7,537 research outputs found
High-Resolution Spectroscopy of Ursa Major Moving Group Stars
We use new and extant literature spectroscopy to address abundances and
membership for UMa moving group stars. We first compare the UMa, Coma, and
Hyades H-R diagrams via a homogeneous set of isochrones, and find that these
three aggregates are essentially coeval. Our spectroscopy of cool UMa dwarfs
reveals striking abundance anomalies--trends with Teff, ionization state, and
excitation potential--like those recently seen in young cool M34, Pleaides, and
Hyades dwarfs. In particular, the trend of rising 7774 Ang-based OI abundance
with declining Teff is markedly subdued in UMa compared to the Pleiades,
suggesting a dependence on age or metallicity. Despite disparate sources of Li
data,our homogeneous analysis indicates that UMa members evince remarkably
small scatter in the Li-Teff plane for Teff>5200 K. Significant star-to-star
scatter suggested by previous studies is seen for cooler stars. Comparison with
the consistently determined Hyades Li-Teff trend reveals differences
qualitatively consistent with this cluster's larger [Fe/H] (and perhaps
slightly larger age). However, quantitative comparison with standard stellar
models indicates the differences are smaller than expected, suggesting the
action of a fourth parameter beyond age, mass, and [Fe/H] controlling Li
depletion.Comment: To appear in Publ. Astron. Soc. Pacif. (September 2005
Study of theory and applicability of laser technique for measuring atmospheric parameters Interim scientific report
Theory and applicability of laser energy interactions for measuring atmospheric parameter
Jet Production by Virtual Photons
The production of jets is studied in collisions of virtual photons, gamma*-p
and gamma*-gamma*, specifically for applications at HERA and LEP2. Photon flux
factors are convoluted with matrix elements involving either direct or resolved
photons and, for the latter, with parton distributions of the photon. Special
emphasis is put on the range of uncertainty in the modeling of the resolved
component. The resulting model is compared with existing data.Comment: 1+10 pages, LaTeX2e, 4 eps figures, to appear in the Proceedings of
the International Conference on the Structure and Interactions of the Photon;
PHOTON99, 23-27 May 1999, Freiburg im Breisgau, German
Atmospheric nitric oxide measurement techniques Final report
Optical radar technique for measuring vertical density distribution of neutral nitric oxide in earth atmospher
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
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John Spaghotte
Author Peter Schuler discusses his thoughts on how ideas of creativity, literature, and pedagogy helped to develop into his first novel, John Spaghotte of Crumb. Schuler is a native of the Coachella Valley in Southern California and writes from a middle-class appreciation of working and living in an area where everything is catered to the wealthy class. Through personal injury and his experience in undergraduate and graduate studies he fought to develop a healthy critical mind and a grasp as to the true nature of identity. As a result, his riveting debut novel about a young, nerdy California version of Don Quixote becomes a cautionary tale about the dangers of failing to recognize oneself among a world full of materialistic pleasures and grandiose, fictional heroes. In the formulation of his novel Schuler argues that artistic creation, appreciation, study, and the development of a critical scope to see the world with lead to a better understand his own identity while his protagonist suffers from the lack of such a development
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
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