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Author name code: lin-yong
ADS astronomy entries on 2022-09-14
author:"Lin, Yong" AND aff:"Oslo"
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Title: The Atacama Cosmology Telescope: A Catalog of >4000
Sunyaev-Zel’dovich Galaxy Clusters
Authors: Hilton, M.; Sifón, C.; Naess, S.; Madhavacheril, M.;
Oguri, M.; Rozo, E.; Rykoff, E.; Abbott, T. M. C.; Adhikari, S.;
Aguena, M.; Aiola, S.; Allam, S.; Amodeo, S.; Amon, A.; Annis, J.;
Ansarinejad, B.; Aros-Bunster, C.; Austermann, J. E.; Avila, S.;
Bacon, D.; Battaglia, N.; Beall, J. A.; Becker, D. T.; Bernstein,
G. M.; Bertin, E.; Bhandarkar, T.; Bhargava, S.; Bond, J. R.; Brooks,
D.; Burke, D. L.; Calabrese, E.; Carrasco Kind, M.; Carretero, J.;
Choi, S. K.; Choi, A.; Conselice, C.; da Costa, L. N.; Costanzi, M.;
Crichton, D.; Crowley, K. T.; Dünner, R.; Denison, E. V.; Devlin,
M. J.; Dicker, S. R.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Duff,
S. M.; Duivenvoorden, A. J.; Dunkley, J.; Everett, S.; Ferraro, S.;
Ferrero, I.; Ferté, A.; Flaugher, B.; Frieman, J.; Gallardo, P. A.;
García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Giles, P.; Golec,
J. E.; Gralla, M. B.; Grandis, S.; Gruen, D.; Gruendl, R. A.; Gschwend,
J.; Gutierrez, G.; Han, D.; Hartley, W. G.; Hasselfield, M.; Hill,
J. C.; Hilton, G. C.; Hincks, A. D.; Hinton, S. R.; Ho, S. -P. P.;
Honscheid, K.; Hoyle, B.; Hubmayr, J.; Huffenberger, K. M.; Hughes,
J. P.; Jaelani, A. T.; Jain, B.; James, D. J.; Jeltema, T.; Kent, S.;
Knowles, K.; Koopman, B. J.; Kuehn, K.; Lahav, O.; Lima, M.; Lin,
Y. -T.; Lokken, M.; Loubser, S. I.; MacCrann, N.; Maia, M. A. G.;
Marriage, T. A.; Martin, J.; McMahon, J.; Melchior, P.; Menanteau, F.;
Miquel, R.; Miyatake, H.; Moodley, K.; Morgan, R.; Mroczkowski, T.;
Nati, F.; Newburgh, L. B.; Niemack, M. D.; Nishizawa, A. J.; Ogando,
R. L. C.; Orlowski-Scherer, J.; Page, L. A.; Palmese, A.; Partridge,
B.; Paz-Chinchón, F.; Phakathi, P.; Plazas, A. A.; Robertson, N. C.;
Romer, A. K.; Carnero Rosell, A.; Salatino, M.; Sanchez, E.; Schaan,
E.; Schillaci, A.; Sehgal, N.; Serrano, S.; Shin, T.; Simon, S. M.;
Smith, M.; Soares-Santos, M.; Spergel, D. N.; Staggs, S. T.; Storer,
E. R.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; To, C.;
Trac, H.; Ullom, J. N.; Vale, L. R.; Van Lanen, J.; Vavagiakis, E. M.;
De Vicente, J.; Wilkinson, R. D.; Wollack, E. J.; Xu, Z.; Zhang, Y.
2021ApJS..253....3H Altcode: 2020arXiv200911043H
We present a catalog of 4195 optically confirmed Sunyaev-Zel’dovich
(SZ) selected galaxy clusters detected with signal-to-noise ratio >4
in 13,211 deg<SUP>2</SUP> of sky surveyed by the Atacama Cosmology
Telescope (ACT). Cluster candidates were selected by applying a
multifrequency matched filter to 98 and 150 GHz maps constructed from
ACT observations obtained from 2008 to 2018 and confirmed using deep,
wide-area optical surveys. The clusters span the redshift range 0.04
< z < 1.91 (median z = 0.52). The catalog contains 222 z > 1
clusters, and a total of 868 systems are new discoveries. Assuming an SZ
signal versus mass-scaling relation calibrated from X-ray observations,
the sample has a 90% completeness mass limit of M <SUB>500c</SUB>
> 3.8 × 10<SUP>14</SUP> M <SUB>⊙</SUB>, evaluated at z = 0.5,
for clusters detected at signal-to-noise ratio >5 in maps filtered
at an angular scale of 2.′4. The survey has a large overlap with
deep optical weak-lensing surveys that are being used to calibrate the
SZ signal mass-scaling relation, such as the Dark Energy Survey (4566
deg<SUP>2</SUP>), the Hyper Suprime-Cam Subaru Strategic Program (469
deg<SUP>2</SUP>), and the Kilo Degree Survey (825 deg<SUP>2</SUP>). We
highlight some noteworthy objects in the sample, including potentially
projected systems, clusters with strong lensing features, clusters with
active central galaxies or star formation, and systems of multiple
clusters that may be physically associated. The cluster catalog will
be a useful resource for future cosmological analyses and studying the
evolution of the intracluster medium and galaxies in massive clusters
over the past 10 Gyr.
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Title: Distinguishing between coronal cloud prominences and channel
prominences and their associations with solar and stellar flares
Authors: Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong; da Silva,
Jacqueline Alves
2016IAUS..320..278M Altcode:
To better understand the differences between coronal cloud prominences
and channel prominences, we systematically identified and analyzed
coronal cloud prominences recorded in SDO/AIA images at 304 Å from
2010 May 20 through 2012 April 28. For the 225 cases identified,
their numbers vary directly with the sunspot number. Their durations
are typically less than 3 days. Their most frequent maximum height is
90,000 + and - 10,000 km. We offer our hypothesis that many coronal
cloud prominences originate from some of the mass of previously erupted
filaments ejected high out of their filament channels; subsequently part
of this mass falls and collects in leaky magnetic troughs among coronal
magnetic fields which constrain the leaked mass to slowly drain downward
along curved trajectories where it appears as coronal rain. Currently
there is inadequate evidence for a convincing correspondence between
either coronal cloud prominences or channel prominences with stellar
prominences detected to date.
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Title: Observing Cascades of Solar Bullets at High Resolution. II.
Authors: Scullion, E.; Engvold, O.; Lin, Y.; Rouppe van der Voort, L.
2015ApJ...814..123S Altcode:
High resolution observations from the Swedish 1-m Solar Telescope
revealed bright, discrete, blob-like structures (which we refer to as
solar bullets) in the Hα 656.28 nm line core that appear to propagate
laterally across the solar atmosphere as clusters in active regions
(ARs). These small-scale structures appear to be field aligned and
many bullets become triggered simultaneously and traverse collectively
as a cluster. Here, we conduct a follow-up study on these rapidly
evolving structures with coincident observations from the Solar Dynamics
Observatory/Atmospheric Imaging Assembly. With the co-aligned data sets,
we reveal (a) an evolving multithermal structure in the bullet cluster
ranging from chromospheric to at least transition region temperatures,
(b) evidence for cascade-like behavior and corresponding bidirectional
motions in bullets within the cluster, which indicate that there is a
common source of the initial instability leading to bullet formation,
and (c) a direct relationship between co-incident bullet velocities
observed in Hα and He ii 30.4 nm and an inverse relationship with
respect to bullet intensity in these channels. We find evidence
supporting that bullets are typically composed of a cooler, higher
density core detectable in Hα with a less dense, hotter, and fainter
co-moving outer sheath. Bullets unequivocally demonstrate the finely
structured nature of the AR corona. We have no clear evidence for
bullets being associated with locally heated (or cooled), fast flowing
plasma. Fast MHD pulses (such as solitons) could best describe the
dynamic properties of bullets whereas the presence of a multithermal
structure is new.
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Title: Distinguishing Between Different Types of Prominences
Associated with Solar Flares
Authors: Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong
2015IAUGA..2255962M Altcode:
In the early days of solar astronomy, any feature that extended above
the solar limb was called a prominence. However, many such coronal
features have been sufficiently studied to justify more specific
names such as flare loops, surges, and flaring arches. Each of these
named phenomena has different properties and involves different
physical processes from other solar prominences. If we exclude
these well-identified phenomena, we find that the majority of the
remaining prominences can be grouped into only two categories that
are distinctly different from each other. The main two types are (1)
channel prominences or channel filaments when seen against the solar
disk and (2) coronal cloud prominences, including narrow, down-flows
named coronal rain. We illustrate the many significant differences
between channel prominences and coronal cloud prominences. One of the
fundamental differences is that channel prominences often have patterns
of mass motions useful in anticipating many flares while coronal cloud
prominences tend to occur hours after major solar flares. We also raise
the question of whether the much taller coronal cloud prominences could
have a counterpart in prominences on solar-like stars with magnetic
fields of greater magnitude than the Sun.
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Title: Prominence seismology using ground- and space-based
observations
Authors: Ballester, J. L.; Arregui, I.; Oliver, R.; Terradas, J.;
Soler, R.; Lin, Y.; Engvold, O.; Langagen, O.; Rouppe van der Voort,
L. H. M.
2012EAS....55..169B Altcode:
Ground- and space-based observations have confirmed the presence of
oscillatory motions in prominences and they have been interpreted in
terms of magnetohydrodynamic (MHD) waves. This interpretation opens the
door to perform prominence seismology, whose main aim is to determine
physical parameters in magnetic and plasma structures (prominences)
that are difficult to measure by direct means. Here, two prominence
seismology applications are presented.
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Title: Small-scale, Dynamic Bright Blobs in Solar Filaments and
Active Regions
Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M.
2012ApJ...747..129L Altcode: 2012arXiv1201.0406L
High-cadence high spatial resolution observations in Hα with the
Swedish 1 m Solar Telescope on La Palma have revealed the existence
of small-scale highly dynamic bright blobs. A fast wavelength
tuning spectropolarimeter provides spectral information of these
structures. The blobs slide along thin magnetic threads at speeds
in the range from 45 km s<SUP>-1</SUP> to 111 km s<SUP>-1</SUP>. The
blobs have a slightly elongated shape and their lengths increase by a
factor of three from close to half an arcsecond when they first appear
until they disappear one to two minutes later. The brightest blobs
show the highest speed. The widths of the Hα line emission of the
blobs correspond to non-thermal velocities in the plasma less than
10 km s<SUP>-1</SUP>, which implies that they are not the result of
shock-driven heating. The dynamic character of the bright blobs is
similar to what can be expected from an MHD fast-mode pulse.
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Title: Filament Thread-like Structures and Their Small-amplitude
Oscillations
Authors: Lin, Yong
2011SSRv..158..237L Altcode: 2010SSRv..tmp..176L
Thanks to gradually improving observational capabilities, both from
space and ground-based observatories, it is now generally accepted
that thin threads (width ∼200 km) constitute the building blocks of
solar filaments and prominences. At ultra-small scales, high quality
image sequences show a non-static picture of filaments and reveal that
their oscillatory behavior is an important dynamic feature of these
structures. Filament seismology sheds light on the internal magnetic
structures of filaments and their interactions with surrounding
solar regions. Understanding the overall magnetic topology of solar
filaments and prominences including their small-scale thread-like
structures is essential in interpretation and understanding of their
oscillations. For this reason we aim here to present an update of the
dynamic and spatial structures of prominences and filaments as inferred
from high resolution observations in the past decennia. Some constraints
in high resolution observations are addressed. Our review focuses mainly
on the observational aspects and aims to summarize recent oscillation
studies of individual filament threads and groups of threads. Finally,
some theoretical interpretations of oscillations of filament threads and
the inferred physical conditions of filament plasma are also discussed.
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Title: Swaying Threads of a Solar Filament
Authors: Lin, Y.; Soler, R.; Engvold, O.; Ballester, J. L.; Langangen,
Ø.; Oliver, R.; Rouppe van der Voort, L. H. M.
2009ApJ...704..870L Altcode: 2009arXiv0909.2792L
From recent high-resolution observations obtained with the Swedish 1
m Solar Telescope in La Palma, we detect swaying motions of individual
filament threads in the plane of the sky. The oscillatory characters of
these motions are comparable with oscillatory Doppler signals obtained
from corresponding filament threads. Simultaneous recordings of motions
in the line of sight and in the plane of the sky give information
about the orientation of the oscillatory plane. These oscillations
are interpreted in the context of the magnetohydrodynamic (MHD)
theory. Kink MHD waves supported by the thread body are proposed as
an explanation of the observed thread oscillations. On the basis of
this interpretation and by means of seismological arguments, we give
an estimation of the thread Alfvén speed and magnetic field strength
by means of seismological arguments.
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Title: On small active region filaments, fibrils and surges
Authors: Lin, Y.; Martin, S. F.; Engvold, O.; Rouppe van der Voort,
L. H. M.; van Noort, M.
2008AdSpR..42..803L Altcode:
High resolution Hα images and magnetograms (0.2 arc s) of an active
region were obtained in alternating time series at 42 s cadences
using the Swedish 1-m Solar Telescope on 2004 August 21. The Hα
filtergrams reveal an active region filament and surges consisting
of thread-like structures which have widths similar to the widths of
chromospheric fibrils, both recorded down to the resolution limit in
the best images. All observed structures in the active region appear
highly dynamic. Fibrils show counterstreaming strongly resembling the
counterstreaming threads in filaments. Streaming, along the threads
of surges extending more than 10 arc s, is higher in speed (∼20
km s<SUP>-1</SUP>) than in the filament and fibrils and appears to
flow independently over and above the chromospheric fibrils. Blue
shifts seen in the Hα Dopplergrams confirm the outward mass motion
of the surges. However, in at least one case, we also see simultaneous
downflows from the same site but in the opposite direction and downward
toward the chromosphere. We suggest that the site between these
two outward and downward flows identifies the place where magnetic
reconnection could occur and thereby cause of the surge. This appears
to imply that the reconnection site is in the high chromosphere or
low corona.
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Title: A Method of Resolving the 180-Degree Ambiguity by Employing
the Chirality of Solar Features
Authors: Martin, S. F.; Lin, Y.; Engvold, O.
2008SoPh..250...31M Altcode: 2008SoPh..tmp..105M
The 180-degree ambiguity in magnetic field direction along polarity
reversal boundaries can be resolved often and reliably by the
chiral method. The chiral method requires (1) identification of
the chirality of at least one solar feature related to a polarity
reversal boundary along which the field direction is sought and (2)
knowledge of the polarity of the network magnetic field on at least
one side of the polarity reversal boundary. In the context of the
Sun, chirality is an observable signature of the handedness of the
magnetic field of a solar feature. We concentrate on how to determine
magnetic field direction from chirality definitions and illustrate
the technique in eight examples. The examples cover the spectrum of
polarity boundaries associated with filament channels and filaments
ranging from those connected with active regions to those on the
quiet Sun. The applicability of the chiral method to all categories of
filaments supports the view that active region filaments and quiescent
filaments are the extreme ends in a continuous spectrum of filaments.
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Title: The Unique 3D Magnetic Structure of Filaments
Authors: Lin, Y.; Engvold, O.; Martin, S.; Panasenco, O.
2008AGUSMSH23A..05L Altcode:
Filaments in active regions most clearly have the form of long
thin ribbons as seen in Hα. The ribbon structure is also readily
demonstrated for quiescent filaments when seen from an end view as
a filament is transported across the east or west limb due to solar
rotation. In addition to the primary ribbon structure, filaments
also have shorter, secondary structures called barbs which connect
some threads of the main ribbon structure to the chromosphere;
these are also seen in the end view of filaments at the limb. This
connection with the chromosphere is corroborated in high resolution
images of filaments recorded against the disk at the 1-meter Swedish
Solar Telescope (SST). In these high resolution Hα movies, the lower
parts of all threads are recognizable because they move less freely
than the higher parts. The connection of the ends of the threads of
the main filament ribbon and the ends of the filament barbs to the
chromosphere/photosphere is strong evidence alone that filaments have
their own magnetic fields separate from surrounding coronal magnetic
fields. The chirality (handedness) of filaments provides further
evidence that filaments have their own magnetic fields. The two forms of
dextral and sinistral chirality are generally manifest in the relative
direction of the deviation of barbs from the main ribbon. However, the
sign of chirality is most clear in the thread structure of all barbs
seen in Hα images from the SST. From a number of characteristics of
the observed mass motions of filament threads of the order of several
to tens of kilometers per second, we have previously concluded that
filament threads are field-aligned. Therefore we use the threads
and their mass motions to construct the 3D configuration of filament
magnetic fields. We end this presentation with movies of filaments
from STEREO/SECCHI/EUVI consistent with our thread model of filaments.
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Title: Measurements of Plasma Motions in Dynamic Fibrils
Authors: Langangen, Øystein; Rouppe van der Voort, Luc; Lin, Yong
2008ApJ...673.1201L Altcode: 2007arXiv0710.1011L
We present a 40 minute time series of filtergrams from the red and
blue wings of the Hα line in an active region near the solar disk
center. From these filtergrams we construct both Dopplergrams and summed
"line center" images. Several dynamic fibrils (DFs) are identified
in the summed images. The data are used to simultaneously measure the
proper motion and the Doppler signals in DFs. For calibration of the
Doppler signals, we use spatially resolved spectrograms of a similar
active region. Significant variations in the calibration constant for
different solar features are observed, and only regions containing
DFs have been used in order to reduce calibration errors. We find
a coherent behavior of the Doppler velocity and the proper motion
that clearly demonstrates that the evolution of DFs involves plasma
motion. The Doppler velocities are found to be a factor of 2-3 smaller
than velocities derived from proper motions in the image plane. The
difference can be explained by the radiative processes involved, as
the Doppler velocity is a result of the local atmospheric velocity
weighted with the response function. As a result, the Doppler velocity
originates from a wide range of heights in the atmosphere. This is
contrasted with the proper-motion velocity, which is measured from the
sharply defined bright tops of the DFs and is therefore a very local
velocity measure. The Doppler signal originates from well below the
top of the DF. Finally, we discuss how this difference, together with
the lower spatial resolution of older observations, has contributed to
some of the confusion about the identity of DFs, spicules, and mottles.
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Title: Evidence of Traveling Waves in Filament Threads
Authors: Lin, Y.; Engvold, O.; Rouppe van der Voort, L. H. M.; van
Noort, M.
2007SoPh..246...65L Altcode:
High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m
Solar Telescope resolve numerous very thin, thread-like structures in
solar filaments. The threads are believed to represent thin magnetic
flux tubes that must be longer than the observable threads. We report
on evidence for small-amplitude (1 - 2 km s<SUP>−1</SUP>) waves
propagating along a number of threads with an average phase velocity of
12 km s<SUP>−1</SUP> and a wavelength of 4″. The oscillatory period
of individual threads vary from 3 to 9 minutes. Temporal variation
of the Doppler velocities averaged over a small area containing a
number of individual threads shows a short-period (3.6 minutes) wave
pattern. These short-period oscillations could possibly represent fast
modes in accordance with numerical fibril models proposed by Díaz et
al. (Astron. Astrophys.379, 1083, 2001). In some cases, it is clear
that the propagating waves are moving in the same direction as the
mass flows.
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Title: Solar Filaments and Photospheric Network
Authors: Lin, Yong; Wiik, Jun Elin; Engvold, Oddbjørn; Van Der Voort,
Luc Rouppe; Frank, Zoe A.
2005SoPh..227..283L Altcode:
The locations of barbs of quiescent solar filaments are compared with
the photospheric/chromospheric network, which thereby serves as a
proxy of regions with enhanced concentrations of magnetic flux. The
study covers quiet regions, where also the photospheric network as
represented by flow converging regions, i.e., supergranular cell
boundaries, contain largely weak magnetic fields. It is shown that
close to 65% of the observed end points of barbs falls within the
network boundaries. The remaining fraction points into the inner areas
of the network cells. This confirms earlier findings (Lin et al.,
Solar Physics, 2004) that quiescent filaments are basically connected
with weaker magnetic fields in the photosphere below.
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Title: Thin Threads of Solar Filaments
Authors: Lin, Yong; Engvold, OddbjØrn; der Voort, Luc Rouppe van;
Wiik, Jun Elin; Berger, Thomas E.
2005SoPh..226..239L Altcode:
High-resolution images obtained in Hα with the new Swedish Solar
Telescope at La Palma, Spain, have been used for studies of fine-scale
threads in solar filaments. The widths of the thin threads are ≤0.3
arcsec. The fact that the width of the thinnest threads is comparable
to the diffraction limit of the telescope of about 0.14 arcsec,
at the wavelength of Hα, suggests that even thinner threads may
exist. Assuming that the threads represent thin magnetic strings,
we conclude that only a small fraction of these are filled with
observable absorbing plasma, at a given time. The absorbing plasma
is continuously flowing along the thread structures at velocities
15± 10 kms<SUP>−1</SUP>, which suggests that the flows must be
field-aligned. In one case where a bundle of thin threads appears
to be rooted in the nearby photosphere, we find that the individual
threads connects with intergranular, dark lanes in the photosphere. We
do not find signs of typical network fields at the `roots' of the fine
threads, as normally evidenced by bright points in associated G-band
images. It is suggested that filament threads are rooted in relatively
weak magnetic fields.
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Title: Multi-wavelength study of a high-latitude EUV filament
Authors: Schmieder, Brigitte; Lin, Yong; Heinzel, Petr; Schwartz, Pavol
2004SoPh..221..297S Altcode:
A large filament was observed during a multi-wavelength coordinated
campaign on June 19, 1998 in the Hα line with the Swedish Vacuum Solar
Telescope (SVST) at La Palma, in the coronal lines Fe ix/x 171 Å and
Fe xi 195 Å with the Transition Region and Coronal Explorer (TRACE)
and in EUV lines with the SOHO/CDS spectrometer and the hydrogen Lyman
series with the SOHO/SUMER spectrometer. Because of its high-latitude
location, it is possible to disentangle the physical properties of the
Hα filament and the filament channel seen in EUV lines. TRACE images
point out a dark region fitting the Hα fine-structure threads and a
dark corridor (filament channel), well extended south of the magnetic
inversion line. A similar pattern is observed in the CDS EUV-line
images. The opacity of the hydrogen and helium resonance continua at
171 Å is almost two orders of magnitude lower than that at the Hi head
(912 Å) and thus similar to the opacity of the Hα line. Since we do
not see the filament channel in Hα, this would imply that it should
also be invisible in TRACE lines. Thus, the diffuse dark corridor is
interpreted as due to the coronal `volume blocking' by a cool plasma
which extends to large altitudes. Such extensions were also confirmed by
computing the heights from the projection geometry and by simulations
of the CDS and TRACE line intensities using the spectroscopic model
of EUV filaments (Heinzel, Anzer, and Schmieder, 2003). Finally,
our NLTE analysis of selected hydrogen Lyman lines observed by SUMER
also leads to a conclusion that the dark filament channel is due to
a presence of relatively cool plasma having low densities and being
distributed at altitudes reaching the Hα filament.
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Title: Magnetic field topology inferred from studies of fine threads
in solar filaments
Authors: Lin, Yong
2004PhDT.......255L Altcode:
No abstract at ADS
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Title: Counterstreaming in a Large Polar Crown Filament
Authors: Lin, Yong; Engvold, OddbjØ rn; Wiik, Jun Elin
2003SoPh..216..109L Altcode:
The motion of small-scale structures is well resolved in high-resolution
filament images that were observed on 19 June 1998 with the Swedish
Vacuum Solar Telescope, La Palma. The filament was between 80 000
and 100 000 km high. The study is based on two hours of narrow-band
observations at three wavelength positions in Hα. Velocities along
the line of sight and in the transverse direction, respectively,
V<SUB>los</SUB> and V<SUB>tr</SUB>, were measured for a large number
of individual small-scale filament structures. Small features are all
moving along nearly parallel threads, some in one direction along
the threads and the remainder in the other direction, a pattern of
motion known as counterstreaming. The net flow velocities in the two
directions are about 8 km s<SUP>−1</SUP> and both are tilted by an
angle δ≃16° relative to the plane of the sky. This angle is less
than expected, by factors between 2.0 and 2.5, relative to the local
horizontal plane. We believe that V<SUB>los</SUB> is underestimated
by these factors due to a line-shift reducing effect by the underlying
Hα absorption line of the chromosphere.
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Title: Filament activation and magnetic reconnection
Authors: Deng, Yuanyong; Lin, Yong; Schmieder, Brigitte; Engvold,
OddbjØrn
2002SoPh..209..153D Altcode:
A curved filament in a decaying active region (AR 8329) was observed
on 9 September 1998 with a combination of several instruments. The
main data base is a 4-hour long time series of 1 min cadence using the
Lockheed tunable filter mounted in the Swedish Vacuum Solar Tower in
La Palma (SVST). Filtergrams obtained at several wavelength positions
in Hα images are used to derive Doppler images. Interleaved images
in the magnetic sensitive Fe i 6302.5 Å line yield corresponding
magnetograms. Supplementing observations are collected from TRACE and
the French Multi-Channel Double Pass spectrograph (MSDP) mounted in
the German VTT in Tenerife. The filament, which consists of several
discrete fragments with nearly horizontal fine structures, undergoes
activity and counter-streaming bulk flow, but without erupting. The
magnetic field inversion line of this active region is complex and
strongly influenced by intrusion of a positive polarity area in a
following negative polarity of the region. The positive polarity
area contains a small sunspot surrounded by moving magnetic features
(MMFs). The MMFs interact directly with the parasitic polarities in
the filament channel, and thereby gives rise to merging and canceling
magnetic flux. When the interaction occurs at the location of the feet
(`barbs') of the filament notable activations are observed (ejection of
`blobs'). The ejections of `blobs' are preceded by twist of filament
threads and the `blobs' move along downward bending field lines towards
the photosphere close to the sound speed.
