471 research outputs found
Seasonal and site-specific variation in vapour and aerosol phase PAHs over Flanders (Belgium) and their relation with anthropogenic activities
Peer reviewe
Time delays in quasi-periodic pulsations observed during the X2.2 solar flare on 2011 February 15
We report observations of quasi-periodic pulsations (QPPs) during the X2.2
flare of 2011 February 15, observed simultaneously in several wavebands. We
focus on fluctuations on time scale 1-30 s and find different time lags between
different wavebands. During the impulsive phase, the Reuven Ramaty High Energy
Solar Spectroscopic Imager (RHESSI) channels in the range 25-100 keV lead all
the other channels. They are followed by the Nobeyama RadioPolarimeters at 9
and 17 GHz and the Extreme Ultra-Violet (EUV) channels of the Euv
SpectroPhotometer (ESP) onboard the Solar Dynamic Observatory (SDO). The
Zirconium and Aluminum filter channels of the Large Yield Radiometer (LYRA)
onboard the Project for On-Board Autonomy (PROBA2) satellite and the SXR
channel of ESP follow. The largest lags occur in observations from the
Geostationary Operational Environmental Satellite (GOES), where the channel at
1-8 {\AA} leads the 0.5-4 {\AA} channel by several seconds. The time lags
between the first and last channels is up to 9 s. We identified at least two
distinct time intervals during the flare impulsive phase, during which the QPPs
were associated with two different sources in the Nobeyama RadioHeliograph at
17 GHz. The radio as well as the hard X-ray channels showed different lags
during these two intervals. To our knowledge, this is the first time that time
lags are reported between EUV and SXR fluctuations on these time scales. We
discuss possible emission mechanisms and interpretations, including flare
electron trapping
Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops
We report the first observation of multiple-periodic propagating disturbances
along a fan-like coronal structure simultaneously detected in both intensity
and Doppler shift in the Fe XII 195 A line with the EUV Imaging Spectrometer
(EIS) onboard Hinode. A new application of coronal seismology is provided based
on this observation. We analyzed the EIS sit-and-stare mode observation of
oscillations using the running difference and wavelet techniques. Two harmonics
with periods of 12 and 25 min are detected. We measured the Doppler shift
amplitude of 1-2 km/s, the relative intensity amplitude of 3%-5% and the
apparent propagation speed of 100-120 km/s. The amplitude relationship between
intensity and Doppler shift oscillations provides convincing evidence that
these propagating features are a manifestation of slow magnetoacoustic waves.
Detection lengths (over which the waves are visible) of the 25 min wave are
about 70-90 Mm, much longer than those of the 5 min wave previously detected by
TRACE. This difference may be explained by the dependence of damping length on
the wave period for thermal conduction. Based on a linear wave theory, we
derive an inclination of the magnetic field to the line-of-sight about 598
deg, a true propagation speed of 12825 km/s and a temperature of
0.70.3 MK near the loop's footpoint from our measurements.Comment: 4 pages and 4 figures, with 3 online figures and 1 online table;
Astron & Astrophys Letter, in pres
The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing
The Sun Watcher with Active Pixels and Image Processing (SWAP) is an EUV
solar telescope on board ESA's Project for Onboard Autonomy 2 (PROBA2) mission
launched on 2 November 2009. SWAP has a spectral bandpass centered on 17.4 nm
and provides images of the low solar corona over a 54x54 arcmin field-of-view
with 3.2 arcsec pixels and an imaging cadence of about two minutes. SWAP is
designed to monitor all space-weather-relevant events and features in the low
solar corona. Given the limited resources of the PROBA2 microsatellite, the
SWAP telescope is designed with various innovative technologies, including an
off-axis optical design and a CMOS-APS detector. This article provides
reference documentation for users of the SWAP image data.Comment: 26 pages, 9 figures, 1 movi
Characterization of the heme pocket structure and ligand binding kinetics of non-symbiotic hemoglobins from the model legume lotus japonicus
Plant hemoglobins (Hbs) are found in nodules of legumes and actinorhizal plants but also in non-symbiotic organs of monocots and dicots. Non-symbiotic Hbs (nsHbs) have been classified into two phylogenetic groups. Class 1 nsHbs show an extremely high O2 affinity and are induced by hypoxia and nitric oxide (NO), whereas class 2 nsHbs have moderate O2 affinity and are induced by cold and cytokinins. The functions of nsHbs are still unclear, but some of them rely on the capacity of hemes to bind diatomic ligands and catalyze the NO dioxygenase (NOD) reaction (oxyferrous Hb + NO ? ferric Hb + nitrate). Moreover, NO may nitrosylate Cys residues of proteins. It is therefore important to determine the ligand binding properties of the hemes and the role of Cys residues. Here, we have addressed these issues with the two class 1 nsHbs (LjGlb1-1 and LjGlb1-2) and the single class 2 nsHb (LjGlb2) of Lotus japonicus, which is a model legume used to facilitate the transfer of genetic and biochemical information into crops. We have employed carbon monoxide (CO) as a model ligand and resonance Raman, laser flash photolysis, and stopped-flow spectroscopies to unveil major differences in the heme environments and ligand binding kinetics of the three proteins, which suggest non-redundant functions. In the deoxyferrous state, LjGlb1-1 is partially hexacoordinate, whereas LjGlb1-2 shows complete hexacoordination (behaving like class 2 nsHbs) and LjGlb2 is mostly pentacoordinate (unlike other class 2 nsHbs). LjGlb1-1 binds CO very strongly by stabilizing it through hydrogen bonding, but LjGlb1-2 and LjGlb2 show lower CO stabilization. The changes in CO stabilization would explain the different affinities of the three proteins for gaseous ligands. These affinities are determined by the dissociation rates and follow the order LjGlb1-1 > LjGlb1-2 > LjGlb2. Mutations LjGlb1-1 C78S and LjGlb1-2 C79S caused important alterations in protein dynamics and stability, indicating a structural role of those Cys residues, whereas mutation LjGlb1-1 C8S had a smaller effect. The three proteins and their mutant derivatives exhibited similarly high rates of NO consumption, which were due to NOD activity of the hemes and not to nitrosylation of Cys residues
Beyond small-scale transients: a closer look at the diffuse quiet solar corona
Within the quiet Sun corona imaged at 1 MK, much of the field of view
consists of diffuse emission that appears to lack the spatial structuring that
is so evident in coronal loops or bright points. We seek to determine if these
diffuse regions are categorically different in terms of their intensity
fluctuations and spatial configuration from the more well-studied dynamic
coronal features. We analyze a time series of observations from Solar Orbiter's
High Resolution Imager in the Extreme Ultraviolet to quantify the
characterization of the diffuse corona at high spatial and temporal
resolutions. We then compare this to the dynamic features within the field of
view, mainly a coronal bright point. We find that the diffuse corona lacks
visible structuring, such as small embedded loops, and that this is persistent
over the 25 min duration of the observation. The intensity fluctuations of the
diffuse corona, which are within +/-5%, are significantly smaller in comparison
to the coronal bright point. Yet, the total intensity observed in the diffuse
corona is of the same order as the bright point. It seems inconsistent with our
data that the diffuse corona is a composition of small loops or jets or that it
is driven by discrete small heating events that follow a power-law-like
distribution. We speculate that small-scale processes like MHD turbulence might
be energizing the diffuse regions, but at this point we cannot offer a
conclusive explanation for the nature of this feature.Comment: Accepted for publication in A&A. 10 pages, 8 figure
The Extreme Ultraviolet Imager (EUI) onboard the SOLAR ORBITER mission
peer reviewedSolar Orbiter will for the first time study the Sun with a full suite of in-situ and remote sensing instruments from inside 0.25 AU and will provide imaging and spectral observations of the Sun’s polar regions, from out of the ecliptic. This proximity to the Sun will also have the significant advantage that the spacecraft will fly in near synchronization with the Sun’s rotation, allowing observations of the solar surface and heliosphere to be studied from a near co-rotating vantage point for almost a complete solar rotation. The mission’s ambitious characteristics draw severe constraints on the design of these instruments. The scientific objectives of Solar Orbiter rely ubiquitously on the Extreme EUV Imager suite (EUI). The EUI instrument suite on board of Solar Orbiter is composed of two high resolution imagers (HRI), one at Lyman α and one dual band at the two 174 and 335 EUV passbands in the extreme UV, and one dual band full-sun imager (FSI) working alternatively at the two 174 and 304 EUV passbands. In all the units, the image is produced by a mirror-telescope, working in nearly normal incidence. The EUV reflectivity of the optical surfaces is obtained with specific EUV multilayered coatings, providing the spectral selection of the EUV units (1HRI and 1 FSI). The spectral selection is complemented with very thin filters rejecting the visible and IR radiation. Due to its orbit, EUI / Solar Orbiter will see 20 solar constants and an entrance baffle to limit the solar heat input into EUI is needed. The paper presents the scientific objectives of EUI and also covers the EUI instrument development plan which will require some trade-off between existing and promising technologies
Dynamics of Coronal Bright Points as seen by Sun Watcher using Active Pixel System detector and Image Processing (SWAP), Atmospheric Imaging Assembly AIA), and Helioseismic and Magnetic Imager (HMI)
The \textit{Sun Watcher using Active Pixel system detector and Image
Processing}(SWAP) on board the \textit{PRoject for OnBoard Autonomy\todash 2}
(PROBA\todash 2) spacecraft provides images of the solar corona in EUV channel
centered at 174 \AA. These data, together with \textit{Atmospheric Imaging
Assembly} (AIA) and the \textit{Helioseismic and Magnetic Imager} (HMI) on
board \textit{Solar Dynamics Observatory} (SDO), are used to study the dynamics
of coronal bright points. The evolution of the magnetic polarities and
associated changes in morphology are studied using magnetograms and
multi-wavelength imaging. The morphology of the bright points seen in
low-resolution SWAP images and high-resolution AIA images show different
structures, whereas the intensity variations with time show similar trends in
both SWAP 174 and AIA 171 channels. We observe that bright points are seen in
EUV channels corresponding to a magnetic-flux of the order of Mx. We
find that there exists a good correlation between total emission from the
bright point in several UV\todash EUV channels and total unsigned photospheric
magnetic flux above certain thresholds. The bright points also show periodic
brightenings and we have attempted to find the oscillation periods in bright
points and their connection to magnetic flux changes. The observed periods are
generally long (10\todash 25 minutes) and there is an indication that the
intensity oscillations may be generated by repeated magnetic reconnection
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