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Author name code: sekii
ADS astronomy entries on 2022-09-14
author:"Sekii, Takashi" 

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Title: Bayesian Rotation Inversion of KIC 11145123
Authors: Hatta, Yoshiki; Sekii, Takashi; Benomar, Othman; Takata, Masao
2022ApJ...927...40H    Altcode: 2021arXiv211212341H
  A scheme of Bayesian rotation inversion, which allows us to compute
  the probability of a model of a stellar rotational profile, is
  developed. The validation of the scheme with simple rotational profiles
  and the corresponding sets of artificially generated rotational shifts
  has been successfully carried out, and we can correctly distinguish
  the (right) rotational model, prepared beforehand for generating
  the artificial rotational shifts, from the other (wrong) rotational
  model. The Bayesian scheme is applied to a γ Dor-δ Sct-type hybrid
  star, KIC 11145123, leading to a result that the convective core
  of the star might be rotating much faster (~10 times faster) than
  the other regions of the star. The result is consistent with that
  previously suggested by Hatta et al. based on a three-zone modeling,
  further strengthening their argument from a Bayesian point of view.

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Title: Nonstandard Modeling of a Possible Blue Straggler Star,
    KIC 11145123
Authors: Hatta, Yoshiki; Sekii, Takashi; Takata, Masao; Benomar, Othman
2021ApJ...923..244H    Altcode: 2021arXiv211006926H
  Nonstandard modeling of KIC 11145123, a possible blue straggler star,
  has been asteroseismically carried out based on a scheme to compute
  stellar models with the chemical compositions in their envelopes
  arbitrarily modified, mimicking the effects of some interactions with
  other stars through which blue straggler stars are thought to be
  born. We have constructed a nonstandard model of the star with the
  following parameters: M = 1.36 M <SUB>⊙</SUB>, Y <SUB>init</SUB>
  = 0.26, Z <SUB>init</SUB> = 0.002, and f <SUB>ovs</SUB> = 0.027,
  where f <SUB>ovs</SUB> is the extent of overshooting described as an
  exponentially decaying diffusive process. The modification is down
  to the depth of r/R ~ 0.6 and the extent ΔX, which is a difference
  in surface hydrogen abundance between the envelope-modified and
  unmodified models, is 0.06. The residuals between the model and the
  observed frequencies are comparable with those for the previous model
  computed assuming standard single-star evolution, suggesting that it
  is possible that the star was born with a relatively ordinary initial
  helium abundance of ~0.26 compared with that of the previous models
  (~0.30-0.40), then experienced some modification of the chemical
  compositions and gained helium in the envelope. Detailed analyses
  of the nonstandard model have implied that the elemental diffusion
  in the deep radiative region of the star might be much weaker than
  that assumed in current stellar evolutionary calculations; we need
  some extra mechanisms inside the star, rendering the star a much more
  intriguing target to be further investigated.

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Title: A journey of exploration to the polar regions of a star:
    probing the solar poles and the heliosphere from high helio-latitude
Authors: Harra, Louise; Andretta, Vincenzo; Appourchaux, Thierry;
   Baudin, Frédéric; Bellot-Rubio, Luis; Birch, Aaron C.; Boumier,
   Patrick; Cameron, Robert H.; Carlsson, Matts; Corbard, Thierry;
   Davies, Jackie; Fazakerley, Andrew; Fineschi, Silvano; Finsterle,
   Wolfgang; Gizon, Laurent; Harrison, Richard; Hassler, Donald M.;
   Leibacher, John; Liewer, Paulett; Macdonald, Malcolm; Maksimovic,
   Milan; Murphy, Neil; Naletto, Giampiero; Nigro, Giuseppina; Owen,
   Christopher; Martínez-Pillet, Valentín; Rochus, Pierre; Romoli,
   Marco; Sekii, Takashi; Spadaro, Daniele; Veronig, Astrid; Schmutz, W.
2021ExA...tmp...93H    Altcode: 2021arXiv210410876H
  A mission to view the solar poles from high helio-latitudes (above 60°)
  will build on the experience of Solar Orbiter as well as a long heritage
  of successful solar missions and instrumentation (e.g. SOHO Domingo et
  al. (Solar Phys. 162(1-2), 1-37 1995), STEREO Howard et al. (Space
  Sci. Rev. 136(1-4), 67-115 2008), Hinode Kosugi et al. (Solar
  Phys. 243(1), 3-17 2007), Pesnell et al. Solar Phys. 275(1-2),
  3-15 2012), but will focus for the first time on the solar poles,
  enabling scientific investigations that cannot be done by any other
  mission. One of the major mysteries of the Sun is the solar cycle. The
  activity cycle of the Sun drives the structure and behaviour of the
  heliosphere and of course, the driver of space weather. In addition,
  solar activity and variability provides fluctuating input into the
  Earth climate models, and these same physical processes are applicable
  to stellar systems hosting exoplanets. One of the main obstructions
  to understanding the solar cycle, and hence all solar activity,
  is our current lack of understanding of the polar regions. In this
  White Paper, submitted to the European Space Agency in response to the
  Voyage 2050 call, we describe a mission concept that aims to address
  this fundamental issue. In parallel, we recognise that viewing the Sun
  from above the polar regions enables further scientific advantages,
  beyond those related to the solar cycle, such as unique and powerful
  studies of coronal mass ejection processes, from a global perspective,
  and studies of coronal structure and activity in polar regions. Not
  only will these provide important scientific advances for fundamental
  stellar physics research, they will feed into our understanding of
  impacts on the Earth and other planets' space environment.

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Title: A Journey of Exploration to the Polar Regions of a Star:
    Probing the Solar Poles and the Heliosphere from High Helio-Latitude
Authors: Finsterle, W.; Harra, L.; Andretta, V.; Appourchaux, T.;
   Baudin, F.; Bellot Rubio, L.; Birch, A.; Boumier, P.; Cameron, R. H.;
   Carlsson, M.; Corbard, T.; Davies, J. A.; Fazakerley, A. N.; Fineschi,
   S.; Gizon, L. C.; Harrison, R. A.; Hassler, D.; Leibacher, J. W.;
   Liewer, P. C.; Macdonald, M.; Maksimovic, M.; Murphy, N.; Naletto, G.;
   Nigro, G.; Owen, C. J.; Martinez-Pillet, V.; Rochus, P. L.; Romoli,
   M.; Sekii, T.; Spadaro, D.; Veronig, A.
2020AGUFMSH0110005F    Altcode:
  A mission to view the solar poles from high helio-latitudes (above
  60°) will build on the experience of Solar Orbiter as well as a long
  heritage of successful solar missions and instrumentation (e.g. SOHO,
  STEREO, Hinode, SDO), but will focus for the first time on the solar
  poles, enabling scientific investigations that cannot be done by
  any other mission. One of the major mysteries of the Sun is the solar
  cycle. The activity cycle of the Sun drives the structure and behaviour
  of the heliosphere and is, of course, the driver of space weather. In
  addition, solar activity and variability provides fluctuating input
  into the Earth climate models, and these same physical processes
  are applicable to stellar systems hosting exoplanets. One of the
  main obstructions to understanding the solar cycle, and hence all
  solar activity, is our current lack of understanding of the polar
  regions. We describe a mission concept that aims to address this
  fundamental issue. In parallel, we recognise that viewing the Sun
  from above the polar regions enables further scientific advantages,
  beyond those related to the solar cycle, such as unique and powerful
  studies of coronal mass ejection processes, from a global perspective,
  and studies of coronal structure and activity in polar regions. Not
  only will these provide important scientific advances for fundamental
  stellar physics research, they will feed into our understanding of
  impacts on the Earth and other planets' space environment.

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Title: Asteroseismic Study of KIC 11145123: Its Structure and Rotation
Authors: Hatta, Yoshiki; Sekii, Takashi; Takata, Masao; Kurtz,
   Donald W.
2020ASSP...57..243H    Altcode:
  KIC 11145123 is one of the Kepler targets that has been actively
  studied asteroseismically. Its well-resolved frequency splittings
  for p, g, and mixed modes have enabled us to infer the 1-dimensional
  surface-to-core rotation of the star (Kurtz et al., Mon Not R Astron
  Soc 444:102, 2014) and to measure the asphericity of the star sensed
  by the modes (Gizon et al., Sci Adv 2:e1601777, 2016). These have been
  the first such attempts for main-sequence stars other than the Sun. In
  this paper, we report further detailed asteroseismic analyses of KIC
  11145123, focusing on inferring 2-dimensional rotation profile and on
  fine-tuning the equilibrium model of the star. Our main results are:
  (1) the convective core might be rotating six times faster than
  the other parts of the star, and (2) adopting diffusion "weaker"
  than the usual settings used in the standard 1-d stellar evolution
  calculations leads to a better agreement with the observed g-mode
  period spacing pattern. These two results suggest that the rotational
  velocity shear might be causing some extra mixing around the boundary
  between convective core and radiative region above, and the extra
  mixing weakens, in effect, the diffusion process there. This resembles
  a mechanism thought to be at work around the solar tachocline.

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Title: The Two-dimensional Internal Rotation of KIC 11145123
Authors: Hatta, Yoshiki; Sekii, Takashi; Takata, Masao; Kurtz,
   Donald W.
2019ApJ...871..135H    Altcode: 2021arXiv211106853H
  The 2D internal rotation of KIC 11145123 has been inferred via
  asteroseismology. Based on the optimally localized averaging method and
  a simple three-zone modeling of the internal rotation, we have found
  evidence for a contrast between the internal rotation of the radiative
  region and that of the convective core; the radiative region rotates
  almost uniformly throughout the region, but the convective core may be
  rotating about 6 times faster than the radiative region above. We have
  also found marginally significant evidence of latitudinal differential
  rotation in the outer envelope. These newly indicated features of the
  internal rotation of the star can help us further constrain the theory
  of angular momentum transport inside stars, as well as understand the
  complex physical properties of the star, which was once thought to
  be a main-sequence A-type star but recently has been proposed to be
  a blue straggler, based on spectroscopy.

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Title: Asteroseismic detection of latitudinal differential rotation
    in 13 Sun-like stars
Authors: Benomar, O.; Bazot, M.; Nielsen, M. B.; Gizon, L.; Sekii,
   T.; Takata, M.; Hotta, H.; Hanasoge, S.; Sreenivasan, K. R.;
   Christensen-Dalsgaard, J.
2018Sci...361.1231B    Altcode: 2018arXiv180907938B
  The differentially rotating outer layers of stars are thought to
  play a role in driving their magnetic activity, but the underlying
  mechanisms that generate and sustain differential rotation are
  poorly understood. We report the measurement using asteroseismology
  of latitudinal differential rotation in the convection zones of 40
  Sun-like stars. For the most significant detections, the stars’
  equators rotate approximately twice as fast as their midlatitudes. The
  latitudinal shear inferred from asteroseismology is much larger than
  predictions from numerical simulations.

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Title: Can high angular degree non-radial pulsations be observed in
    roAp stars?
Authors: Mathys, Gautier; Shibahashi, Hiromoto; Quintero Noda, Carlos;
   Sekii, Takashi
2018phos.confE..43M    Altcode:
  In the presence of a magnetic field, stellar spectral lines may
  appear systematically broader in one circular polarisation than in
  the opposite one. This rotational crossover effect, which is observed
  in some Ap stars, results from a correlation between the rotational
  Doppler shift and the different Zeeman shifts of the circularly
  polarised components. <P />Crossover of non-rotational origin has been
  detected in a number of roAp stars as well as in some noAp stars. The
  most plausible interpretation is that it is induced by the pulsational
  velocity gradients across the photospheric layer. Pulsational crossover
  is expected to be detectable even in the case of high angular degree
  pulsation modes, contrary to luminosity variations. Thus, it may open
  a new window into unexplored physics in roAp stars.

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Title: Spectroscopic and asteroseismic analysis of the remarkable
    main-sequence A star KIC 11145123
Authors: Takada-Hidai, Masahide; Kurtz, Donald W.; Shibahashi,
   Hiromoto; Murphy, Simon J.; Takata, Masao; Saio, Hideyuki; Sekii,
   Takashi
2017MNRAS.470.4908T    Altcode: 2017arXiv170604314T
  A spectroscopic analysis was carried out to clarify the properties of
  KIC 11145123 - the first main-sequence star with a directly measured
  core-to-surface rotation profile - based on spectra observed with
  the High Dispersion Spectrograph (HDS) of the Subaru telescope. The
  atmospheric parameters (T<SUB>eff</SUB> = 7600 K, log g = 4.2, ξ =
  3.1 km s<SUP>-1</SUP> and [Fe/H] = -0.71 dex), the radial and rotation
  velocities, and elemental abundances were obtained by analysing line
  strengths and fitting line profiles, which were calculated with a 1D
  LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low
  [Fe/H] = -0.71 ± 0.11 dex and a high radial velocity of -135.4 ± 0.2
  km s<SUP>-1</SUP>. These are remarkable among late-A stars. Our best
  asteroseismic models with this low [Fe/H] have slightly high helium
  abundance and low masses of 1.4 M<SUB>⊙</SUB>. All of these results
  strongly suggest that KIC 11145123 is a Population II blue straggler;
  (2) the projected rotation velocity confirms the asteroseismically
  predicted slow rotation of the star; (3) comparisons of abundance
  patterns between KIC 11145123 and Am, Ap, and blue stragglers show that
  KIC 11145123 is neither an Am star nor an Ap star, but has abundances
  consistent with a blue straggler. We conclude that the remarkably long
  100-d rotation period of this star is a consequence of it being a blue
  straggler, but both pathways for the formation of blue stragglers -
  merger and mass loss in a binary system - pose difficulties for our
  understanding of the exceedingly slow rotation. In particular, we show
  that there is no evidence of any secondary companion star, and we put
  stringent limits on the possible mass of any such purported companion
  through the phase modulation technique.

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Title: The double-ridge structure of the high-frequency time-distance
    crosscorrelation function in local helioseismology
Authors: Kambara, Nagaaki; Sekii, Takashi
2017SPD....4810902K    Altcode:
  We model helioseismic high-frequency cross-correlation function and
  carry out comparison with observational data.We also discuss the
  source depth of the acoustic waves, one of the model parameters.It
  has been reported that when time-distance analysis is applied to the
  high-frequency acoustic waves, with frequencies above the critical
  cutoff frequency, time-distance cross-correlation function exhibits
  double-ridge structure. It has been pointed out, however, that in such
  analyses subcritical components (frequency &lt; 5.3 MHz) may not be
  completely filtered out, and a hypothesis is that the double ridges
  are generated as artificial interference patterns of the subcritical
  waves and the supercritical waves. We test this hypothesis using
  SDO/HMI data.The data are put through a frequency filter before the
  cross-correlation function is computed. We vary the width and central
  frequency of the filter and examine when double ridges appear. When both
  the supercritical and the subcritical components are present in the
  filtered power spectrum, double ridges appear. When there is only one
  of the components, however, double ridges do not appear, confirming
  that interference between the two components is necessary for the
  double ridges.Next, we construct a simple model of cross-correlation
  function by ray-tracing the waves generated at a certain depth. The
  model reproduces the double-ridge structure well, indeed by interference
  between the supercritical part and the subcritical part, each of which
  by itself exhibits only a single ridge. We find that the successful
  reproduction of the observations depends sharply on the source depth
  of the acoustic wave, one of the input parameters to the model.This
  indicates a possibility that we can measure the source depth of the
  acoustic waves precisely, using the double ridges.

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Title: SOLARIS: Solar Sail Investigation of the Sun
Authors: Appourchaux, Thierry; Auchère, Frédéric; Antonucci, Ester;
   Gizon, Laurent; MacDonald, Malcolm; Hara, Hirohisa; Sekii, Takashi;
   Moses, Daniel; Vourlidas, Angelos
2017arXiv170708193A    Altcode:
  In this paper, we detail the scientific objectives and outline
  a strawman payload of the SOLAR sail Investigation of the Sun
  (SOLARIS). The science objectives are to study the 3D structure
  of the solar magnetic and velocity field, the variation of total
  solar irradiance with latitude, and the structure of the corona. We
  show how we can meet these science objective using solar-sail
  technologies currently under development. We provide a tentative
  mission profile considering several trade-off approaches. We also
  provide a tentative mass budget breakdown and a perspective for a
  programmatic implementation.

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Title: Helioseismology and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Brun, A. S.; Culhane, J. L.; Gizon, L.;
   Roth, M.; Sekii, T.
2017hdsi.book.....T    Altcode:
  No abstract at ADS

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Title: Future Mission Concepts for Helioseismology
Authors: Sekii, Takashi; Appourchaux, Thierry; Fleck, Bernhard;
   Turck-Chièze, Sylvaine
2017hdsi.book..291S    Altcode:
  No abstract at ADS

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Title: Preface: Helioseismology and Dynamics of the Solar Interior
Authors: Gizon, Laurent; Thompson, Michael J.; Brun, A. Sacha; Culhane,
   J. Len; Roth, Markus; Sekii, Takashi
2017hdsi.book....1G    Altcode:
  No abstract at ADS

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Title: Shape of a slowly rotating star measured by asteroseismology
Authors: Gizon, L.; Sekii, T.; Takata, M.; Kurtz, D. W.; Shibahashi,
   H.; Bazot, M.; Benomar, O.; Birch, A. C.; Sreenivasan, K. R.
2016SciA....2E1777G    Altcode: 2016arXiv161106435G
  Stars are not perfectly spherically symmetric. They are deformed by
  rotation and magnetic fields. Until now, the study of stellar shapes
  has only been possible with optical interferometry for a few of the
  fastest-rotating nearby stars. We report an asteroseismic measurement,
  with much better precision than interferometry, of the asphericity of
  an A-type star with a rotation period of 100 days. Using the fact that
  different modes of oscillation probe different stellar latitudes, we
  infer a tiny but significant flattening of the star's shape of $\Delta
  R/R = (1.8 \pm 0.6) \times 10^{-6}$. For a stellar radius $R$ that is
  $2.24$ times the solar radius, the difference in radius between the
  equator and the poles is $\Delta R = 3 \pm 1$ km. Because the observed
  $\Delta R/R$ is only one-third of the expected rotational oblateness,
  we conjecture the presence of a weak magnetic field on a star that
  does not have an extended convective envelope. This calls to question
  the origin of the magnetic field.

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Title: Statistics of the two-point cross-covariance function of
    solar oscillations
Authors: Nagashima, Kaori; Sekii, Takashi; Gizon, Laurent; Birch,
   Aaron C.
2016A&A...593A..41N    Altcode: 2016arXiv160606497N
  Context. The cross-covariance of solar oscillations observed at
  pairs of points on the solar surface is a fundamental ingredient in
  time-distance helioseismology. Wave travel times are extracted from
  the cross-covariance function and are used to infer the physical
  conditions in the solar interior. <BR /> Aims: Understanding the
  statistics of the two-point cross-covariance function is a necessary
  step towards optimizing the measurement of travel times. <BR /> Methods:
  By modeling stochastic solar oscillations, we evaluate the variance
  of the cross-covariance function as function of time-lag and distance
  between the two points. <BR /> Results: We show that the variance of
  the cross-covariance is independent of both time-lag and distance in
  the far field, that is, when they are large compared to the coherence
  scales of the solar oscillations. <BR /> Conclusions: The constant
  noise level for the cross-covariance means that the signal-to-noise
  ratio for the cross-covariance is proportional to the amplitude of
  the expectation value of the cross-covariance. This observation is
  important for planning data analysis efforts.

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Title: Future Mission Concepts for Helioseismology
Authors: Sekii, Takashi; Appourchaux, Thierry; Fleck, Bernhard;
   Turck-Chièze, Sylvaine
2015SSRv..196..285S    Altcode: 2015SSRv..tmp...15S
  Future space-mission concepts currently discussed in the helioseismology
  community are reviewed. One popular idea is to observe the Sun from high
  latitudes, to explore the polar regions as well as to probe the deep
  interior using stereoscopic techniques, by combining observations from
  high latitudes with observations from within the ecliptic plane. Another
  idea is to stay within the ecliptic plane but still aim for stereoscopic
  helioseismology for deep layers. A new instrument and a novel mission
  concept for studying the solar core regions are also discussed.

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Title: Asteroseismic measurement of surface-to-core rotation in a
    main-sequence star
Authors: Kurtz, Donald W.; Saio, Hideyuki; Takata, Masao; Shibahashi,
   Hiromoto; Murphy, Simon J.; Sekii, Takashi
2015EPJWC.10101007K    Altcode:
  We have discovered rotationally split core g-mode triplets and surface
  p-mode triplets and quintuplets in a terminal age main-sequence A
  star, KIC 11145123, that shows both δ Sct p-mode pulsations and γ
  Dor g-mode pulsations. This gives the first robust determination of
  the rotation of the deep core and surface of a main-sequence star,
  essentially model-independently. We find its rotation to be nearly
  uniform with a period near 100 d, but we show with high confidence that
  the surface rotates slightly faster than the core. A strong angular
  momentum transfer mechanism must be operating to produce the nearly
  rigid rotation, and a mechanism other than viscosity must be operating
  to produce a more rapidly rotating surface than core. Our asteroseismic
  result, along with previous asteroseismic constraints on internal
  rotation in some B stars, and measurements of internal rotation in
  some subgiant, giant and white dwarf stars, has made angular momentum
  transport in stars throughout their lifetimes an observational science.

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Title: Recent discoveries of structures and physical processes in
    local helioseismology
Authors: Sekii, T.; Shibahashi, H.
2015exse.book..180S    Altcode:
  No abstract at ADS

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Title: Asteroseismic measurement of slow, nearly uniform
    surface-to-core rotation in the main-sequence F star KIC 9244992
Authors: Saio, Hideyuki; Kurtz, Donald W.; Takata, Masao; Shibahashi,
   Hiromoto; Murphy, Simon J.; Sekii, Takashi; Bedding, Timothy R.
2015MNRAS.447.3264S    Altcode: 2014arXiv1412.5362S
  We have found a rotationally split series of core g-mode triplets
  and surface p-mode multiplets in a main-sequence F star, KIC
  9244992. Comparison with models shows that the star has a mass of about
  1.45 M<SUB>⊙</SUB>, and is at an advanced stage of main-sequence
  evolution in which the central hydrogen abundance mass fraction is
  reduced to about 0.1. This is the second case, following KIC 11145123,
  of an asteroseismic determination of the rotation of the deep core
  and surface of an A-F main-sequence star. We have found, essentially
  model independently, that the rotation near the surface, obtained
  from p-mode splittings, is 66 d, slightly slower than the rotation
  of 64 d in the core, measured by g-mode splittings. KIC 9244992 is
  similar to KIC 11145123 in that both are near the end of main-sequence
  stage with very slow and nearly uniform rotation. This indicates the
  angular momentum transport in the interior of an A-F star during the
  main-sequence stage is much stronger than that expected from standard
  theoretical formulations.

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Title: Solar rotation inferred from radial velocities of the
    Sun-as-a-star during the 2012 May 21 eclipse*
Authors: Takeda, Yoichi; Ohshima, Osamu; Kambe, Eiji; Toda, Hiroyuki;
   Koyano, Hisashi; Sato, Bun'ei; Nakamura, Yasuhisa; Narita, Norio;
   Sekii, Takashi
2015PASJ...67...10T    Altcode: 2014arXiv1411.1481T; 2015PASJ..tmp..147T
  With the aim of examining how much information of solar rotation can be
  obtained purely spectroscopically by observing the Sun-as-a-star during
  the 2012 May 21 eclipse at Okayama Astrophysical Observatory, we studied
  the variation of radial velocities (V<SUB>r</SUB>), which were derived
  by using the iodine-cell technique based on a set of 184 high-dispersion
  spectra consecutively obtained over a time span of ∼ 4 hr. The
  resulting V<SUB>r</SUB>(t) was confirmed to show the characteristic
  variation (Rossiter-McLaughlin effect) caused by time-varying visibility
  of the solar disk. By comparing the observed V<SUB>r</SUB>(t) curve
  with the theoretical ones [which were simulated with the latitude (ψ)
  dependent solar rotation law ω<SUB>sidereal</SUB>(ψ) = A + B sin
  <SUP>2</SUP>ψ (degree d<SUP>-1</SUP>)] we found that the relation B
  ≃ -5.5A + 77 gives the best fit, though separate determinations of A
  and B were not possible. Since this relationship is consistent with the
  real values known for the Sun (A ≃ 14.5, B ≃ -2.8), we may state
  that our analysis yielded satisfactory results. This consequence may
  provide the prospect of getting useful information on stellar rotation
  of eclipsing binaries from radial-velocity studies during eclipse,
  if many spectra of sufficiently high time-resolution are available.

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Title: Asteroseismic measurement of surface-to-core rotation in a
    main-sequence A star, KIC 11145123
Authors: Kurtz, Donald W.; Saio, Hideyuki; Takata, Masao; Shibahashi,
   Hiromoto; Murphy, Simon J.; Sekii, Takashi
2014MNRAS.444..102K    Altcode: 2014arXiv1405.0155K
  We have discovered rotationally split core g-mode triplets and surface
  p-mode triplets and quintuplets in a terminal age main-sequence A star,
  KIC 11145123, that shows both δ Sct p-mode pulsations and γ Dor g-mode
  pulsations. This gives the first robust determination of the rotation
  of the deep core and surface of a main-sequence star, essentially model
  independently. We find its rotation to be nearly uniform with a period
  near 100 d, but we show with high confidence that the surface rotates
  slightly faster than the core. A strong angular momentum transfer
  mechanism must be operating to produce the nearly rigid rotation,
  and a mechanism other than viscosity must be operating to produce a
  more rapidly rotating surface than core. Our asteroseismic result,
  along with previous asteroseismic constraints on internal rotation in
  some B stars, and measurements of internal rotation in some subgiant,
  giant and white dwarf stars, has made angular momentum transport in
  stars throughout their lifetimes an observational science.

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Title: Avoided Crossing and Synchronization
Authors: Sekii, T.; Shibahashi, H.
2013ASPC..479..573S    Altcode:
  We examine avoided crossing of stellar pulsations in the nonlinear
  regime, where synchronization may occur, based on a simple model of
  weakly coupled van der Pol oscillators with close frequencies. For this
  simple case, avoided crossing is unaffected in the sense that there is
  a frequency difference between the symmetric and antisymmetric modes,
  but as a result of synchronization, unlike the linear oscillations case,
  the system can vibrate in only one of the modes.

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Title: A Statistical Study of Coronal Active Events in the North
    Polar Region
Authors: Sako, Nobuharu; Shimojo, Masumi; Watanabe, Tetsuya; Sekii,
   Takashi
2013ApJ...775...22S    Altcode:
  In order to study the relationship between characteristics of polar
  coronal active events and the magnetic environment in which such events
  take place, we analyze 526 X-ray jets and 1256 transient brightenings
  in the polar regions and in regions around the equatorial limbs. We
  calculate the occurrence rates of these polar coronal active events
  as a function of distance from the boundary of coronal holes, and
  find that most events in the polar quiet regions occur adjacent to
  and equatorward of the coronal hole boundaries, while events in the
  polar coronal holes occur uniformly within them. Based primarily on
  the background intensity, we define three categories of regions that
  produce activity: polar coronal holes, coronal hole boundary regions,
  and polar quiet regions. We then investigate the properties of the
  events produced in these regions. We find no significant differences
  in their characteristics, for example, length and lifetime, but there
  are differences in the occurrence rates. The mean occurrence rate of
  X-ray jets around the boundaries of coronal holes is higher than that
  in the polar quiet regions, equatorial quiet regions, and polar coronal
  holes. Furthermore, the mean occurrence rate of transient brightenings
  is also higher in these regions. We make comparison with the occurrence
  rates of emerging and canceling magnetic fields in the photosphere
  reported in previous studies, and find that they do not agree with
  the occurrence rates of transient brightenings found in this study.

---------------------------------------------------------
Title: Probing the Shallow Convection Zone: Rising Motion of
    Subsurface Magnetic Fields in the Solar Active Region
Authors: Toriumi, Shin; Ilonidis, Stathis; Sekii, Takashi; Yokoyama,
   Takaaki
2013ApJ...770L..11T    Altcode: 2013arXiv1305.3023T
  In this Letter, we present a seismological detection of a rising motion
  of magnetic flux in the shallow convection zone of the Sun, and show
  estimates of the emerging speed and its decelerating nature. In order to
  evaluate the speed of subsurface flux that creates an active region, we
  apply six Fourier filters to the Doppler data of NOAA AR 10488, observed
  with the Solar and Heliospheric Observatory/Michelson Doppler Imager,
  to detect the reduction of acoustic power at six different depths from
  -15 to -2 Mm. All the filtered acoustic powers show reductions, up to 2
  hr before the magnetic flux first appears at the visible surface. The
  start times of these reductions show a rising trend with a gradual
  deceleration. The obtained velocity is first several km s<SUP>-1</SUP>
  in a depth range of 15-10 Mm, then ~1.5 km s<SUP>-1</SUP> at 10-5 Mm,
  and finally ~0.5 km s<SUP>-1</SUP> at 5-2 Mm. If we assume that the
  power reduction is actually caused by the magnetic field, the velocity
  of the order of 1 km s<SUP>-1</SUP> is well in accordance with previous
  observations and numerical studies. Moreover, the gradual deceleration
  strongly supports the theoretical model that the emerging flux slows
  down in the uppermost convection zone before it expands into the
  atmosphere to build an active region.

---------------------------------------------------------
Title: Helioseismic Detection of the Pre-emerging Magnetic Flux in
    the Shallow Convection Zone
Authors: Toriumi, S.; Ilonidis, S.; Sekii, T.; Yokoyama, T.
2013enss.confE..25T    Altcode:
  We detect the rising magnetic flux in the shallower convection zone
  of the Sun by observing acoustic power reduction, and evaluate its
  rising speed. Here we aim to reveal the rising speed of the magnetic
  flux in the shallow convection zone, before the active region are
  created. We apply six different Fourier filters to the Doppler data of
  NOAA AR 10488 taken by SOHO/MDI, to detect the reduction of acoustic
  power at six different depths from -15 to -2 Mm. The filtered powers
  show reductions before the start of flux appearance at the visible
  surface. The start times of these reductions show a rising trend,
  first at several km/s in a depth range of 15-10 Mm, then ∼1.5 km/s
  at 10-5 Mm, and finally at ∼0.5 km/s at 5-2 Mm. If we assume that
  the power reduction is actually caused by the rising magnetic flux,
  the rising rate of the order of 1 km/s is well in accordance with
  previous observations and numerical simulations. Moreover, the gradual
  deceleration supports our simulations and theoretical model that the
  rising flux slows down in the uppermost convection zone, just before
  its further emergence into the solar atmosphere.

---------------------------------------------------------
Title: Local-Helioseismology Study of Supergranulation in the
    Polar Region
Authors: Nagashima, K.; Zhao, J.; Kosovichev, A. G.; Sekii, T.
2012ASPC..454...19N    Altcode:
  Hinode/SOT data have been used to study supergranulation in the polar
  region. Although foreshortening generally makes it difficult to observe
  the polar region in detail, to partially overcome the difficulty we
  use the high-resolution Hinode/SOT observations of the polar regions
  during the period of the highest inclination of the solar axis to the
  ecliptic. By time-distance helioseismology we have found 'alignment'
  of the supergranular cells peculiar in the polar region. <P />This
  might be an indication of the giant-cell structure in the polar region.

---------------------------------------------------------
Title: The 3rd Hinode Science Meeting
Authors: Sekii, T.; Watanabe, T.; Sakurai, T.
2012ASPC..454.....S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Helioseismic Investigation of Sub-Photospheric Properties of
    a Coronal Hole
Authors: Zharkov, S.; Harra, L. K.; Sekii, T.
2012ASPC..454...27Z    Altcode:
  We present initial results of our investigation into sub-photospheric
  properties of an equatorial coronal hole obtained via helioseismic
  analysis using Hinode and MDI observational data. As at photospheric
  level coronal holes are characterised by open magnetic field we look
  for seismic signatures of such fields and compare those to the ones
  observed in plages.

---------------------------------------------------------
Title: Effects of Spectral Line Formation Height in Time-Distance
    Helioseismology
Authors: Nagashima, K.; Parchevsky, K. V.; Zhao, J.; Duvall, T. L.,
   Jr.; Kosovichev, A. G.; Sekii, T.
2012ASPC..456...57N    Altcode:
  To understand the effect of the formation-height difference in
  time-distance helioseismology analyses, we consider the wave behavior
  above the surface. We show that by using the numerically-simulated
  wavefields at two different heights this difference may cause
  travel-time shifts due to the non-stationary character of waves excited
  by near-surface acoustic sources. This needs to be taken into account
  in multi-wavelength helioseismology and measurements close to the
  solar limb.

---------------------------------------------------------
Title: Links between photospheric and chromospheric oscillations
Authors: Kosovichev, A. G.; Kitiashvili, I. N.; Mitra-Kraev, U.;
   Sekii, T.
2012decs.confE..97K    Altcode:
  Oscillations excited by turbulent convection play important in the
  dynamics and energetics of the solar atmosphere. Oscillations below the
  acoustic cut-off frequency form photospheric resonant modes trapped
  in the interior but also penetrating into the chromosphere. Above
  the frequency cut-off, the oscillations represent traveling waves
  in the chromosphere that form pseudo-modes due to interference with
  waves coming from the interior. The physics of the chromospheric
  oscillations, their coupling to the photospheric oscillations, and
  their role in the chromospheric dynamics and energetics are not fully
  understood. The observed oscillation properties strongly depend on
  the excitation mechanism, interaction with turbulence and radiation,
  and local structure and dynamics of the chromosphere. Significant
  advances can be made through multi-wavelength observations of
  atmospheric oscillations and realistic numerical radiative hydrodynamics
  simulations. Using Hinode/SOT data we investigate the basic properties
  of solar oscillations observed at two levels in the solar atmosphere,
  in the G-band (formed in the photosphere) and in the CaII H line
  (chromospheric emission). We analyzed the data by calculating the
  individual power spectra as well as the cross-spectral properties,
  i.e., coherence and phase shift. The observational properties are
  compared with theoretical models and numerical simulations. The
  results reveal significant frequency shifts between the CaII H and
  G-band spectra, in particular above the acoustic cutoff frequency for
  pseudo-modes. The cross-spectrum phase shows peaks associated with
  the acoustic oscillation (p-mode) lines, and begins to increase with
  frequency around the acoustic cut-off. However, we find no phase shift
  for the (surface gravity wave) f-mode. The observed properties for
  the p-modes are qualitatively reproduced in a model that includes a
  correlated background due to radiative effects. Our results show that
  multi-wavelength observations of solar oscillations, in combination
  with radiative hydrodynamics modeling, help to understand the coupling
  between photospheric and chromospheric oscillations.

---------------------------------------------------------
Title: Measuring Acoustic Travel Times in Higher-Latitude Regions
    of the Sun using Hinode and SDO Data
Authors: Nagashima, K.; Duvall, T.; Zhao, J.; Kosovichev, A. G.;
   Parchevsky, K.; Sekii, T.
2011AGUFMSH51B2016N    Altcode:
  The interior structure and dynamics of the Sun can be probed by
  measuring and inverting travel times of acoustic waves, widely
  known as time-distance helioseismology. Recent high-resolution
  observations of solar oscillations with Hinode/SOT and SDO/HMI
  provide us with an opportunity to investigate the flow dynamics in
  higher-latitude regions of the Sun. Of particular interest is the
  meridional circulation flow, which is crucial for understanding the
  solar dynamo mechanism and predicting the solar activity cycles. We
  investigate systematic uncertainties of the travel times due to
  the center-to-limb variations, which may significantly affect the
  helioseismic inferences of the meridional flows. We present the results
  of analysis of the cross-correlations in the Doppler velocity, line
  core and intensity observations, and the corresponding travel-time fits
  for various positions on the solar disk. We discuss the origin of the
  center-to-limb variations, including the foreshortening effect, the
  difference in the line formation height, and other effects. For better
  understanding of the relative role of these effects we use 3D numerical
  simulations of solar oscillations in a realistic model of the Sun.

---------------------------------------------------------
Title: Global Helioseismology
Authors: Sekii, Takashi
2011sdmi.confE..12S    Altcode:
  Global helioseismology has been extremely successful in probing the
  solar interior. Unlike local helioseismology, which was more recently
  developed, global helioseismology relies on precise determination of
  eigenfrequencies and their inversions, which renders the global approach
  suited for measuring long-term averages of symmetric structures in the
  sun. Strengths and limitations of global helioseismology are discussed,
  as well as its main results and their impacts on our understanding of
  the sun.

---------------------------------------------------------
Title: Multi-wavelength time-distance helioseismology analyses
Authors: Nagashima, Kaori; Zhao, Junwei; Duvall, Thomas, Jr.;
   Kosovichev, Alexander G.; Parchevsky, Konstantin; Sekii, Takashi
2011sdmi.confE..37N    Altcode:
  Travel times of the acoustic waves in the Sun tell us the structure
  and the dynamics of the Sun. This information have been used to probe
  the solar interior. If we exploit multi-layer observation datasets,
  however, it will provide us with means to study the wave propagation
  between the layers as well (Nagashima et al. 2009). In this study, using
  multi-wavelength datasets obtained by Hinode/SOT, SDO/HMI, and SDO/AIA
  we calculate the cross-correlation function of the wavefield and carry
  out time-distance helioseismology analyses. Our preliminary results show
  that when we cross-correlate the wavefields of two different layers
  the cross-correlation functions between these layers are different
  from the cross-correlation functions of both single layers, and this
  provides us with an insight of wave propagation properties. We also
  use numerical simulations of solar oscillations to help interpret our
  observational results.

---------------------------------------------------------
Title: The SOLAR-C mission: current status
Authors: Shimizu, Toshifumi; Tsuneta, Saku; Hara, Hirohisa; Ichimoto,
   Kiyoshi; Kusano, Kanya; Sakao, Taro; Sekii, Takashi; Suematsu,
   Yoshinori; Watanabe, Tetsuya
2011SPIE.8148E..0BS    Altcode: 2011SPIE.8148E..10S
  Two mission concepts (plan A: out-of-ecliptic mission and plan B:
  high resolution spectroscopic mission) have been studied for the next
  Japanese-led solar mission Solar-C, which will follow the scientific
  success of the Hinode mission. The both mission concepts are concluded
  as equally important and attractive for the promotion of space solar
  physics. In the meantime we also had to make efforts for prioritizing
  the two options, in order to proceed to next stage of requesting the
  launch of Solar-C mission at the earliest opportunity. This paper
  briefly describes the two mission concepts and the current status
  on our efforts for prioritizing the two options. More details are
  also described for the plan B option as the first-priority Solar-C
  mission. The latest report from the Solar-C mission concept studies
  was documented as "Interim Report on the Solar-C Mission Concept."

---------------------------------------------------------
Title: Detection of Supergranulation Alignment in Polar Regions of
    the Sun by Helioseismology
Authors: Nagashima, Kaori; Zhao, Junwei; Kosovichev, Alexander G.;
   Sekii, Takashi
2011ApJ...726L..17N    Altcode: 2010arXiv1011.1025N
  We report on a new phenomenon of "alignment" of supergranulation cells
  in the polar regions of the Sun. Recent high-resolution data sets
  obtained by the Solar Optical Telescope on board the Hinode satellite
  enabled us to investigate supergranular structures in high-latitude
  regions of the Sun. We have carried out a local helioseismology
  time-distance analysis of the data and detected acoustic travel-time
  variations due to the supergranular flows. The supergranulation cells
  in both the north and south polar regions show systematic alignment
  patterns in the north-south direction. The south-pole data sets obtained
  in a month-long Hinode campaign indicate that the supergranulation
  alignment property may be quite common in the polar regions. We also
  discuss the latitudinal dependence of the supergranulation cell sizes;
  the data show that the east-west cell size decreases toward higher
  latitudes.

---------------------------------------------------------
Title: Helioseismology Study of Subsurface Dynamics in the Polar
    Regions of the Sun
Authors: Nagashima, K.; Zhao, J.; Kosovichev, A. G.; Sekii, T.
2010AGUFM.S32A..03N    Altcode:
  We report on our time-distance helioseismology study of the
  subsurface dynamics in the polar regions of the Sun. It is generally
  difficult to observe the polar regions in details because of severe
  foreshortening. The high-resolution data obtained by Solar Optical
  Telescope (SOT) onboard the Hinode satellite, however, enabled
  us to investigate dynamics in the regions with up to 80 degrees
  in latitude. The measurements are obtained by calculating the
  cross-covariance function of the random solar oscillations observed
  as fluctuations of intensity of the Ca II H line, and by fitting a
  Gabor-wavelet function for estimating the phase and group travel times
  of solar acoustic waves. We obtain the maps of subsurface velocity field
  by inverting the differences of the phase travel times, calculated for
  the cross-correlations with positive and negative lag times, using a
  ray-path approximation. Among the subsurface dynamical processes in the
  polar region, we focus on supergranulation in this study. Supergranules
  are thought to be one of convective cells in the convective envelope
  of the Sun. Typical temporal and spatial scales of supergranular cells
  are 1 day and 30 Mm, respectively. The supergranulation is considered
  to play important roles in the magnetic flux transport and formation
  of the magnetic network. However, we still do not have sufficient
  knowledge of their origin and properties. In our study, we have observed
  a curious alignment of the supergranular cells in the polar regions
  approximately in the North-South direction. The alignment was seen
  in both northern and southern polar regions. We discuss properties
  and temporal evolution of the supergranular structures in the region,
  as well as the possibilities of measuring the differential rotation
  and meridional flows in the polar regions, which are critical for the
  solar dynamo theories.

---------------------------------------------------------
Title: Supergranulation in the Polar Regions Observed by Hinode/SOT
Authors: Nagashima, Kaori; Zhao, J.; Kosovichev, A.; Sekii, T.
2010AAS...21640002N    Altcode: 2010BAAS...41..855N
  We report on our investigation of the supergranular structure in the
  polar regions of the Sun by local helioseismology. Supergranules
  represent large-scale convective cells: the horizontal spatial
  scale is about 30 Mm and the lifetime is about 1 day. They play
  important role in the magnetic flux transport and formation of the
  magnetic network. Recent helioseismological studies have found
  that the depth of the cells is much smaller than the horizontal
  scale, and that the supergranulation pattern exhibits a wave-like
  behavior. However, we still do not have sufficient knowledge of
  the origin and properties of the supergranulation. In this work, we
  have carried out a new time-distance helioseismology analysis using
  high-resolution datasets of the polar regions of the Sun obtained
  by the Solar Optical Telescope (SOT) onboard the Hinode satellite
  during the periods of the high inclination of the solar axis to the
  ecliptic. Because of the foreshortening such measurements are not
  currently possible with any other helioseismology instrument. We have
  measured the travel-time shifts of acoustic waves traveling to various
  depth below the photosphere, and obtain the subphotospheric horizontal
  flow maps by inversion. We have detected the supergranular cells in
  the polar regions and studied their properties. For comparison we did a
  similar analysis for low-latitude regions at the East limb of the Sun,
  and at the disk center. Comparing with the cells in the lower-latitude
  regions, we have observed a curious alignment of the cells in the polar
  regions, approximately in the North-South direction. This `alignment'
  has been found in both the North and the South polar regions. In
  the presentation, we discuss the alignment phenomenon as well as the
  physical properties of the supergranular cells in the polar regions.

---------------------------------------------------------
Title: The quest for the solar g modes
Authors: Appourchaux, T.; Belkacem, K.; Broomhall, A. -M.; Chaplin,
   W. J.; Gough, D. O.; Houdek, G.; Provost, J.; Baudin, F.; Boumier,
   P.; Elsworth, Y.; García, R. A.; Andersen, B. N.; Finsterle, W.;
   Fröhlich, C.; Gabriel, A.; Grec, G.; Jiménez, A.; Kosovichev, A.;
   Sekii, T.; Toutain, T.; Turck-Chièze, S.
2010A&ARv..18..197A    Altcode: 2010A&ARv.tmp....1A; 2009arXiv0910.0848A
  Solar gravity modes (or g modes)—oscillations of the solar interior
  on which buoyancy acts as the restoring force—have the potential
  to provide unprecedented inference on the structure and dynamics of
  the solar core, inference that is not possible with the well-observed
  acoustic modes (or p modes). The relative high amplitude of the g-mode
  eigenfunctions in the core and the evanesence of the modes in the
  convection zone make the modes particularly sensitive to the physical
  and dynamical conditions in the core. Owing to the existence of the
  convection zone, the g modes have very low amplitudes at photospheric
  levels, which makes the modes extremely hard to detect. In this article,
  we review the current state of play regarding attempts to detect g
  modes. We review the theory of g modes, including theoretical estimation
  of the g-mode frequencies, amplitudes and damping rates. Then we go
  on to discuss the techniques that have been used to try to detect g
  modes. We review results in the literature, and finish by looking to
  the future, and the potential advances that can be made—from both
  data and data-analysis perspectives—to give unambiguous detections
  of individual g modes. The review ends by concluding that, at the time
  of writing, there is indeed a consensus amongst the authors that there
  is currently no undisputed detection of solar g modes.

---------------------------------------------------------
Title: High-Resolution Helioseismic Imaging of Subsurface Structures
    and Flows of a Solar Active Region Observed by Hinode
Authors: Zhao, Junwei; Kosovichev, Alexander G.; Sekii, Takashi
2010ApJ...708..304Z    Altcode: 2009arXiv0911.1161Z
  We analyze a solar active region observed by the Hinode Ca II H line
  using the time-distance helioseismology technique, and infer wave-speed
  perturbation structures and flow fields beneath the active region
  with a high spatial resolution. The general subsurface wave-speed
  structure is similar to the previous results obtained from Solar and
  Heliospheric Observatory/Michelson Doppler Imager observations. The
  general subsurface flow structure is also similar, and the downward
  flows beneath the sunspot and the mass circulations around the sunspot
  are clearly resolved. Below the sunspot, some organized divergent flow
  cells are observed, and these structures may indicate the existence of
  mesoscale convective motions. Near the light bridge inside the sunspot,
  hotter plasma is found beneath, and flows divergent from this area
  are observed. The Hinode data also allow us to investigate potential
  uncertainties caused by the use of phase-speed filter for short travel
  distances. Comparing the measurements with and without the phase-speed
  filtering, we find out that inside the sunspot, mean acoustic travel
  times are in basic agreement, but the values are underestimated by a
  factor of 20%-40% inside the sunspot umbra for measurements with the
  filtering. The initial acoustic tomography results from Hinode show
  a great potential of using high-resolution observations for probing
  the internal structure and dynamics of sunspots.

---------------------------------------------------------
Title: Recent Progress and Future Directions for Helioseismology
Authors: Kosovichev, A.; Zhao, J.; Sekii, T.; Nagashima, K.;
   Mitra-Kraev, U.
2009ASPC..415..399K    Altcode:
  Hinode/SOT observations provide unique data for high-resolution
  helioseismology. These data have allowed us for the first
  time to resolve the subsurface convective boundary layer, obtain
  high-resolution images of structures and mass flows beneath a sunspot,
  detect flare-generated MHD waves in the sunspot umbra, carry out
  multi-wavelength studies of solar oscillations, and obtain unique
  helioseismic data for probing the subsurface dynamics in near-polar
  regions. Future directions in helioseismology will be focused on
  understanding the mechanism of solar dynamo, diagnostics of emerging
  magnetic flux, formation and evolution of sunspot regions and their
  flaring activity. Of particular interest are investigations of solar
  convection dynamics, differential rotation and meridional flows
  in the near polar regions. These tasks require development of new
  helioseismology methods for probing conditions in strong magnetic
  field regions and improving temporal and spatial resolutions. The new
  developments in helioseismology will be supported by realistic MHD
  simulations and based on massive data analysis from Hinode and Solar
  Dynamics Observatory.

---------------------------------------------------------
Title: Travel-Time Analyses of an Emerging-Flux Region
Authors: Nagashima, K.; Sekii, T.; Kosovichev, A. G.; Zhao, J.;
   Tarbell, T. D.
2009ASPC..415..417N    Altcode:
  Travel-time analyses of a newly-formed plage region are presented. The
  dataset has been obtained from the 12-hr Hinode observation of an
  emerging-flux region (to be NOAA AR 10975) close to the disc center
  on 23 November 2007. The SOT provides data in Ca II H line and in
  Fe I 557.6nm line; we use both chromospheric intensity oscillation
  data and photospheric Dopplergrams for travel-time measurement by
  a cross-correlation method. In the plage region, we have detected
  a travel-time anomaly in the chromospheric data, but not in the
  photospheric data. This can be interpreted as a signature of downflows
  in the chromosphere. This result illustrates how time-distance
  techniques can be used to study chromospheric flows.

---------------------------------------------------------
Title: Hinode/SOT Helioseismic Observations
Authors: Sekii, T.
2009ASPC..415..405S    Altcode:
  Helioseismic observations by the Hinode Solar Optical Telescope
  (SOT) are reviewed. The benefit of the SOT high-resolution
  capability for local helioseismology has already been demonstrated
  in mapping subsurface flows and {revealing the fine structure of
  umbral flashes}. The phase relations between the photospheric and
  the chromospheric oscillations in the sub-critical frequency range
  are also discussed, as are possible future directions of the SOT
  helioseismology programme.

---------------------------------------------------------
Title: New Results of High-Resolution Helioseismology from Hinode
Authors: Kosovichev, A.; Zhao, J.; Sekii, T.; Nagashima, K.;
   Mitra-Kraev, U.
2009ASPC..416...41K    Altcode:
  The Solar Optical Telescope of Hinode provides unique multi-wavelength
  high-resolution data for local helioseismic diagnostics of the
  sub-surface structure and dynamics of the Sun. The helioseismology data
  from Hinode have allowed us for the first time to observe oscillations
  of very high angular degree and high frequencies, and substantially
  improve the spatial resolution of time-distance helioseismology in
  near-surface layers of the Sun, compared to the previous SOHO/MDI
  data. The Hinode data have also provided important insight on the
  nature of sunspot oscillations, and the correlated component of
  stochastic excitation. Initial attempts have been made to investigate
  the dynamics of the polar regions, critical for dynamo modeling, but
  previously unaccessible for helioseismology. In addition, a new type
  of flare-excited MHD oscillations was detected from Hinode observations
  of the solar flare of December 13, 2006.

---------------------------------------------------------
Title: Subsurface Structures and Flow Fields of an Active Region
    Observed by Hinode
Authors: Zhao, J.; Kosovichev, A. G.; Sekii, T.
2009ASPC..415..411Z    Altcode:
  We analyze a solar active region observed by Hinode Ca II H line using
  the time-distance helioseismology technique, and derive the subsurface
  structure and flow fields of this active region. The basic subsurface
  wave speed structure is essentially the same as the previous results
  obtained from MDI observations. The subsurface flow structure is
  also similar to the previous results, but the downward flows are more
  resolved. Additionally, vertical mass circulations outside the sunspot
  are more clearly detected, although no mass conservation constraints
  are imposed in the inversion procedure. Near a light bridge area,
  hotter plasma is found beneath, and flows divergent from this area
  are observed. Inside the sunspot umbra and penumbra, some organized
  divergent flow cells of an intermediate size between granulation and
  supergranulation are also observed. These initial results demonstrate
  the potential and importance of high-resolution helioseismology of
  sunspots.

---------------------------------------------------------
Title: Subsurface Flows in Solar Active Regions and Polar Areas from
    Hinode Observations
Authors: Zhao, Junwei; Kosovichev, A. G.; Sekii, T.
2009SPD....40.0706Z    Altcode:
  High-resolution observations of Ca II H line intensity made by Hinode
  have provided us an opportunity to study subsurface flow fields of
  solar active regions with an unprecedented high spatial resolution,
  and a possibility to study subsurface meridional flows in the solar
  polar areas. For a large active region, we have found a strong
  downdraft below the sunspot, a mass circulation around the spot, and
  an evidence of magnetoconvection beneath the strong field area. For
  the polar regions, we have been able to derive a poleward meridional
  flow of an order of 5 m/s for the first time using the time-distance
  helioseismology technique.

---------------------------------------------------------
Title: Helioseismic Signature of Chromospheric Downflows in Acoustic
    Travel-Time Measurements From Hinode
Authors: Nagashima, Kaori; Sekii, Takashi; Kosovichev, Alexander G.;
   Zhao, Junwei; Tarbell, Theodore D.
2009ApJ...694L.115N    Altcode: 2009arXiv0903.1323N
  We report on a signature of chromospheric downflows in two emerging
  flux regions detected by time-distance helioseismology analysis. We
  use both chromospheric intensity oscillation data in the Ca II H line
  and photospheric Dopplergrams in the Fe I 557.6 nm line obtained
  by Hinode/SOT for our analyses. By cross-correlating the Ca II
  oscillation signals, we have detected a travel-time anomaly in the
  plage regions; outward travel times are shorter than inward travel
  times by 0.5-1 minute. However, such an anomaly is absent in the Fe
  I data. These results can be interpreted as evidence of downflows in
  the lower chromosphere. The downflow speed is estimated to be below
  10 km s<SUP>-1</SUP>. This result demonstrates a new possibility of
  studying chromospheric flows by time-distance analysis.

---------------------------------------------------------
Title: Solar Dynamo and Magnetic Self-Organization
Authors: Kosovichev, A. G.; Arlt, R.; Bonanno, A.; Brandenburg,
   A.; Brun, A. S.; Busse, F.; Dikpati, M.; Hill, F.; Gilman, P. A.;
   Nordlund, A.; Ruediger, G.; Stein, R. F.; Sekii, T.; Stenflo, J. O.;
   Ulrich, R. K.; Zhao, J.
2009astro2010S.160K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: High-Resolution Helioseismology from Hinode
Authors: Kosovichev, A. G.; Zhao, J.; Sekii, T.; Nagashima, K.;
   Mitra-Kraev, U.
2008AGUFMSH41B1627K    Altcode:
  The Solar Optical Telescope (SOT) on the Hinode space mission provides
  unique multi-wavelength high-resolution data for local helioseismic
  diagnostics of the sub-photospheric structure and dynamics of the
  Sun. The helioseismology data from Hinode have allowed us for the
  first time to observe oscillations of very high angular degree and
  high frequencies. The Hinde data provide a potential for substantial
  improvement of the spatial resolution of time-distance helioseismology
  in near-surface layers of the Sun, compared to the previous SOHO/MDI
  data. The Hinode data have also provided important insight in the nature
  of sunspot oscillations. Simultaneous observations of solar oscillations
  in two different spectral interval have allowed us to investigate the
  mode physics and the correlated component of stochastic excitation. In
  addition, a new type of flare-excited MHD oscillations was detected
  from Hinode observations of the solar flare of December 13, 2006.

---------------------------------------------------------
Title: Helioseismic Measurement of Subsurface Flows at Solar High
    Latitude
Authors: Zhao, J.; Kosovichev, A. G.; Sekii, T.
2008AGUFMSH44A..03Z    Altcode:
  The solar polar magnetic field is of great interest as it is where
  solar magnetic field reversal starts. Surface and subsurface plasma
  flows are very important in understanding the field reversal because
  magnetic field flux is transported to solar high latitude from lower
  latitude according to flux transport theory. Local helioseismology
  has been able to derive subsurface flow fields, rotation rates,
  and meridional flows up to 30 Mm in depth. The results obtained by
  time-distance helioseismology during Solar Cycle 23 from SOHO/MDI have
  also revealed significant changes of the speed and the longitudinal
  structure of the flows. We used these measurements to compare with the
  magnetic flux transport determined from the magnetic field synoptic
  data. Furthermore, by use of MDI dynamic campaign observations and
  a recent high resolution observation of solar South Pole by Hinode,
  we explore the possibility to detect subsurface flow fields in solar
  high latitude.

---------------------------------------------------------
Title: AsteroFLAG — from the Sun to the stars
Authors: Chaplin, W. J.; Appourchaux, T.; Arentoft, T.; Ballot, J.;
   Baudin, F.; Bazot, M.; Bedding, T. R.; Christensen-Dalsgaard, J.;
   Creevey, O. L.; Duez, V.; Elsworth, Y.; Fletcher, S. T.; García,
   R. A.; Gough, D. O.; Jiménez, A.; Jiménez-Reyes, S. J.; Houdek, G.;
   Kjeldsen, H.; Lazrek, M.; Leibacher, J. W.; Monteiro, M. J. P. F. G.;
   Neiner, C.; New, R.; Régulo, C.; Salabert, D.; Samadi, R.; Sekii,
   T.; Sousa, S. G.; Toutain, T.; Turck-Chièze, S.
2008JPhCS.118a2048C    Altcode:
  We stand on the threshold of a critical expansion of asteroseismology
  of Sun-like stars, the study of stellar interiors by observation
  and analysis of their global acoustic modes of oscillation. The
  Sun-like oscillations give a very rich spectrum allowing the internal
  structure and dynamics to be probed down into the stellar cores to
  very high precision. Asteroseismic observations of many stars will
  allow multiple-point tests of crucial aspects of stellar evolution
  and dynamo theory. The aims of the asteroFLAG collaboration are to
  help the community to refine existing, and to develop new, methods
  for analysis of the asteroseismic data on the Sun-like oscillators.

---------------------------------------------------------
Title: Loop Morphology and Flows and their Relation to the Magnetic
    Field
Authors: Teriaca, L.; Wiegelmann, T.; Lagg, A.; Solanki, S. K.; Curdt,
   W.; Sekii, T.
2008ASPC..397..196T    Altcode:
  In November 2006 we obtained several rasters of a large sunspot
  and its trailing region using the SUMER spectrometer on SOHO. The
  observations consist of spectroheliograms in the continuum around
  142 nm and in several spectral lines formed between 80000 K and
  0.6 MK, covering the temperature range from the chromosphere to
  the lower corona. The observed profiles provide LOS velocity and
  Doppler width maps. TRACE images in the EUV passbands and in the 160
  nm continuum provide a clear picture of the coronal loops and the
  chromosphere near their footpoints. The same target was also observed
  by all the instruments aboard Hinode and, in particular, by the SOT
  spectro-polarimeter measuring the photospheric magnetic vector. We
  combined SOT and MDI data (covering a larger FOV) to infer the coronal
  magnetic field of the active region by a nonlinear force-free field
  extrapolation. The observed radiance and velocity patterns at the
  various heights/temperatures throughout the solar atmosphere are
  compared with the field topology.

---------------------------------------------------------
Title: AsteroFLAG: First results from hare-and-hounds Exercise #1
Authors: Chaplin, W. J.; Appourchaux, T.; Arentoft, T.; Ballot, J.;
   Christensen-Dalsgaard, J.; Creevey, O. L.; Elsworth, Y.; Fletcher,
   S. T.; García, R. A.; Houdek, G.; Jiménez-Reyes, S. J.; Kjeldsen,
   H.; New, R.; Régulo, C.; Salabert, D.; Sekii, T.; Sousa, S. G.;
   Toutain, T.; rest of asteroFLAG Group
2008AN....329..549C    Altcode: 2008arXiv0803.4143C
  We report on initial results from the first phase of Exercise #1 of the
  asteroFLAG hare and hounds. The asteroFLAG group is helping to prepare
  for the asteroseismology component of NASA's Kepler mission, and the
  first phase of Exercise #1 is concerned with testing extraction of
  estimates of the large and small frequency spacings of the low-degree p
  modes from Kepler-like artificial data. These seismic frequency spacings
  will provide key input for complementing the exoplanet search data.

---------------------------------------------------------
Title: Initial Helioseismology Results from Hinode
Authors: Kosovichev, A.; Zhao, J.; Sekii, T.; Nagashima, K.
2008AGUSMSP21A..01K    Altcode:
  Solar Optical Telescope of Hinode provides unique multi-wavelength
  high-resolution data for local helioseismic diagnostics of the
  sub-surface structure and dynamics of the Sun. The helioseismology data
  from Hinode have allowed us for the first time to observe oscillations
  of very high angular degree and high frequencies, and substantially
  improve the spatial resolution of time-distance helioseismology in
  near-surface layers of the Sun, compared to the previous SOHO/MDI
  data. The Hinode data have also provided important insight in the
  nature of sunspot oscillations. Initial attempts have been made to
  investigate the dynamics of the polar regions, previously unaccessible
  for helioseismology. We present the first results and discuss the
  potential and perspective of the Hinode helioseismology program.

---------------------------------------------------------
Title: First Detection of MHD Oscillations Excited by Solar Flare
    in Sunspot Umbra
Authors: Kosovichev, A.; Sekii, T.
2008AGUSMSP21B..07K    Altcode:
  We report on detection of a new type of flare-excited oscillations
  from Hinode observations of the solar flare of December 13, 2006. The
  oscillations observed in Ca II H images appeared in the sunspot
  umbra immediately after the impulsive phase of the flare. They had
  the amplitude 2-4 times larger than the pre-flare oscillations in
  the umbra. Also, their frequency seemed to be higher. There is an
  evidence that during the first 30-40 min the oscillations represent
  waves traveling through the umbra in the direction away from the flare
  ribbon with a speed of 50-100 km/s. Then, the oscillation become more
  irregular with some occasional wave packets. The lifetime of these
  oscillations is probable about 8 hours. The estimated speed indicates
  that the waves are of an MHD type, and if their speed is of the order
  of magnitude of the Alfven speed then they should propagate rather low
  in the sunspot chromosphere. Sunspot oscillations have been studied
  intensively for many years but the Hinode observations are the first
  that show enhanced oscillations in the umbra, associated with a solar
  flare. Further investigations of these oscillations are of great
  interest for understanding the processes in solar flares and sunspots.

---------------------------------------------------------
Title: Properties of high-degree oscillation modes of the Sun observed
    with Hinode/SOT
Authors: Mitra-Kraev, U.; Kosovichev, A. G.; Sekii, T.
2008A&A...481L...1M    Altcode: 2007arXiv0711.2210M
  Aims:With the Solar Optical Telescope on Hinode, we investigate
  the basic properties of high-degree solar oscillations observed at
  two levels in the solar atmosphere, in the G-band (formed in the
  photosphere) and in the Ca II H line (chromospheric emission). <BR
  />Methods: We analyzed the data by calculating the individual power
  spectra as well as the cross-spectral properties, i.e., coherence and
  phase shift. The observational properties are compared with a simple
  theoretical model, which includes the effects of correlated noise. <BR
  />Results: The results reveal significant frequency shifts between the
  Ca II H and G-band spectra, in particular above the acoustic cut-off
  frequency for pseudo-modes. The cross-spectrum phase shows peaks
  associated with the acoustic oscillation (p-mode) lines, and begins to
  increase with frequency around the acoustic cut-off. However, we find
  no phase shift for the (surface gravity wave) f-mode. The observed
  properties for the p-modes are qualitatively reproduced in a simple
  model with a correlated background if the correlated noise level in
  the Ca II H data is higher than in the G-band data. These results
  suggest that multi-wavelength observations of solar oscillations,
  in combination with the traditional intensity-velocity observations,
  may help to determine the level of the correlated background noise
  and to determine the type of wave excitation sources on the Sun.

---------------------------------------------------------
Title: Development of Iodine Cells for Subaru HDS and Okayama
    HIDES. III. An Improvement on the Radial-Velocity Measurement
    Technique
Authors: Kambe, Eiji; Ando, Hiroyasu; Sato, Bun'ei; Izumiura, Hideyuki;
   Sekii, Takashi; Paulson, Daine B.; Yanagisawa, Kenshi; Masuda, Seiji;
   Shibahashi, Hiromoto; Hatzes, Artie P.; Martic, Milena; Lebrun,
   Jean-Claude; Mkrtichian, David E.; Kiss, Laszlo L.; Bruntt, Hans;
   O'Toole, Simon J.; Bedding, Timothy R.
2008PASJ...60...45K    Altcode:
  An improvement of the radial-velocity measurement accuracy is crucial
  for the detection of tiny stellar oscillations and exoplanets. Through
  the analysis of week-long extensive observations of solar-type stars
  (Procyon in 2000, 2002, and 2006/2007 and τ Cet in 2002 and 2006/2007),
  we have carefully examined, revised, and finely tuned the widely used
  multiple Gaussian IP fitting method for the spectrograph, HIDES. By
  determining a necessary and sufficient number of free parameters in the
  model as well as introducing an iterative process in the radial-velocity
  analysis, we can reach a precision of below 3ms<SUP>-1</SUP>, which
  is much smaller than the precision of 6ms<SUP>-1</SUP> officially
  announced so far for HIDES. We also make our technique refined for the
  2002 McDonald Procyon data. Even with our revised method, slow radial
  velocity variations with an amplitude of about 10ms<SUP>-1</SUP>
  are left in the Procyon data. We emphasize that it is neither due
  to particular observing instruments nor radial-velocity analysis,
  and thus could be due to stellar origin. The analysis presented
  here makes the foundations of our next scientific analysis of the
  radial-velocity variations of Procyon, which will be presented in our
  forthcoming papers.

---------------------------------------------------------
Title: Hinode SOT observations of plume upflows and cascading
    downflows in quiescent solar prominences
Authors: Berger, T.; Shine, R.; Slater, G.; Tarbell, T.; Title, A.;
   Lites, B.; Tsuneta, S.; Okamoto, T. J.; Ichimoto, K.; Katsukawa, Y.;
   Sekii, T.; Suematsu, Y.; Shimizu, T.
2007AGUFMSH53A1065B    Altcode:
  We present several Hinode SOT filtergram movies of quiescent solar
  prominences that show newly discovered "plume-like" upflows and
  cascading "waterfall-like" downflows that persist for the entire
  multi-hour duration of the observations. The flow speeds are on the
  order of 10 km/sec with typical widths of 400-700 km. Preliminary
  calculations show that if the upflows are buoyancy driven, the
  associated thermal perturbation is on the order of 10,000 K, sufficient
  to explain the dark appearance of the upflows in the interference
  filter passbands. In addition we observe rotational vortices and
  body oscillations within the prominences. These new observations
  challenge current magnetostatic models of solar prominences by showing
  that prominence plasmas are in constant motion, often in directions
  perpendicular to the magnetic field lines proposed by the models. TRACE,
  Hinode/EIS, and Hinode/XRT observations are used to investigate the
  differential topology of the flows across temperature regimes.

---------------------------------------------------------
Title: Initial Observations of Sunspot Oscillations Excited by
    Solar Flare
Authors: Kosovichev, A. G.; Sekii, T.
2007ApJ...670L.147K    Altcode: 2007arXiv0710.1808K
  Observations of a large solar flare on 2006 December 13 using Solar
  Optical Telescope (SOT) on board the Hinode spacecraft revealed
  high-frequency oscillations excited by the flare in the sunspot
  chromosphere. These oscillations are observed in the region of strong
  magnetic field of the sunspot umbra and may provide a new diagnostic
  tool for probing the structure of sunspots and understanding physical
  processes in solar flares.

---------------------------------------------------------
Title: Initial Helioseismic Observations by Hinode/SOT
Authors: Sekii, Takashi; Kosovichev, Alexander G.; Zhao, Junwei;
   Tsuneta, Saku; Shibahashi, Hiromoto; Berger, Thomas E.; Ichimoto,
   Kiyoshi; Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu,
   Toshifumi; Shine, Richard A.; Suematsu, Yoshinori; Tarbell, Theodore
   D.; Title, Alan M.
2007PASJ...59S.637S    Altcode: 2007arXiv0709.1806S
  Results from initial helioseismic observations by the Solar Optical
  Telescope on-board Hinode are reported. It has been demonstrated
  that intensity oscillation data from the Broadband Filter Imager
  can be used for various helioseismic analyses. The k - ω power
  spectra, as well as the corresponding time-distance cross-correlation
  function, which promise high-resolution time-distance analysis below
  the 6-Mm travelling distance, were obtained for G-band and CaII-H
  data. Subsurface supergranular patterns were observed from our first
  time-distance analysis. The results show that the solar oscillation
  spectrum is extended to much higher frequencies and wavenumbers, and
  the time-distance diagram is extended to much shorter travel distances
  and times than were observed before, thus revealing great potential
  for high-resolution helioseismic observations from Hinode.

---------------------------------------------------------
Title: Observations of Sunspot Oscillations in G Band and CaII H
    Line with Solar Optical Telescope on Hinode
Authors: Nagashima, Kaori; Sekii, Takashi; Kosovichev, Alexander G.;
   Shibahashi, Hiromoto; Tsuneta, Saku; Ichimoto, Kiyoshi; Katsukawa,
   Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
   Richard A.; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.
2007PASJ...59S.631N    Altcode: 2007arXiv0709.0569N
  Exploiting high-resolution observations made by the Solar Optical
  Telescope on board Hinode, we investigate the spatial distribution
  of the power spectral density of the oscillatory signal in and around
  the active region NOAA 10935. The G-band data show that in the umbra
  the oscillatory power is suppressed in all frequency ranges. On
  the other hand, in CaII H intensity maps oscillations in the umbra,
  so-called umbral flashes, are clearly seen with the power peaking around
  5.5mHz. The CaII H power distribution shows the enhanced elements with
  the spatial scale of the umbral flashes over most of the umbra, but
  there is a region with suppressed power at the center of the umbra. The
  origin and property of this node-like feature remain unexplained.

---------------------------------------------------------
Title: Calibration of SOT Dopplergrams
Authors: Katsukawa, Y.; Ichimoto, K.; Sekii, T.; Suematsu, Y.; Tsuneta,
   S.; Shine, R. A.; Tarbell, T. D.
2007ASPC..369...43K    Altcode:
  Narrow-band Filter Imager on SOT provides Dopplergrams (DGs) which
  are images of Doppler (line- of-sight) velocities. Observations with
  DGs are critically important in studies of photospheric dynamics and
  helioseismology. The primary photospheric line used for DGs is Fe I 5576
  Å which is a line insensitive to Zeeman effect. We made a calibration
  function for the 5576 Å DGs to get actual Doppler velocities from
  velocity indexes using an atlas spectrum and simulated transmission
  profiles for the tunable filter (TF) on SOT. Using data sets taken
  in the natural sun-light test, we quantitatively evaluated accuracy
  of the DGs by comparing the rotational speed of the Sun measured
  with DGs with the expected one. There was a little systematic error
  in the velocity obtained by SOT, but the error was less than 20 %
  of the predicted velocities.

---------------------------------------------------------
Title: Distribution of MDI p-mode power correlation coefficients
Authors: Y Chang, H.; Sekii, T.
2006ESASP.624E.132Y    Altcode: 2006soho...18E.132Y
  No abstract at ADS

---------------------------------------------------------
Title: The internal structure of the Sun inferred from g modes and
    low-frequency p modes
Authors: Elsworth, Y. P.; Baudin, F.; Chaplin, W; Andersen, B;
   Appourchaux, T.; Boumier, P.; Broomhall, A. -M.; Corbard, T.;
   Finsterle, W.; Fröhlich, C.; Gabriel, A.; García, R. A.; Gough,
   D. O.; Grec, G.; Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii,
   T.; Toutain, T.; Turck-Chièze, S.
2006ESASP.624E..22E    Altcode: 2006soho...18E..22E
  The Phoebus group is an international collaboration of
  helioseismologists, its aim being to detect low-frequency solar g
  modes. Here, we report on recent work, including the development and
  application of new techniques based on the detection of coincidences
  in contemporaneous datasets and the asymptotic properties of the g-mode
  frequencies. The length of the time series available to the community is
  now more than ten years, and this has reduced significantly the upper
  detection limits on the g-mode amplitudes. Furthermore, low-degree p
  modes can now be detected clearly at frequencies below 1000 μHz.

---------------------------------------------------------
Title: Rotation inversions of artificial solarFLAG Sun-as-a-star data
Authors: Chaplin, W. J.; Sekii, T.; Appourchaux, T.; Baudin, F.;
   Boumier, P.; Corbard, T.; Elsworth, Y.; Fletcher, S. T.; Garcia,
   R. A.; Jiménez-Reyes, S. J.; Lazrek, M.; New, R.; Salabert, D.;
   Toutain, T.; Wachter, R.
2006ESASP.624E..82C    Altcode: 2006soho...18E..82C
  No abstract at ADS

---------------------------------------------------------
Title: Recent Progresses on g-Mode Search
Authors: Appourchaux, T.; Andersen, B.; Baudin, F.; Boumier, P.;
   Broomhall, A. -M.; Chaplin, W.; Corbard, T.; Elsworth, Y.; Finsterle,
   W.; Fröhlich, C.; Gabriel, A.; Garcia, R.; Gough, D. O.; Grec, G.;
   Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii, T.; Toutain, T.;
   Turck-Chièze, S.
2006ESASP.617E...2A    Altcode: 2006soho...17E...2A
  No abstract at ADS

---------------------------------------------------------
Title: Seismology of Solar Internal Rotation
Authors: Sekii, Takashi
2005HiA....13..424S    Altcode:
  Helioseismologists have been highly successful in revealing how
  the solar interior differentially rotates through observations of
  rotationally split eigen p modes of the sun. What we currently know
  about the internal rotation of the sun including how it varies over
  the solar cycle is reviewed. Seismic inference of internal rotation
  based on low-degree modes is also discussed.

---------------------------------------------------------
Title: Annual Report of the National Astronomical Observatory of
    Japan, Volume 7 Fiscal 2004
Authors: Tanikawa, Kiyotaka; Imanishi, Masatoshi; Ueda, Akitoshi; Oe,
   Masafumi; Sekii, Takashi; Sôma, Mitsuru; Miyoshi, Makoto; Yamashita,
   Yoshiko
2005ARAOJ...7.....T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Annual Report of the National Astronomical Observatory of
    Japan, Volume 6 Fiscal 2003
Authors: Tanikawa, Kiyotaka; Imanishi, Masatoshi; Ueda, Akitoshi; Oe,
   Masashi; Sekii, Takashi; Sôma, Mitsuru; Miyoshi, Makoto; Yamashita,
   Yoshiko
2005naoj.book.....T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the detectability of a rotation-rate gradient in the
    solar core
Authors: Chaplin, W. J.; Sekii, T.; Elsworth, Y.; Gough, D. O.
2004MNRAS.355..535C    Altcode: 2004MNRAS.tmp..451C
  We consider the problem of uncovering a possible gradient of rotation
  in the solar core using seismic frequency splittings of low-degree
  p-modes. The data are presumed to come from full-disc observations of
  the Sun. In particular, we formulate an approach for determining the
  diagnostic potential of a low-l splitting set to uncover, by inversion,
  a difference in rotation between two target radii: one deep in the core,
  the other in the mid-regions of the radiative zone. Our formulation
  assumes the underlying rotation rate to be flat in the outer part
  of the zone, but to vary linearly in the core (with the breakpoint
  in behaviour located between the two target radii). Artificial data
  are used to test the formulation, and to investigate the relative
  importance at low l of deeply penetrating, high-order modes and
  relatively shallow, low-order modes. Our results suggest that in
  order to detect a significant difference between the rotation at r=
  0.1R and 0.35R- with the input splitting data coming from a 10-yr
  set of high-quality observations - that difference would need to be
  a significant fraction of the rotation rate itself.

---------------------------------------------------------
Title: SOT Local-Helioseismology Programme
Authors: Sekii, T.
2004ASPC..325...87S    Altcode:
  Local helioseismology is proving to be a powerful tool in revealing
  small-scale flow and inhomogeneity in subsurface layers. The Solar
  Optical Telescope (SOT) onboard SolarB is capable of producing
  high-resolution Doppler-grams that can be used for this new method
  of helioseismology. It is reviewed and discussed what can be learned
  from SOT local helioseismology, as well as what should be done for a
  successful programme.

---------------------------------------------------------
Title: The Solar-B Mission and the Forefront of Solar Physics
Authors: Sakurai, T.; Sekii, T.
2004ASPC..325.....S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: An Alternative Interpretation of the Double-Ridge Structure
    in the - Frequency Time-Distance Autocorrelation Function?
Authors: Sekii, T.; Shibahashi, H.; Jefferies, S. M.
2004ESASP.559..619S    Altcode: 2004soho...14..619S
  No abstract at ADS

---------------------------------------------------------
Title: Helioseismic measurement of solar rotation
Authors: Sekii, Takashi
2004ceme.symp...25S    Altcode:
  Helioseismology has been successful in investigating the otherwise
  invisible solar interior, and one of its greatest success is in
  revealing how the interior of the sun rotates. It is briefly reviewed
  how this is done, what we have learnt, and what they imply.

---------------------------------------------------------
Title: Annual Report of the National Astronomical Observatory of
    Japan, Volume 5 Fiscal 2002
Authors: Tanikawa, Kiyotaka; Imanishi, Masatoshi; Miyoshi, Makoto;
   Muramatsu, Toshiya; Sekii, Takashi; Sôma, Mitsuru; Ueda, Akitoshi;
   Yamashita, Yoshiko; Yasuda, Naoki
2004naoj.book.....T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Autocorrelation analysis of MDI high-frequency data
Authors: Sekii, T.; Shibahashi, H.; Kosovichev, A. G.
2003ESASP.517..385S    Altcode: 2003soho...12..385S
  We have analyzed MDI data using time-distance autocorrelation function,
  in a high-frequency range above the acoustic cut-off frequency of the
  solar atmosphere. The MDI velocity, intensity and line-depth signals
  were looked at. The wave reflection rate at the photosphere has been
  found to be around 10 per cent for l = 125 and ν = 6.75mHz. The result
  is compared with a previous measurement.

---------------------------------------------------------
Title: On averaged time-distance autocorrelation diagrams
Authors: Sekii, T.; Shibahashi, H.
2003ESASP.517..389S    Altcode: 2003soho...12..389S
  To calculate time-distance autocorrelation for local-helioseismic
  analyses, the correlation function is often put in a form which permits
  application of the convolution theorem so that CPU-intensive direct
  integration is alleviated. It is normally justified by a statistical
  argument with a certain assumption on properties of power distribution
  of the wavefield; the results are then interpreted as ensemble
  averages of the autocorrelation. However, the same results can also
  be obtained by taking spatial averages without any assumption on the
  power distribution, thereby providing a different interpretation to the
  results obtained through convolution theorem. It is straightforward
  to demonstrate the above in the case of wavefield in infinite
  two-dimensional space. Here we present a direct demonstration of the
  same equivalence of the averages in the case of spherical geometry,
  which has turned out to be less straightforward.

---------------------------------------------------------
Title: Annual Report of the National Astronomical Observatory of
    Japan, Volume 4 Fiscal 2001
Authors: Tanikawa, Kiyotaka; Honma, Mareki; Imanishi, Masatoshi; Kuno,
   Nario; Muramatsu, Toshiya; Sekii, Takashi; Sôma, Mitsuru; Yamashita,
   Yoshiko; Yasuda, Naoki
2003naoj.book.....T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Seismology of solar rotation
Authors: Sekii, Takashi
2003safd.book..263S    Altcode:
  Helioseismology provides us with means to investigate the otherwise
  invisible solar interior. The seismic approach is indispensable for the
  study of internal structure and evolution of the sun. It is even more
  so, however, for the study of dynamical aspects of the sun, because
  of the lack of other reliable means. The current status of seismology
  of solar rotation is reviewed and outstanding problems are discussed.

---------------------------------------------------------
Title: Seismology of Solar Internal Rotation
Authors: Sekii, Takashi
2003IAUJD..12E..36S    Altcode:
  Helioseismologists have been highly successful in revealing how
  the solar interior differentially rotates through observations of
  rotationally split eigen p modes of the sun. What we currently know
  about the internal rotation of the sun including how it varies over
  the solar cycle is reviewed. Seismic inference of internal rotation
  based on low-degree modes is also discussed.

---------------------------------------------------------
Title: Acoustic Tomography of the Sun's Interior with SDO:
    Possibilities and Limitations
Authors: Kosovichev, A. G.; Duvall, T. L.; Birch, A. C.; Gizon, L.;
   Zhao, J.; Sekii, T.; Shibahashi, H.
2002AGUFMSH21C..06K    Altcode:
  Helioseismic and Magnetic Imager on board SDO will significantly expand
  the possibilities for imaging plasma flows and structures in the solar
  interior. It will provide for the first time high-resolution data for
  continuous monitoring of emerging flux and developing active regions in
  the upper convection zone. It will also allow us to look for localized
  structures and flows in the tachocline region and deeper interior,
  and also investigate the near-polar regions. The expected results may
  give important clues of how the solar dynamo works and active regions
  develop. HMI will observe the entire spectrum of the solar acoustic
  and surface gravity waves, and provide the most comprehensive data
  for global and local helioseismology. The high-frequency part of the
  oscillation spectrum will be used for studying seismic properties of
  the solar atmosphere in the quiet Sun and active regions. The method
  of acoustic tomography or time-distance helioseismology is one of the
  primary tools of the HMI investigation. It is based on measurements and
  inversions of travel-time delays of solar waves, caused by plasma flows
  and variations of temperature and magnetic field. The data analysis
  requires deep understanding of the physics of wave propagation in the
  Sun and substantial computer resources. One of the important goals
  is to provide the flow and sound-speed maps of the upper convection
  zone in near-real time for space weather applications. We present the
  current status of the field, and discuss plans and challenges for the
  HMI data analyses and interpretation.

---------------------------------------------------------
Title: On the effect of error correlation on linear inversions
Authors: Gough, D. O.; Sekii, T.
2002MNRAS.335..170G    Altcode:
  We have examined the effect on linear helioseismic inversions of
  correlations in data errors, taking an example from one-dimensional
  rotational splitting inversion. Artificial data with correlated errors
  were generated and then inverted with or without using the proper
  covariance matrix. The effects of using incorrect covariance matrices,
  on solutions as well as on trade-offs, are discussed. It is found
  that improper account of the correlations can be deleterious to the
  faithfulness of the inversions, and yields incorrect error estimates,
  which under some circumstances can lead to misleading inferences.

---------------------------------------------------------
Title: What have we learnt with the Luminosity Oscillations Imager
    over the past 6 years?
Authors: Appourchaux, T.; Andersen, B.; Sekii, T.
2002ESASP.508...47A    Altcode: 2002soho...11...47A
  We summarize what we achieved with 6 years of LOI data. We present
  old as well as new results regarding the p-mode parameters dependence
  upon solar activity. We have also derived the dependence of the solar
  background noise upon solar activity and solar disk position. Inversions
  done using LOI frequencies and higher-degree mode frequencies from
  GONG confirm previous velocity inversions.

---------------------------------------------------------
Title: Local-area helioseismology by SOT on-board Solar-B
Authors: Sekii, T.; Shibahashi, H.; Kosovichev, A. G.; Duvall, T. L.,
   Jr.; Berger, T. E.; Bush, R.; Scherrer, P. H.
2001ESASP.464..327S    Altcode: 2001soho...10..327S
  Solar-B satellite, a successor to Yohkoh, will be launched
  in 2005. Placed in a sun-synchronous orbit, it will carry out
  multi-wavelength observation in optical, EUV and X-ray ranges. One of
  the instruments on Solar-B, Solar Optical Telescope (SOT), a Japan/US
  collaboration, aims at measuring the magnetic field and the Doppler
  velocity field in the solar photosphere. Although it is not specifically
  designed for helioseismic observations, the high-resolution Dopplergram
  produced by SOT is potentially a very powerful tool for detailed
  seismic investigation of subsurface magnetic and thermal structures
  and associated mass flows. If successful, these measurements will be
  an important contribution to the main goal of the Solar-B project:
  understanding the origin and dynamics of the basic magnetic structures
  and their effects on the solar corona. We discuss the prospect and
  challenges of local-area helioseismology by SOT.

---------------------------------------------------------
Title: Comparison of phase inversion and time-distance analysis of
    one-dimensional artificial seismic data
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
2001ESASP.464..207G    Altcode: 2001soho...10..207G
  We have studied the application of a phase inversion technique (Gough,
  Merryfield and Toomre 1991, 1993, 1998; Gough, Sekii and Toomre 1998,
  2000) to stochastically excited damped oscillations in an inhomogeneous
  one-dimensional loop, using artificial seismic data (Gough, Sekii and
  Toomre 2000). It has been found that within a parameter range that might
  be relevant to the solar case, strong damping can significantly degrade
  inversions for the wave propagation speed. Here we analyse the same
  artificial data by a time-distance technique, to compare how the two
  techniques differ in their response to the presence of strong damping.

---------------------------------------------------------
Title: g-mode detection: Where do we stand?
Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.;
   Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema,
   T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.;
   Toutain, T.
2001ESASP.464..467A    Altcode: 2001soho...10..467A
  We review the recent developments in determining the upper limits to
  g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We
  address how this limit can be improved by way of new helioseismic
  instruments and/or new collaborations, hopefully providing in the not
  too distant future unambiguous g-mode detection.

---------------------------------------------------------
Title: On measuring low-degree p-mode frequency splitting with
    full-disc integrated data
Authors: Appourchaux, T.; Chang, H. -Y.; Gough, D. O.; Sekii, T.
2000MNRAS.319..365A    Altcode:
  The standard method of measuring rotational splitting from solar
  full-disc oscillation data, based on maximum-likelihood fitting of
  multi-Lorentzian profiles to oscillation power spectra, systematically
  overestimates the splitting. One of the reasons is that the maximum
  likelihood estimators (MLE) become unbiased only asymptotically as
  the number of data tends to infinity; for a finite data set they
  are often biased, inducing a systematic error. In this paper we
  assess by Monte Carlo simulations the amount of systematic error
  in the splitting measurement, using artificially generated power
  spectra. The simulations are carried out for multiplets of degree
  S(t) = Σ<SUB>k</SUB>S<SUB>k</SUB>(t), l=1, 2 and 3 with various
  signal-to-noise ratios, linewidths and observing times. We address
  the possible use of non-MLE estimators that could provide a smaller
  or negligible systematic error. The implication for asteroseismology
  is also discussed.

---------------------------------------------------------
Title: Solar Interior: Inversions of Helioseismic Data
Authors: Sekii, T.
2000eaa..bookE2248S    Altcode:
  Once the eigenfrequencies of the solar oscillations are measured (see
  HELIOSEISMIC OBSERVATIONS), they are analysed further to investigate
  the solar interior. For example, we can use these frequencies to reveal
  how the adiabatic soundspeed varies with depth, or how the interior
  of the Sun rotates differentially, both in depth and in latitude. This
  procedure is called inversion, because the proced...

---------------------------------------------------------
Title: Phase inversion of one-dimensional artificial seismic data
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
2000SoPh..195....1G    Altcode:
  Oscillations of an inhomogeneous one-dimensional loop have been
  simulated for the purpose of examining the effect of excitation and
  damping on the sound-speed inversion based on phase analysis. It has
  been demonstrated that the procedure is robust against the realization
  noise arising from frequent, stochastic excitation of weakly damped
  waves, but that strong damping can spoil the inversion.

---------------------------------------------------------
Title: Observational Upper Limits to Low-Degree Solar g-Modes
Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.;
   Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema,
   J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.;
   Sekii, T.; Toutain, T.
2000ApJ...538..401A    Altcode:
  Observations made by the Michelson Doppler Imager (MDI) and Variability
  of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and
  Heliospheric Observatory (SOHO) and by the ground-based Birmingham
  Solar Oscillations Network (BiSON) and Global Oscillations Network
  Group (GONG) have been used in a concerted effort to search for solar
  gravity oscillations. All spectra are dominated by solar noise in the
  frequency region from 100 to 1000 μHz, where g-modes are expected to be
  found. Several methods have been used in an effort to extract any g-mode
  signal present. These include (1) the correlation of data-both full-disk
  and imaged (with different spatial-mask properties)-collected over
  different time intervals from the same instrument, (2) the correlation
  of near-contemporaneous data from different instruments, and (3) the
  extraction-through the application of complex filtering techniques-of
  the coherent part of data collected at different heights in the solar
  atmosphere. The detection limit is set by the loss of coherence
  caused by the temporal evolution and the motion (e.g., rotation)
  of superficial structures. Although we cannot identify any g-mode
  signature, we have nevertheless set a firm upper limit to the amplitudes
  of the modes: at 200 μHz, they are below 10 mm s<SUP>-1</SUP> in
  velocity, and below 0.5 parts per million in intensity. The velocity
  limit corresponds very approximately to a peak-to-peak vertical
  displacement of δR/R<SUB>solar</SUB>=2.3×10<SUP>-8</SUP> at the
  solar surface. These levels which are much lower than prior claims,
  are consistent with theoretical predictions.

---------------------------------------------------------
Title: Prospects for Measuring Differential Rotation in White Dwarfs
    through Asteroseismology
Authors: Kawaler, Steven D.; Sekii, Takashi; Gough, Douglas
1999ApJ...516..349K    Altcode: 1998astro.ph.11286K
  We examine the potential of asteroseismology for exploring the internal
  rotation of white dwarf stars. Data from global observing campaigns
  have revealed a wealth of frequencies, some of which show the signature
  of rotational splitting. Tools developed for helioseismology to use
  many solar p-mode frequencies for inversion of the rotation rate with
  depth are adapted to the case of more limited numbers of modes of
  low degree. We find that the small number of available modes in white
  dwarfs, coupled with the similarity between the rotational-splitting
  kernels of the modes, renders direct inversion unstable. Accordingly,
  we adopt what we consider to be plausible functional forms for the
  differential rotation profile; this is sufficiently restrictive to
  enable us to carry out a useful calibration. We show examples of this
  technique for PG 1159 stars and pulsating DB white dwarfs. Published
  frequency splittings for white dwarfs are currently not accurate
  enough for meaningful inversions; reanalysis of existing data can
  provide splittings of sufficient accuracy when the frequencies of
  individual peaks are extracted via least-squares fitting or multipeak
  decompositions. We find that, when mode trapping is evident in the
  period spacing of g modes, the measured splittings can constrain dΩ/dr.

---------------------------------------------------------
Title: Phase Inversion of One-Dimensional Artificial Seismic Data
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
1999soho....9E..30G    Altcode:
  It has been pointed out (Sekii 1997; Gough, Sekii &amp; Toomre 1998,
  1999) that the application of the phase inversion technique (Gough,
  Merryfield &amp; Toomre 1991, 1993, 1998) to the solar high-degree
  sectoral data, for detecting the background inhomogeneity in the
  solar equatorial region, may be facing difficulty arising from the
  presence of excitation and damping. We have studied the implication of
  the effects of these, using a simple model of stochastically excited
  damped oscillations of a one-dimensional loop. The results of phase
  inversions for various cases will be presented and various strategies
  to overcome the difficulty will be discussed.

---------------------------------------------------------
Title: Helioseismic Studies of Differential Rotation in the Solar
    Envelope by the Solar Oscillations Investigation Using the Michelson
    Doppler Imager
Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush,
   R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.;
   Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.;
   Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.;
   Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell,
   T. D.; Title, A. M.; Thompson, M. J.; Toomre, J.
1998ApJ...505..390S    Altcode:
  The splitting of the frequencies of the global resonant acoustic modes
  of the Sun by large-scale flows and rotation permits study of the
  variation of angular velocity Ω with both radius and latitude within
  the turbulent convection zone and the deeper radiative interior. The
  nearly uninterrupted Doppler imaging observations, provided by the
  Solar Oscillations Investigation (SOI) using the Michelson Doppler
  Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
  positioned at the L<SUB>1</SUB> Lagrangian point in continuous sunlight,
  yield oscillation power spectra with very high signal-to-noise ratios
  that allow frequency splittings to be determined with exceptional
  accuracy. This paper reports on joint helioseismic analyses of
  solar rotation in the convection zone and in the outer part of the
  radiative core. Inversions have been obtained for a medium-l mode set
  (involving modes of angular degree l extending to about 250) obtained
  from the first 144 day interval of SOI-MDI observations in 1996. Drawing
  inferences about the solar internal rotation from the splitting data
  is a subtle process. By applying more than one inversion technique
  to the data, we get some indication of what are the more robust
  and less robust features of our inversion solutions. Here we have
  used seven different inversion methods. To test the reliability and
  sensitivity of these methods, we have performed a set of controlled
  experiments utilizing artificial data. This gives us some confidence
  in the inferences we can draw from the real solar data. The inversions
  of SOI-MDI data have confirmed that the decrease of Ω with latitude
  seen at the surface extends with little radial variation through much
  of the convection zone, at the base of which is an adjustment layer,
  called the tachocline, leading to nearly uniform rotation deeper
  in the radiative interior. A prominent rotational shearing layer in
  which Ω increases just below the surface is discernible at low to
  mid latitudes. Using the new data, we have also been able to study the
  solar rotation closer to the poles than has been achieved in previous
  investigations. The data have revealed that the angular velocity
  is distinctly lower at high latitudes than the values previously
  extrapolated from measurements at lower latitudes based on surface
  Doppler observations and helioseismology. Furthermore, we have found
  some evidence near latitudes of 75° of a submerged polar jet which
  is rotating more rapidly than its immediate surroundings. Superposed
  on the relatively smooth latitudinal variation in Ω are alternating
  zonal bands of slightly faster and slower rotation, each extending
  some 10° to 15° in latitude. These relatively weak banded flows
  have been followed by inversion to a depth of about 5% of the solar
  radius and appear to coincide with the evolving pattern of “torsional
  oscillations” reported from earlier surface Doppler studies.

---------------------------------------------------------
Title: The Solar Internal Rotation from GOLF Splittings
Authors: Corbard, T.; Di Mauro, M. P.; Sekii, T.; GOLF Team
1998ESASP.418..741C    Altcode: 1998soho....6..741C; 1998astro.ph..6254C
  The low degree splittings obtained from one year of GOLF data analysis
  are combined with the MDI medium-l 144-day splittings in order to
  infer the solar internal rotation as a function of the radius down to
  0.2R_sun. Several inverse methods are applied to the same data and the
  uncertainties on the solution as well as the resolution reachable are
  discussed. The results are compared with the one obtained from the
  low degree splittings estimated from GONG network.

---------------------------------------------------------
Title: Helioseismic Determination of the Solar Tachocline Thickness
Authors: Elliott, J. R.; Gough, D. O.; Sekii, T.
1998ESASP.418..763E    Altcode: 1998soho....6..763E
  Inversions of rotational splitting data reveal the existence of a
  shear layer at the base of the convection zone, which is known as the
  tachocline. The angular velocity in the convection zone varies with
  latitude, whereas the angular velocity in the outer layers of the
  radiative envelope is more nearly uniform. The differential rotation
  of the convection zone is no doubt driven by anisotropic Reynolds
  stresses associated with the turbulent convection. It is likely
  that the radiative envelope is held rigid by a large-scale magnetic
  field. The transition between the two is too sharp to be resolved
  by the seismic splitting data. However, it must necessarily support
  an Ekman circulation (Spiegel &amp; Zahn, 1992), which advects heavy
  elements that have settled under gravity back into the convection zone,
  causing an abrupt discontinuity in chemical composition at the base of
  the tachocline, thereby modifying the hydrostatic stratification. We
  have calibrated theoretical solar models incorporating the tachocline
  mixing against the latest seismic data from SOI/MDI, from which we have
  obtained a value for the tachocline thickness which is substantially
  more precise than the formal resolving power of the seismic data.

---------------------------------------------------------
Title: Some Comments on Phase Inversions
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
1998ESASP.418..789G    Altcode: 1998soho....6..789G
  The method of phase inversion have been proposed and tested for simple
  cases by Gough, Merryfield and Toomre(1991,1993,1998) for detection of
  inhomogeneity in media by observing wave propagation. We discuss some of
  the difficulties that are encountered with the procedure in practice,
  and what might be done to overcome them in transferring the technique
  to the solar case, such as in the study of horizontal inhomogeneity in
  the solar cavity along the equator using the MDI sectoral-mode data. A
  complication seems to arise, aside from observational problems, from
  the fact that the waves are not only scattered by inhomogeneity, but
  are also excited and damped, as is observed in the broadening of the
  ridges in the k-ω diagram.

---------------------------------------------------------
Title: Observational Upper Limits for Low-Degree Solar g-modes
Authors: Fröhlich, C.; Finsterle, W.; Andersen, B.; Appourchaux, T.;
   Chaplin, W. J.; Elsworth, Y.; D. O. Gough; Hoeksema, J. T.; Isaak,
   G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.;
   Toutain, T.
1998ESASP.418...67F    Altcode: 1998soho....6...67F
  No abstract at ADS

---------------------------------------------------------
Title: Recent topics in helioseismology.
Authors: Sekii, T.
1998AstHe..91...92S    Altcode:
  Selected topics from the recent development in helioseismology are
  reviewed. The emphasis is on those findings from the SOHO satellite.

---------------------------------------------------------
Title: On the Influence of Unaccounted Error Correlations of Linear
    Inversions
Authors: Gough, D. O.; Sekii, T.
1998ESASP.418..787G    Altcode: 1998soho....6..787G
  Continuing our previous study (Gough 1996, also see Kosovichev et
  al. 1995) on the effects of correlated errors on linear inversions,
  we investigate how the optimally localized averaging method and the
  regularized least-square fitting method, both of which are `optimal'
  in different ways, respond differently to the use of wrong covariance
  matrices in one-dimensional rotation inversions. Our results demonstrate
  how important it is to exercise care in estimating error correlations
  when trying to extract mode frequencies from helioseismic data.

---------------------------------------------------------
Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes
Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.;
   Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.;
   Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T.
1998ESASP.418...95A    Altcode: 1998soho....6...95A
  The amplitudes of solar p-modes decrease steeply with decreasing
  radial order below about 17. The background solar signal (solar noise)
  in general increases steadily with decreasing frequency. For the
  irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this
  combination makes it difficult to detect low degree modes below about
  1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the
  ground based BISON network is significantly lower in this region than
  in intensity measurements. This allows low degree modes to be observed
  close to 1 mHz. We present results of detection and charaterization
  of the lowest order observable p-modes both in velocity and intensity
  measurements. Where applicable the properties of the modes observed
  with the two methods are compared.

---------------------------------------------------------
Title: Rotation and Zonal Flows in the Solar Envelope from the
    SOHO/MDI Observations
Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.;
   Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.;
   Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich,
   A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell,
   T.; Title, A. M.; Thompson, M. J.; Toomre, J.
1997AAS...191.7310S    Altcode: 1997BAAS...29.1322S
  We report on the latest inferences concerning solar differential
  rotation that have been drawn from the helioseismic data that are now
  available from the Solar Oscillations Investigation (SOI) using the
  Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
  (SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth
  Lagrangian point L_1, in order to obtain continuous Doppler-imaged
  observations of the sun with high spatial fidelity. Doppler velocity,
  intensity and magnetic field images are recorded, based on modulations
  of the 676.8 nm Ni I solar absorption line. The high spatial resolution
  of MDI thereby permits the study of many millions of global resonant
  modes of solar oscillation. Determination and subsequent inversion
  of the frequencies of these modes, including the degeneracy-splitting
  by the rotation of the sun, enables us to infer how the sun's angular
  velocity varies throughout much of the interior. The current MDI data
  are providing substantial refinements to the helioseismic deductions
  that can be made about differential rotation both within the convection
  zone and in its transition to the radiative interior. The shearing
  layer evident in the angular velocity Omega just below the solar
  surface is becoming better defined, as is the adjustment layer or
  tachocline near the base of the convection zone. The MDI data are also
  revealing a prominent decrease in Omega at high latitudes from the
  rotation rate expressed by a simple three-term expansion in latitude
  that was originally deduced from surface Doppler measurements. Further,
  there are indications that a submerged polar vortex involving somewhat
  faster Omega than its surroundings exists at about 75(deg) in latitudes.

---------------------------------------------------------
Title: Structure and Rotation of the Solar Interior: Initial Results
    from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
   Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
   Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
   K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
   W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
   Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
   Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
   Milford, P. N.
1997SoPh..170...43K    Altcode:
  The medium-l program of the Michelson Doppler Imager instrument on board
  SOHO provides continuous observations of oscillation modes of angular
  degree, l, from 0 to ∽ 300. The data for the program are partly
  processed on board because only about 3% of MDI observations can be
  transmitted continuously to the ground. The on-board data processing,
  the main component of which is Gaussian-weighted binning, has been
  optimized to reduce the negative influence of spatial aliasing of the
  high-degree oscillation modes. The data processing is completed in a
  data analysis pipeline at the SOI Stanford Support Center to determine
  the mean multiplet frequencies and splitting coefficients. The initial
  results show that the noise in the medium-l oscillation power spectrum
  is substantially lower than in ground-based measurements. This enables
  us to detect lower amplitude modes and, thus, to extend the range of
  measured mode frequencies. This is important for inferring the Sun's
  internal structure and rotation. The MDI observations also reveal the
  asymmetry of oscillation spectral lines. The line asymmetries agree
  with the theory of mode excitation by acoustic sources localized in the
  upper convective boundary layer. The sound-speed profile inferred from
  the mean frequencies gives evidence for a sharp variation at the edge
  of the energy-generating core. The results also confirm the previous
  finding by the GONG (Gough et al., 1996) that, in a thin layer just
  beneath the convection zone, helium appears to be less abundant than
  predicted by theory. Inverting the multiplet frequency splittings from
  MDI, we detect significant rotational shear in this thin layer. This
  layer is likely to be the place where the solar dynamo operates. In
  order to understand how the Sun works, it is extremely important to
  observe the evolution of this transition layer throughout the 11-year
  activity cycle.

---------------------------------------------------------
Title: Structure inversions with the VIRGO data
Authors: Appourchaux, Th.; Sekii, Takashi; Gough, Douglas; Lee, Umin;
   Wehrli, Christoph; Virgo Team
1997IAUS..181..159A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Internal structure and rotation of the Sun: First results
    from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
   Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
   De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
   Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
   J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
   Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
   Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
   C. J.; Zayer, I.; Milford, P. N.
1997IAUS..181..203K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Internal Solar rotation
Authors: Sekii, T.
1997IAUS..181..189S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: First results from VIRGO on SoHO
Authors: Frohlich, C.; Andersen, B. N.; Appourchaux, T.; Berthomieu,
   G.; Crommelynck, D. A.; Domingo, V.; Fichot, A.; Finsterle, W.;
   Gómez, M. F.; Gough, D.; Jiménez, A.; Leifsen, T.; Lombaerts, M.;
   Pap, J. M.; Provost, J.; Roca Cortés, T.; Romero, J.; Roth, H. -J.;
   Sekii, T.; Telljohann, U.; Toutain, T.; Wehrli, C.
1997IAUS..181...67F    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: First Results from VIRGO, the Experiment for Helioseismology
    and Solar Irradiance Monitoring on SOHO
Authors: Fröhlich, Claus; Andersen, Bo N.; Appourchaux, Thierry;
   Berthomieu, Gabrielle; Crommelynck, Dominique A.; Domingo, Vicente;
   Fichot, Alain; Finsterle, Wolfgang; Gómez, Maria F.; Gough, Douglas;
   Jiménez, Antonio; Leifsen, Torben; Lombaerts, Marc; Pap, Judit M.;
   Provost, Janine; Roca Cortés, Teodoro; Romero, José; Roth, Hansjörg;
   Sekii, Takashi; Telljohann, Udo; Toutain, Thierry; Wehrli, Christoph
1997SoPh..170....1F    Altcode:
  First results from the VIRGO experiment (Variability of solar IRradiance
  and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and
  Heliospheric Observatory) are reported. The observations started
  mid-January 1996 for the radiometers and sunphotometers and near the
  end of March for the luminosity oscillation imager. The performance of
  all the instruments is very good, and the time series of the first 4-6
  months are evaluated in terms of solar irradiance variability, solar
  background noise characteristics and p-mode oscillations. The solar
  irradiance is modulated by the passage of active regions across the
  disk, but not all of the modulation is straightforwardly explained in
  terms of sunspot flux blocking and facular enhancement. Helioseismic
  inversions of the observed p-mode frequencies are more-or-less in
  agreement with the latest standard solar models. The comparison of
  VIRGO results with earlier ones shows evidence that magnetic activity
  plays a significant role in the dynamics of the oscillations beyond
  its modulation of the resonant frequencies. Moreover, by comparing
  the amplitudes of different components ofp -mode multiplets, each of
  which are influenced differently by spatial inhomogeneity, we have
  found that activity enhances excitation.

---------------------------------------------------------
Title: The seismic structure of the Sun from GONG
Authors: Anderson, E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre,
   S. M.; Christensen-Dalsgaard, J.; Eff-Darwich, A.; Elliott, J. R.;
   Giles, P. M.; Gough, D. O.; Guzik, J. A.; Harvey, J. W.; Hill,
   F.; Leibacher, J. W.; Kosovichev, A. G.; Monteiro, M. J. P. F. G.;
   Richard, O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.;
   Toomre, J.; Vauclair, S.; Vorontsov, S. V.
1997IAUS..181..151A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Seismic Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toomre, J.; Anderson,
   E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre, S. M.;
   Christensen-Dalsgaard, J.; Dziembowski, W. A.; Eff-Darwich, A.;
   Elliott, J. R.; Giles, P. M.; Goode, P. R.; Guzik, J. A.; Harvey,
   J. W.; Hill, F.; Leibacher, J. W.; Monteiro, M. J. P. F. G.; Richard,
   O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.; Vauclair,
   S.; Vorontsov, S. V.
1996Sci...272.1296G    Altcode:
  Global Oscillation Network Group data reveal that the internal
  structure of the sun can be well represented by a calibrated standard
  model. However, immediately beneath the convection zone and at the
  edge of the energy-generating core, the sound-speed variation is
  somewhat smoother in the sun than it is in the model. This could be a
  consequence of chemical inhomogeneity that is too severe in the model,
  perhaps owing to inaccurate modeling of gravitational settling or to
  neglected macroscopic motion that may be present in the sun. Accurate
  knowledge of the sun's structure enables inferences to be made about
  the physics that controls the sun; for example, through the opacity,
  the equation of state, or wave motion. Those inferences can then be
  used elsewhere in astrophysics.

---------------------------------------------------------
Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
   Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
   J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
   D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
   A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
   Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
1996Sci...272.1300T    Altcode:
  Splitting of the sun's global oscillation frequencies by large-scale
  flows can be used to investigate how rotation varies with radius
  and latitude within the solar interior. The nearly uninterrupted
  observations by the Global Oscillation Network Group (GONG) yield
  oscillation power spectra with high duty cycles and high signal-to-noise
  ratios. Frequency splittings derived from GONG observations confirm
  that the variation of rotation rate with latitude seen at the surface
  carries through much of the convection zone, at the base of which is
  an adjustment layer leading to latitudinally independent rotation at
  greater depths. A distinctive shear layer just below the surface is
  discernible at low to mid-latitudes.

---------------------------------------------------------
Title: Inferring Spatial Variation of Solar Properties from
    Helioseismic Data
Authors: Gough, D. O.; Sekii, T.; Stark, P. B.
1996ApJ...459..779G    Altcode:
  A common method to infer that solar properties vary with position is
  to compare linear estimates of averages of those properties centered
  at different locations. If some of the confidence intervals for the
  averages do not overlap, one concludes that the property varies. In
  order for this conclusion to be statistically valid, the lengths of
  the intervals must be adjusted to obtain the correct "simultaneous
  coverage probability." We illustrate the notion of simultaneous coverage
  probability using coin tossing as an example. We present four methods
  for adjusting the lengths of confidence intervals for linear estimates,
  and a complementary approach to infer changes based on constructing
  a linear estimator that is directly sensitive to changes. The first
  method for constructing simultaneous confidence intervals is based
  on Bonferroni's inequality, and applies generally to confidence
  intervals for any set of parameters, from dependent or independent
  observations. The second method is based on a 2 measure of fit to the
  data, which allows one to compute s1multaneous confidence intervals for
  any number of linear functionals of the model. The third method uses a
  ^{2 }distribution in the space of estimates, which yields "Scheffe'"
  confidence intervals for the functionals. The fourth method, which
  produces the shortest confidence intervals, uses the infinity-norm
  in the space of estimates to construct "maximum-modulus" confidence
  intervals. We apply the four methods to search for radial changes in
  averages of solar angular velocity, using data from Big Bear Solar
  Observatory (BBSO) averaged for the 4 yr 1986, 1988-1990. Finally,
  we apply the new differencing estimator to the BBSO data, finding
  strong evidence that the average solar angular velocity is lower near
  the poles than near the equator over a range of depths, as is observed
  at the surface as well.

---------------------------------------------------------
Title: On Frequency Determination and Temporal Data Sampling
Authors: Chang, H. -Y.; Gough, D.; Sekii, T.
1995ESASP.376b.175C    Altcode: 1995soho....2..175C; 1995help.confP.175C
  The authors have further developed the procedure described by Chang
  and Gough (1995) in GONG94 to analyse low-degree helioseismic time
  series. An idealized model was used to construct artifical data
  representing a superposition of undamped oscillations in a cavity which
  is varying slowly with time in an unknown manner. The procedure involves
  matching a model of the data to the actual data by minimizing a measure
  of misfit. This requires a multidimensional parameter search which,
  if a generic procedure such as the simplex algorithm used for GONG94
  is employed, is computationally expensive. The authors have developed
  an efficient scheme tailored explicitly to the problem in hand, which
  uses a combination of an approximate factorization of the parameter
  space with an alternation of a jumping algorithm between local minima
  and Newton-Ralphson iteration.

---------------------------------------------------------
Title: Observational Constraints on the Internal Solar Angular
    Velocity
Authors: Sekii, T.; Genovese, C. R.; Gough, D. O.; Stark, P. B.
1995ESASP.376b.279S    Altcode: 1995help.confP.279S; 1995soho....2..279S
  No abstract at ADS

---------------------------------------------------------
Title: The 1 ⊗ 1 Rotation Inversion with Expansion Coefficients
Authors: Sekii, T.
1995ESASP.376b.285S    Altcode: 1995help.confP.285S; 1995soho....2..285S
  No abstract at ADS

---------------------------------------------------------
Title: Linear Inversions in Helioseismology: Testing New
    Regularization Techniques for Solving Large Systems of Linear
    Algebraic Equations
Authors: Strakhov, V. N.; Vorontsov, S. V.; Sekii, T.
1995ASPC...76..492S    Altcode: 1995gong.conf..492S
  No abstract at ADS

---------------------------------------------------------
Title: Angular Inversions of Rotational Splitting Coefficients
Authors: Sekii, T.
1995ASPC...76...74S    Altcode: 1995gong.conf...74S
  No abstract at ADS

---------------------------------------------------------
Title: Asymptotic Signatures of Jovian Discontinuities
Authors: Gough, D. O.; Sekii, T.
1995ASPC...76..374G    Altcode: 1995gong.conf..374G
  No abstract at ADS

---------------------------------------------------------
Title: Working Group 9 - Interior Structure and Inversions
Authors: Kosovichev, A. G.; Basu, S.; Christensen-Dalsgaard, J.;
   Eff-Darwich, A.; Gough, D. O.; Iglesias, C. A.; Pérez-Hernández,
   F.; Rogers, F.; Sekii, T.; Shibahashi, H.
1995ESASP.376a.211K    Altcode: 1995heli.conf..211K
  No abstract at ADS

---------------------------------------------------------
Title: Inversions of BBSO Rotational Splitting Data
Authors: Sekii, T.; Gough, D. O.; Kosovichev, A. G.
1995ASPC...76...59S    Altcode: 1995gong.conf...59S
  No abstract at ADS

---------------------------------------------------------
Title: How Regularization Influences Rotation Inversion
Authors: Sekii, T.
1995ASPC...76...67S    Altcode: 1995gong.conf...67S
  No abstract at ADS

---------------------------------------------------------
Title: Invitation to helioseismology II.
Authors: Shibahashi, H.; Sekii, T.
1993AstHe..86..461S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A new strategy for 2D inversion for solar rotation
Authors: Sekii, Takashi
1993MNRAS.264.1018S    Altcode:
  In the linearized integral formula for rotational splitting of solar
  p-mode frequencies, the dominant term in the kernel is a product of
  two terms, one depending on the radial coordinate alone, and the other
  depending solely on the colatitude. By retaining only this term in the
  equation, two-dimensional inverse techniques for the solar internal
  rotation can be formulated in such a way that the angular and radial
  inversions can be carried out separately. Thus the 2D inversion is
  reduced to two successive 1D inversions. This strategy leads to a
  dramatic reduction in computational burden when one is inverting
  huge data sets. It is also possible to improve the quality of the
  inversions significantly by a modification to the radial inversion
  procedure. In this paper, regularized least-squares data fitting and
  a modified optimally localized averaging are applied to the angular
  inversion and the radial inversion, respectively. The quality of the
  inversions is illustrated by means of the resulting averaging kernels.

---------------------------------------------------------
Title: Invitation to helioseismology I.
Authors: Shibahashi, H.; Sekii, T.
1993AstHe..86..416S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Seismic evidence of modulation of the structure and angular
    velocity of the Sun associated with the solar cycle
Authors: Gough, D. O.; Kosovichev, A. G.; Sekii, T.; Libbrecht, K. G.;
   Woodard, M. F.
1993ASPC...40...93G    Altcode: 1993IAUCo.137...93G; 1993ist..proc...93G
  No abstract at ADS

---------------------------------------------------------
Title: The Form of the Angular Velocity in the Solar Convection Zone
Authors: Gough, D. O.; Kosovichev, A. G.; Sekii, T.; Libbrecht, K. G.;
   Woodard, M. F.
1993ASPC...42..213G    Altcode: 1993gong.conf..213G
  No abstract at ADS

---------------------------------------------------------
Title: on the Detection of Convective Overshoot
Authors: Gough, D. O.; Sekii, T.
1993ASPC...42..177G    Altcode: 1993gong.conf..177G
  No abstract at ADS

---------------------------------------------------------
Title: A procedure for two-dimensional asymptotic rotational-splitting
    inversion
Authors: Sekii, T.; Gough, D. O.
1993ASPC...40..569S    Altcode: 1993IAUCo.137..569S; 1993ist..proc..569S
  No abstract at ADS

---------------------------------------------------------
Title: on an R/1XR/1 Inversion Technique for Solar Rotation
Authors: Sekii, T.
1993ASPC...42..237S    Altcode: 1993gong.conf..237S
  No abstract at ADS

---------------------------------------------------------
Title: Two-Dimensional Inversion for Solar Internal Rotation
Authors: Sekii, Takashi
1991PASJ...43..381S    Altcode:
  The internal rotation of the sun is inferred by solving a fully
  two-dimensional inverse problem of the rotational splitting data of
  Libbrecht (1989, AAA 080.006). We solve a set of integral equations
  which relate the rotational splittings of the eigenfrequencies of
  the sun to the internal rotation rate of the sun, the latter being
  considered as a function of both the distance from the center and the
  latitude. For this purpose we suggest an inverse method and apply
  it to the present problem. The integral equations are descretized
  and reduced to a set of linear equations. First, we impose an
  error-weighted least-squares condition with some boundary constraints
  at the surface. Second, we impose a flatness condition: the average of
  the first derivatives of the rotation rate is required to be as small as
  possible under the first constraint. Inversions were carried out while
  fully utilizing singular-value decomposition. In order to stabilize
  the solution to observational and numeric errors, we discarded small
  singular values. The results of numerical experiments show that the
  best resolution is obtained within a depth range of 0.6 &lt;~ r/R &lt;~
  0.9 in the low-latitude region. By inverting the observed splittings,
  we found that the solar internal rotation in the low-latitude region
  is slightly faster than the surface rotation rate in the outer ten
  percent of the radius, and decreases to about five percent less than
  the surface rotation rate within the lower levels of the convection
  zone. In the region 0.7 &lt;~ r/R &lt;~ 0.8, the rotation rate within
  the low-latitude zone is as fast as the surface rate, but is slower
  than the surface rate at r/R &lt;~ 0.7. The rotation rate within the
  mid-latitude region decreases with depth in the outer twenty percent
  of the radius, and gradually increases inward to be faster than the
  surface rate.

---------------------------------------------------------
Title: Two-Dimensional Inversion of Rotational Splitting Data
Authors: Sekii, Takashi
1990LNP...367..337S    Altcode: 1990psss.conf..337S
  We solve a two-dimensional inverse problem of the rotational frequency
  splitting to infer the rotation rate in the sun as a function of both
  the radius and the latitude. We use Libbrecht's (1989) observational
  data of the solar p-mode frequency splitting. We discretize a set
  of linear integral equations for rotational splittings and reduce
  them a set of linear algebraic equations. We solve the resultant
  algebraic equations by imposing an error-weighted least squares
  condition cooperated with boundary constraint at the surface. In order
  to stabilize the solution to observational and numerical errors, we
  discard small singular values of the coefficient matrix, and this keeps
  some parameters undetermined. To determine these parameters we impose
  a flatness condition. The inverted results show the solar internal
  rotation becomes slower at low latitudes and faster at high latitudes
  with increasing depth. The most significant deviation from this trend
  is that rotation is slow at low latitudes in the convection zone.

---------------------------------------------------------
Title: An asymptotic inversion method of inferring the sound velocity
    distribution in the sun from the spectrum of p-mode oscillations
Authors: Sekii, Takashi; Shibahashi, Hiromoto
1989PASJ...41..311S    Altcode:
  An inversion method for inferring the sound velocity distribution in
  the sun from its p-mode oscillation data is presented. The method is
  applied to a set of theoretically calculated eigenfrequencies of a
  solar model. It is shown that the method improves the accuracy and
  effectiveness of the asymptotic inversion method of inferring the
  internal structure of the sun, in particular, the deep interior of
  the sun.

---------------------------------------------------------
Title: An inversion method based on the Moore-Penrose generalized
    inverse matrix.
Authors: Sekii, T.; Shibahashi, H.
1988ESASP.286..521S    Altcode: 1988ssls.rept..521S
  The authors present an inversion method based on solving the algebraic
  equations by means of the Moore-Penrose generalized inverse matrix of
  inferring the solar internal rotation, and evaluate its validity.

---------------------------------------------------------
Title: Sound velocity distribution in the Sun inferred from the
    asymptotic inversion of p-mode spectra.
Authors: Shibahashi, H.; Sekii, T.
1988ESASP.286..471S    Altcode: 1988ssls.rept..471S
  The authors solve the inverse problem of the solar p-mode spectrum
  based on a recently developed asymptotic inversion method, and infer
  the sound velocity distribution with the accuracy better than a few
  percent. In this method, the equation governing high order p-mode
  oscillations has been reduced to a form of the Schrödinger equation
  in quantum mechanics. By using the quantization rule based on the
  WKBJ method, the authors formulated an integral equation to infer
  the form of the "acoustic potential". The acoustic potential itself
  consists of two parts. One of them is dependent on the degree l and
  the sound velocity and is the dominant term in the deep interior while
  the other is independent of l and dominates in the outer envelope. By
  examining the l-dependence of the acoustic potential thus inferred,
  the authors separate these two terms and then they infer the sound
  velocity distribution in the Sun. They apply this method to the real
  observational data of Duvall et al. and Libbrecht and Kaufman and obtain
  the sound velocity distribution in the Sun. They compare the result
  with their model and find that there is a small discrepancy between
  the model and the inferred result in the range of 0.3 &lt; r/R &lt; 0.4.

---------------------------------------------------------
Title: White Dwarf Seismology - Inverse Problem of G-Mode Oscillations
Authors: Shibahashi, H.; Sekii, T.; Kawaler, S.
1988LNP...305...86S    Altcode: 1988IAUCo.108...86S; 1988adse.conf...86S
  No abstract at ADS

---------------------------------------------------------
Title: Inverse Problem of Solar Oscillations
Authors: Sekii, Takashi; Shibahashi, Hiromoto
1987LNP...274..322S    Altcode: 1987stpu.conf..322S
  We present some preliminary results of numerical simulation to
  infer the sound velocity distribution in the solar interior from the
  oscillation data of the Sun as the inverse problem. We analyze the
  acoustic potential itself by taking account of some factors other than
  the sound velocity, and we can infer fairly well the sound velocity
  distribution in the deep interior of the Sun.