464 research outputs found
Warm Breeze from the starboard bow: a new population of neutral helium in the heliosphere
We investigate the signals from neutral He atoms observed from Earth orbit in
2010 by IBEX. The full He signal observed during the 2010 observation season
can be explained as a superposition of pristine neutral interstellar He gas and
an additional population of neutral He that we call the Warm Breeze. The Warm
Breeze is approximately two-fold slower and 2.5 times warmer than the primary
interstellar He population, and its density in front of the heliosphere is ~7%
that of the neutral interstellar helium. The inflow direction of the Warm
Breeze differs by ~19deg from the inflow direction of interstellar gas. The
Warm Breeze seems a long-term feature of the heliospheric environment. It has
not been detected earlier because it is strongly ionized inside the
heliosphere, which brings it below the threshold of detection via pickup ion
and heliospheric backscatter glow observations, as well as by the direct
sampling of GAS/Ulysses. Possible sources for the Warm Breeze include (1) the
secondary population of interstellar helium, created via charge exchange and
perhaps elastic scattering of neutral interstellar He atoms on interstellar He+
ions in the outer heliosheath, or (2) a gust of interstellar He originating
from a hypothetic wave train in the Local Interstellar Cloud. A secondary
population is expected from models, but the characteristics of the Warm Breeze
do not fully conform to modeling results. If, nevertheless, this is the
explanation, IBEX-Lo observations of the Warm Breeze provide key insights into
the physical state of plasma in the outer heliosheath. If the second hypothesis
is true, the source is likely to be located within a few thousand of AU from
the Sun, which is the propagation range of possible gusts of interstellar
neutral helium with the Warm Breeze characteristics against dissipation via
elastic scattering in the Local Cloud.Comment: submitted to ApJ
Interstellar neutral helium in the heliosphere from IBEX observations. III. Mach number of the flow, velocity vector, and temperature from the first six years of measurements
We analyzed observations of interstellar neutral helium (ISN~He) obtained
from the Interstellar Boundary Explorer (IBEX) satellite during its first six
years of operation. We used a refined version of the ISN~He simulation model,
presented in the companion paper by Sokol_et al. 2015, and a sophisticated data
correlation and uncertainty system and parameter fitting method, described in
the companion paper by Swaczyna et al 2015. We analyzed the entire data set
together and the yearly subsets, and found the temperature and velocity vector
of ISN~He in front of the heliosphere. As seen in the previous studies, the
allowable parameters are highly correlated and form a four-dimensional tube in
the parameter space. The inflow longitudes obtained from the yearly data
subsets show a spread of ~6 degree, with the other parameters varying
accordingly along the parameter tube, and the minimum chi-square value is
larger than expected. We found, however, that the Mach number of the ISN~He
flow shows very little scatter and is thus very tightly constrained. It is in
excellent agreement with the original analysis of ISN~He observations from IBEX
and recent reanalyses of observations from Ulysses. We identify a possible
inaccuracy in the Warm Breeze parameters as the likely cause of the scatter in
the ISN~He parameters obtained from the yearly subsets, and we suppose that
another component may exist in the signal, or a process that is not accounted
for in the current physical model of ISN~He in front of the heliosphere. From
our analysis, the inflow velocity vector, temperature, and Mach number of the
flow are equal to lambda_ISNHe = 255.8 +/- 0.5 degree, beta_ISNHe = 5.16 +/-
0.10 degree, T_ISNHe = 7440 +/- 260 K, v_ISNHe = 25.8 +/- 0.4$ km/s, and
M_ISNHe = 5.079 +/- 0.028, with uncertainties strongly correlated along the
parameter tube.Comment: Updated reference
Non-Maxwellian Proton Velocity Distributions in Nonradiative Shocks
The Balmer line profiles of nonradiative supernova remnant shocks provide the
means to measure the post-shock proton velocity distribution. While most
analyses assume a Maxwellian velocity distribution, this is unlikely to be
correct. In particular, neutral atoms that pass through the shock and become
ionized downstream form a nonthermal distribution similar to that of pickup
ions in the solar wind. We predict the H alpha line profiles from the
combination of pickup protons and the ordinary shocked protons, and we consider
the extent to which this distribution could affect the shock parameters derived
from H alpha profiles. The Maxwellian assumption could lead to an underestimate
of shock speed by up to about 15%. The isotropization of the pickup ion
population generates wave energy, and we find that for the most favorable
parameters this energy could significantly heat the thermal particles.
Sufficiently accurate profiles could constrain the strength and direction of
the magnetic field in the shocked plasma, and we discuss the distortions from a
Gaussian profile to be expected in Tycho's supernova remnant.Comment: 13 pages, 6 figure
Evolving outer heliosphere: Large-scale stability and time variations observed by the Interstellar Boundary Explorer
The first all-sky maps of Energetic Neutral Atoms (ENAs) from the Interstellar Boundary Explorer (IBEX) exhibited smoothly varying, globally distributed flux and a narrow ribbon of enhanced ENA emissions. In this study we compare the second set of sky maps to the first in order to assess the possibility of temporal changes over the 6 months between views of each portion of the sky. While the large-scale structure is generally stable between the two sets of maps, there are some remarkable changes that show that the heliosphere is also evolving over this short timescale. In particular, we find that (1) the overall ENA emissions coming from the outer heliosphere appear to be slightly lower in the second set of maps compared to the first, (2) both the north and south poles have significantly lower (similar to 10-15%) ENA emissions in the second set of maps compared to the first across the energy range from 0.5 to 6 keV, and (3) the knot in the northern portion of the ribbon in the first maps is less bright and appears to have spread and/or dissipated by the time the second set was acquired. Finally, the spatial distribution of fluxes in the southernmost portion of the ribbon has evolved slightly, perhaps moving as much as 6 degrees (one map pixel) equatorward on average. The observed large-scale stability and these systematic changes at smaller spatial scales provide important new information about the outer heliosphere and its global interaction with the galaxy and help inform possible mechanisms for producing the IBEX ribbon
Malaria Immunity in Man and Mosquito: Insights Into Unsolved Mysteries of a Deadly Infectious Disease
Malaria is a mosquito-borne disease caused by parasites of the obligate intracellular Apicomplexa family, the most deadly of which, Plasmodium falciparum, prevails in Africa. Malaria imposes a huge health burden on the world’s most vulnerable populations, claiming the lives of nearly a million children and pregnant women each year in Africa alone. Although there is keen interest in eradicating malaria, we do not yet have the necessary tools to meet this challenge, including an effective malaria vaccine and adequate vector control strategies. Here we review what is known about the mechanisms at play in immune resistance to malaria in both the human and mosquito hosts at each step in the parasite’s complex life cycle with a view towards developing the tools that will contribute to the prevention of disease and death and ultimately the goal of malaria eradication. In so doing we hope to inspire immunologists to participate in defeating this devastating disease
Effect of the heliospheric interface on the distribution of interstellar hydrogen atom inside the heliosphere
This paper deals with the modeling of the interstellar hydrogen atoms (H
atoms) distribution in the heliosphere. We study influence of the heliospheric
interface, that is the region of the interaction between solar wind and local
interstellar medium, on the distribution of the hydrogen atoms in vicinity of
the Sun. The distribution of H atoms obtained in the frame of the
self-consistent kinetic-gasdynamic model of the heliospheric interface is
compared with a simplified model which assumes Maxwellian distribution of H
atoms at the termination shock and is called often as 'hot' model. This
comparison shows that the distribution of H atoms is significantly affected by
the heliospheric interface not only at large heliocentric distances, but also
in vicinity of the Sun at 1-5 AU. Hence, for analysis of experimental data
connected with direct or undirect measurements of the interstellar atoms one
necessarily needs to take into account effects of the heliospheric interface.
In this paper we propose a new model that is relatively simple but takes into
account all major effects of the heliospheric interface. This model can be
applied for analysis of backscattered Ly-alpha radiation data obtained on board
of different spacecraft.Comment: published in Astronomy Letter
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