1,068 research outputs found
Downloading a Defendant: Is Categorizing Internet Contracts a Departure from the Minimum Contacts Test?
Guidelines and Methods for Conducting Porperty Transfer Site Histories
HWRIC Project 90-077NTIS PB91-10508
Zirconium, Barium, Lanthanum and Europium Abundances in Open Clusters
We present an analysis of the s-process elements Zr, Ba, and La and the
r-process element Eu in a sample of 50 stars in 19 open clusters. Stellar
abundances of each element are based on measures of a minimum of two lines per
species via both equivalent width and spectrum synthesis techniques. We
investigate cluster mean neutron-capture abundance trends as a function of
cluster age and location in the Milky Way disk and compare them to results
found in other studies in the literature. We find a statistically significant
trend of increasing cluster [Ba/Fe] as a function of decreasing cluster age, in
agreement with recent findings for other open cluster samples, supporting the
increased importance of low-mass asymptotic giant branch stars to the
generation of s-process elements. However, the other s-process elements,
[La/Fe] and [Zr/Fe], do not show similar dependences, in contrast to
theoretical expectations and the limited observational data from other studies.
Conversely, cluster [Eu/Fe] ratios show a slight increase with increasing
cluster age, although with marginal statistical significance. Ratios of
[s/r]-process abundances, [Ba/Eu] and [La/Eu], however, show more clearly the
increasing efficiency of s-process relative to r-process enrichment in open
cluster chemical evolution, with significant increases among younger clusters.
Last, cluster neutron-capture element abundances appear to be independent of
Galactocentric distance. We conclude that a homogeneous analysis of a larger
sample of open clusters is needed to resolve the apparent discrepant
conclusions between different studies regarding s-process element abundance
trends with age to better inform models of galactic chemical evolution.Comment: 24 pages, 13 figures, 10 tables; published in The Astronomical
Journa
Liberty and Justice: A History of Law and Lawyers in Rhode Island, 1636-1998, by Patrick T. Conley
Iron abundances from high-resolution spectroscopy of the open clusters NGC 2506, NGC 6134, and IC 4651
This is the first of a series of papers devoted to derive the metallicity of
old open clusters in order to study the time evolution of the chemical
abundance gradient in the Galactic disk. We present detailed iron abundances
from high resolution (R~40000) spectra of several red clump and bright giant
stars in the open clusters IC 4651, NGC 2506 and NGC 6134. We observed 4 stars
of NGC 2506, 3 stars of NGC 6134, and 5 stars of IC 4651 with the FEROS
spectrograph at the ESO 1.5 m telescope; moreover, 3 other stars of NGC 6134
were observed with the UVES spectrograph on Kueyen (VLT UT2). After excluding
the cool giants near the red giant branch tip (one in IC 4651 and one in NGC
2506), we found overall [Fe/H] values of -0.20 +/- 0.01, rms = 0.02 dex (2
stars) for NGC 2506, +0.15 +/- 0.03, rms = 0.07 dex (6 stars) for NGC 6134, and
+0.11 +/- 0.01, rms = 0.01 dex (4 stars) for IC 4651. The metal abundances
derived from line analysis for each star were extensively checked using
spectrum synthesis of about 30 to 40 Fe I lines and 6 Fe II lines. Our
spectroscopic temperatures provide reddening values in good agreement with
literature data for these clusters, strengthening the reliability of the
adopted temperature and metallicity scale. Also, gravities from the Fe
equilibrium of ionization agree quite well with expectations based on cluster
distance moduli and evolutionary masses.Comment: 13 pages, 7 figures, uses aa.cls, accepted for publication on
Astronomy & Astrophysic
Extended Stromgren Photoelectric Photometry in NGC 752
Photoelectric photometry on the extended Stromgren system (uvbyCa) is
presented for 7 giants and 21 main sequence stars in the old open cluster, NGC
752. Analysis of the hk data for the turnoff stars yields a new determination
of the cluster mean metallicity. From 10 single-star members, [Fe/H] = -0.06
+/- 0.03, where the error quoted is the standard error of the mean and the
Hyades abundance is set at [Fe/H] = +0.12. This result is unchanged if all 20
stars within the limits of the hk metallicity calibration are included. The
derived [Fe/H] is in excellent agreement with past estimates using
properly-zeroed m1 data, transformed moderate-dispersion spectroscopy, and
recent high dispersion spectroscopy.Comment: 14 tex'd pages including 2 tables; 2 separate files with eps figures
Accepted for PASP March 200
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