditions. In a separate paper we will examine the
implications of these results for the thermal structure of the interstellar
medium. Finally, we investigate the potential importance of photoelectric
heating in H II regions, including the warm ionized medium. We find that
photoelectric heating could be comparable to or exceed heating due to
photoionization of H for high ratios of the radiation intensity to the gas
density. We also find that photoelectric heating by dust can account for the
observed variation of temperature with distance from the galactic midplane in
the warm ionized medium.Comment: 50 pages, including 18 figures; corrected title and abstract field
Enriquecimento de tilápias alimentadas com fontes de ácidos graxos poliinsaturados da série N-3.
O objetivo deste trabalho foi avaliar o desempenho, a composição química e a composição em ácidos graxos de tilápias vermelhas (Oreochromis sp.) alimentadas com dietas enriquecidas com fontes de ácidos graxos poliinsaturados
A Quasi-Model-Independent Search for New Physics at Large Transverse Momentum
We apply a quasi-model-independent strategy ("Sleuth") to search for new high
p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV
collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron.
Over thirty-two e mu X, W+jets-like, Z+jets-like, and 3(lepton/photon)X
exclusive final states are systematically analyzed for hints of physics beyond
the standard model. Simultaneous sensitivity to a variety of models predicting
new phenomena at the electroweak scale is demonstrated by testing the method on
a particular signature in each set of final states. No evidence of new high p_T
physics is observed in the course of this search, and we find that 89% of an
ensemble of hypothetical similar experimental runs would have produced a final
state with a candidate signal more interesting than the most interesting
observed in these data.Comment: 28 pages, 17 figures. Submitted to Physical Review
B Physics at the Tevatron: Run II and Beyond
This report provides a comprehensive overview of the prospects for B physics
at the Tevatron. The work was carried out during a series of workshops starting
in September 1999. There were four working groups: 1) CP Violation, 2) Rare and
Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and
Spectroscopy. The report also includes introductory chapters on theoretical and
experimental tools emphasizing aspects of B physics specific to hadron
colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a
Summary.Comment: 583 pages. Further information on the workshops, including
transparencies, can be found at the workshop's homepage:
http://www-theory.lbl.gov/Brun2/. The report is also available in 2-up
http://www-theory.lbl.gov/Brun2/report/report2.ps.gz or chapter-by-chapter
http://www-theory.lbl.gov/Brun2/report
Search for Electroweak Production of Single Top Quarks in ppbar Collisions
We present a search for electroweak production of single top quarks in the
electron+jets and muon+jets decay channels. The measurements use ~90 pb^-1 of
data from Run 1 of the Fermilab Tevatron collider, collected at 1.8 TeV with
the DZero detector between 1992 and 1995. We use events that include a tagging
muon, implying the presence of a b jet, to set an upper limit at the 95%
confidence level on the cross section for the s-channel process ppbar->tb+X of
39 pb. The upper limit for the t-channel process ppbar->tqb+X is 58 pb.Comment: 11 pages, 2 figures. This is the published versio
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