784 research outputs found
Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations
Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scatterin
On the Spatial Coherence of Magnetic Ejecta: Measurements of Coronal Mass Ejections by Multiple Spacecraft Longitudinally Separated by 0.01 AU
Measurements of coronal mass ejections (CMEs) by multiple spacecraft at small
radial separations but larger longitudinal separations is one of the ways to
learn about the three-dimensional structure of CMEs. Here, we take advantage of
the orbit of the Wind spacecraft that ventured to distances of up to 0.012
astronomical units (au) from the Sun-Earth line during the years 2000 to 2002.
Combined with measurements from ACE, which is in a tight halo orbit around L1,
the multipoint measurements allow us to investigate how the magnetic field
inside magnetic ejecta (MEs) changes on scales of 0.005 - 0.012 au. We identify
21 CMEs measured by these two spacecraft for longitudinal separations of 0.007
au or more. We find that the time-shifted correlation between 30-minute
averages of the non-radial magnetic field components measured at the two
spacecraft is systematically above 0.97 when the separation is 0.008 au or
less, but is on average 0.89 for greater separations. Overall, these newly
analyzed measurements, combined with 14 additional ones when the spacecraft
separation is smaller, point towards a scale length of longitudinal magnetic
coherence inside MEs of 0.25 - 0.35 au for the magnitude of the magnetic field
but 0.06 - 0.12 au for the magnetic field components. This finding raises
questions about the very nature of MEs. It also highlights the need for
additional "mesoscale" multi-point measurements of CMEs with longitudinal
separations of 0.01 - 0.2 au.Comment: Published in ApJL, 6 page
Topical Issue in Solar Physics: Flux-rope Structure of Coronal Mass Ejections Preface
This Topical Issue of Solar Physics, devoted to the study of flux-rope
structure in coronal mass ejections (CMEs), is based on two Coordinated Data
Analysis Workshops (CDAWs) held in 2010 (20 - 23 September in Dan Diego,
California, USA) and 2011 (September 5-9 in Alcala, Spain). The primary purpose
of the CDAWs was to address the question: Do all CMEs have flux rope structure?
There are 18 papers om this topical issue, including this preface.Comment: 4 page
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Solar Energetic Particles Produced by a Slow Coronal Mass Ejection at ∼0.25 au
We present an analysis of Parker Solar Probe (PSP) IS⊙IS observations of ~30–300 keV n⁻¹ ions on 2018 November 11 when PSP was about 0.25 au from the Sun. Five hours before the onset of a solar energetic particle (SEP) event, a coronal mass ejection (CME) was observed by STEREO-A/COR2, which crossed PSP about a day later. No shock was observed locally at PSP, but the CME may have driven a weak shock earlier. The SEP event was dispersive, with higher energy ions arriving before the lower energy ones. Timing suggests the particles originated at the CME when it was at ~7.4R_⊙. SEP intensities increased gradually from their onset over a few hours, reaching a peak, and then decreased gradually before the CME arrived at PSP. The event was weak, having a very soft energy spectrum (−4 to −5 spectral index). The earliest arriving particles were anisotropic, moving outward from the Sun, but later, the distribution was observed to be more isotropic. We present numerical solutions of the Parker transport equation for the transport of 30–300 keV n⁻¹ ions assuming a source comoving with the CME. Our model agrees well with the observations. The SEP event is consistent with ion acceleration at a weak shock driven briefly by the CME close to the Sun, which later dissipated before arriving at PSP, followed by the transport of ions in the interplanetary magnetic field
Two close binaries across the hydrogen-burning limit in the Praesepe open cluster
We present Keck I/OSIRIS and Keck II/NIRC2 adaptive optics imaging of two
member candidates of the Praesepe stellar cluster (d=186.180.11 pc;
590-790 Myr), UGC J08451066+2148171 (L1.50.5) and UGCS J083019352003293
(no spectroscopic classification). We resolved UGCS J084510662148171 into a
binary system in the near-infrared, with a -band wavelength flux ratio of
0.890.04, a projected separation of 60.31.3 mas (11.20.7 au;
1). We also resolved UGCS J083019352003293 into a binary system with
a flux ratio of 0.460.03 and a separation of 62.50.9 mas. Assuming
zero eccentricity, we estimate minimum orbital periods of 100 years for
both systems. According to theoretical evolutionary models, we derive masses in
the range of 0.074-0.078 M and 0.072-0.076 M for the
primary and secondary of UGCS J084510662148171 for an age of 700100
Myr. In the case of UGCS J083019352003293, the primary is a low-mass star at
the stellar/substellar boundary (0.070-0.078 M) while the companion
candidate might be a brown dwarf (0.051-0.065 M). These are the first
two binaries composed of L dwarfs in Praesepe. They are benchmark systems to
derive the location of the substellar limit at the age and metallicity of
Praesepe, determine the age of the cluster based on the lithium depletion
boundary test, derive dynamical masses, and improve low-mass stellar and
substellar evolutionary models at a well-known age and metallicity.Comment: 12 pages, 5 figures, 3 tables, accepted for publication in MNRA
The 1989 and 2015 outbursts of V404 Cygni: a global study of wind-related optical features
The black hole transient V404 Cygni exhibited a bright outburst in June 2015
that was intensively followed over a wide range of wavelengths. Our team
obtained high time resolution optical spectroscopy (~90 s), which included a
detailed coverage of the most active phase of the event. We present a database
consisting of 651 optical spectra obtained during this event, that we combine
with 58 spectra gathered during the fainter December 2015 sequel outburst, as
well as with 57 spectra from the 1989 event. We previously reported the
discovery of wind-related features (P-Cygni and broad-wing line profiles)
during both 2015 outbursts. Here, we build diagnostic diagrams that enable us
to study the evolution of typical emission line parameters, such as line fluxes
and equivalent widths, and develop a technique to systematically detect outflow
signatures. We find that these are present throughout the outburst, even at
very low optical fluxes, and that both types of outflow features are observed
simultaneously in some spectra, confirming the idea of a common origin. We also
show that the nebular phases depict loop patterns in many diagnostic diagrams,
while P-Cygni profiles are highly variable on time-scales of minutes. The
comparison between the three outbursts reveals that the spectra obtained during
June and December 2015 share many similarities, while those from 1989 exhibit
narrower emission lines and lower wind terminal velocities. The diagnostic
diagrams presented in this work have been produced using standard measurement
techniques and thus may be applied to other active low-mass X-ray binaries.Comment: Accepted for publication in MNRAS. 23 pages paper, plus a 9 pages
appendix with extra tables and figures. 18 figures are included in the paper
and 8 in the appendi
FACTORES DE RIESGO PARA EMBARAZO EN ADOLESCENTES DE LOS ESTRATOS 1 Y 2 DE LA CIUDAD DE PAMPLONA NORTE DE SANTANDER DURANTE EL SEGUNDO PERIODO DE 2012
Objetivo: Identificar los Factores de Riesgo para embarazo en adolescentes de los estratos 1 y 2 de la cuidad de Pamplona, Norte de Santander, en el segundo periodo del año 2012. Materiales y métodos: En el periodo comprendido de septiembre a diciembre del año 2012, se realizó el presente estudio. Los casos fueron adolescentes primigestas con edades entre 14 y 19 años, de cualquier edad gestacional que asisten al control en un Hospital de la ciudad, mientras que los controles fueron adolescentes escolares de estratos 1 y 2 de la ciudad de Pamplona. El tamaño de la muestra calculado fue de 135 adolescentes con una relación caso-control de 1:2. Se calcularon los OR para obtener asociaciones con un IC al 95%; y se realizaron ajustes por edad. Resultados: Se encontró asociación entre el conocimiento de los métodos anticonceptivos y el uso de estos métodos como factor protector para el desarrollo de embarazo, no se encontró relación entre la edad en que la madre tuvo su primer hijo, la religión o el consumo de drogas, se realizo un ajuste por edad donde se encontró que independiente de la edad las personas que usan y conocen los métodos anticonceptivos disminuyen la posibilidad tener un embarazo. Conclusiones: El conocimiento y uso de los métodos anticonceptivos es un factor protector para el embarazo, lo que indica que se deben realizar estrategias para que los jóvenes conozcan estos métodos y así disminuir la cantidad de embarazos adolescentes
Transgenic expression of the dicotyledonous pattern recognition receptor EFR in rice leads to ligand-dependent activation of defense responses
Plant plasma membrane localized pattern recognition receptors (PRRs) detect extracellular pathogen-associated molecules. PRRs such as Arabidopsis EFR and rice XA21 are taxonomically restricted and are absent from most plant genomes. Here we show that rice plants expressing EFR or the chimeric receptor EFR::XA21, containing the EFR ectodomain and the XA21 intracellular domain, sense both Escherichia coli- and Xanthomonas oryzae pv. oryzae (Xoo)-derived elf18 peptides at sub-nanomolar concentrations. Treatment of EFR and EFR::XA21 rice leaf tissue with elf18 leads to MAP kinase activation, reactive oxygen production and defense gene expression. Although expression of EFR does not lead to robust enhanced resistance to fully virulent Xoo isolates, it does lead to quantitatively enhanced resistance to weakly virulent Xoo isolates. EFR interacts with OsSERK2 and the XA21 binding protein 24 (XB24), two key components of the rice XA21-mediated immune response. Rice-EFR plants silenced for OsSERK2, or overexpressing rice XB24 are compromised in elf18-induced reactive oxygen production and defense gene expression indicating that these proteins are also important for EFR-mediated signaling in transgenic rice. Taken together, our results demonstrate the potential feasibility of enhancing disease resistance in rice and possibly other monocotyledonous crop species by expression of dicotyledonous PRRs. Our results also suggest that Arabidopsis EFR utilizes at least a subset of the known endogenous rice XA21 signaling components
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