81 research outputs found
The application of a Trous wave filtering and Monte Carlo analysis on SECIS 2001 solar eclipse observations
8000 images of the Solar corona were captured during the June 2001 total
Solar eclipse. New software for the alignment of the images and an automated
technique for detecting intensity oscillations using multi scale wavelet
analysis were developed. Large areas of the images covered by the Moon and the
upper corona were scanned for oscillations and the statistical properties of
the atmospheric effects were determined. The a Trous wavelet transform was used
for noise reduction and Monte Carlo analysis as a significance test of the
detections. The effectiveness of those techniques is discussed in detail.Comment: 17 pages, 8 figures, accepted by Solar Physics Journal for
publication in Topical Issue: "Frontiers in Solar Image Processing
The detection of ultra-relativistic electrons in low Earth orbit
Aims. To better understand the radiation environment in low Earth orbit
(LEO), the analysis of in-situ observations of a variety of particles, at
different atmospheric heights, and in a wide range of energies, is needed.
Methods. We present an analysis of energetic particles, indirectly detected by
the Large Yield RAdiometer (LYRA) instrument on board ESA's Project for
On-board Autonomy 2 (PROBA2) satellite as background signal. Combining
Energetic Particle Telescope (EPT) observations with LYRA data for an
overlapping period of time, we identified these particles as electrons with an
energy range of 2 to 8 MeV. Results. The observed events are strongly
correlated to geo-magnetic activity and appear even during modest disturbances.
They are also well confined geographically within the L=4-6 McIlwain zone,
which makes it possible to identify their source. Conclusions. Although highly
energetic particles are commonly perturbing data acquisition of space
instruments, we show in this work that ultra-relativistic electrons with
energies in the range of 2-8 MeV are detected only at high latitudes, while not
present in the South Atlantic Anomaly region.Comment: Topical Issue: Flares, CMEs and SEPs and their space weather impacts;
20 pages; 7 figures; Presented during 13th European Space Weather Week, 201
Diffuse Light in the Virgo Cluster
We present deep optical imaging of the inner 1.5 x 1.5 degrees of the Virgo
cluster to search for diffuse intracluster light (ICL). Our image reaches a 1
sigma depth of mu_v=28.5 mag/arcsec^2 -- 1.5 mag/arcsec^2 deeper than previous
surveys -- and reveals an intricate web of diffuse intracluster light. We see
several long (>100 kpc) tidal streamers, as well as a myriad of smaller-scale
tidal tails and bridges between galaxies. The diffuse halo of M87 is traced out
to nearly 200 kpc, appearing very irregular on these scales, while significant
diffuse light is also detected around the M84/M86 pair. Several galaxies in the
core are embedded in common envelopes, suggesting they are true physical
subgroups. The complex substructure of Virgo's diffuse ICL reflects the
hierarchical nature of cluster assembly, rather than being the product of
smooth accretion around a central galaxy.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Dust Streamers in the Virgo Galaxy M86 from Ram Pressure Stripping of its Companion VCC 882
The giant elliptical galaxy M86 in Virgo has a ~28 kpc long dust trail inside
its optical halo that points toward the nucleated dwarf elliptical galaxy, VCC
882. The trail seems to be stripped material from the dwarf. Extinction
measurements suggest that the ratio of the total gas mass in the trail to the
blue luminosity of the dwarf is about unity, which is comparable to such ratios
in dwarf irregular galaxies. The ram pressure experienced by the dwarf galaxy
in the hot gaseous halo of M86 was comparable to the internal gravitational
binding energy density of the presumed former gas disk in VCC 882. Published
numerical models of this case are consistent with the overall trail-like
morphology observed here. Three concentrations in the trail may be evidence for
the predicted periodicity of the mass loss. The evaporation time of the trail
is comparable to the trail age obtained from the relative speed of the galaxies
and the trail length. Thus the trail could be continuously formed from stripped
replenished gas if the VCC 882 orbit is bound. However, the high gas mass and
the low expected replenishment rate suggest that this is only the first
stripping event. Implications for the origin of nucleated dwarf ellipticals are
briefly discussed.Comment: 22 pages, 7 figures, Astronomical Journal, August 2000, in pres
Eclipse observations of high-frequency oscillations in active region coronal loops
One of the mechanisms proposed for heating the corona above solar active
regions is the damping of magnetohydrodynamic (MHD) waves. Continuing on
previous work, we provide observational evidence for the existence of
high-frequency MHD waves in coronal loops observed during the August 1999 total
solar eclipse. A wavelet analysis is used to identify twenty 4x4 arcsec2 areas
showing intensity oscillations. All detections lie in the frequency Hz (5-3 s),
last for at least 3 periods at a confidence level of more than 99% and arise
just outside known coronal loops. This leads us to suggest that they occur in
low emission-measure or different temperature loops associated with the active
region.Comment: 6 pages, 6 figure
Re-Arrest Among Juvenile Justice-Involved Youth: An Examination Of The Static And Dynamic Risk Factors
The purpose of this study is to investigate the static and dynamic risk factors for re-arrest among detained youth by examining gender, race/ethnicity, age, special education and mental health variables (i.e., anger/irritability, depression/anxiety, somatic complaints, suicide ideation, thought disturbances, and traumatic experiences). The demographic profiles of detained youth with one admit were also compared with those with multiple admits to the juvenile detention center. With regards to static risk factors, older, white, and special education were significantly at risk of re-arrest. Concerning dynamic risk factors, only anger/irritability predicted re-arrest. Practice implications are also discussed
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