170 research outputs found
Differences between Doppler velocities of ions and neutral atoms in a solar prominence
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.Context. In astrophysical systems with partially ionized plasma the motion of ions is governed by the magnetic field while the neutral
particles can only feel the magnetic field’s Lorentz force indirectly through collisions with ions. The drift in the velocity between
ionized and neutral species plays a key role in modifying important physical processes like magnetic reconnection, damping of
magnetohydrodynamic waves, transport of angular momentum in plasma through the magnetic field, and heating.
Aims. This paper investigates the differences between Doppler velocities of calcium ions and neutral hydrogen in a solar prominence
to look for velocity differences between the neutral and ionized species.
Methods. We simultaneously observed spectra of a prominence over an active region in H I 397 nm, H I 434 nm, Ca II 397 nm, and
Ca II 854 nm using a high dispersion spectrograph of the Domeless Solar Telescope at Hida observatory, and compared the Doppler
velocities, derived from the shift of the peak of the spectral lines presumably emitted from optically-thin plasma.
Results. There are instances when the difference in velocities between neutral atoms and ions is significant, e.g. 1433 events (∼ 3 %
of sets of compared profiles) with a difference in velocity between neutral hydrogen atoms and calcium ions greater than 3σ of the
measurement error. However, we also found significant differences between the Doppler velocities of two spectral lines emitted from
the same species, and the probability density functions of velocity difference between the same species is not significantly different
from those between neutral atoms and ions.
Conclusions. We interpreted the difference of Doppler velocities as a result of motions of different components in the prominence
along the line of sight, rather than the decoupling of neutral atoms from plasma.This work was supported by a Grant-in-Aid for Scientific
Research (No. 22244013, P.I. K. Ichimoto; No. 15K17609, P.I. T. Anan; No.
16H01177, P.I. T. Anan) from the Ministry of Education, Culture, Sports, Science
and Technology of Japan. A.H. is supported by his STFC Emest Rutherford
Fellowship grant number ST/L00397X/2
Magnetic Flux Loss and Flux Transport in a Decaying Active Region
We estimate the temporal change of magnetic flux perpendicular to the solar
surface in a decaying active region by using a time series of the spatial
distribution of vector magnetic fields in the photosphere. The vector magnetic
fields are derived from full spectropolarimetric measurements with the Solar
Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux
transport rate in a decaying sunspot and its surrounding moat region. The
amount of magnetic flux that decreases in the sunspot and moat region is very
similar to magnetic flux transported to the outer boundary of the moat region.
The flux loss rates [] of magnetic elements with positive and
negative polarities are balanced each other around the outer boundary of the
moat region. These results suggest that most of the magnetic flux in the
sunspot is transported to the outer boundary of the moat region as moving
magnetic features, and then removed from the photosphere by flux cancellation
around the outer boundary of the moat region.Comment: 16 pages, 7 figures, Accepted for publication in Ap
The Evershed Effect with SOT/Hinode
The Solar Optical Telescope onboard Hinode revealed the fine-scale structure
of the Evershed flow and its relation to the filamentary structures of the
sunspot penumbra. The Evershed flow is confined in narrow channels with nearly
horizontal magnetic fields, embedded in a deep layer of the penumbral
atmosphere. It is a dynamic phenomenon with flow velocity close to the
photospheric sound speed. Individual flow channels are associated with tiny
upflows of hot gas (sources) at the inner end and downflows (sinks) at the
outer end. SOT/Hinode also discovered ``twisting'' motions of penumbral
filaments, which may be attributed to the convective nature of the Evershed
flow. The Evershed effect may be understood as a natural consequence of thermal
convection under a strong, inclined magnetic field. Current penumbral models
are discussed in the lights of these new Hinode observations.Comment: To appear in "Magnetic Coupling between the Interior and the
Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and
Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200
Chromospheric polarimetry through multi-line observations of the 850 nm spectral region
Future solar missions and ground-based telescopes aim to understand the
magnetism of the solar chromosphere. We performed a supporting study in
Quintero Noda et al. (2016) focused on the infrared Ca II 8542 A line and we
concluded that is one of the best candidates because it is sensitive to a large
range of atmospheric heights, from the photosphere to the middle chromosphere.
However, we believe that it is worth to try improving the results produced by
this line observing additional spectral lines. In that regard, we examined the
neighbour solar spectrum looking for spectral lines that could increase the
sensitivity to the atmospheric parameters. Interestingly, we discovered several
photospheric lines that greatly improve the photospheric sensitivity to the
magnetic field vector. Moreover, they are located close to a second
chromospheric line that also belongs to the Ca II infrared triplet, i.e. the Ca
II 8498 A line, and enhances the sensitivity to the atmospheric parameters at
chromospheric layers. We conclude that the lines in the vicinity of the Ca II
8542 A line not only increase its sensitivity to the atmospheric parameters at
all layers, but also they constitute an excellent spectral window for
chromospheric polarimetry.Comment: 11 pages, 8 figures, 1 tabl
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