233 research outputs found
Evidence of quiet Sun chromospheric activity related to an emerging small-scale magnetic loop
Aims: We investigate the temporal evolution of magnetic flux emergence in the
quiet Sun atmosphere close to disk center. Methods: We combine high-resolution
SoHO/MDI magnetograms with TRACE observations taken in the 1216 {\AA} channel
in order to analyze the temporal evolution of an emerging small-scale magnetic
loop and its traces in the chromosphere. Results: At first place, we find
signatures of flux emergence very close to the edge of a supergranular network
boundary located at disk center. The new emerging flux appears first in the MDI
magnetograms in form of an asymmetric bipolar element, i.e. the patch with
negative polarity is roughly two-times weaker than the corresponding patch with
opposite polarity. The average values of magnetic flux and magnetic flux
densities reach 1.6 x 10^18 Mx, -8.5 x 10^17 Mx, and 55 Mx cm^-2, -30 Mx cm^-2,
respectively. The spatial distance between the opposite polarity patches of the
emerged feature increases from about 2.5" to 5.0" during the lifetime of the
loop which was not longer than 36 min. A more precise lifetime-estimate of the
feature was not possible because of a gap in the temporal sequence of the MDI
magnetograms. The chromospheric response to the emerged magnetic dipole occurs
~ 9 minutes later with respect to the photospheric magnetograms. It consists of
a quasi-periodic sequence of time-localized brightenings visible in the 1216
{\AA} TRACE channel apparent for ~ 14 minutes and being co-spatial with the
axis connecting the two patches of opposite magnetic polarity. Conclusions: We
identify the observed event as a small-scale magnetic loop emerging at
photospheric layers and subsequently rising up to the chromosphere. We discuss
the possibility that the fluctuations detected in the chromospheric emission
probably reflect magnetic field oscillations which propagate to the
chromosphere in form of waves.Comment: 6 pages, 4 figures, 1 table, Astronomy and Astrophysics, in pres
Astrophysics Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop
ABSTRACT Aims. We investigate the temporal evolution of magnetic flux emergence in the quiet-Sun atmosphere close to disk center. Methods. We combined high-resolution SoHO/MDI magnetograms with TRACE observations taken in the 1216 Ă
channel to analyze the temporal evolution of an emerging small-scale magnetic loop and its traces in the chromosphere. Results. We find signatures of flux emergence very close to the edge of a supergranular network boundary located at disk center. The new emerging flux appeared first in the MDI magnetograms in form of an asymmetric bipolar element, i.e., the patch with negative polarity is roughly twice as weak as the corresponding patch with opposite polarity. The average values of magnetic flux and magnetic flux densities reached 1.6 Ă 10 18 Mx, â8.5 Ă 10 17 Mx, and 55 Mx cm â2 , -30 Mx cm â2 , respectively. The spatial distance between the opposite polarity patches of the emerged feature increased from about 2. 5 to 5. 0 during the lifetime of the loop, which was 36 min. A more precise lifetime-estimate of the feature was not possible because of a gap in the temporal sequence of the MDI magnetograms. The chromospheric response to the emerged magnetic dipole occurred âŒ9 min later than in the photospheric magnetograms. It consisted of a quasi-periodic sequence of time-localized brightenings visible in the 1216 Ă
TRACE channel for âŒ14 min that were co-spatial with the axis connecting the two patches of opposite magnetic polarity. Conclusions. We identify the observed event as a small-scale magnetic loop emerging at photospheric layers that subsequently rose to the chromosphere. We discuss the possibility that the fluctuations detected in the chromospheric emission probably reflect magneticfield oscillations which propagate to the chromosphere in the form of waves
The GREGOR Fabry-P\'erot Interferometer
The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light
instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio
del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated
mounting. Thanks to its large-format, high-cadence CCD detectors with
sophisticated computer hard- and software it is capable of scanning spectral
lines with a cadence that is sufficient to capture the dynamic evolution of the
solar atmosphere. The field-of-view (FOV) of 50" x 38" is well suited for quiet
Sun and sunspot observations. However, in the vector spectropolarimetric mode
the FOV reduces to 25" x 38". The spectral coverage in the spectroscopic mode
extends from 530-860 nm with a theoretical spectral resolution R of about
250,000, whereas in the vector spectropolarimetric mode the wavelength range is
at present limited to 580-660 nm. The combination of fast narrow-band imaging
and post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales down to
about 50 km on the solar surface.Comment: 14 pages, 17 figures, 4 tables; pre-print of AN 333, p.880-893, 2012
(AN special issue to GREGOR
A retrospective of the GREGOR solar telescope in scientific literature
In this review, we look back upon the literature, which had the GREGOR solar
telescope project as its subject including science cases, telescope subsystems,
and post-focus instruments. The articles date back to the year 2000, when the
initial concepts for a new solar telescope on Tenerife were first presented at
scientific meetings. This comprehensive bibliography contains literature until
the year 2012, i.e., the final stages of commissioning and science
verification. Taking stock of the various publications in peer-reviewed
journals and conference proceedings also provides the "historical" context for
the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.Comment: 6 pages, 2 color figures, this is the pre-peer reviewed version of
Denker et al. 2012, Astron. Nachr. 333, 81
The solar chromosphere at high resolution with IBIS. I. New insights from the Ca II 854.2 nm line
(Abridged)
Aims: In this paper, we seek to establish the suitability of imaging
spectroscopy performed in the Ca II 854.2 nm line as a means to investigate the
solar chromosphere at high resolution.
Methods: We utilize monochromatic images obtained with the Interferometric
BIdimensional Spectrometer (IBIS) at multiple wavelengths within the Ca II
854.2 nm line and over several quiet areas. We analyze both the morphological
properties derived from narrow-band monochromatic images and the average
spectral properties of distinct solar features such as network points,
internetwork areas and fibrils.
Results: The spectral properties derived over quiet-Sun targets are in full
agreement with earlier results obtained with fixed-slit spectrographic
observations, highlighting the reliability of the spectral information obtained
with IBIS. Furthermore, the very narrowband IBIS imaging reveals with much
clarity the dual nature of the Ca II 854.2 nm line: its outer wings gradually
sample the solar photosphere, while the core is a purely chromospheric
indicator. The latter displays a wealth of fine structures including bright
points, akin to the Ca II H2V and K2V grains, as well as fibrils originating
from even the smallest magnetic elements. The fibrils occupy a large fraction
of the observed field of view even in the quiet regions, and clearly outline
atmospheric volumes with different dynamical properties, strongly dependent on
the local magnetic topology. This highlights the fact that 1-D models
stratified along the vertical direction can provide only a very limited
representation of the actual chromospheric physics.Comment: 13 pages, 8 figures. Accepted in A&A. Revised version after referee's
comments. New Fig. 1 and 7. Higher quality figures in
http://www.arcetri.astro.it/~gcauzzi/papers/ibis.caii.pd
The role of dimensionality in neuronal network dynamics
The research leading to these results has received funding from the European Unionâs Seventh Framework Programme under grant agreement FP7 ICT 2011 â 284553 (Acronym: Si-CODE), the NEUROSCAFFOLDS Project n. 604263, the National Natural Science Foundation of China (Grant number: 51361130033) and the Ministry of Science and Technology of China (973 Grant number: 2014CB965003)
The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding
rocket payload built to study the crucial interface between the solar
chromosphere and the corona by observing the strongest line in the solar
spectrum, the Ly-a line at 1216 {\AA}. In two flights, VAULT succeeded in
obtaining the first ever sub-arcsecond (0.5") images of this region with high
sensitivity and cadence. Detailed analyses of those observations have
contributed significantly to new ideas about the nature of the transition
region. Here, we present a broad overview of the Ly-a atmosphere as revealed by
the VAULT observations, and bring together past results and new analyses from
the second VAULT flight to create a synthesis of our current knowledge of the
high-resolution Ly-a Sun. We hope that this work will serve as a good reference
for the design of upcoming Ly-a telescopes and observing plans.Comment: 28 pages, 11 figure
The Imaging Magnetograph eXperiment (IMaX) for the Sunrise balloon-borne solar observatory
The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by
four institutions in Spain that flew on board the Sunrise balloon-borne
telesocope in June 2009 for almost six days over the Arctic Circle. As a
polarimeter IMaX uses fast polarization modulation (based on the use of two
liquid crystal retarders), real-time image accumulation, and dual beam
polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the
instrument uses a LiNbO3 etalon in double pass and a narrow band pre-filter to
achieve a spectral resolution of 85 mAA. IMaX uses the high Zeeman sensitive
line of Fe I at 5250.2 AA and observes all four Stokes parameters at various
points inside the spectral line. This allows vector magnetograms, Dopplergrams,
and intensity frames to be produced that, after reconstruction, reach spatial
resolutions in the 0.15-0.18 arcsec range over a 50x50 arcsec FOV. Time
cadences vary between ten and 33 seconds, although the shortest one only
includes longitudinal polarimetry. The spectral line is sampled in various ways
depending on the applied observing mode, from just two points inside the line
to 11 of them. All observing modes include one extra wavelength point in the
nearby continuum. Gauss equivalent sensitivities are four Gauss for
longitudinal fields and 80 Gauss for transverse fields per wavelength sample.
The LOS velocities are estimated with statistical errors of the order of 5-40
m/s. The design, calibration and integration phases of the instrument, together
with the implemented data reduction scheme are described in some detail.Comment: 17 figure
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