673 research outputs found
Near-infrared spectropolarimetry of a delta-spot
Sunspots harboring umbrae of both magnetic polarities within a common
penumbra (delta-spots) are often but not always related to flares. We present
first near-infrared (NIR) observations (Fe I 1078.3 nm and Si I 1078.6 nm
spectra) obtained with the Tenerife Infrared Polarimeter (TIP) at the Vacuum
Tower Telescope (VTT) in Tenerife on 2012 June 17, which afford accurate and
sensitive diagnostics to scrutinize the complex fields along the magnetic
neutral line of a delta-spot within active region NOAA 11504. We examine the
vector magnetic field, line-of-sight (LOS) velocities, and horizontal proper
motions of this rather inactive delta-spot. We find a smooth transition of the
magnetic vector field from the main umbra to that of opposite polarity
(delta-umbra), but a discontinuity of the horizontal magnetic field at some
distance from the delta-umbra on the polarity inversion line. The magnetic
field decreases faster with height by a factor of two above the delta-umbra.
The latter is surrounded by its own Evershed flow. The Evershed flow coming
from the main umbra ends at a line dividing the spot into two parts. This line
is marked by the occurrence of central emission in the Ca II 854.2 nm line.
Along this line, high chromospheric LOS-velocities of both signs appear. We
detect a shear flow within the horizontal flux transport velocities parallel to
the dividing line.Comment: 4 pages, will appear as Letter in Astronomy & Astrophysic
Properties of the inner penumbral boundary and temporal evolution of a decaying sunspot
It was empirically determined that the umbra-penumbra boundaries of stable
sunspots are characterized by a constant value of the vertical magnetic field.
We analyzed the evolution of the photospheric magnetic field properties of a
decaying sunspot belonging to NOAA 11277 between August 28 - September 3, 2011.
The observations were acquired with the spectropolarimeter on-board of the
Hinode satellite. We aim to proof the validity of the constant vertical
magnetic-field boundary between the umbra and penumbra in decaying sunspots. A
spectral-line inversion technique was used to infer the magnetic field vector
from the full-Stokes profiles. In total, eight maps were inverted and the
variation of the magnetic properties in time were quantified using linear or
quadratic fits. We found a linear decay of the umbral vertical magnetic field,
magnetic flux, and area. The penumbra showed a linear increase of the vertical
magnetic field and a sharp decay of the magnetic flux. In addition, the
penumbral area quadratically decayed. The vertical component of the magnetic
field is weaker on the umbra-penumbra boundary of the studied decaying sunspot
compared to stable sunspots. Its value seem to be steadily decreasing during
the decay phase. Moreover, at any time of the shown sunspot decay, the inner
penumbra boundary does not match with a constant value of the vertical magnetic
field, contrary to what was seen in stable sunspots. During the decaying phase
of the studied sunspot, the umbra does not have a sufficiently strong vertical
component of the magnetic field and is thus unstable and prone to be
disintegrated by convection or magnetic diffusion. No constant value of the
vertical magnetic field was found for the inner penumbral boundary.Comment: Accepted for publication in Astronomy & Astrophysics, 6 pages, 7
figure
Magnetic loop emergence within a granule
We investigate the temporal evolution of magnetic flux emerging within a
granule in the quiet-Sun internetwork at disk center. We combined IR
spectropolarimetry performed in two Fe I lines at 1565 nm with
speckle-reconstructed G-band imaging. We determined the magnetic field
parameters by a LTE inversion of the full Stokes vector using the SIR code, and
followed their evolution in time. To interpret the observations, we created a
geometrical model of a rising loop in 3D. The relevant parameters of the loop
were matched to the observations where possible. We then synthesized spectra
from the 3D model for a comparison to the observations. We found signatures of
magnetic flux emergence within a growing granule. In the early phases, a
horizontal magnetic field with a distinct linear polarization signal dominated
the emerging flux. Later on, two patches of opposite circular polarization
signal appeared symmetrically on either side of the linear polarization patch,
indicating a small loop-like structure. The mean magnetic flux density of this
loop was roughly 450 G, with a total magnetic flux of around 3x10^17 Mx. During
the ~12 min episode of loop occurrence, the spatial extent of the loop
increased from about 1 to 2 arcsec. The middle part of the appearing feature
was blueshifted during its occurrence, supporting the scenario of an emerging
loop. The temporal evolution of the observed spectra is reproduced to first
order by the spectra derived from the geometrical model. The observed event can
be explained as a case of flux emergence in the shape of a small-scale loop.Comment: 10 pages, 13 figures; accepted for Astronomy and Astrophysics; ps and
eps figures in full resolution are available at
http://www.astro.sk/~koza/figures/aa2009_loop
Ca II 8542 \AA\ brightenings induced by a solar microflare
We study small-scale brightenings in Ca II 8542 \AA\ line-core images to
determine their nature and effect on localized heating and mass transfer in
active regions. High-resolution 2D spectroscopic observations of an active
region in the Ca II 8542 \AA\ line were acquired with the GFPI attached to the
1.5-meter GREGOR telescope. Inversions of the spectra were carried out using
NICOLE. We identified three brightenings of sizes up to 2"x2". We found
evidence that the brightenings belonged to the footpoints of a microflare (MF).
The properties of the observed brightenings disqualified the scenarios of
Ellerman bombs or IRIS bombs. However, this MF shared some common properties
with flaring active-region fibrils or flaring arch filaments (FAFs): (1) FAFs
and MFs are both apparent in chromospheric and coronal layers according to the
AIA channels, and (2) both show flaring arches with lifetimes of about 3.0-3.5
min and lengths of about 20". The inversions revealed heating by 600 K at the
footpoint location in the ambient chromosphere during the impulsive phase.
Connecting the footpoints, a dark filamentary structure appeared in the Ca II
line-core images. Before the start of the MF, the spectra of this structure
already indicated average blueshifts, meaning upward motions of the plasma
along the LOS. During the impulsive phase, these velocities increased up to
-2.2 km/s. Downflows dominated at the footpoints. However, in the upper
photosphere, slight upflows occurred during the impulsive phase. Hence,
bidirectional flows are present in the footpoints of the MF. Conclusions: We
detected Ca II brightenings that coincided with the footpoint location of an
MF. The MF event led to a rise of plasma in the upper photosphere, both before
and during the impulsive phase. Excess mass, previously raised to at most
chromospheric layers, slowly drained downward along arches toward the
footpoints of the MF.Comment: Accepted for publication in Astronomy & Astrophysics, 13 pages, 6
figures, 1 online movi
Temporal evolution of arch filaments as seen in He I 10830 \r{A}
We study the evolution of an arch filament system (AFS) and of its individual
arch filaments to learn about the processes occurring in them. We observed the
AFS at the GREGOR solar telescope on Tenerife at high cadence with the very
fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I
10830 \AA\ spectral range. The He I triplet profiles were fitted with analytic
functions to infer line-of-sight (LOS) velocities to follow plasma motions
within the AFS. We tracked the temporal evolution of an individual arch
filament over its entire lifetime, as seen in the He I 10830 \AA\ triplet. The
arch filament expanded in height and extended in length from 13" to 21". The
lifetime of this arch filament is about 30 min. About 11 min after the arch
filament is seen in He I, the loop top starts to rise with an average Doppler
velocity of 6 km/s. Only two minutes later, plasma drains down with supersonic
velocities towards the footpoints reaching a peak velocity of up to 40 km/s in
the chromosphere. The temporal evolution of He I 10830 \AA\ profiles near the
leading pore showed almost ubiquitous dual red components of the He I triplet,
indicating strong downflows, along with material nearly at rest within the same
resolution element during the whole observing time. We followed the arch
filament as it carried plasma during its rise from the photosphere to the
corona. The material then drained toward the photosphere, reaching supersonic
velocities, along the legs of the arch filament. Our observational results
support theoretical AFS models and aids in improving future models.Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 15
figures, 1 online movi
Physiologically based pharmacokinetic model for T84.66: A monoclonal anti-CEA antibody
Antibodies directed against tumor associated antigens are being increasingly used for detection and treatment of cancers; however, there is an incomplete understanding of the physiological determinants of antibody pharmacokinetics and tumor distribution. The purpose of this study is to (a) compare the plasma pharmacokinetics of T84.66, a monoclonal anti-CEA antibody directed against tumor associated carcinoembryonic antigen (CEA), in control and CEA expressing LS174T xenograft bearing mice, and (b) to develop a physiologically based pharmacokinetic (PBPK) model capable of integrating the influence of CEA and the IgG salvage receptor, FcRn, on T84.66 disposition. T84.66 pharmacokinetics were studied following i.v. administration (1, 10, 25 mg/kg) in control and xenograft bearing mice. In control mice, no significant differences in clearance were observed across the dose range studied. In mice bearing xenograft tumors, clearance was increased by four- to sevenfold, suggesting the presence of a “target mediated” elimination pathway. T84.66 plasma disposition was characterized with a PBPK model, and the model was applied to successfully predict antibody concentrations in tumor tissue. The PBPK model will be used to assist in the development of antibody-based targeting strategies for CEA-positive tumors. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1582–1600, 2010Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64917/1/21918_ftp.pd
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