189 research outputs found
Solar neutrinos, helioseismology and the solar internal dynamics
Neutrinos are fundamental particles ubiquitous in the Universe. Their
properties remain elusive despite more than 50 years of intense research
activity. In this review we remind the reader of the noticeable properties of
these particles and of the stakes of the solar neutrino puzzle. The Standard
Solar Model triggered persistent efforts in fundamental Physics to predict the
solar neutrino fluxes, and its constantly evolving predictions have been
regularly compared to the detected neutrino signals. Anticipating that this
standard model could not reproduce the internal solar dynamics, a SEismic Solar
Model was developed which enriched theoretical neutrino flux predictions with
in situ observation of acoustic waves propagating in the Sun. This review
reminds the historical steps, from the pioneering Homestake detection, the
GALLEX- SAGE captures of the first pp neutrinos and emphasizes the importance
of the Superkamiokande and SNO detectors to demonstrate that the solar-emitted
electronic neutrinos are partially transformed into other neutrino flavors
before reaching the Earth. The success of BOREXINO in detecting the 7 Be
neutrino signal justifies the building of a new generation of detectors to
measure the entire solar neutrino spectrum. A coherent picture emerged from
neutrino physics and helioseismology. Today, new paradigms take shape:
determining the masses of neutrinos and the research on the Sun is focusing on
the dynamical aspects and on signature of dark matter. The third part of the
review is dedicated to this prospect. The understanding of the crucial role of
both rotation and magnetism in solar physics benefit from SoHO, SDO, and PICARD
space observations. For now, the particle and stellar challenges seem
decoupled, but this is only a superficial appearance. The development of
asteroseismology shows the far-reaching impact of Neutrino and Stellar
Astronomy.Comment: 60 pages, 12 figures Invited review in press in Report on Progress in
Physic
Contamination by Surface Effects of Time-distance Helioseismic Inversions for Sound Speed Beneath Sunspots
Using Doppler velocity data from the SOI/MDI instrument onboard the SoHO
spacecraft, we do time-distance helioseismic inversions for sound-speed
perturbations beneath 16 sunspots observed in high-resolution mode. We clearly
detect ring-like regions of enhanced sound speed beneath most sunspot
penumbrae, extending from near the surface to depths of about 3.5 Mm. Due to
their location and dependence on frequency bands of p-modes used, we believe
these rings to be artifacts produced by a surface signal probably associated
with the sunspot magnetic field.Comment: accepted by Ap
Numerical Models of Travel-Time Inhomogeneities in Sunspots
We investigate the direct contribution of strong, sunspot-like magnetic
fields to helioseismic wave travel-time shifts via two numerical forward
models, a 3D ideal MHD solver and MHD ray theory. The simulated data cubes are
analyzed using the traditional time-distance center-to-annulus measurement
technique. We also isolate and analyze the direct contribution from purely
thermal perturbations to the observed travel-time shifts, confirming some
existing ideas and bring forth new ones: (i) that the observed travel-time
shifts in the vicinity of sunspots are largely governed by MHD physics, (ii)
the travel-time shifts are sensitively dependent on frequency and phase-speed
filter parameters and the background power below the ridge, and finally,
(iii) despite its seeming limitations, ray theory succeeds in capturing the
essence of the travel-time variations as derived from the MHD simulations.Comment: 13 Pages, 3 Figures. ApJ Letters Accepte
The Rotation Of The Deep Solar Layers
From the analysis of low-order GOLF+MDI sectoral modes and LOWL data (l > 3),
we derive the solar radial rotation profile assuming no latitudinal dependance
in the solar core. These low-order acoustic modes contain the most
statistically significant information about rotation of the deepest solar
layers and should be least influenced by internal variability associated with
the solar dynamo. After correction of the sectoral splittings for their
contamination by the rotation of the higher latitudes, we obtain a flat
rotation profile down to 0.2 solar radius.Comment: accepted in ApJ Letters 5 pages, 2 figure
Helioseismic and Magnetic Imager observations of linear polarization from a loop prominence system
White-light observations by the Solar Dynamics Observatory's Helioseismic and
Magnetic Imager of a loop-prominence system occurring in the aftermath of an
X-class flare on 2013 May 13 near the eastern solar limb show a linearly
polarized component, reaching up to 20% at an altitude of 33 Mm,
about the maximal amount expected if the emission were due solely to Thomson
scattering of photospheric light by the coronal material. The mass associated
with the polarized component was 8.210 g. At 15 Mm altitude, the
brightest part of the loop was 3(+/-0.5)% linearly polarized, only about 20% of
that expected from pure Thomson scattering, indicating the presence of an
additional unpolarized component at wavelengths near Fe I (617.33 nm), probably
thermal emission. We estimated the free electron density of the white-light
loop system to possibly be as high as 1.810 cm.Comment: 9 pages, 5 figure
Deep-Focus Diagnostics of Sunspot Structure
In sequel to Moradi et al. [2009, ApJ, 690, L72], we employ two established
numerical forward models (a 3D ideal MHD solver and MHD ray theory) in
conjunction with time-distance helioseismology to probe the lateral extent of
wave-speed perturbations produced in regions of strong, near-surface magnetic
fields. We continue our comparisons of forward modeling approaches by extending
our previous surface-focused travel-time measurements with a common midpoint
deep-focusing scheme that avoids the use of oscillation signals within the
sunspot region. The idea is to also test MHD ray theory for possible
application in future inverse methods.Comment: 8 pages, 4 figures, published in the conference proceedings "Magnetic
Coupling between the Interior and Atmosphere of the Sun", edited by S.S.
Hasan and R.J. Rutten; Astrophysics and Space Science Proceeding
Time--Distance Helioseismology Data Analysis Pipeline for Helioseismic and Magnetic Imager onboard Solar Dynamics Observatory (SDO/HMI) and Its Initial Results
The Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory
(SDO/HMI) provides continuous full-disk observations of solar oscillations. We
develop a data-analysis pipeline based on the time-distance helioseismology
method to measure acoustic travel times using HMI Doppler-shift observations,
and infer solar interior properties by inverting these measurements. The
pipeline is used for routine production of near-real-time full-disk maps of
subsurface wave-speed perturbations and horizontal flow velocities for depths
ranging from 0 to 20 Mm, every eight hours. In addition, Carrington synoptic
maps for the subsurface properties are made from these full-disk maps. The
pipeline can also be used for selected target areas and time periods. We
explain details of the pipeline organization and procedures, including
processing of the HMI Doppler observations, measurements of the travel times,
inversions, and constructions of the full-disk and synoptic maps. Some initial
results from the pipeline, including full-disk flow maps, sunspot subsurface
flow fields, and the interior rotation and meridional flow speeds, are
presented.Comment: Accepted by Solar Physics topical issue 'Solar Dynamics Observatory
Helioseismology, Neutrinos and Radiative Zones
The solar interior has been scrutinized by two different and independent
probes during the last twenty years with important revisions of the solar
model, including a recent heavy element abundance revision. Today, we get a
quantitatively coherent picture (even incomplete) of the solar (stellar)
radiative zones. In this review, we recall the clues for solar gravitational
settling definitively established by the seismic determination of the
photospheric helium content. We comment also on the need for mixing in the
transition region between radiation and convection in the case of the Sun and
of population II stars. We finally list the open questions and the importance
to continue more precise investigations of the solar (stellar) radiative zone
in detecting gravity modes with the project DynaMICS.Comment: 6 pages, 2 figures, 1 table, will be published in EAS Publications
series, Conference 2005: Element stratification in stars: 40 years of Atomic
diffusion, ed: G. Alecian & S. Vauclai
Helioseismic Travel-Time Definitions and Sensitivity to Horizontal Flows Obtained From Simulations of Solar Convection
We study the sensitivity of wave travel times to steady and spatially
homogeneous horizontal flows added to a realistic simulation of the solar
convection performed by Robert F. Stein, Ake Nordlund, Dali Georgobiani, and
David Benson. Three commonly used definitions of travel times are compared. We
show that the relationship between travel-time difference and flow amplitude
exhibits a non-linearity depending on the travel distance, the travel-time
definition considered, and the details of the time-distance analysis (in
particular, the impact of the phase-speed filter width). For times measured
using a Gabor wavelet fit, the travel-time differences become nonlinear in the
flow strength for flows of about 300 m/s, and this non-linearity reaches almost
60% at 1200 m/s (relative difference between actual travel time and expected
time for a linear behaviour). We show that for travel distances greater than
about 17 Mm, the ray approximation predicts the sensitivity of travel-time
shifts to uniform flows. For smaller distances, the ray approximation can be
inaccurate by more than a factor of three.Comment: 24 pages, 10 figure
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