-
[show abstract]
[hide abstract]
ABSTRACT: We have performed power spectral analysis of surface temperatures,
velocities, and magnetic fields, using spectro-polarimetric data taken with the
Hinode Solar Optical Telescope. When we make power spectra in a field-of-view
covering the super-granular scale, kinetic and thermal power spectra have a
prominent peak at the granular scale while the magnetic power spectra have a
broadly distributed power over various spatial scales with weak peaks at both
the granular and supergranular scales. To study the power spectra separately in
internetwork and network regions, power spectra are derived in small
sub-regions extracted from the field-of-view. We examine slopes of the power
spectra using power-law indices, and compare them with the unsigned magnetic
flux density averaged in the sub-regions. The thermal and kinetic spectra are
steeper than the magnetic ones at the sub-granular scale in the internetwork
regions, and the power-law indices differ by about 2. The power-law indices of
the magnetic power spectra are close to or smaller than -1 at that scale, which
suggests the total magnetic energy mainly comes from either the granular scale
magnetic structures or both the granular scale and smaller ones contributing
evenly. The slopes of the thermal and kinetic power spectra become less steep
with increasing unsigned flux density in the network regions. The power-law
indices of all the thermal, kinetic, and magnetic power spectra become similar
when the unsigned flux density is larger than 200 Mx cm^-2.
09/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: The quiet Sun internetwork is permeated by weak and highly inclined magnetic
fields whose physical properties, dynamics, and magnetic interactions are not
fully understood. High spatial resolution magnetograms show them as discrete
magnetic elements that appear/emerge and disappear/cancel continuously over the
quiet Sun surface. The 4-m European Solar Telescope (EST) and the Advanced
Technology Solar Telescope (ATST) will obtain two-dimensional, high cadence,
high precision polarimetric measurements at the diffraction limit (30 km).
Here, we compile the basic requirements for the observation of internetwork
fields with EST and ATST (field of view, cadence, instrument configuration,
etc). More specifically, we concentrate on the field-of-view requirements. To
set them we analyze the proper motion of internetwork magnetic elements across
the solar surface. We use 13 hours of magnetograms taken with the Hinode
satellite to identify and track thousands of internetwork magnetic element in
an isolated supergranular cell. We calculate the velocity components of each
element and the mean distance they travel. The results show that, on average,
magnetic elements in the interior of supergranular cells move toward the
network. The radial velocity is observed to depend on the distance to the
center of the supergranule. Internetwork magnetic elements travel 400 on
average. These results suggest that ATST and EST should cover, at least, one
supergranular cell to obtain a complete picture of the quiet Sun internetwork.
03/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents results from the analysis of high signal-to-noise ratio spectropolarimetric data taken at four heliocentric angles in quiet-Sun internetwork regions with the Hinode satellite. First, we find that the total circular and total linear polarization signals vary with heliocentric angle, at least for fields with large polarization signals. We also report changes on the Stokes V amplitude asymmetry histograms with viewing angle for fields weaker than 200 G. Then, we subject the data to a Milne-Eddington inversion and analyze the variation of the field vector probability density functions with heliocentric angle. Weak, highly inclined fields permeate the internetwork at all heliocentric distances. For fields weaker than 200 G, the distributions of field inclinations peak at 90° and do not vary with viewing angle. The inclination distributions change for fields stronger than 200 G. We argue that the shape of the inclination distribution for weak fields partly results from the presence of coherent, loop-like magnetic features at all heliocentric distances and not from tangled fields within the field of view. We also find that the average magnetic field strength is about 180 G (for 75% of the pixels) and is constant with heliocentric angle. The average vertical and horizontal magnetic field components are 70 and 150 G. The latter (former) is slightly greater (smaller) near the limb. Finally, the ratio between the horizontal and vertical components of the fields ranges from ~1 for strong fields to ~3.5 for weak fields, suggesting that the magnetic field vector is not isotropically distributed within the field of view.
The Astrophysical Journal 02/2012; 746(2):182. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A sunspot penumbra is observationally examined to reveal properties of small-scale flow structures and how they are related to the filamentary magnetic structures and the Evershed flow. We also study how the photospheric dynamics is related to chromospheric activities. The study is based on data analysis of spectro-polarimetric observations of photospheric Fe I lines with the Solar Optical Telescope aboard Hinode in a sunspot penumbra at different heliocentric angles. Vector magnetic fields and velocities are derived using the spectro-polarimetric data and a Stokes inversion technique. An observation with a Ca II H filtergram co-spatial and co-temporal with the spectro-polarimetric one is also used to study possible chromospheric responses. We find small patches with downflows at photospheric layers. The downflow patches have a size of 0.5" or smaller and have a geometrical configuration different from that of the Evershed flow. The downflow velocity is about 1 km/s at lower photspheric layers, and is almost zero in the upper layers. Some of the downflow patches are associated with brightenings seen in Ca II H images. The downflows are possible observational signatures of downward flows driven by magnetic reconnection in the interlaced magnetic field configuration, where upward flows make brightenings in the chromosphere. Another possibility is that they are concentrated downward flows of overturning magnetoconvection. Comment: 9 pages, 7 figures, accepted for publication in Astronomy & Astrophysics
07/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: High resolution and seeing-free spectroscopic observations of a decaying
sunspot were done with the Solar Optical Telescope aboard Hinode
satellite. We report the magnetic structure and Doppler velocity fields
around umbral dots (UDs), based on the Milne-Eddington inversion of the
two iron absorption lines at 6302 Å.
The histograms of magnetic field strength (B), inclination angle (i), and
Doppler velocity (v) of UDs showed a center-to-limb variation. Observed at the
disk center, UDs had (i) slightly smaller field strength (ΔB = -17 Gauss)
and (ii) relative blue shifts (Δv =28 m s-1) compared to their
surroundings. When the sunspot approached to the limb, UDs and their surroundings
showed almost no difference in the magnetic and Doppler values. This center-to-limb
variation can be understood by the formation height difference in a cusp-shaped
magnetized atmosphere around UDs, due to the weakly magnetized hot gas intrusion.
In addition, some UDs showed oscillatory light curves with multiple peaks
around 10 min, which may indicate the presence of the oscillatory convection.
11/2009; 415:378.
-
[show abstract]
[hide abstract]
ABSTRACT: We report on the discovery of mostly horizontal field channels just outside sunspot penumbrae (in the so-called "moat" region) that are seen to sustain supersonic flows (line-of-sight component of 6 km s–1). The spectral signature of these supersonic flows corresponds to circular polarization profiles with an additional, satellite, third lobe of the same sign as the parent sunspot' Stokes V blue lobe, for both downflows and upflows. This is consistent with an outward directed flow that we interpret as the continuation of the magnetized Evershed flow outside sunspots at supersonic speeds. In Stokes Q and U, a clear signature of a transverse field connecting the two flow streams is observed. Such an easily detectable spectral signature should allow for a clear identification of these horizontal field channels in other spectropolarimetric sunspot data. For the spot analyzed in this paper, a total of five channels with this spectral signature have been unambiguously found.
The Astrophysical Journal 08/2009; 701(2):L79. · 6.02 Impact Factor
-
S. Tsuneta,
K. Ichimoto, Y. Katsukawa,
B. W. Lites,
K. Matsuzaki,
S. Nagata,
D. Orozco Suárez,
T. Shimizu,
M. Shimojo,
R. A. Shine,
Y. Suematsu,
T. K. Suzuki,
T. D. Tarbell,
and A. M. Title
[show abstract]
[hide abstract]
ABSTRACT: We present observations of the magnetic landscape of the polar region of the Sun that are unprecedented in terms of spatial resolution, field of view, and polarimetric precision. They were carried out with the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington inversion, we find many vertically oriented magnetic flux tubes with field strengths as strong as 1 kG scattered in latitude between 70° and 90°. They all have the same polarity, consistent with the global polarity of the polar region. The field vectors are observed to diverge from the centers of the flux elements, consistent with a view of magnetic fields that are expanding and fanning out with height. The polar region is also found to have ubiquitous horizontal fields. The polar regions are the source of the fast solar wind, which is channeled along unipolar coronal magnetic fields whose photospheric source is evidently rooted in the strong-field, vertical patches of flux. We conjecture that vertical flux tubes with large expansion around the photospheric-coronal boundary serve as efficient chimneys for Alfvén waves that accelerate the solar wind.
The Astrophysical Journal 12/2008; 688(2):1374. · 6.02 Impact Factor
-
L. R. Bellot Rubio,
S. Tsuneta,
K. Ichimoto, Y. Katsukawa,
B. W. Lites,
S. Nagata,
T. Shimizu,
R. A. Shine,
Y. Suematsu,
T. D. Tarbell,
A. M. Title,
and J. C. del Toro Iniesta
[show abstract]
[hide abstract]
ABSTRACT: We present spectropolarimetric measurements of dark-cored penumbral filaments taken with Hinode at a resolution of 0.3''. Our observations demonstrate that dark-cored filaments are more prominent in polarized light than in continuum intensity. Far from disk center, the Stokes profiles emerging from these structures are very asymmetric and show evidence for magnetic fields of different inclinations along the line of sight, together with strong Evershed flows of at least 6-7 km s-1. In sunspots closer to disk center, dark-cored penumbral filaments exhibit regular Stokes profiles with little asymmetries due to the vanishing line-of-sight component of the horizontal Evershed flow. An inversion of the observed spectra indicates that the magnetic field is weaker and more inclined in the dark cores as compared with the surrounding bright structures. This is compatible with the idea that dark-cored filaments are the manifestation of flux tubes carrying hot Evershed flows.
The Astrophysical Journal 12/2008; 668(1):L91. · 6.02 Impact Factor
-
R. Centeno,
H. Socas-Navarro,
B. Lites,
M. Kubo,
Z. Frank,
R. Shine,
T. Tarbell,
A. Title,
K. Ichimoto,
S. Tsuneta, Y. Katsukawa,
Y. Suematsu,
T. Shimizu,
and S. Nagata
[show abstract]
[hide abstract]
ABSTRACT: We study the emergence of magnetic flux at very small spatial scales (less than 2'') in the quiet-Sun internetwork. To this aim, a time series of spectropolarimetric maps was taken at disk center using the instrument SP/SOT on board Hinode. The LTE inversion of the full Stokes vector measured in the Fe I 6301 and 6302 Å lines allows us to retrieve the magnetic flux and topology in the region of study. In the example presented here, the magnetic flux emerges within a granular structure. The horizontal magnetic field appears prior to any significant amount of vertical field. As time goes on, the traces of the horizontal field disappear, while the vertical dipoles drift—carried by the plasma motions—toward the surrounding intergranular lanes. These events take place within typical granulation timescales.
The Astrophysical Journal 12/2008; 666(2):L137. · 6.02 Impact Factor
-
B. W. Lites,
M. Kubo,
H. Socas-Navarro,
T. Berger,
Z. Frank,
R. Shine,
T. Tarbell,
A. Title,
K. Ichimoto, Y. Katsukawa,
S. Tsuneta,
Y. Suematsu,
T. Shimizu,
and S. Nagata
[show abstract]
[hide abstract]
ABSTRACT: Observations of very quiet Sun using the Solar Optical Telescope/Spectro-Polarimeter (SOT/SP) aboard the Hinode spacecraft reveal that the quiet internetwork regions are pervaded by horizontal magnetic flux. The spatial average horizontal apparent flux density derived from wavelength-integrated measures of Zeeman-induced linear polarization is BTapp = 55 Mx cm −2, as compared to the corresponding average vertical apparent flux density of | BLapp| = 11 Mx cm −2. Distributions of apparent flux density are presented. Magnetic fields are organized on mesogranular scales, with both horizontal and vertical fields showing "voids" of reduced flux density of a few granules spatial extent. The vertical fields are concentrated in the intergranular lanes, whereas the stronger horizontal fields are somewhat separated spatially from the vertical fields and occur most commonly at the edges of the bright granules. High-S/N observations from disk center to the limb help to constrain possible causes of the apparent imbalance between | BLapp| and BTapp, with unresolved structures of linear dimension on the surface smaller by at least a factor of 2 relative to the SOT/SP angular resolution being one likely cause of this discrepancy. Other scenarios for explaining this imbalance are discussed. The horizontal fields are likely the source of the "seething" fields of the quiet Sun discovered by Harvey et al. The horizontal fields may also contribute to the "hidden" turbulent flux suggested by studies involving Hanle effect depolarization of scattered radiation.
The Astrophysical Journal 12/2008; 672(2):1237. · 6.02 Impact Factor
-
D. Orozco Suárez,
L. R. Bellot Rubio,
J. C. del Toro Iniesta,
S. Tsuneta,
B. W. Lites,
K. Ichimoto, Y. Katsukawa,
S. Nagata,
T. Shimizu,
R. A. Shine,
Y. Suematsu,
T. D. Tarbell,
and A. M. Title
[show abstract]
[hide abstract]
ABSTRACT: We analyze Fe I 630 nm observations of the quiet Sun at disk center taken with the spectropolarimeter of the Solar Optical Telescope aboard the Hinode satellite. A significant fraction of the scanned area, including granules, turns out to be covered by magnetic fields. We derive field strength and inclination probability density functions from a Milne-Eddington inversion of the observed Stokes profiles. They show that the internetwork consists of very inclined, hG fields. As expected, network areas exhibit a predominance of kG field concentrations. The high spatial resolution of Hinode's spectropolarimetric measurements brings to an agreement the results obtained from the analysis of visible and near-infrared lines.
The Astrophysical Journal 12/2008; 670(1):L61. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Proper motions in a sunspot group with a δ-configuration and close to the solar disk center have been studied by employing local correlation tracking techniques. The analysis is based on a more than 1 hr time series of G-band images. Radial outflows with a mean speed of 0.67 km s-1 have been detected around the spots, the well-known sunspots moats. However, these outflows are not found in those umbral core sides without penumbra. Moreover, moat flows are only found in those sides of penumbrae located in the direction marked by the penumbral filaments. Penumbral sides perpendicular to them show no moat flow. These results strongly suggest a relation between the moat flow and the well-known, filament-aligned Evershed flow. The standard picture of a moat flow originating from a blocking of the upward propagation of heat is discussed in some detail.
The Astrophysical Journal 12/2008; 660(2):L165. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Hinode discovered a beautiful giant jet with both cool and hot components at
the solar limb on 2007 February 9. Simultaneous observations by the Hinode SOT,
XRT, and TRACE 195 satellites revealed that hot (5x10^6 K) and cool (10^4 K)
jets were located side by side and that the hot jet preceded the associated
cool jet (1-2 minutes). A current-sheet-like structure was seen in optical (Ca
IIH), EUV (195A), and soft X-ray emissions, suggesting that magnetic
reconnection is occurring in the transition region or upper chromosphere.
Alfven waves were also observed with Hinode SOT. These propagated along the jet
at velocities of 200 km/s with amplitudes (transverse velocity) of 5-15 km/s
and a period of 200 s. We performed two-dimensional MHD simulation of the jets
on the basis of the emerging flux-reconnection model, by extending Yokoyama and
Shibata's model. We extended the model with a more realistic initial condition
(10^6 K corona) and compared our model with multiwavelength observations. The
improvement of the coronal temperature and density in the simulation model
allowed for the first time the reproduction of the structure and evolution of
both the cool and hot jets quantitatively, supporting the magnetic reconnection
model. The generation and the propagation of Alfven waves are also reproduced
self-consistently in the simulation model.
10/2008;
-
[show abstract]
[hide abstract]
ABSTRACT: High time cadence unprecedented images at the limb with Ca II H line
filtergraph from the Solar Optical Telescope (SOT) aboard Hinode have
revealed that a spicule consists of highly dynamic multi-threads
(typically twin) as thin as a few tenths of an arcsecond, and shows
prominent lateral movement or oscillation with rotation on its axis
during its life. This multi-thread structure and lateral motion indicate
that the spicules can be driven by magnetic reconnection at unresolved
spatial scales at their footpoints.
08/2008; 397:27.
-
[show abstract]
[hide abstract]
ABSTRACT: We investigate the dependence of penumbral microjets inclination on the position within penumbra. The high cadence observations taken on 10 November 2006 with the Hinode satellite through the \ion{Ca}{ii} H and G--band filters were analysed to determine the inclination of penumbral microjets. The results were then compared with the inclination of the magnetic field determined through the inversion of the spectropolarimetric observations of the same region. The penumbral microjet inclination is increasing towards the outer edge of the penumbra. The results suggest that the penumbral microjet follows the opening magnetic field lines of a vertical flux tube that creates the sunspot. Comment: 4 pages, 4 figures, A&A Letter in press
08/2008;
-
K. Kobayashi,
S. Tsuneta,
T. Tamura,
K. Kumagai, Y. Katsukawa,
M. Kubo,
Y. Sakamoto,
N. Kohara,
T. Yamagami,
Y. Saito,
K. Mori
[show abstract]
[hide abstract]
ABSTRACT: Spectroscopic observation of solar flares in the hard X-ray energy range, particularly the 20 ∼ 100keV region, is an invaluable
tool for investigating the flare mechanism. This paper describes the design and performance of a balloon-borne hard X-ray
spectrometer using CdTe detectors developed for solar flare observation. The instrument is a small balloon payload (gondola
weight 70kg) with sixteen 10×10×0.5mm CdTe detectors, designed for a 1-day flight at 41km altitude. It observes in an energy
range of 20−120keV and has an energy resolution of 3keV at 60keV. The second flight on 24 May 2002 succeeded in observing
a class M1.1 flare.
Solar Physics 07/2008; 250(2):431-441. · 2.78 Impact Factor
-
M Kubo,
B. W. Lites,
K. Ichimoto,
T Shimizu,
Y. Suematsu, Y. Katsukawa,
T. D. Tarbell,
R. A. Shine,
A. M. Title,
S Nagata,
S. Tsuneta
[show abstract]
[hide abstract]
ABSTRACT: Continuous observations of sunspot penumbrae with the Solar Optical Telescope aboard \textit{Hinode} clearly show that the outer boundary of the penumbra fluctuates around its averaged position. The penumbral outer boundary moves inward when granules appear in the outer penumbra. We discover that such granules appear one after another while moving magnetic features (MMFs) are separating from the penumbral ``spines'' (penumbral features that have stronger and more vertical fields than those of their surroundings). These granules that appear in the outer penumbra often merge with bright features inside the penumbra that move with the spines as they elongate toward the moat region. This suggests that convective motions around the penumbral outer boundary are related to the disintegration of magnetic flux in the sunspot. We also find that dark penumbral filaments frequently elongate into the moat region in the vicinity of MMFs that detach from penumbral spines. Such elongating dark penumbral filaments correspond to nearly horizontal fields extending from the penumbra. Pairs of MMFs with positive and negative polarities are sometimes observed along the elongating dark penumbral filaments. This strongly supports the notion that such elongating dark penumbral filaments have magnetic fields with a ``sea serpent''-like structure. Evershed flows, which are associated with the penumbral horizontal fields, may be related to the detachment of the MMFs from the penumbral spines, as well as to the formation of the MMFs along the dark penumbral filaments that elongate into the moat region. Comment: Accepted for publication in ApJ
06/2008;
-
S. Tsuneta,
K. Ichimoto, Y. Katsukawa,
S. Nagata,
M. Otsubo,
T. Shimizu,
Y. Suematsu,
M. Nakagiri,
M. Noguchi,
T. Tarbell, [......],
G. Kushner,
M. Levay,
B. Lites,
D. Elmore,
T. Matsushita,
N. Kawaguchi,
H. Saito,
I. Mikami,
L. D. Hill,
J. K. Owens
[show abstract]
[hide abstract]
ABSTRACT: The Solar Optical Telescope (SOT) aboard the Hinode satellite (formerly called Solar-B) consists of the Optical Telescope Assembly (OTA) and the Focal Plane Package (FPP). The OTA is a 50-cm diffraction-limited
Gregorian telescope, and the FPP includes the narrowband filtergraph (NFI) and the broadband filtergraph (BFI), plus the Stokes
Spectro-Polarimeter (SP). The SOT provides unprecedented high-resolution photometric and vector magnetic images of the photosphere
and chromosphere with a very stable point spread function and is equipped with an image-stabilization system with performance
better than 0.01arcsec rms. Together with the other two instruments on Hinode (the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS)), the SOT is poised to address many fundamental questions
about solar magnetohydrodynamics. This paper provides an overview; the details of the instrument are presented in a series
of companion papers.
Solar Physics 05/2008; 249(2):167-196. · 2.78 Impact Factor
-
Y. Suematsu,
S. Tsuneta,
K. Ichimoto,
T. Shimizu,
M. Otsubo, Y. Katsukawa,
M. Nakagiri,
M. Noguchi,
T. Tamura,
Y. Kato, [......],
M. Kubo,
I. Mikami,
H. Saito,
T. Matsushita,
N. Kawaguchi,
T. Nakaoji,
K. Nagae,
S. Shimada,
N. Takeyama,
T. Yamamuro
[show abstract]
[hide abstract]
ABSTRACT: The Solar Optical Telescope (SOT) aboard the Solar-B satellite (Hinode) is designed to perform high-precision photometric and polarimetric observations of the Sun in visible light spectra (388 – 668nm)
with a spatial resolution of 0.2 – 0.3arcsec. The SOT consists of two optically separable components: the Optical Telescope
Assembly (OTA), consisting of a 50-cm aperture Gregorian with a collimating lens unit and an active tip-tilt mirror, and an
accompanying Focal Plane Package (FPP), housing two filtergraphs and a spectro-polarimeter. The optomechanical and optothermal
performance of the OTA is crucial to attain unprecedented high-quality solar observations. We describe in detail the instrument
design and expected stable diffraction-limited on-orbit performance of the OTA, the largest state-of-the-art solar telescope
yet flown in space.
Solar Physics 05/2008; 249(2):197-220. · 2.78 Impact Factor
-
K. Ichimoto,
B. Lites,
D. Elmore,
Y. Suematsu,
S. Tsuneta, Y. Katsukawa,
T. Shimizu,
R. Shine,
T. Tarbell,
A. Title,
J. Kiyohara,
K. Shinoda,
G. Card,
A. Lecinski,
K. Streander,
M. Nakagiri,
M. Miyashita,
M. Noguchi,
C. Hoffmann,
T. Cruz
[show abstract]
[hide abstract]
ABSTRACT: The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial
resolution of 0.2 – 0.3arcsec. Aphotometric accuracy of 10−3 is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is
required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by
the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end
calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter
of the SOT and its final polarization characteristics.
Solar Physics 05/2008; 249(2):233-261. · 2.78 Impact Factor
