31 research outputs found
Improved SOT (Hinode mission) high resolution solar imaging observations
We consider the best today available observations of the Sun free of
turbulent Earth atmospheric effects, taken with the Solar Optical Telescope
(SOT) onboard the Hinode spacecraft. Both the instrumental smearing and the
observed stray light are analyzed in order to improve the resolution. The Point
Spread Function (PSF) corresponding to the blue continuum Broadband Filter
Imager (BFI) near 450 nm is deduced by analyzing i/ the limb of the Sun and ii/
images taken during the transit of the planet Venus in 2012. A combination of
Gaussian and Lorentzian functions is selected to construct a PSF in order to
remove both smearing due to the instrumental diffraction effects (PSF core) and
the large-angle stray light due to the spiders and central obscuration (wings
of the PSF) that are responsible for the parasitic stray light. A
Max-likelihood deconvolution procedure based on an optimum number of iterations
is discussed. It is applied to several solar field images, including the
granulation near the limb. The normal non-magnetic granulation is compared to
the abnormal granulation which we call magnetic. A new feature appearing for
the first time at the extreme- limb of the disk (the last 100 km) is discussed
in the context of the definition of the solar edge and of the solar diameter. A
single sunspot is considered in order to illustrate how effectively the
restoration works on the sunspot core. A set of 125 consecutive deconvolved
images is assembled in a 45 min long movie illustrating the complexity of the
dynamical behavior inside and around the sunspot.Comment: 15 pages, 22 figures, 1 movi
Predicting the Amplitude of a Solar Cycle Using the North-South Asymmetry in the Previous Cycle: II. An Improved Prediction for Solar Cycle~24
Recently, using Greenwich and Solar Optical Observing Network sunspot group
data during the period 1874-2006, (Javaraiah, MNRAS, 377, L34, 2007: Paper I),
has found that: (1) the sum of the areas of the sunspot groups in 0-10 deg
latitude interval of the Sun's northern hemisphere and in the time-interval of
-1.35 year to +2.15 year from the time of the preceding minimum of a solar
cycle n correlates well (corr. coeff. r=0.947) with the amplitude (maximum of
the smoothed monthly sunspot number) of the next cycle n+1. (2) The sum of the
areas of the spot groups in 0-10 deg latitude interval of the southern
hemisphere and in the time-interval of 1.0 year to 1.75 year just after the
time of the maximum of the cycle n correlates very well (r=0.966) with the
amplitude of cycle n+1. Using these relations, (1) and (2), the values 112 + or
- 13 and 74 + or -10, respectively, were predicted in Paper I for the amplitude
of the upcoming cycle 24. Here we found that in case of (1), the north-south
asymmetry in the area sum of a cycle n also has a relationship, say (3), with
the amplitude of cycle n+1, which is similar to (1) but more statistically
significant (r=0.968) like (2). By using (3) it is possible to predict the
amplitude of a cycle with a better accuracy by about 13 years in advance, and
we get 103 + or -10 for the amplitude of the upcoming cycle 24. However, we
found a similar but a more statistically significant (r=0.983) relationship,
say (4), by using the sum of the area sum used in (2) and the north-south
difference used in (3). By using (4) it is possible to predict the amplitude of
a cycle by about 9 years in advance with a high accuracy and we get 87 + or - 7
for the amplitude of cycle 24.Comment: 21 pages, 7 figures, Published in Solar Physics 252, 419-439 (2008
The Measurement of Solar Diameter and Limb Darkening Function with the Eclipse Observations
The Total Solar Irradiance varies over a solar cycle of 11 years and maybe
over cycles with longer period. Is the solar diameter variable over time too?
We introduce a new method to perform high resolution astrometry of the solar
diameter from the ground, through the observations of eclipses by reconsidering
the definition of the solar edge. A discussion of the solar diameter and its
variations must be linked to the Limb Darkening Function (LDF) using the
luminosity evolution of a Baily's Bead and the profile of the lunar limb
available from satellite data. This approach unifies the definition of solar
edge with LDF inflection point for eclipses and drift-scan or heliometric
methods. The method proposed is applied for the videos of the eclipse in 15
January 2010 recorded in Uganda and in India. The result shows light at least
0.85 arcsec beyond the inflection point, and this suggests to reconsider the
evaluations of the historical eclipses made with naked eye.Comment: 16 pages, 11 figures, accepted in Solar Physics. arXiv admin note:
text overlap with arXiv:astro-ph/0601109 by other author
A resonant-term-based model including a nascent disk, precession, and oblateness: application to GJ 876
Investigations of two resonant planets orbiting a star or two resonant
satellites orbiting a planet often rely on a few resonant and secular terms in
order to obtain a representative quantitative description of the system's
dynamical evolution. We present a semianalytic model which traces the orbital
evolution of any two resonant bodies in a first- through fourth-order
eccentricity or inclination-based resonance dominated by the resonant and
secular arguments of the user's choosing. By considering the variation of
libration width with different orbital parameters, we identify regions of phase
space which give rise to different resonant ''depths,'' and propose methods to
model libration profiles. We apply the model to the GJ 876 extrasolar planetary
system, quantify the relative importance of the relevant resonant and secular
contributions, and thereby assess the goodness of the common approximation of
representing the system by just the presumably dominant terms. We highlight the
danger in using ''order'' as the metric for accuracy in the orbital solution by
revealing the unnatural libration centers produced by the second-order, but not
first-order, solution, and by demonstrating that the true orbital solution lies
somewhere ''in-between'' the third- and fourth-order solutions. We also present
formulas used to incorporate perturbations from central-body oblateness and
precession, and a protoplanetary or protosatellite thin disk with gaps, into a
resonant system. We quantify these contributions to the GJ 876 system, and
thereby highlight the conditions which must exist for multi-planet exosystems
to be significantly influenced by such factors. We find that massive enough
disks may convert resonant libration into circulation; such disk-induced
signatures may provide constraints for future studies of exoplanet systems.Comment: 39 pages of body text, 21 figures, 5 tables, 1 appendix, accepted for
publication in Celestial Mechanics and Dynamical Astronom
Advances in Global and Local Helioseismology: an Introductory Review
Helioseismology studies the structure and dynamics of the Sun's interior by
observing oscillations on the surface. These studies provide information about
the physical processes that control the evolution and magnetic activity of the
Sun. In recent years, helioseismology has made substantial progress towards the
understanding of the physics of solar oscillations and the physical processes
inside the Sun, thanks to observational, theoretical and modeling efforts. In
addition to the global seismology of the Sun based on measurements of global
oscillation modes, a new field of local helioseismology, which studies
oscillation travel times and local frequency shifts, has been developed. It is
capable of providing 3D images of the subsurface structures and flows. The
basic principles, recent advances and perspectives of global and local
helioseismology are reviewed in this article.Comment: 86 pages, 46 figures; "Pulsation of the Sun and Stars", Lecture Notes
in Physics, Vol. 832, Rozelot, Jean-Pierre; Neiner, Coralie (Eds.), 201
Comment on: Past, present and future measurements of the solar diameter by G. Thuillier et al., Adv. Space Res. 35, 329340, 2005
Advances in Space Research, v. 37, n. 8, p. 1649-1650, 2006. http://dx.doi.org/10.1016/j.asr.2006.01.021International audienc
Morphologie et propriétés physiques des trous coronaux solaires
Les trous coronaux, par leurs caractéristiques particulières induisent sur la terre des variations climatiques et des effets cycliques peu connus. L’étude de ces trous a longtemps été négligée du fait de la faible densité électronique et de la température anormalement basse.
L’auteur présente ici les résultats des observations faites depuis leur découverte vers 1955.
Il donne ensuite quelques résultats nouveaux, fournit un modèle théorique et pose des questions mal connues ouvrant des voies nouvelles de recherche
Is it possible to find a solar signature in the current climatic warming?
Physics and Chemistry of the Earth, Parts A/B/C, v. 31, n. 1-3, p. 41-45, 2006. http://dx.doi.org/10.1016/j.pce.2005.01.005International audienc
Rights and wrongs of the temporal solar radius variability
From time immemorial men have strived to measure the size of celestial bodies. Among
them, the diameter of the Sun was a source of curiosity and study. Tackled by Greek
astronomers from a geometric point of view, an estimate, although incorrect, has been
first determined, not truly called into question for several centuries. One must wait up
to the XVIIth century to get the first precise determinations made by the French school of
astronomy. Gradually, as the techniques were more and more sophisticated, many other solar
diameter measurements were carried out, notably in England, Germany, Italy and US.
However, even with instruments at the cutting edge of progress, no absolute value of the
solar diameter has been provided yet, even if the community has adopted a canonical radius
of 959''̣63, given in all ephemeris since the end of the XIXth century. One of the major
difficulties is to define a correct solar diameter. Another issue is the possible temporal
variability of the size of the Sun, as first advocated at the end of the XIXth century by
the Italian school. Today, this question is just on the way to being solved in spite of
considerable efforts developed on ground-based facilities or on board space experiments.
We will here give a review of some of the most remarkable techniques used in the past,
emphasising how incorrect measurements have driven new ideas, leading to develop new
statements for the underlying physics. On such new grounds, it can be speculated that the
roundness of the Sun is not perfect, but developing a thin “cantaloupe skin” in periods of
higher activity, with departures from sphericity being inevitably bounded by a few
kilometers (around 80 km or 10 to 15 mas)