667 research outputs found
A European X-ray astrophysics mission
Five instruments (Bragg Spectrometer, Large Area Proportional and Scintillation Counter Detectors, Wide Field X-ray Cameras and a Gamma-Ray Burst Monitor) are discussed and estimates of their performance are given. Their scientific aims are summarized and sample observing programmes are discussed
Experimental study of spectral and spatial distribution of solar X-rays
The study of the physical conditions within the solar corona and the development of instrumentation and technical expertise necessary for advanced studies of solar X-ray emission are reported. Details are given on the Aerobee-borne-X-ray spectrometer/monochromator and also on the observing program. Preliminary discussions of some results are presented and include studies of helium-like line emission, mapping O(VII) and Ne(IX) lines, survey of O(VII) and Ne(IX) lines, study of plage regions and small flares, and analysis of line emission from individual active regions. It is concluded that the use of large-area collimated Bragg spectrometers to scan narrow wavelength intervals and the capability of the SPARCS pointing control to execute a complex observing program are established
Flows and Non-thermal Velocities in Solar Active Regions Observed with the Extreme-ultraviolet Imaging Spectrometer on Hinode: A Tracer of Active Region Sources of Heliospheric Magnetic Fields?
From Doppler velocity maps of active regions constructed from spectra
obtained by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
spacecraft we observe large areas of outflow (20-50 km/s) that can persist for
at least a day. These outflows occur in areas of active regions that are faint
in coronal spectral lines formed at typical quiet Sun and active region
temperatures. The outflows are positively correlated with non-thermal
velocities in coronal plasmas. The bulk mass motions and non-thermal velocities
are derived from spectral line centroids and line widths, mostly from a strong
line of Fe XII at 195.12 Angstroms. The electron temperature of the outflow
regions estimated from an Fe XIII to Fe XII line intensity ratio is about
1.2-1.4 MK. The electron density of the outflow regions derived from a density
sensitive intensity ratio of Fe XII lines is rather low for an active region.
Most regions average around 7E10+8 cm(-3), but there are variations on pixel
spatial scales of about a factor of 4. We discuss results in detail for two
active regions observed by EIS. Images of active regions in line intensity,
line width, and line centroid are obtained by rastering the regions. We also
discuss data from the active regions obtained from other orbiting spacecraft
that support the conclusions obtained from analysis of the EIS spectra. The
locations of the flows in the active regions with respect to the longitudinal
photospheric magnetic fields suggest that these regions might be tracers of
long loops and/or open magnetic fields that extend into the heliosphere, and
thus the flows could possibly contribute significantly to the solar wind.Comment: one tex file, 11 postscript figure file
Transition region features observed with Hinode/EIS
Two types of active region feature prominent at transition region
temperatures are identified in Hinode/EIS data of AR 10938 taken on 2007
January 20. The footpoints of 1 MK TRACE loops are shown to emit strongly in
emission lines formed at log T=5.4-5.8, allowing the temperature increase along
the footpoints to be clearly seen. A density diagnostic of Mg VII yields the
density in the footpoints, with one loop showing a decrease from 3x10^9 cm^-3
at the base to 1.5x10^9 cm^-3 at a projected height of 20 Mm. The second
feature is a compact active region transition region brightening which is
particularly intense in O V emission (log T=5.4) but also has a signature at
temperatures up to log T=6.3. The Mg VII diagnostic gives a density of 4x10^10
cm^-3, and emission lines of Mg VI and Mg VII show line profiles broadened by
50 km/s and wings extending beyond 200 km/s. Continuum emission in the short
wavelength band is also found to be enhanced, and is suggested to be free-bound
emission from recombination onto He^+.Comment: 11 pages, 9 figures, submitted to PASJ Hinode first results issu
Flows in the solar atmosphere due to the eruptions on the 15th July, 2002
<p>Which kind of flows are present during flares? Are they compatible with the present understanding of energy release and which model best describes the observations? We analyze successive flare events in order to answer these questions. The flares were observed in the magnetically complex NOAA active region (AR) 10030 on 15 July 2002. One of them is of GOES X-class. The description of these flares and how they relate to the break-out model is presented in Gary & Moore (2004). The Coronal Diagnostic Spectrometer on board SOHO observed this active region for around 14 h. The observed emission lines provided data from the transition region to the corona with a field of view covering more than half of the active region. In this paper we analyse the spatially resolved flows seen in the atmosphere from the preflare to the flare stages. We find evidence for evaporation occurring before the impulsive phase. During the main phase, the ongoing magnetic reconnection is demonstrated by upflows located at the edges of the flare loops (while downflows are found in the flare loops themselves). We also report the impact of a filament eruption on the atmosphere, with flows up to 300 km s<sup>-1</sup> observed at transition-region temperatures in regions well away from the location of the pre-eruptive filament. Our results are consistent with the predictions of the break out model before the impulsive phase of the flare; while, as the flare progresses, the directions of the flows are consistent with flare models invoking evaporation followed by cooling and downward plasma motions in the flare loops.</p>
A comparison of global magnetic field skeletons and active-region upflows
Plasma upflows have been detected in active regions using Doppler velocity maps. The origin and nature of these upflows is not well known with many of their characteristics determined from the examination of single events. In particular, some studies suggest these upflows occur along open field lines and, hence, are linked to sources of the solar wind. To investigate the relationship these upflows may have with the solar wind, and to probe what may be driving them, this paper considers seven active regions observed on the solar disc using the Extreme ultraviolet Imaging Spectrometer aboard Hinode between August 2011 and September 2012. Plasma upflows are observed in all these active regions. The locations of these upflows are compared to the global potential magnetic field extrapolated from the Solar Dynamics Observatory, Helioseismic and Magnetic Imager daily synoptic magnetogram taken on the day the upflows were observed. The structure of the magnetic field is determined by constructing its magnetic skeleton in order to help identify open-field regions and also sites where magnetic reconnection at global features is likely to occur. As a further comparison, measurements of the temperature, density and composition of the plasma are taken from regions with active-region upflows. In most cases the locations of the upflows in the active regions do not correspond to areas of open field, as predicted by a global coronal potential-field model, and therefore these upflows are not always sources of the slow solar wind. The locations of the upflows are, in general, intersected by separatrix surfaces associated with null points located high in the corona; these could be important sites of reconnection with global consequences.PostprintPeer reviewe
How Can Active Region Plasma Escape into the Solar Wind from below a Closed Helmet Streamer?
Recent studies show that active-region (AR) upflowing plasma, observed by the
EUV-Imaging Spectrometer (EIS), onboard Hinode, can gain access to open
field-lines and be released into the solar wind (SW) via magnetic-interchange
reconnection at magnetic null-points in pseudo-streamer configurations. When
only one bipolar AR is present on the Sun and it is fully covered by the
separatrix of a streamer, such as AR 10978 in December 2007, it seems unlikely
that the upflowing AR plasma can find its way into the slow SW. However,
signatures of plasma with AR composition have been found at 1 AU by Culhane et
al. (2014) apparently originating from the West of AR 10978. We present a
detailed topology analysis of AR 10978 and the surrounding large-scale corona
based on a potential-field source-surface (PFSS) model. Our study shows that it
is possible for the AR plasma to get around the streamer separatrix and be
released into the SW via magnetic reconnection, occurring in at least two main
steps. We analyse data from the Nan\c{c}ay Radioheliograph (NRH) searching for
evidence of the chain of magnetic reconnections proposed. We find a noise storm
above the AR and several varying sources at 150.9 MHz. Their locations suggest
that they could be associated with particles accelerated during the first-step
reconnection process and at a null point well outside of the AR. However, we
find no evidence of the second-step reconnection in the radio data. Our results
demonstrate that even when it appears highly improbable for the AR plasma to
reach the SW, indirect channels involving a sequence of reconnections can make
it possible.Comment: 26 pages, 10 figures. appears in Solar Physics, 201
EUV emission lines and diagnostics observed with Hinode/EIS
Quiet Sun and active region spectra from the Hinode/EIS instrument are
presented, and the strongest lines from different temperature regions
discussed. A list of emission lines recommended to be included in EIS
observation studies is presented based on analysis of blending and diagnostic
potential using the CHIANTI atomic database. In addition we identify the most
useful density diagnostics from the ions covered by EIS.Comment: 14 pages, 3 figures, submitted to PASJ Hinode first results issu
Comment on "CAWSES November 7-8, 2004, superstorm: Complex solar and interplanetary features in the post-solar maximum phase" by B. T. Tsurutani, E. Echer, F. L. Guarnieri, and J. U. Kozyra
Recently Tsurutani et al., (2008) (Paper 1) analyzed the complex
interplanetary structures during 7 to 8 November, 2004 to identify their
properties as well as resultant geomagnetic effects and the solar origins.
Besides mentioned paper by Gopalswamy et al., (2006) the solar and
interplanetary sources of geomagnetic storm on 7-10 November, 2004 have also
been discussed in details in series of other papers. Some conclusions of these
works essentially differ from conclusions of the Paper 1 but have not been
discussed by authors of Paper 1. In this comment we would like to discuss some
of these distinctions.Comment: Submitted for publication in Geophysical Research Letter
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
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