10,008 research outputs found
New solar opacities, abundances, helioseismology, and neutrino fluxes
We construct solar models with the newly calculated radiative opacities from
the Opacity Project (OP) and recently determined (lower) heavy element
abundances. We compare results from the new models with predictions of a series
of models that use OPAL radiative opacities, older determinations of the
surface heavy element abundances, and refinements of nuclear reaction rates.
For all the variations we consider, solar models that are constructed with the
newer and lower heavy element abundances advocated by Asplund et al. (2005)
disagree by much more than the estimated measuring errors with
helioseismological determinations of the depth of the solar convective zone,
the surface helium composition, the internal sound speeds, and the density
profile. Using the new OP radiative opacities, the ratio of the 8B neutrino
flux calculated with the older and larger heavy element abundances (or with the
newer and lower heavy element abundances) to the total neutrino flux measured
by the Sudbury Neutrino Observatory is 1.09 (0.87) with a 9% experimental
uncertainty and a 16% theoretical uncertainty, 1 sigma errors.Comment: ApJ Letters (in press), added 3 references, detailed numerical solar
models and distributions of neutrino fluxes available at
http://www.sns.ias.edu/~jnb (models go back to 1982
How much do helioseismological inferences depend upon the assumed reference model?
We investigate systematic uncertainties in determining the profiles of the
solar sound speed, density, and adiabatic index by helioseismological
techniques. We find that rms uncertainties-averaged over the sun of ~ 0.2%-0.4%
are contributed to the sound speed profile by each of three sources: 1)the
choice of assumed reference model, 2) the width of the inversion kernel, and 3)
the measurements errors. The density profile is about an order of magnitude
less well determined by the helioseismological measurements. The profile of the
adiabatic index is determined to an accuracy of about 0.2% . We find that even
relatively crude reference models yield reasonably accurate solar parameters.Comment: Accepted for publication in ApJ . Related material at
http://www.sns.ias.edu/~jn
'Rapid fire' spectroscopy of Kepler solar-like oscillators
The NASA Kepler mission has been continuously monitoring the same field of
the sky since the successful launch in March 2009, providing high-quality
stellar lightcurves that are excellent data for asteroseismology, far superior
to any other observations available at the present. In order to make a
meaningful analysis and interpretation of the asteroseismic data, accurate
fundamental parameters for the observed stars are needed. The currently
available parameters are quite uncertain as illustrated by e.g. Thygesen et al.
(A&A 543, A160, 2012), who found deviations as extreme as 2.0 dex in [Fe/H] and
log g, compared to catalogue values. Thus, additional follow-up observations
for these targets are needed in order to put firm limits on the parameter space
investigated by the asteroseismic modellers. Here, we propose a metod for
deriving accurate metallicities of main sequence and subgiant solar-like
oscillators from medium resolution spectra with a moderate S/N. The method
takes advantage of the additional constraints on the fundamental parameters,
available from asteroseismology and multi-color photometry. The approach
enables us to reduce the analysis overhead significantly when doing spectral
synthesis, which in turn will increases the efficiency of follow-up
observations.Comment: 3 pages, 2 figures. Proceedings from Asteroseismology of Stellar
Populations in the Milky Way 2013 to appear in 'Astrophysics and Space
Science Proceedings
Structure of the near-surface layers of the Sun: asphericity and time variation
We present results on the structure of the near-surface layers of the Sun
obtained by inverting frequencies of high-degree solar modes from "ring
diagrams". We have results for eight epochs between June 1996 and October 2003.
The frequencies for each epoch were obtained from ring diagrams constructed
from MDI Dopplergrams spanning complete Carrington rotations. We find that
there is a substantial latitudinal variation of both sound speed and the
adiabatic index Gamma_1 in the outer 2% of the Sun. We find that both the
sound-speed and Gamma_1 profiles change with changes in the level of solar
activity. In addition, we also study differences between the northern and
southern hemispheres of the Sun and find a small asymmetry that appears to
reflect the difference in magnetic activity between the two hemispheres.Comment: To appear in ApJ (January 2007
Helioseismic analysis of the hydrogen partition function in the solar interior
The difference in the adiabatic gradient gamma_1 between inverted solar data
and solar models is analyzed. To obtain deeper insight into the issues of
plasma physics, the so-called ``intrinsic'' difference in gamma_1 is extracted,
that is, the difference due to the change in the equation of state alone. Our
method uses reference models based on two equations of state currently used in
solar modeling, the Mihalas-Hummer-Dappen (MHD) equation of state, and the OPAL
equation of state (developed at Livermore). Solar oscillation frequencies from
the SOI/MDI instrument on board the SOHO spacecraft during its first 144 days
in operation are used. Our results confirm the existence of a subtle effect of
the excited states in hydrogen that was previously studied only theoretically
(Nayfonov & Dappen 1998). The effect stems from internal partition function of
hydrogen, as used in the MHD equation of state. Although it is a pure-hydrogen
effect, it takes place in somewhat deeper layers of the Sun, where more than
90% of hydrogen is ionized, and where the second ionization zone of helium is
located. Therefore, the effect will have to be taken into account in reliable
helioseismic determinations of the astrophysically relevant helium-abundance of
the solar convection zone.Comment: 30 pages, 4 figures, 1 table. Revised version submitted to Ap
Helioseismological Implications of Recent Solar Abundance Determinations
We show that standard solar models are in good agreement with the
helioseismologically determined sound speed and density as a function of solar
radius, the depth of the convective zone, and the surface helium abundance, as
long as those models do not incorporate the most recent heavy element abundance
determinations. However, sophisticated new analyses of the solar atmosphere
infer lower abundances of the lighter metals (like C, N, O, Ne, and Ar) than
the previously widely used surface abundances. We show that solar models that
include the lower heavy element abundances disagree with the solar profiles of
sound speed and density as well as the depth of the convective zone and the
helium abundance. The disagreements for models with the new abundances range
from factors of several to many times the quoted uncertainties in the
helioseismological measurements. The disagreements are at temperatures below
what is required for solar interior fusion reactions and therefore do not
significantly affect solar neutrino emission. If errors in thecalculated OPAL
opacities are solely responsible for the disagreements, then the corrections in
the opacity must extend from 2 times 10^6 K (R = 0.7R_Sun)to 5 times 10^6 K (R
= 0.4 R_Sun), with opacity increases of order 10%.Comment: ApJ in press; clarified Figure
Isospin asymmetric nuclear matter and properties of axisymmetric neutron stars
Pure hadronic compact stars, above a limiting value (1.6 M)
of their gravitational masses, to which predictions of most of other equations
of state (EoSs) are restricted, can be reached from the equation of state (EoS)
obtained using DDM3Y effective interaction. This effective interaction is found
to be quite successful in providing unified description of elastic and
inelastic scattering, various radioactivities and nuclear matter properties. We
present a systematic study of the properties of pure hadronic compact stars.
The -equilibrated neutron star matter using this EoS with a thin crust
is able to describe highly-massive compact stars, such as PSR B1516+02B with a
mass M=1.94 M and PSR J0751+1807 with a mass
M=2.10.2 M to a 1 confidence level.Comment: 5 pages, 4 figure
Gravity of higher-dimensional global defects
Solutions of Einstein's equations are found for global defects in a
higher-dimensional spacetime with a nonzero cosmological constant Lambda. The
defect has a (p-1)-dimensional core (brane) and a `hedgehog' scalar field
configuration in the n extra dimensions. For Lambda = 0 and n > 2, the
solutions are characterized by a flat brane worldsheet and a solid angle
deficit in the extra dimensions. For Lambda > 0, one class of solutions
describes spherical branes in an inflating higher-dimensional universe.
Instantons obtained by a Euclidean continuation of such solutions describe
quantum nucleation of the entire inflating brane-world, or of a spherical brane
in an inflating higher-dimensional universe. For Lambda < 0, one class of
solutions exhibits an exponential warp factor. It is similar to spacetimes
previously discussed by Randall and Sundrum for n = 1 and by Gregory for n = 2.Comment: 18 pages, no figures, uses revte
Multi-parameter deformed and nonstandard Yangian symmetry in integrable variants of Haldane-Shastry spin chain
By using `anyon like' representations of permutation algebra, which pick up
nontrivial phase factors while interchanging the spins of two lattice sites, we
construct some integrable variants of Haldane-Shastry (HS) spin chain. Lax
equations for these spin chains allow us to find out the related conserved
quantities. However, it turns out that such spin chains also possess a few
additional conserved quantities which are apparently not derivable from the Lax
equations. Identifying these additional conserved quantities, and the usual
ones related to Lax equations, with different modes of a monodromy matrix, it
is shown that the above mentioned HS like spin chains exhibit multi-parameter
deformed and `nonstandard' variants of Yangian symmetry.Comment: 18 pages, latex, no figure
The extinct, giant giraffid Sivatherium giganteum: skeletal reconstruction and body mass estimation
Sivatherium giganteum is an extinct giraffid from the Plio–Pleistocene boundary of the Himalayan foothills. To date, there has been no rigorous skeletal reconstruction of this unusual mammal. Historical and contemporary accounts anecdotally state that Sivatherium rivalled the African elephant in terms of its body mass, but this statement has never been tested. Here, we present a three-dimensional composite skeletal reconstruction and calculate a representative body mass estimate for this species using a volumetric method. We find that the estimated adult body mass of 1246 kg (857—1812 kg range) does not approach that of an African elephant, but confirms that Sivatherium was certainly a large giraffid, and may have been the largest ruminant mammal that has ever existed. We contrast this volumetric estimate with a bivariate scaling estimate derived from Sivatherium's humeral circumference and find that there is a discrepancy between the two. The difference implies that the humeral circumference of Sivatherium is greater than expected for an animal of this size, and we speculate this may be linked to a cranial shift in centre of mass
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