5,276 research outputs found
Redefining the boundaries of interplanetary coronal mass ejections from observations at the ecliptic plane
On 2015 January 6-7, an interplanetary coronal mass ejection (ICME) was
observed at L1. This event, which can be associated with a weak and slow
coronal mass ejection, allows us to discuss on the differences between the
boundaries of the magnetic cloud and the compositional boundaries. A fast
stream from a solar coronal hole surrounding this ICME offers a unique
opportunity to check the boundaries' process definition and to explain
differences between them. Using Wind and ACE data, we perform a complementary
analysis involving compositional, magnetic, and kinematic observations
providing relevant information regarding the evolution of the ICME as
travelling away from the Sun. We propose erosion, at least at the front
boundary of the ICME, as the main reason for the difference between the
boundaries, and compositional signatures as the most precise diagnostic tool
for the boundaries of ICMEs.Comment: 9 pages and 7 figures in the original forma
BOND: Bayesian Oxygen and Nitrogen abundance Determinations in giant H II regions using strong and semi-strong lines
We present BOND, a Bayesian code to simultaneously derive oxygen and nitrogen
abundances in giant H II regions. It compares observed emission lines to a grid
of photoionization models without assuming any relation between O/H and N/O.
Our grid spans a wide range in O/H, N/O and ionization parameter U, and covers
different starburst ages and nebular geometries. Varying starburst ages
accounts for variations in the ionizing radiation field hardness, which arise
due to the ageing of H II regions or the stochastic sampling of the initial
mass function. All previous approaches assume a strict relation between the
ionizing field and metallicity. The other novelty is extracting information on
the nebular physics from semi-strong emission lines. While strong lines ratios
alone ([O III]/Hbeta, [O II]/Hbeta and [N II]/Hbeta) lead to multiple O/H
solutions, the simultaneous use of [Ar III]/[Ne III] allows one to decide
whether an H II region is of high or low metallicity. Adding He I/Hbeta pins
down the hardness of the radiation field. We apply our method to H II regions
and blue compact dwarf galaxies, and find that the resulting N/O vs O/H
relation is as scattered as the one obtained from the temperature-based method.
As in previous strong-line methods calibrated on photoionization models, the
BOND O/H values are generally higher than temperature-based ones, which might
indicate the presence of temperature fluctuations or kappa distributions in
real nebulae, or a too soft ionizing radiation field in the models.Comment: MNRAS in press; 21 pages, 22 figures, 2 tables; code, data and
results available at http://bond.ufsc.b
A Carrington-like geomagnetic storm observed in the 21st century
In September 1859 the Colaba observatory measured the most extreme
geomagnetic disturbance ever recorded at low latitudes related to solar
activity: the Carrington storm. This paper describes a geomagnetic disturbance
case with a profile extraordinarily similar to the disturbance of the
Carrington event at Colaba: the event on 29 October 2003 at Tihany magnetic
observatory in Hungary. The analysis of the H-field at different locations
during the "Carrington-like" event leads to a re-interpretation of the 1859
event. The major conclusions of the paper are the following: (a) the global Dst
or SYM-H, as indices based on averaging, missed the largest geomagnetic
disturbance in the 29 October 2003 event and might have missed the 1859
disturbance, since the large spike in the horizontal component (H) of
terrestrial magnetic field depends strongly on magnetic local time (MLT); (b)
the main cause of the large drop in H recorded at Colaba during the Carrington
storm was not the ring current but field-aligned currents (FACs), and (c) the
very local signatures of the H-spike imply that a Carrington-like event can
occur more often than expected.Comment: 18 pages, 2 figures, accepted for publication in SWS
Supergranular-scale magnetic flux emergence beneath an unstable filament
Here we report evidence of a large solar filament eruption on 2013, September
29. This smooth eruption, which passed without any previous flare, formed after
a two-ribbon flare and a coronal mass ejection towards Earth. The coronal mass
ejection generated a moderate geomagnetic storm on 2013, October 2 with very
serious localized effects. The whole event passed unnoticed to flare-warning
systems.
We have conducted multi-wavelength analyses of the Solar Dynamics Observatory
through Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager
(HMI) data. The AIA data on 304, 193, 211, and 94 \AA sample the transition
region and the corona, respectively, while HMI provides photospheric
magnetograms, continuum, and linear polarization data, in addition to the fully
inverted data provided by HMI.
[...]
We have observed a supergranular-sized emergence close to a large filament in
the boundary of the active region NOAA11850. Filament dynamics and magnetogram
results suggest that the magnetic flux emergence takes place in the
photospheric level below the filament. Reconnection occurs underneath the
filament between the dipped lines that support the filament and the
supergranular emergence. The very smooth ascent is probably caused by this
emergence and torus instability may play a fundamental role, which is helped by
the emergence.Comment: 9 pages, 6 figures, online material at Journa
Effects of an extra gauge boson on the top quark decay
The effects of an extra gauge boson with family nonuniversal fermion
couplings on the rare top quark decay gamma10^{-8}m_{Z'}=500Z'B(t --> c
\gamma)\sim 10^{-6}m_{Z'}=1$ TeV.Comment: New paragraphs included to clarify our results, conclusion remains
unchange
Acyclic orientations with path constraints
Many well-known combinatorial optimization problems can be stated over the
set of acyclic orientations of an undirected graph. For example, acyclic
orientations with certain diameter constraints are closely related to the
optimal solutions of the vertex coloring and frequency assignment problems. In
this paper we introduce a linear programming formulation of acyclic
orientations with path constraints, and discuss its use in the solution of the
vertex coloring problem and some versions of the frequency assignment problem.
A study of the polytope associated with the formulation is presented, including
proofs of which constraints of the formulation are facet-defining and the
introduction of new classes of valid inequalities
Transition (LINER/HII) nuclei as evolved Composite (Seyfert 2/Starburst) nuclei
We compare the circumnuclear stellar population and environmental properies
of Seyfert and Composite (Seyfert + Starburst) nuclei with those of LINERs and
LINER/HII transition galaxies (TOs), and discuss evidences for evolution from
Seyfert/Composite to LINER/TO nuclei.Comment: 2 pages, 1 figure; to appear in the Proceedings of IAU Symp. No. 222:
The Interplay among Black Holes, Stars and ISM in Galactic Nuclei, CUP, eds.
T. Storchi-Bergmann, L. Ho and H. R. Schmit
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