34 research outputs found
Evidence for a three-nucleon-force effect in proton-deuteron elastic scattering
Developments in spin-polarized internal targets for storage rings have
permitted measurements of 197 MeV polarized protons scattering from vector
polarized deuterons. This work presents measurements of the polarization
observables A_y, iT_11, and C_y,y in proton-deuteron elastic scattering. When
compared to calculations with and without three-nucleon forces, the
measurements indicate that three-nucleon forces make a significant contribution
to the observables. This work indicates that three-body forces derived from
static nuclear properties appear to be crucial to the description of dynamical
properties.Comment: 8 pages 2 figures Latex, submitted to Phys. Rev. Letter
Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data
Recent radiative lifetime measurements accurate to +/- 5% using laser-induced
fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have
been combined with new branching fractions measured using a Fourier transform
spectrometer (FTS) to determine transition probabilities for 921 lines of Ce
II. This improved laboratory data set has been used to determine a new solar
photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45
lines), a value in excellent agreement with the recommended meteoritic
abundance, log epsilon = 1.61 +/- 0.02. Revised Ce abundances have also been
derived for the r-process-rich metal-poor giant stars BD+17 3248, CS 22892-052,
CS 31082-001, HD 115444 and HD 221170. Between 26 and 40 lines were used for
determining the Ce abundance in these five stars, yielding a small statistical
uncertainty of 0.01 dex similar to the Solar result. The relative abundances in
the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun,
matches r-process only model predictions for Solar System material. This
consistent match with small scatter over a wide range of stellar metallicities
lends support to these predictions of elemental fractions. A companion paper
includes an interpretation of these new precision abundance results for Ce as
well as new abundance results and interpretations for Pr, Dy and Tm.Comment: 84 pages, 8 Figures, 14 Tables; To appear in the Astrophysical
Journal Supplemen
The Lyman-alpha Forest and Heavy Element Systems of GB1759+7539
(abridged) We present observations of the high-redshift QSO GB1759+7539
(z=3.05) obtained with HIRES on the Keck 10m telescope. The spectrum has a
resolution of FWHM = 7 km/s, and a typical signal-to-noise ratio per 2 km/s
pixel of ~25 in the Ly-alpha forest region, and ~60 longward of the Ly-alpha
emission. The observed Ly-alpha forest systems have a mean redshift of z=2.7.
There is marginal evidence of clustering along the line of sight over the
velocity range 100 < v < 250 km/s. The 1-point and 2-point joint probability
distributions of the transmitted flux for the Ly-alpha forest were calculated,
and shown to be very insensitive to the heavy element contamination. We could
find no evidence of Voigt profile departures due to infalling gas, as observed
in the simulated forest spectra. Twelve heavy-element absorption systems were
identified, including damped Lyman-alpha systems at z=2.62 and 2.91. The C, N,
O, Al, Si, P, S, Mg, Fe, and Ni absorption features of these systems were
studied, and the elemental abundances calculated for the weak unsaturated
lines. The systems have metallicities of Z(2.62) ~1/20 Z(solar) and Z(2.91)
\~1/45 Z(solar). Both systems appear to have a low dust content. They show an
over-abundance of alpha-elements relative to Fe-peak elements, and an
under-abundance of odd atomic number elements relative to even. Nitrogen was
observed, and found to be under-abundant relative to oxygen, in line with the
time delay model of primary nitrogen production. C II* was also seen, allowing
us to determine an upper limit to the cosmic microwave background temperature
at z=2.62 of T(CMB)<12.9K.Comment: Added reference, and new S & N abundance determinations for z=2.91
syste
Metal abundances and ionization conditions in a possibly dust-free damped Ly-alpha system at z=2.3
We have obtained a high resolution, high S/N UVES spectrum of the bright QSO
HE2243-6031 to analyze the damped Ly-alpha system (DLA) observed at z=2.33. The
metallicity of this system is 1/12 solar at a neutral hydrogen column density
of log N(HI)=20.7. From the observed ratios [Zn/Cr]=-0.01+/-0.05 and
[S/Si]=-0.06+/-0.03$ we conclude that dust is very likely absent from the ISM
of this protogalaxy. We observe an enhancement of the alpha/Fe-peak ratios of
+0.2 dex for various elements, a marked odd-even effect in Mn, and a strong
underabundance of N relative to Si and S, [N/Si,S]=-1 at [Si/H]=-0.86. All of
these ratios support an environment that is in an early evolutionary stage,
where the onset of star formation has begun only shortly before the DLA was
observed. We also perform a cloud-by-cloud analysis -- without precedent at
high redshift -- and find a tight correlation of all low-ionization species
with respect to FeII extending over 2.5 orders of magnitude in N(FeII). We
interpret this trend as being due to homogeneous physical conditions (very mild
ionization effects, common dust-destruction histories, same chemical
composition) and propose that this line of sight encounters absorbing clouds
that share a common environment. In addition, photoionization models show that
these single clouds are shielded from the external ionizing radiation, so the
fraction of ionized gas is small and, except for argon, does not influence the
measured metal abundances. The observed AlIII/low-ion ratios suggest the mildly
ionized gas occurs in shells surrounding neutral cores of AlII.Comment: To be published in A&
A new comprehensive set of elemental abundances in DLAs - II. Data analysis and chemical variation studies
We present new elemental abundance studies of seven damped Lyman-alpha
systems (DLAs). Together with the four DLAs analyzed in Dessauges-Zavadsky et
al. (2004), we have a sample of eleven DLA galaxies with uniquely comprehensive
and homogeneous abundance measurements. These observations allow one to study
the abundance patterns of 22 elements and the chemical variations in the
interstellar medium of galaxies outside the Local Group. Comparing the
gas-phase abundance ratios of these high redshift galaxies, we found that they
show low RMS dispersions, reaching only up 2-3 times the statistical errors for
the majority of elements. This uniformity is remarkable given that the quasar
sightlines cross gaseous regions with HI column densities spanning over one
order of magnitude and metallicities ranging from 1/55 to 1/5 solar. The
gas-phase abundance patterns of interstellar medium clouds within the DLA
galaxies detected along the velocity profiles show, on the other hand, a high
dispersion in several abundance ratios, indicating that chemical variations
seem to be more confined to individual clouds within the DLA galaxies than to
integrated profiles. The analysis of the cloud-to-cloud chemical variations
within seven individual DLAs reveals that five of them show statistically
significant variations, higher than 0.2 dex at more than 3 sigma. The sources
of these variations are both the differential dust depletion and/or ionization
effects; however, no evidence for variations due to different star formation
histories could be highlighted. These observations place large constraints on
the mixing timescales of protogalaxies and on scenarios of galaxy formation
within the CDM hierarchical theory. Finally, we provide an astrophysical
determination of the oscillator strength of the NiII 1317 transition.Comment: 45 pages, 33 figures (high-resolution figures available on request
from the authors or in the A&A journal). Accepted for publication in A&
New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars
We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and
Lu for the solar photosphere and for five very metal-poor, neutron-capture
r-process-rich giant stars. The photospheric values for all five elements are
in good agreement with meteoritic abundances. For the low metallicity sample,
these abundances have been combined with new Ce abundances from a companion
paper, and reconsideration of a few other elements in individual stars, to
produce internally-consistent Ba, rare-earth, and Hf (56<= Z <= 72) element
distributions. These have been used in a critical comparison between stellar
and solar r-process abundance mixes.Comment: 48 pages, 11 figures, 12 tables: To appear in the Astrophysical
Journal Supplemen