146 research outputs found
Why one-dimensional models fail in the diagnosis of average spectra from inhomogeneous stellar atmospheres
We investigate the feasibility of representing a structured multi-dimensional
stellar atmosphere with a single one-dimensional average stratification for the
purpose of spectral diagnosis of the atmosphere's average spectrum. In
particular we construct four different one-dimensional stratifications from a
single snapshot of a magneto-hydrodynamic simulation of solar convection: one
by averaging its properties over surfaces of constant height, and three
different ones by averaging over surfaces of constant optical depth at 500 nm.
Using these models we calculate continuum, and atomic and molecular line
intensities and their center-to-limb variations. From analysis of the emerging
spectra we identify three main reasons why these average representations are
inadequate for accurate determination of stellar atmospheric properties through
spectroscopic analysis. These reasons are: non-linearity in the Planck function
with temperature, which raises the average emergent intensity of an
inhomogeneous atmosphere above that of an average-property atmosphere, even if
their temperature-optical depth stratification is identical; non-linearities in
molecular formation with temperature and density, which raise the abundance of
molecules of an inhomogeneous atmosphere over that in a one-dimensional model
with the same average properties; the anisotropy of convective motions, which
strongly affects the center-to-limb variation of line-core intensities. We
argue therefore that a one-dimensional atmospheric model that reproduces the
mean spectrum of an inhomogeneous atmosphere necessarily does not reflect the
average physical properties of that atmosphere, and are therefore inherently
unreliable.Comment: 27 pages, 9 figure
Efectos de la aplicación de un protocolo de técnicas de liberación miofascial en secretarias con dolor de cuello
71 p.El dolor de cuello es una afección que se presenta frecuentemente entre el 30% y el 50% de la población mundial anual. En Chile, constituye una enfermedad profesional y puede encontrarse en trabajadores que realizan esfuerzos repetidos y que presentan largas jornadas laborales en posturas mantenidas.
El objetivo de esta investigación fue determinar los efectos de la aplicación de un protocolo de Técnicas de Liberación Miofascial en el dolor, rango de inclinación y la activación muscular del trapecio superior en siete Secretarias con dolor de cuello entre 40 y 55 años de la Universidad de Talca. Se midieron las variables; Dolor Subjetivo (DS), Dolor Objetivo (DO), Rango de inclinación (RDI) y Activación Muscular (AM), se evaluaron en 4 sesiones: basal, sesión 1, sesión 2 (48 hrs) y sesión 3 (posterior 5 días). Se realizó posteriormente un modelo lineal general de medidas repetidas para analizar cada variable.El DS no presentó diferencias significativas, en cambio el DO hubo diferencias significativas inmediatamente después de aplicación de TLM y el RDI presentó diferencias significativas post 48hrs. Sin embargo la AM no presenta cambios significativos en ninguno de sus análisis comparativos durante la actividad funcional (ACT).A través del análisis descriptivo todas las variables evidencian un comportamiento hacia la mejoría. DS presenta una disminución considerable la cual perdura en el tiempo, DO muestra un aumento del umbral del dolor el cual también perdura post a 5 días. A su vez RDI refleja mejorías que se mantienen y son sumativas en el tiempo, finalemnte la AM no muestra variaciones.
Todas las variables analizadas, presentan diferencias significativas en el análisis inter-sujetos, en cambio intra-sujetos no se observaron en ninguno de los análisis diferencias significativas.La aplicación de TLM sobre la musculatura TS disminuye el dolor, aumenta rangos de inclinación y no mejora la activación muscular después de la aplicación
Fundamental Parameters and Chemical Composition of Arcturus
We derive a self-consistent set of atmospheric parameters and abundances of
17 elements for the red giant star Arcturus: Teff = 4286+/-30 K, logg =
1.66+/-0.05, and [Fe/H] = -0.52+/-0.04. The effective temperature was
determined using model atmosphere fits to the observed spectral energy
distribution from the blue to the mid-infrared (0.44 to 10 um). The surface
gravity was calculated using the trigonometric parallax of the star and stellar
evolution models. A differential abundance analysis relative to the solar
spectrum allowed us to derive iron abundances from equivalent width
measurements of 37 FeI and 9 FeII lines, unblended in the spectra of both
Arcturus and the Sun; the [Fe/H] value adopted is derived from FeI lines. We
also determine the mass, radius, and age of Arcturus: M = 1.08+/-0.06 Msun, R =
25.4+/-0.2 Rsun, and t = 7.1(+1.5/-1.2) Gyr. Finally, abundances of the
following elements are measured from an equivalent width analysis of atomic
features: C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn. We
find the chemical composition of Arcturus typical of that of a local thick-disk
star, consistent with its kinematics.Comment: ApJ, in pres
On the solar nickel and oxygen abundances
Determinations of the solar oxygen content relying on the neutral forbidden
transition at 630 nm depend upon the nickel abundance, due to a Ni I blend.
Here we rederive the solar nickel abundance, using the same ab initio 3D
hydrodynamic model of the solar photosphere employed in the recent revision of
the abundances of C, N, O and other elements. Using 17 weak, unblended lines of
Ni I together with the most accurate atomic and observational data available we
find log epsilon_Ni = 6.17 +/- 0.02 (statistical) +/- 0.05 (systematic), a
downwards shift of 0.06 to 0.08 dex relative to previous 1D-based abundances.
We investigate the implications of the new nickel abundance for studies of the
solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun.
Furthermore, we demonstrate that the oxygen abundance implied by the recent
sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be
revised downwards from log epsilon_O = 8.86 +/- 0.07 to 8.71 +/- 0.10. This
revision is based on the new nickel abundance, application of the best
available gf-value for the 630 nm forbidden oxygen line, and a more transparent
treatment of CO formation. Determinations of the solar oxygen content relying
on forbidden lines now appear to converge around log epsilon_O = 8.7.Comment: v2 matches published versio
Primary producers and anthropic signs related to the flood plain soils of the Tablas de Daimiel Wetland
In the Tablas de Daimiel National Park (TDNP) wetlands, a semi-arid wetland system in Spain that is of international importance, it is believed that pollutants from a variety of sources accumulate. In the study reported here, we evaluated soils from the flooded part of this wetland in an effort to establish relationships between the abundance/structure of microbial communities (mainly cyanobacteria) and certain soil properties (redox potential, dissolved oxygen, organic matter, soil reaction, electrical conductivity, calcium carbonate, total nitrogen, soluble phosphorus and total phosphorus). This objective was achieved by establishing one transect from the entrance to exit of the flood plain, including sampling from potentially polluted sites. Substantial variations between sampling sites were found in soil in terms of salinity, dissolved oxygen (DO), organic matter (OM), total phosphorus (TP) and nitrogen (TN). The presence of primary producers was more evident in contaminated samples. In addition to calcium, high levels of oxidizable organic matter, traces of dissolved oxygen, and considerable amounts of nitrate and phosphates probably stimulated the growth of cyanobacteria, these latter characteristics can be explained as being due to the influence of wastewaters from urban, industrial and agricultural activities that run off directly into this unique wetland. In the future it will be necessary to understand the synergic effects of other soil properties.The authors are grateful to the Autonomous Organism Parques Naturales of Spain (OAPN) for providing financial assistanc
The Solar Heavy Element Abundances: II. Constraints from Stellar Atmospheres
Estimates of the bulk metal abundance of the Sun derived from the latest
generation of model atmospheres are significantly lower than the earlier
standard values. In Paper I we demonstrated that a low solar metallicity is
inconsistent with helioseismology if the quoted errors in the atmospheres
models (of order 0.05 dex) are correct. In this paper we undertake a critical
analysis of the solar metallicity and its uncertainty from a model atmospheres
perspective, focusing on CNO. We argue that the non-LTE corrections for
abundances derived from atomic features are overestimated in the recent
abundance studies, while systematic errors in the absolute abundances are
underestimated. If we adopt the internal consistency between different
indicators as a measure of goodness of fit, we obtain intermediate abundances
[C/H] = 8.44 +/- 0.06, [N/H] = 7.96 +/- 0.10 and [O/H] = 8.75 +/- 0.08. The
errors are too large to conclude that there is a solar abundance problem, and
permit both the high and low scales. However, the center-to-limb continuum flux
variations predicted in the simulations appear to be inconsistent with solar
data, which would favor the traditional thermal structure and lead to high CNO
abundances of (8.52, 7.96, 8.80) close to the seismic scale. We argue that
further empirical tests of non-LTE corrections and the thermal structure are
required for precise absolute abundances. The implications for beryllium
depletion and possible sources of error in the numerical simulations are
discussed.Comment: 36 pages, 4 figures, submitted Ap
The Enrichment of the Intergalactic Medium with Adiabatic Feedback I: Metal Cooling and Metal Diffusion
A study of the IGM metal enrichment using a series of SPH simulations is
presented, employing metal cooling and turbulent diffusion of metals and
thermal energy. An adiabatic feedback mechanism was adopted where gas cooling
was prevented to generate galactic winds without explicit wind particles. The
simulations produced a cosmic star formation history (SFH) that is broadly
consistent with observations until z 0.5, and a steady evolution of the
universal neutral hydrogen fraction (). At z=0, about 40% of
the baryons are in the warm-hot intergalactic medium (WHIM), but most metals
(80%-90%) are locked in stars. At higher z the proportion of metals in the IGM
is higher due to more efficient loss from galaxies. The IGM metals primarily
reside in the WHIM throughout cosmic history. The metallicity evolution of the
gas inside galaxies is broadly consistent with observations, but the diffuse
IGM is under enriched at z 2.5. Galactic winds most efficiently enrich
the IGM for halos in the intermediate mass range M_{\sun} -
M_{\sun}. At the low mass end gas is prevented from accreting onto
halos and has very low metallicities. At the high mass end, the fraction of
halo baryons escaped as winds declines along with the decline of stellar mass
fraction of the galaxies. This is likely because of the decrease in star
formation activity and in wind escape efficiency. Metals enhance cooling which
allows WHIM gas to cool onto galaxies and increases star formation. Metal
diffusion allows winds to mix prior to escape, decreasing the IGM metal content
in favour of gas within galactic halos and star forming gas. Diffusion
significantly increases the amount of gas with low metallicities and changes
the density-metallicity relation.Comment: 18 pages, 11 figures, Accepted for publication in MNRA
Light bosons and photospheric solutions to the solar abundance problem
It is well known that current spectroscopic determinations of the chemical
composition of the Sun are starkly at odds with the metallicity implied by
helioseismology. We investigate whether the discrepancy may be due to
conversion of photons to a new light boson in the solar photosphere. We examine
the impact of particles with axion-like interactions with the photon on the
inferred photospheric abundances, showing that resonant axion-photon conversion
is not possible in the region of the solar atmosphere in which line-formation
occurs. Although non-resonant conversion in the line-forming regions can in
principle impact derived abundances, constraints from axion-photon conversion
experiments rule out the couplings necessary for these effects to be
detectable. We show that this extends to hidden photons and chameleons (which
would exhibit similar phenomenological behaviour), ruling out known theories of
new light bosons as photospheric solutions to the solar abundance problem.Comment: 11 pages, PDFLaTeX. v2: Major revision. Inclusion of refractive index
effect on photon-ALP conversion strengthens our conclusion that such an
effect cannot explain the solar abundance problem with a coupling allowed by
experimental axion-like particle searches. We now include a discussion of
chameleons and hidden photons, with similar conclusion
Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds
[Abridged] The magnetic and kinematic properties of the photospheric Evershed
flow are relatively well known, but we are still far from a complete
understanding of its nature. The evolution of the flow with time, which is
mainly due to appearance of velocity packets called Evershed clouds (ECs), may
provide information to further constrain its origin. Here we undertake a
detailed analysis of the evolution of the Evershed flow by studying the
properties of ECs. In this first paper we determine the sizes, proper motions,
location in the penumbra, and frequency of appearance of ECs, as well as their
typical Doppler velocities, linear and circular polarization signals, Stokes V
area asymmetries, and continuum intensities. High-cadence, high-resolution,
full vector spectropolarimetric measurements in visible and infrared lines are
used to derive these parameters. We find that ECs appear in the mid penumbra
and propage outward along filaments with large linear polarization signals and
enhanced Evershed flows. The frequency of appearance of ECs varies between 15
and 40 minutes in different filaments. ECs exhibit the largest Doppler
velocities and linear-to-circular polarization ratios of the whole penumbra. In
addition, lines formed deeper in the atmosphere show larger Doppler velocities,
much in the same way as the ''quiescent'' Evershed flow. According to our
observations, ECs can be classified in two groups: type I ECs, which vanish in
the outer penumbra, and type II ECs, which cross the outer penumbral boundary
and enter the sunspot moat. Most of the observed ECs belong to type I. On
average, type II ECs can be detected as velocity structures outside of the spot
for only about 14 min. Their proper motions in the moat are significantly
reduced with respect to the ones they had in the penumbra.Comment: Accepted for publication in A&
Natures of a clump-origin bulge: a pseudobulge-like but old metal-rich bulge
Bulges in spiral galaxies have been supposed to be classified into two types:
classical bulges or pseudobulges. Classical bulges are thought to form by
galactic merger with bursty star formation, whereas pseudobulges are suggested
to form by secular evolution due to spiral arms and a barred structure
funneling gas into the galactic centre. Noguchi (1998,1999) suggested another
bulge formation scenario, `clump-origin bulge'. He demonstrated using a
numerical simulation that a galactic disc suffers dynamical instability to form
clumpy structures in the early stage of disc formation since the premature disc
is expected to be highly gas-rich, then the clumps are sucked into the galactic
centre by dynamical friction and merge into a single bulge at the centre. This
bulge formation scenario, which is expected to happen only at the
high-redshift, is different from the galactic merger and the secular evolution.
Therefore, clump-origin bulges may have their own unique properties. We perform
a high-resolution N-body/smoothed particle hydrodynamics (SPH) simulation for
the formation of the clump-origin bulge in an isolated galaxy model and study
dynamical and chemical properties of the clump-origin bulge. We find that the
clump-origin bulge resembles pseudobulges in dynamical properties, a nearly
exponential surface density profile, a barred boxy shape and a significant
rotation. We also find that this bulge consists of old and metal-rich stars,
displaying resemblance to classical bulges. These natures, old metal-rich
population but pseudobulge-like structures, mean that the clump-origin bulge
can not be simply classified into classical bulges nor pseudobulges. From these
results, we discuss similarities of the clump-origin bulge to the Milky Way
bulge.Comment: 13 pages, 10 figures, Accepted for publication in MNRA
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