348 research outputs found
New Results on Standard Solar Models
We describe the current status of solar modelling and focus on the problems
originated with the introduction of solar abundance determinations with low CNO
abundance values. We use models computed with solar abundance compilations
obtained during the last decade, including the newest published abundances by
Asplund and collaborators. Results presented here make focus both on
helioseismic properties and the models as well as in the neutrino fluxes
predictions. We also discuss changes in radiative opacities to restore
agreement between helioseismology, solar models, and solar abundances and show
the effect of such modifications on solar neutrino fluxes.Comment: 9 pages. Review talk presented at "Synergies between solar and
stellar modelling", Rome, June 2009. To be published by Astrophysics and
Space Scienc
An intermediate-depth source of hydrothermal 3He and dissolved iron in the North Pacific
We observed large water column anomalies in helium isotopes and trace metal concentrations above the Loihi Seamount. The 3He/4He of the added helium was 27.3 times the atmospheric ratio, clearly marking its origin to a primitive mantle plume. The dissolved iron to 3He ratio (dFe:3He) exported to surrounding waters was 9.3 ± 0.3 × 106. We observed the Loihi 3He and dFe “signal” at a depth of 1100 m at several stations within ∼100 – 1000 km of Loihi, which exhibited a distal dFe:3He ratio of ∼4 × 106, about half the proximal ratio. These ratios were remarkably similar to those observed over and near the Southern East Pacific Rise (SEPR) despite greatly contrasting geochemical and volcanictectonic origins. In contrast, the proximal and distal dMn:3He ratios were both ∼ 1 × 106, less than half of that observed at the SEPR. Dissolved methane was minimally enriched in waters above Loihi Seamount and was distally absent. Using an idealized regional-scale model we replicated the historically observed regional 3He distribution, requiring a hydrothermal 3He source from Loihi of 10.4 ± 4.2 mola−1, ∼2% of the global abyssal hydrothermal 3He flux. From this we compute a corresponding dFe flux of ∼40 Mmola−1. Global circulation model simulations suggest that the Loihi-influenced waters eventually upwell along the west coast of North America, also extending into the shallow northwest Pacific, making it a possibly important determinant of marine primary production in the subpolar North Pacific
Quantifying internal stress and internal resistance associated with thermal ageing and creep in a polycrystalline material
Stellar evolution and modelling stars
In this chapter I give an overall description of the structure and evolution
of stars of different masses, and review the main ingredients included in
state-of-the-art calculations aiming at reproducing observational features. I
give particular emphasis to processes where large uncertainties still exist as
they have strong impact on stellar properties derived from large compilations
of tracks and isochrones, and are therefore of fundamental importance in many
fields of astrophysics.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Dynamic screening in solar and stellar nuclear reactions
In the hot, dense plasma of solar and stellar interiors, the Coulomb
interaction is screened by the surrounding plasma. Although the standard
Salpeter approximation for static screening is widely accepted and used in
stellar modeling, the question of dynamic screening has been revisited. In
particular, Shaviv and Shaviv apply the techniques of molecular dynamics to the
conditions in the solar core in order to numerically determine the dynamic
screening effect. By directly calculating the motion of ions and electrons due
to Coulomb interactions, they compute the effect of screening without the
mean-field assumption inherent in the Salpeter approximation. Here we reproduce
their numerical analysis of the screening energy in the plasma of the solar
core and conclude that the effects of dynamic screening are relevant and should
be included in the treatment of the plasma, especially in the computation of
stellar nuclear reaction rates.Comment: Astrophysics and Space Science, Special Issue Solar & Stellar
Modelling Corrected sign error. Now consistent with final published versio
CoRoT/ESTA-TASK 1 and TASK 3 comparison of the internal structure and seismic properties of representative stellar models: Comparisons between the ASTEC, CESAM, CLES, GARSTEC and STAROX codes
We compare stellar models produced by different stellar evolution codes for
the CoRoT/ESTA project, comparing their global quantities, their physical
structure, and their oscillation properties. We discuss the differences between
models and identify the underlying reasons for these differences. The stellar
models are representative of potential CoRoT targets. Overall we find very good
agreement between the five different codes, but with some significant
deviations. We find noticeable discrepancies (though still at the per cent
level) that result from the handling of the equation of state, of the opacities
and of the convective boundaries. The results of our work will be helpful in
interpreting future asteroseismology results from CoRoT.Comment: 26 pages, 21 figures, accepted for publication in Astrophysics and
Space Science, CoRoT/ESTA Volum
Chondrules – ubiquitous chondritic solids tracking the evolution of the solar protoplanetary disk
Prospects for asteroseismology
The observational basis for asteroseismology is being dramatically
strengthened, through more than two years of data from the CoRoT satellite, the
flood of data coming from the Kepler mission and, in the slightly longer term,
from dedicated ground-based facilities. Our ability to utilize these data
depends on further development of techniques for basic data analysis, as well
as on an improved understanding of the relation between the observed
frequencies and the underlying properties of the stars. Also, stellar modelling
must be further developed, to match the increasing diagnostic potential of the
data. Here we discuss some aspects of data interpretation and modelling,
focussing on the important case of stars with solar-like oscillations.Comment: Proc. HELAS Workshop on 'Synergies between solar and stellar
modelling', eds M. Marconi, D. Cardini & M. P. Di Mauro, Astrophys. Space
Sci., in the press Revision: correcting abscissa labels on Figs 1 and
Influência da heparina sódica na ocorrência de laminite eqüina induzida por sobrecarga de carboidratos
The TESS-Keck Survey. II. An Ultra-Short-Period Rocky Planet And Its Siblings Transiting The Galactic Thick-Disk Star TOI-561
We report the discovery of TOI-561, a multiplanet system in the galactic thick disk that contains a rocky, ultra-short-period planet. This bright (V = 10.2) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P = 0.44 days, Rp = 1.45 ± 0.11 R⊕), c (TOI-561.01, P = 10.8 days, Rp = 2.90 ± 0.13 R⊕), and d (TOI-561.03, P = 16.3 days, Rp = 2.32 ± 0.16 R⊕). The star is chemically ([Fe/H] = −0.41 ± 0.05, [α/Fe] = +0.23 ± 0.05) and kinematically consistent with the galactic thick-disk population, making TOI-561 one of the oldest (10 ± 3 Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of 3.2 ± 0.8 M⊕ and g cm−3, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is 7.0 ± 2.3 M⊕ and 1.6 ± 0.6 g cm−3, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, ground-based photometric follow-up, and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies
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