304 research outputs found
Emergence of Small-Scale Magnetic Loops in the Quiet Sun Internetwork
We study the emergence of magnetic flux at very small spatial scales (less
than 2 arcsec) 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 A 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 the vertical dipoles drift -carried by the
plasma motions- towards the surrounding intergranular lanes. These events take
place within typical granulation timescales.Comment: 9 pages (referee format), 3 figures. Accepted for publication in ApJ
Letter
Sunspot observations from the SOUP instrument on Spacelab 2
A series of white light images obtained by the SOUP instrument on Spacelab 2 of active region 4682 on August 5, 1985 were analyzed in the area containing sunspots. Although the umbra of the spot is underexposed, the film is well exposed in the penumbral regions. These data were digitally processed to remove noise and to separate p-mode oscillations from low velocity material motions. The results of this preliminary investigation include: (1) proper motion measurements of a radial outflow in the photospheric granulation pattern just outside the penumbra; (2) discovery of occasional bright structures (streakers) that appear to be ejected outward from the penumbra; (3) broad dark clouds moving outward in the penumbra in addition to the well known bright penumbral grains moving inward; (4) apparent extensions and contractions of penumbral filaments over the photosphere; and (5) observation of a faint bubble or loop-like structure which seems to expand from two bright penumbral filaments into the photosphere
Vector spectropolarimetry of dark-cored penumbral filaments with Hinode
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. 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.Comment: Accepted for publication in ApJ Letters. Use the Postscript version
for high quality figure
Strategy for the inversion of Hinode spectropolarimetric measurements in the quiet Sun
In this paper we propose an inversion strategy for the analysis of
spectropolarimetric measurements taken by {\em Hinode} in the quiet Sun. The
spectropolarimeter of the Solar Optical Telescope aboard {\em Hinode} records
the Stokes spectra of the \ion{Fe}{i} line pair at 630.2 nm with unprecendented
angular resolution, high spectral resolution, and high sensitivity. We discuss
the need to consider a {\em local} stray-light contamination to account for the
effects of telescope diffraction. The strategy is applied to observations of a
wide quiet Sun area at disk center. Using these data we examine the influence
of noise and initial guess models in the inversion results. Our analysis yields
the distributions of magnetic field strengths and stray-light factors. They
show that quiet Sun internetwork regions consist mainly of hG fields with
stray-light contaminations of about 0.8.Comment: To appear in Publications of the Astronomical Society of Japan, 8
pages, 10 figure
Formation Process of a Light Bridge Revealed with the Hinode Solar Optical Telescope
The Solar Optical Telescope (SOT) aboard HINODE successfully and continuously
observed a formation process of a light bridge in a matured sunspot of the NOAA
active region 10923 for several days with high spatial resolution. During its
formation, many umbral dots were observed emerging from the leading edges of
penumbral filaments, and intruding into the umbra rapidly. The precursor of the
light bridge formation was also identified as the relatively slow inward motion
of the umbral dots which emerged not near the penumbra, but inside the umbra.
The spectro-polarimeter on SOT provided physical conditions in the photosphere
around the umbral dots and the light bridges. We found the light bridges and
the umbral dots had significantly weaker magnetic fields associated with
upflows relative to the core of the umbra, which implies that there was hot gas
with weak field strength penetrating from subphotosphere to near the visible
surface inside those structures. There needs to be a mechanism to drive the
inward motion of the hot gas along the light bridges. We suggest that the
emergence and the inward motion are triggered by a buoyant penumbral flux tube
as well as the subphotospheric flow crossing the sunspot.Comment: 8 pages, 6 figures, accepted in the PASJ Hinode special issu
Flare Ribbons Observed with G-band and FeI 6302A Filters of the Solar Optical Telescope on Board Hinode
The Solar Optical Telescope (SOT) on board Hinode satellite observed an X3.4
class flare on 2006 December 13. Typical two-ribbon structure was observed, not
only in the chromospheric CaII H line but also in G-band and FeI 6302A line.
The high-resolution, seeing-free images achieved by SOT revealed, for the first
time, the sub-arcsec fine structures of the "white light" flare. The G-band
flare ribbons on sunspot umbrae showed a sharp leading edge followed by a
diffuse inside, as well as previously known core-halo structure. The underlying
structures such as umbral dots, penumbral filaments and granules were visible
in the flare ribbons. Assuming that the sharp leading edge was directly heated
by particle beam and the diffuse parts were heated by radiative back-warming,
we estimate the depth of the diffuse flare emission using the intensity profile
of the flare ribbon. We found that the depth of the diffuse emission is about
100 km or less from the height of the source of radiative back-warming. The
flare ribbons were also visible in the Stokes-V images of FeI 6302A, as a
transient polarity reversal. This is probably related to "magnetic transient"
reported in the literature. The intensity increase in Stokes-I images indicates
that the FeI 6302A line was significantly deformed by the flare, which may
cause such a magnetic transient.Comment: 14 pages, 7 figures, PASJ in pres
A Tale Of Two Spicules: The Impact of Spicules on the Magnetic Chromosphere
We use high-resolution observations of the Sun in Ca II H 3968 A from the
Solar Optical Telescope on Hinode to show that there are at least two types of
spicules that dominate the structure of the magnetic solar chromosphere. Both
types are tied to the relentless magnetoconvective driving in the photosphere,
but have very different dynamic properties. ``Type-I'' spicules are driven by
shock waves that form when global oscillations and convective flows leak into
the upper atmosphere along magnetic field lines on 3-7 minute timescales.
``Type-II'' spicules are much more dynamic: they form rapidly (in ~10s), are
very thin (<200km wide), have lifetimes of 10-150s (at any one height) and seem
to be rapidly heated to (at least) transition region temperatures, sending
material through the chromosphere at speeds of order 50-150 km/s. The
properties of Type II spicules suggest a formation process that is a
consequence of magnetic reconnection, typically in the vicinity of magnetic
flux concentrations in plage and network. Both types of spicules are observed
to carry Alfven waves with significant amplitudes of order 20 km/s.Comment: 8 pages, 5 figures, accepted for Hinode special issue of PAS
Quiet Sun internetwork magnetic fields from the inversion of Hinode measurements
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.Comment: To appear in ApJ letter
Chromospheric Anemone Jets as Evidence of Ubiquitous Reconnection
The heating of the solar chromosphere and corona is a long-standing puzzle in
solar physics. Hinode observations show the ubiquitous presence of
chromospheric anemone jets outside sunspots in active regions. They are
typically 3 to 7 arc seconds = 2000 to 5000 kilometers long and 0.2 to 0.4 arc
second = 150 to 300 kilometers wide, and their velocity is 10 to 20 kilometers
per second. These small jets have an inverted Y-shape, similar to the shape of
x-ray anemone jets in the corona. These features imply that magnetic
reconnection similar to that in the corona is occurring at a much smaller
spatial scale throughout the chromosphere and suggest that the heating of the
solar chromosphere and corona may be related to small-scale ubiquitous
reconnection.Comment: 10 pages, 5 figure
Lead‐Free Semiconductors: Soft Chemistry, Dimensionality Control, and Manganese‐Doping of Germanium Halide Perovskites
Lead halide perovskites have drawn enormous interest due to their exceptional photovoltaic and optoelectronic properties. However, the heavy metal lead is harmful to humans and the environment resulting in a need for strategies to replace this toxic element. Herein, we report a facile aqueous synthesis of CsGeX3 (X=I, Br) perovskite nanocrystals with size control achieved by varying the concentration of a cysteammonium halide ligand. We observe a variety of morphologies including pyramidal, hexagonal, and spheroidal. CsGeX3 nanocrystals undergo a lattice expansion due to partial replacement of Cs+ with larger cysteNH3+ cations into their lattice. We successfully dope Mn2+into the CsGeX3 lattice for the first time with incorporation of up to 29% in bulk and 16% in nano samples. XRD peak shifts and EPR hyperfine splitting strongly indicate that Mn2+ is doped into the lattice. Our results introduce a new member to the lead‐free halide perovskite family and set the fundamental stage for their use in optoelectronic devices
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