179 research outputs found
The Chemical Compositions of the SRd Variable Stars-- II. WY Andromedae, VW Eridani, and UW Librae
Chemical compositions are derived from high-resolution spectra for three
stars classed as SRd variables in the General Catalogue of Variable Stars.
These stars are shown to be metal-poor supergiants: WY And with [Fe/H] = -1.0,
VW Eri with [Fe/H] = -1.8, and UW Lib with [Fe/H] = -1.2. Their compositions
are identical to within the measurement errors with the compositions of
subdwarfs, subgiants, and less evolved giants of the same FeH. The stars are at
the tip of the first giant branch or in the early stages of evolution along the
asymptotic giant branch (AGB). There is no convincing evidence that these SRd
variables are experiencing thermal pulsing and the third dredge-up on the AGB.
The SRds appear to be the cool limit of the sequence of RV Tauri variables.Comment: 14 pages, 1 figure, 4 table
Heavy element abundances in giant stars of the globular clusters M4 and M5
We present a comprehensive abundance analysis of 27 heavy elements in bright
giant stars of the globular clusters M4 and M5 based on high resolution, high
signal-to-noise ratio spectra obtained with the Magellan Clay Telescope. We
confirm and expand upon previous results for these clusters by showing that (1)
all elements heavier than, and including, Si have constant abundances within
each cluster, (2) the elements from Ca to Ni have indistinguishable
compositions in M4 and M5, (3) Si, Cu, Zn, and all s-process elements are
approximately 0.3 dex overabundant in M4 relative to M5, and (4) the r-process
elements Sm, Eu, Gd, and Th are slightly overabundant in M5 relative to M4. The
cluster-to-cluster abundance differences for Cu and Zn are intriguing,
especially in light of their uncertain nucleosynthetic origins. We confirm that
stars other than Type Ia supernovae must produce significant amounts of Cu and
Zn at or below the clusters' metallicities. If intermediate-mass AGB stars or
massive stars are responsible for the Cu and Zn enhancements in M4, the similar
[Rb/Zr] ratios and (preliminary) Mg isotope ratios in both clusters may be
problematic for either scenario. For the elements from Ba to Hf, we assume that
the s- and r-process contributions are scaled versions of the solar s- and
r-process abundances. We quantify the relative fractions of s- and r-process
material for each cluster and show that they provide an excellent fit to the
observed abundances.Comment: Accepted for publication in Ap
Comparison of âLook-Alikeâ Implant Prosthetic Retaining Screws
: The maximum preload torque of implant prosthetic retaining screws from four manufacturers and of two alloy types was measured to determine one index of interchangeability of intersystem components. Materials and Methods : Implant prosthetic retaining screws from four manufacturers (3i Implant Innovations Inc, West Palm Beach, FL; Impla-Med Inc, Sunrise, FL; Nobelpharma USA Inc, Chicago, IL; and Implant Support Systems Inc, Irvine, CA) and of two metal types (gold and titanium) were investigated using an in vitro simulation model. Five screws of each type were tightened down against a gold cylinder using a Tohnichi BTG-6 torque gauge (Tohnichi American Corporation, Northbrook, IL) until fracture occurred. Results : The 3i Implant Innovations gold and the Nobelpharma gold were not significantly different. The 3i Implant Innovations titanium and the Impla-Med gold were able to withstand less preload torque than the 3i Implant Innovations gold and the Nobelpharma gold. The Implant Support Systems titanium was able to withstand significantly more preload torque than all of the other screws. Conclusions : Interchanging implant prosthetic retaining screws could introduce new and unknown variables that may affect the long-term survival of implant fixtures and/or the implant prostheses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74593/1/j.1532-849X.1995.tb00310.x.pd
Rubidium and lead abundances in giant stars of the globular clusters M 13 and NGC 6752
We present measurements of the neutron-capture elements Rb and Pb in five
giant stars of the globular cluster NGC 6752 and Pb measurements in four giants
of the globular cluster M 13. The abundances were derived by comparing
synthetic spectra with high resolution, high signal-to-noise ratio spectra
obtained using HDS on the Subaru telescope and MIKE on the Magellan telescope.
The program stars span the range of the O-Al abundance variation. In NGC 6752,
the mean abundances are [Rb/Fe] = -0.17 +/- 0.06 (sigma = 0.14), [Rb/Zr] =
-0.12 +/- 0.06 (sigma = 0.13), and [Pb/Fe] = -0.17 +/- 0.04 (sigma = 0.08). In
M 13 the mean abundance is [Pb/Fe] = -0.28 +/- 0.03 (sigma = 0.06). Within the
measurement uncertainties, we find no evidence for a star-to-star variation for
either Rb or Pb within these clusters. None of the abundance ratios [Rb/Fe],
[Rb/Zr], or [Pb/Fe] are correlated with the Al abundance. NGC 6752 may have
slightly lower abundances of [Rb/Fe] and [Rb/Zr] compared to the small sample
of field stars at the same metallicity. For M 13 and NGC 6752 the Pb abundances
are in accord with predictions from a Galactic chemical evolution model. If
metal-poor intermediate-mass asymptotic giant branch stars did produce the
globular cluster abundance anomalies, then such stars do not synthesize
significant quantities of Rb or Pb. Alternatively, if such stars do synthesize
large amounts of Rb or Pb, then they are not responsible for the abundance
anomalies seen in globular clusters.Comment: Accepted for publication in Ap
The Chemical Compositions of the SRd Variable Stars. III. KK Aquilae, AG Aurigae, Z Aurigae, W Leo Minoris, and WW Tauri
Chemical compositions are derived from high-resolution spectra for five field
SRd variables. These supergiants not previously analysed are shown to be
metal-poor: KK Aql with [Fe/H] = -1.2, AG Aur with [Fe/H] = -1.8, Z Aur with
[Fe/H] = -1.4, W LMi with [Fe/H] = -1.1, and WW Tau with [Fe/H] = -1.1. Their
compositions are, except for two anomalies, identical to within the measurement
errors with the compositions of subdwarfs, subgiants, and less evolved giants
of the same [Fe/H]. One anomaly is an s-process enrichment for KK Aql, the
first such enrichment reported for a SRd variable. The second and more
remarkable anomaly is a strong lithium enrichment for W LMi, also a first for
field SRds. The Li I 6707 A profile is not simply that of a photospheric line
but includes strong absorption from red-shifted gas, suggesting, perhaps, that
lithium enrichment results from accretion of Li-rich gas. This potential clue
to lithium enrichment is discussed in light of various proposals for lithium
synthesis in evolved stars.Comment: 18 pages of text, 8 tables, 2 figures. Accepted for publication in
PAS
The Interstellar Rubidium Isotope Ratio toward Rho Ophiuchi A
The isotope ratio, 85Rb/87Rb, places constraints on models of the
nucleosynthesis of heavy elements, but there is no precise determination of the
ratio for material beyond the Solar System. We report the first measurement of
the interstellar Rb isotope ratio. Our measurement of the Rb I line at 7800 A
for the diffuse gas toward rho Oph A yields a value of 1.21 +/- 0.30 (1-sigma)
that differs significantly from the meteoritic value of 2.59. The Rb/K
elemental abundance ratio for the cloud also is lower than that seen in
meteorites. Comparison of the 85Rb/K and 87Rb/K ratios with meteoritic values
indicates that the interstellar 85Rb abundance in this direction is lower than
the Solar System abundance. We attribute the lower abundance to a reduced
contribution from the r-process. Interstellar abundances for Kr, Cd, and Sn are
consistent with much less r-process synthesis for the solar neighborhood
compared to the amount inferred for the Solar System.Comment: 12 pages with 2 figures and 1 table; will appear in ApJ Letter
Carbon and Strontium Abundances of Metal-Poor Stars
We present carbon and strontium abundances for 100 metal-poor stars measured
from R7000 spectra obtained with the Echellette Spectrograph and Imager
at the Keck Observatory. Using spectral synthesis of the G-band region, we have
derived carbon abundances for stars ranging from [Fe/H] to
[Fe/H]. The formal errors are dex in [C/Fe]. The strontium
abundance in these stars was measured using spectral synthesis of the resonance
line at 4215 {\AA}. Using these two abundance measurments along with the barium
abundances from our previous study of these stars, we show it is possible to
identify neutron-capture-rich stars with our spectra. We find, as in other
studies, a large scatter in [C/Fe] below [Fe/H]. Of the stars with
[Fe/H], 94% can be classified as carbon-rich metal-poor stars. The Sr
and Ba abundances show that three of the carbon-rich stars are
neutron-capture-rich, while two have normal Ba and Sr. This fraction of carbon
enhanced stars is consistent with other studies that include this metallicity
range.Comment: ApJ, Accepte
Rubidium and lead abundances in giant stars of the globular clusters M4 and M5
We present measurements of the neutron-capture elements Rb and Pb for bright
giants in the globular clusters M4 and M5. The clusters are of similar
metallicity ([Fe/H] = -1.2) but M4 is decidedly s-process enriched relative to
M5: [Ba/Fe] = +0.6 for M4 but 0.0 for M5. The Rb and Pb abundances were derived
by comparing synthetic spectra with high-resolution, high signal-to-noise ratio
spectra obtained with MIKE on the Magellan telescope. Abundances of Y, Zr, La,
and Eu were also obtained. In M4, the mean abundances from 12 giants are
[Rb/Fe] = 0.39 +/- 0.02 (sigma = 0.07), [Rb/Zr] = 0.17 +/- 0.03 (sigma = 0.08),
and [Pb/Fe] = 0.30 +/- 0.02 (sigma = 0.07). In M5, the mean abundances from two
giants are [Rb/Fe] = 0.00 +/- 0.05 (sigma = 0.06), [Rb/Zr] = 0.08 +/- 0.08
(sigma = 0.11), and [Pb/Fe] = -0.35 +/- 0.02 (sigma = 0.04). Within the
measurement uncertainties, the abundance ratios [Rb/Fe], [Pb/Fe] and [Rb/X] for
X = Y, Zr, La are constant from star-to-star in each cluster and none of these
ratios are correlated with O or Na abundances. While M4 has a higher Rb
abundance than M5, the ratios [Rb/X] are similar in both clusters indicating
that the nature of the s-products are very similar for each cluster but the gas
from which M4's stars formed had a higher concentration of these products.Comment: Accepted for publication in Ap
BIGRE: a low cross-talk integral field unit tailored for extrasolar planets imaging spectroscopy
Integral field spectroscopy (IFS) represents a powerful technique for the
detection and characterization of extrasolar planets through high contrast
imaging, since it allows to obtain simultaneously a large number of
monochromatic images. These can be used to calibrate and then to reduce the
impact of speckles, once their chromatic dependence is taken into account. The
main concern in designing integral field spectrographs for high contrast
imaging is the impact of the diffraction effects and the non-common path
aberrations together with an efficient use of the detector pixels. We focus our
attention on integral field spectrographs based on lenslet-arrays, discussing
the main features of these designs: the conditions of appropriate spatial and
spectral sampling of the resulting spectrograph's slit functions and their
related cross-talk terms when the system works at the diffraction limit. We
present a new scheme for the integral field unit (IFU) based on a dual-lenslet
device (BIGRE), that solves some of the problems related to the classical TIGER
design when used for such applications. We show that BIGRE provides much lower
cross-talk signals than TIGER, allowing a more efficient use of the detector
pixels and a considerable saving of the overall cost of a lenslet-based
integral field spectrograph.Comment: 17 pages, 18 figures, accepted for publication in Ap
QSO Absorbing Galaxies at z<~1: Deep Imaging and Spectroscopy in the Field of 3C 336
We present very deep WFPC2 images and FOS spectroscopy from the Hubble Space
Telescope (HST) together with numerous supporting ground-based observations of
the field of the quasar 3C 336 (). The observations are designed
to investigate the nature of galaxies producing metal line absorption systems
in the spectrum of the QSO. Along a single line of sight, we find at least 6
metal line absorption systems (of which 3 are newly discovered) ranging in
redshift from 0.317 to 0.892. Through an extensive program of optical and IR
imaging, QSO spectroscopy, and faint galaxy spectroscopy, we have identified 5
of the 6 metal line absorption systems with luminous (L_K > 0.1 L*_K) galaxies.
These have morphologies ranging from very late-type spiral to S0, and exhibit a
wide range of inclination and position angles with respect to the QSO
sightline. The only unidentified absorber, despite our intensive search, is a
damped Lyman system at . Analysis of the absorption
spectrum suggests that the metal abundances ([Fe/H]) in this system are
similar to those in damped systems at , and to the two other damped
systems for which abundances have been determined at . We have found no
examples of intrinsically faint galaxies () at small impact
parameters that might have been missed as absorber candidates in our previous
ground-based imaging and spectroscopic programs on MgII absorbing galaxies.
There are no bright galaxies (L > 0.1 L_K) within 50h^{-1} kpc which do not
produce detectable metal lines (of Mg II 2796, 2803 and/or C IV 1548, 1550) in
the QSO spectrum. All of these results generally support the inferences which
we have previously reached from a larger survey for absorption-selected
galaxies at z\simlt 1.Comment: 32 pages latex (AAS v4.0 style). 8 Postscript figures (including HST
plate) available at ftp://astro.caltech.edu/users/ccs/3c336_figs.ps.gz .
Submitted to Ap
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