5,782 research outputs found
Fe I and Fe II Abundances of Solar-Type Dwarfs in the Pleiades Open Cluster
We have derived Fe abundances of 16 solar-type Pleiades dwarfs by means of an
equivalent width analysis of Fe I and Fe II lines in high-resolution spectra
obtained with the Hobby - Eberly Telescope and High Resolution Spectrograph.
Abundances derived from Fe II lines are larger than those derived from Fe I
lines (herein referred to as over-ionization) for stars with Teff < 5400 K, and
the discrepancy (deltaFe = [Fe II/H] - [Fe I/H]) increases dramatically with
decreasing Teff, reaching over 0.8 dex for the coolest stars of our sample. The
Pleiades joins the open clusters M 34, the Hyades, IC 2602, and IC 2391, and
the Ursa Major moving group, demonstrating ostensible over-ionization trends.
The Pleiades deltaFe abundances are correlated with Ca II infrared triplet and
Halpha chromospheric emission indicators and relative differences therein.
Oxygen abundances of our Pleiades sample derived from the high-excitation O I
triplet have been previously shown to increase with decreasing Teff, and a
comparison with the deltaFe abundances suggests that the over-excitation
(larger abundances derived from high excitation lines relative to low
excitation lines) and over-ionization effects that have been observed in cool
open cluster and disk field main sequence (MS) dwarfs share a common origin.
Star-to-star Fe I abundances have low internal scatter, but the abundances of
stars with Teff < 5400 K are systematically higher compared to the warmer
stars. The cool star [Fe I/H] abundances cannot be connected directly to
over-excitation effects, but similarities with the deltaFe and O I triplet
trends suggest the abundances are dubious. Using the [Fe I/H] abundances of
five stars with Teff > 5400 K, we derive a mean Pleiades cluster metallicity of
[Fe/H] = +0.01 +/- 0.02.Comment: 32 pages, 7 figures, 7 tables; accepted by PAS
Li I and K I Scatter in Cool Pleiades Dwarfs
We utilize high-resolution (R~60,000), high S/N (~100) spectroscopy of 17
cool Pleiades dwarfs to examine the confounding star-to-star scatter in the
6707 Li I line strengths in this young cluster. Our Pleiads, selected for their
small projected rotational velocity and modest chromospheric emission, evince
substantial scatter in the linestrengths of 6707 Li I feature that is absent in
the 7699 K I resonance line. The Li I scatter is not correlated with that in
the high-excitation 7774 O I feature, and the magnitude of the former is
greater than the latter despite the larger temperature sensitivity of the O I
feature. These results suggest that systematic errors in linestrength
measurements due to blending, color (or color-based T_eff) errors, or line
formation effects related to an overlying chromosphere are not the principal
source of Li I scatter in our stars. There do exist analytic spot models that
can produce the observed Li scatter without introducing scatter in the K I line
strengths or the color-magnitude diagram. However, these models predict factor
of >3 differences in abundances derived from the subordinate 6104 and resonance
6707 Li I features; we find no difference in the abundances determined from
these two features. These analytic spot models also predict CN line strengths
significantly larger than we observe in our spectra. The simplest explanation
of the Li, K, CN, and photometric data is that there must be a real abundance
component to the Pleiades Li dispersion. We suggest that this real abundance
component is the manifestation of relic differences in erstwhile
pre-main-sequence Li burning caused by effects of surface activity on stellar
structure. We discuss observational predictions of these effects.Comment: 35 pages, 7 figures; accepted by Ap
Are the reactions a challenge for the factorized Pomeron at high energies?
We would like to point to the strong violation of the putative factorized
Pomeron exchange model in the reactions in the
high-energy region where this model works fairly well in all other cases.Comment: 4 pages, LaTex, 1 fig. in postscript, minor typos corrected, to be
published in Phys. Rev. D 60, 117503 (1999
Quarkonium production in hadronic collisions
We summarize the theoretical description of charmonium and bottonium
production in hadronic collisions and compare it to the available data from
hadron-nucleon interactions. With the parameters of the theory established by
these data, we obtain predictions for quarkonium production at RHIC and LHC
energies.Comment: 11 pages (Plain Tex), 16 figures available on request by fax (41-22)
782 391
Oxygen in Open Cluster Dwarfs: Pleiades and M34
We analyze the high-excitation O I lambda7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172 K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation lambda6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] lambda6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]6300=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]Trip at a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures
Lightweight Bulldozer Attachment for Construction and Excavation on the Lunar Surface
A lightweight bulldozer blade prototype has been designed and built to be used as an excavation implement in conjunction with the NASA Chariot lunar mobility platform prototype. The combined system was then used in a variety of field tests in order to characterize structural loads, excavation performance and learn about the operational behavior of lunar excavation in geotechnical lunar simulants. The purpose of this effort was to evaluate the feasibility of lunar excavation for site preparation at a planned NASA lunar outpost. Once the feasibility has been determined then the technology will become available as a candidate element in the NASA Lunar Surface Systems Architecture. In addition to NASA experimental testing of the LANCE blade, NASA engineers completed analytical work on the expected draft forces using classical soil mechanics methods. The Colorado School of Mines (CSM) team utilized finite element analysis (FEA) to study the interaction between the cutting edge of the LANCE blade and the surface of soil. FEA was also used to examine various load cases and their effect on the lightweight structure of the LANCE blade. Overall it has been determined that a lunar bulldozer blade is a viable technology for lunar outpost site preparation, but further work is required to characterize the behavior in 1/6th G and actual lunar regolith in a vacuum lunar environment
High-Resolution Spectroscopy of the Planetary Host HD 13189: Highly-Evolved and Metal-Poor
We report on the abundances of 13 elements in the planetary host HD 13189, a
massive giant star. Abundances are found to be sub-solar, with [Fe/H] = -0.58
+/- 0.04$; HD 13189 is one of the most metal-poor planetary hosts yet
discovered. Abundance ratios relative to Fe show no peculiarities with respect
to random field stars. A census of metallicities of the seven currently known
planet-harboring giants results in a distribution that is more metal-poor than
the well-known metal-rich distribution of main sequence (MS) planetary hosts.
This finding is discussed in terms of accretion of H-depleted material, one of
the possible mechanisms responsible for the high-metallicity distribution of MS
stars with planets. We estimate the mass of the HD 13189 progenitor to be 3.5
M_sun but cannot constrain this value to better than 2-6 M_sun. A stellar mass
of 3.5 M_sun implies a planetary mass of m sin i = 14.0 +/- 0.8 M_J, placing
the companion at the planet/brown dwarf boundary. Given its physical
characteristics, the HD 13189 system is potentially unique among planetary
systems, and its continued investigation should provide invaluable data to
extrasolar planetary research.Comment: 14 pages, 2 figures; Accepted for publication in ApJ Letter
Pagamento por serviços ambientais hídricos no Brasil: experiências iniciais e os desafios do monitoramento.
Ao avaliar os projetos de pagamentos por serviços ambientais (PSA) no Brasil, observam-se dificuldades recorrentes relacionadas à falta de consolidação das metodologias para a seleção de áreas prioritárias e, sobretudo, para o monitoramento das áreas de prestação dos serviços. A estratégia de pagamentos por serviços ambientais é cada vez mais presente nas políticas ambientais, devido ao reconhecimento da necessidade de novos mecanismos de estímulo à conservação e à manutenção de serviços essenciais à vida, como a provisão de água. A partir da análise das experiências vivenciadas em projetos de Pagamento por Serviços Ambientais (PSA) relacionados à água de alguns estados brasileiros, o trabalho apresenta um panorama destas experiências, de maneira a identificar as tendências, os obstáculos enfrentados e, sobretudo, os aspectos relevantes das metodologias de monitoramento aplicadas
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