1,376 research outputs found
The elemental composition of the Sun II. The iron group elements Sc to Ni
We redetermine the abundances of all iron group nuclei in the Sun, based on
neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar
spectrum. We employ a realistic 3D hydrodynamic model solar atmosphere,
corrections for departures from local thermodynamic equilibrium (NLTE),
stringent line selection procedures and high quality observational data. We
have scoured the literature for the best quality oscillator strengths,
hyperfine constants and isotopic separations available for our chosen lines. We
find , , ,
, , ,
and . Our uncertainties factor in both statistical
and systematic errors (the latter estimated for possible errors in the model
atmospheres and NLTE line formation). The new abundances are generally in good
agreement with the CI meteoritic abundances but with some notable exceptions.
This analysis constitutes both a full exposition and a slight update of the
preliminary results we presented in Asplund, Grevesse, Sauval & Scott
(arXiv:0909.0948), including full line lists and details of all input data we
employed.Comment: 10 figures, 24 pages + 10 online-only pages of tables. v2. Matches
version accepted by A&
The elemental composition of the Sun III. The heavy elements Cu to Th
We re-evaluate the abundances of the elements in the Sun from copper ()
to thorium (). Our results are mostly based on neutral and singly-ionised
lines in the solar spectrum. We use the latest 3D hydrodynamic solar model
atmosphere, and in a few cases also correct for departures from local
thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in
1D. In order to minimise statistical and systematic uncertainties, we make
stringent line selections, employ the highest-quality observational data and
carefully assess oscillator strengths, hyperfine constants and isotopic
separations available in the literature, for every line included in our
analysis. Our results are typically in good agreement with the abundances in
the most pristine meteorites, but there are some interesting exceptions. This
analysis constitutes both a full exposition and a slight update of the relevant
parts of the preliminary results we presented in Asplund, Grevesse, Sauval &
Scott (arXiv:0909.0948), including full line lists and details of all input
data that we have employed.Comment: 5 figures, 18 pages + 6 online-only pages of tables. v2. Matches
version accepted by A&
Detailed Topography of the Fermi Surface of Sr2RuO4
We apply a novel analysis of the field and angle dependence of the
quantum-oscillatory amplitudes in the unconventional superconductor Sr2RuO4 to
map its Fermi surface in unprecedented detail, and to obtain previously
inaccessible information on the band dispersion. The three quasi-2D Fermi
surface sheets not only exhibit very diverse magnitudes of warping, but also
entirely different dominant warping symmetries. We use the data to reassess
recent results on c-axis transport phenomena.Comment: REVTeX, 4 page
Rigid-Band Shift of the Fermi Level in a Strongly Correlated Metal: Sr(2-y)La(y)RuO(4)
We report a systematic study of electron doping of Sr2RuO4 by non-isovalent
substitution of La^(3+) for Sr^(2+). Using a combination of de Haas-van Alphen
oscillations, specific heat, and resistivity measurements, we show that
electron doping leads to a rigid-band shift of the Fermi level corresponding to
one doped electron per La ion, with constant many-body quasiparticle mass
enhancement over the band mass. The susceptibility spectrum is substantially
altered and enhanced by the doping but this has surprisingly little effect on
the strength of the unconventional superconducting pairing.Comment: 4 pages, 3 figure
Interpretation of the angular dependence of the de Haas-van Alphen effect in MgB_2
We present detailed results for the amplitude and field dependence of the de
Haas-van Alphen (dHvA) signal arising from the electron-like sheet of
Fermi surface in MgB_2. Our data and analysis show that the dip in dHvA
amplitude when the field is close to the basal plane is caused by a beat
between two very similar dHvA frequencies and not a spin-zero effect as
previously assumed. Our results imply that the Stoner enhancement factors in
MgB_2 are small on both the Sigma and Pi sheets.Comment: 4 pages with figures. Submitted to PR
The influence of planetary engulfment on stellar rotation in metal-poor main-sequence stars
The method of gyrochronology relates the age of its star to its rotation
period. However, recent evidence of deviations from gyrochronology relations
was reported in the literature. Here, we study the influence of tidal
interaction between a star and its companion on the rotation velocity of the
star, in order to explain peculiar stellar rotation velocities. The interaction
of a star and its planet is followed using a comprehensive numerical framework
that combines tidal friction, magnetic braking, planet migration, and detailed
stellar evolution models from the GARSTEC grid. We focus on close-in companions
from 1 to 20 M orbiting low-mass, 0.8 and 1 M, main-sequence
stars with a broad metallicity range from [Fe/H] = -1 to solar. Our simulations
suggest that the dynamical interaction between a star and its companion can
have different outcomes, which depend on the initial semi-major axis and the
mass of the planet, as well as the mass and metallicity of its host star. In
most cases, especially in the case of planet engulfment, we find a catastrophic
increase in stellar rotation velocity from 1 kms to over 40 kms,
while the star is still on the main-sequence. The main prediction of our model
is that low-mass main-sequence stars with abnormal rotation velocities should
be more common at low-metallicity, as lower [Fe/H] favours faster planet
engulfment, provided occurrence rate of close in massive planets is similar at
all metallicities. Our scenario explains peculiar rotation velocities of
low-mass main-sequence stars by the tidal interaction between the star and its
companion. Current observational samples are too small and incomplete, and thus
do not allow us to test our model.Comment: 10 pages, 6 figures, accepted for publication in A&
The solar abundance problem and eMSTOs in clusters
We study the impact of accretion from protoplanetary discs on stellar
evolution of AFG-type stars. We use a simplified disc model computed using the
Two-Pop-Py code that contains the growth and drift of dust particles in the
protoplanetary disc. It is used to model the accretion scenarios for a range of
physical conditions of protoplanetary discs. Two limiting cases are combined
with the evolution of stellar convective envelopes computed using the Garstec
stellar evolution code. We find that the accretion of metal-poor (gas) or
metal-rich (dust) material has a significant impact on the chemical composition
of the stellar convective envelope. As a consequence, the evolutionary track of
the star diverts from the standard scenario predicted by canonical stellar
evolution models, which assume a constant and homogeneous chemical composition
after the assembly of the star has finished. In the case of the Sun, we find a
modest impact on the solar chemical composition. Accretion of metal-poor
material indeed reduces the overall metallicity of the solar atmosphere, and it
is consistent, within the uncertainty, with the solar Z reported by Caffau et
al. (2011), but our model is not consistent with the measurement by Asplund et
al. (2009). Another effect is the change of the position of the star in the
colour-magnitude diagram. We compare our predictions to a set of open clusters
from the Gaia DR2 and show that it is possible to produce a scatter close to
the turn-off of young clusters that could contribute to explain the observed
scatter in CMDs. Detailed measurements of metallicities and abundances in the
nearby open clusters will provide a stringent observational test of our
proposed scenario.Comment: 10 pages, 7 figures, 1 table. Accepted for publication in A&
Determining the superconducting gap structure in Sr2RuO4 from sound attenuation studies below Tc
This work presents a quantitative theoretical study of the sound attenuation
in the unconventional multiband superconductor Sr2RuO4 below the
superconducting transition temperature Tc. Sound attenuation in this material
is shown to have the remarkable property of being able to identify different
nodal structures on different bands. The nodal structures on the \gamma band on
the one hand, and on the \alpha and \beta bands on the other, are both found to
be characterized by the existence of point nodes, but are significantly
different in their quantitative aspects.Comment: 7 pages, REVTe
On the likelihoods of finding very metal-poor (and old) stars in the Milky Way’s disc, bulge, and halo
Recent observational studies have uncovered a small number of very metal-poor (VMP) stars with cold kinematics in the Galactic disc and bulge. However, their origins remain enigmatic. We select a total of 138 Milky Way (MW) analogues from the TNG50 cosmological simulation based on their z = 0 properties: discy morphology, stellar mass, and local environment. In order to make more predictive statements for the MW, we further limit the spatial volume coverage of stellar populations in galaxies to that targeted by the upcoming 4MOST high-resolution survey of the Galactic disc and bulge. We find that across all galaxies, ∼20 per cent of VMP ([Fe/H] < −2) stars belong to the disc, with some analogues reaching 30 per cent. About 50 ± 10 per cent of the VMP disc stars are, on average, older than 12.5 Gyr and ∼70 ± 10 per cent come from accreted satellites. A large fraction of the VMP stars belong to the halo (∼70) and have a median age of 12 Gyr. Our results with the TNG50 cosmological simulation confirm earlier findings with simulations of fewer individual galaxies, and suggest that the stellar disc of the MW is very likely to host significant amounts of very- and extremely-metal-poor stars that, although mostly of ex situ origin, can also form in situ, reinforcing the idea of the existence of a primordial Galactic disc
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