30 research outputs found
Photoionization rates for helium: update
The NIS He gas has been observed at a few AU to the Sun almost from the
beginning of the space age. To model its flow an estimate of the loss rates due
to ionization by solar extreme-ultraviolet (EUV) flux is needed. The EUV
irradiance has been measured directly from mid 1990-ties, but with high
temporal and spectral resolution only from 2002. Beforehand only EUV proxies
are available. A new method of reconstruction of the Carrington rotation
averaged photoionization rates for neutral interstellar helium (NIS He) in the
ecliptic at 1 AU to the Sun before 2002 is presented. We investigate the
relation between the solar rotation averaged time series of the ionization
rates for NIS He at 1 AU derived from TIMED measurements of EUV irradiance and
the solar 10.7 cm flux (F10.7) only. We perform a weighted iterative fit of a
nonlinear model to data split into sectors. The obtained formula allows to
reconstruct the solar rotation averages of photoionization rates for He between
~1947 and 2002 with an uncertainty ranging from less than 10% during solar
minimum up to 20% for solar maximum.Comment: 12 pages, 4 figure
The energy-dependent position of the IBEX ribbon due to the solar wind structure
Observations of energetic neutral atoms (ENAs) allow for remote studies of
the plasma condition in the heliosphere and the neighboring local interstellar
medium. The first IBEX results revealed an arc-like enhancement of the ENA
intensity in the sky, known as the ribbon. The ribbon was not expected from the
heliospheric models prior to the IBEX launch. One of the proposed explanations
of the ribbon is the mechanism of the secondary ENA emission. The ribbon
reveals energy-dependent structure in the relative intensity along its
circumference and in the position. Namely, the ribbon geometric center varies
systematically by about 10 in the energy range 0.7-4.3 keV. Here, we
show by analytic modeling that this effect is a consequence of the
helio-latitudinal structure of the solar wind reflected in the secondary ENAs.
Along with a recently measured distance to the ribbon source just beyond the
heliopause, our findings support the connection of the ribbon with the local
interstellar magnetic field by the mechanism of the secondary ENA emission.
However, the magnitude of the center shift in the highest IBEX energy channel
is much larger in the observations than expected from the modeling. This may be
due to another, not currently recognized, process of ENA generation.Comment: 14 pages, 8 figures, 1 table, v3: corrected caption to Figure
Interstellar Neutral Gas Species And Their Pickup Ions Inside The Heliospheric Termination Shock. Ionization Rates For H, O, Ne, And He
Solar ionizing factors are responsible for modulation of interstellar neutral
gas and its derivative populations inside the heliosphere. We provide an
overview of the current state of knowledge about them for heliospheric
particles inside the termination shock. We discuss charge exchange with solar
wind particles, photoionization, and electron impact ionization for hydrogen,
oxygen, neon, and helium from 1985 to 2018 both in the ecliptic plane and in
the polar regions. We discuss ionization rates as a function of time, distance
to the Sun, and latitude. We compare the total ionization rates among the
species within a consistent and homogeneous system of calculation of the
ionization rates. The highest total ionization rates at 1 au in the ecliptic
plane are for hydrogen and oxygen, and the lowest are for helium. In the polar
regions, the strongest ionization losses are for oxygen, regardless of the
solar activity. Photoionization is the dominant ionization reaction for helium
and neon, and a reaction of high significance for oxygen. Charge exchange with
solar wind particles is the dominant ionization reaction for hydrogen and the
second important ionization reaction for oxygen. Electron impact ionization is
an important ionization reaction for Ne and He, with the contribution to the
total ionization rates stronger within 1 au and smaller outside. The total
ionization rates for He and Ne vary in time with the solar activity, whereas
the total ionization rates for H and O follow the cyclic solar wind variations
out of the ecliptic plane and aperiodic variations in the ecliptic plane.Comment: 12 pages, 8 figures, 2 tables, published in The Astrophysical Journa
Interstellar Neutral Gas Species And Their Pickup Ions Inside The Heliospheric Termination Shock. The Large-scale Structures
We study the distribution of the interstellar neutral (ISN) gas density and
the pick-up ion (PUI) density of hydrogen, helium, neon, and oxygen in the
heliosphere for heliocentric distances from inside 1 au up to the solar wind
termination shock (TS), both in and out of the ecliptic plane. We discuss
similarities and differences in the large-scale structures of the ISN gas and
PUIs formed in the heliosphere between various species. We discuss the
distribution of ISN gas and PUI densities for two extreme phases of the solar
activity cycle, it is the solar minimum and the solar maximum. We identify the
location of the ISN gas density cavity of various species. We study the
relative abundance ratios of Ne/O, H/He, Ne/He, and O/He for ISN gas and PUIs
densities and their variation with location in the heliosphere. We also discuss
the modulation of relative abundance ratios of ISN gas and PUIs along the TS.
We conclude that the preferable locations for detection of He and Ne
PUIs are in the downwind hemisphere within 1~au, whereas for H and O
PUIs the preferable locations for detection are for distances from Jupiter to
Pluto orbits.Comment: 18 figures, 2 tables, Published in The Astrophysical Journa
Reconstruction of Helio-latitudinal Structure of the Solar Wind Proton Speed and Density
The modeling of the heliosphere requires continuous three-dimensional solar
wind data. The in-situ out-of-ecliptic measurements are very rare, so that
other methods of solar wind detection are needed. We use the remote-sensing
data of the solar wind speed from observations of interplanetary scintillation
(IPS) to reconstruct spatial and temporal structures of the solar wind proton
speed from 1985 to 2013. We developed a method of filling the data gaps in the
IPS observations to obtain continuous and homogeneous solar wind speed records.
We also present a method to retrieve the solar wind density from the solar wind
speed, utilizing the invariance of the solar wind dynamic pressure and energy
flux with latitude. To construct the synoptic maps of the solar wind speed we
use the decomposition into spherical harmonics of each of the Carrington
rotation map. To fill the gaps in time we apply the singular spectrum analysis
to the time series of the coefficients of spherical harmonics. We obtained
helio-latitudinal profiles of the solar wind proton speed and density over
almost three recent solar cycles. The accuracy in the reconstruction is, due to
computational limitations, about 20%. The proposed methods allow us to improve
the spatial and temporal resolution of the model of the solar wind parameters
presented in our previous paper (Sok\'o{\l} et al. 2013) and give a better
insight into the time variations of the solar wind structure. Additionally, the
solar wind density is reconstructed more accurately and it fits better to the
in-situ measurements from Ulysses.Comment: Accepted to Solar Physics (doi:10.1007/s11207-015-0800-2). 26 pages,
13 figure
Solar cycle variation of interstellar neutral He, Ne, O density and pick-up ions along the Earth's orbit
We simulated the modulation of the interstellar neutral (ISN) He, Ne, and O
density and pick-up ion (PUI) production rate and count rate along the Earth's
orbit over the solar cycle from 2002 to 2013 to verify if solar cycle-related
effects may modify the inferred ecliptic longitude of the ISN inflow direction.
We adopted the classical PUI model with isotropic distribution function and
adiabatic cooling, modified by time- and heliolatitude-dependent ionization
rates and non-zero injection speed of PUIs. We found that the ionization losses
have a noticeable effect on the derivation of the ISN inflow longitude based on
the Gaussian fit to the crescent and cone peak locations. We conclude that the
non-zero radial velocity of the ISN flow and the energy range of the PUI
distribution function that is accumulated are of importance for a precise
reproduction of the PUI count rate along the Earth orbit. However, the temporal
and latitudinal variations of the ionization in the heliosphere, and
particularly their variation on the solar cycle time-scale, may significantly
modify the shape of PUI cone and crescent and also their peak positions from
year to year and thus bias by a few degrees the derived longitude of the ISN
gas inflow direction.Comment: Published in the Monthly Notices of the Royal Astronomical Society,
vol. 458, Issue 4, pp 3691-3704, doi:10.1093/mnras/stw51
Interstellar neutral helium in the heliosphere from IBEX observations. II. The Warsaw Test Particle Model (WTPM)
We have developed a refined and optimized version of the Warsaw Test Particle
Model of interstellar neutral gas in the heliosphere, specially tailored for
analysis of IBEX-Lo observations. The former version of the model was used in
the analysis of neutral He observed by IBEX that resulted in an unexpected
conclusion that the interstellar neutral He flow vector was different than
previously thought and that a new population of neutral He, dubbed the Warm
Breeze, exists in the heliosphere. It was also used in the reanalysis of
Ulysses observations that confirmed the original findings on the flow vector,
but suggested a significantly higher temperature. The present version model has
two strains targeted for different applications, based on an identical
paradigm, but differing in the implementation and in the treatment of
ionization losses. We present the model in detail and discuss numerous effects
related to the measurement process that potentially modify the resulting flux
of ISN He observed by IBEX, and identify those of them that should not be
omitted in the simulations to avoid biasing the results. This paper is part of
a coordinated series of papers presenting the current state of analysis of
IBEX-Lo observations of ISN He. Details of the analysis method are presented by
Swaczyna et al. 2015, and results of the analysis are presented by Bzowski et
al. 2015.Comment: This paper is a part of the special issue of Astrophysical Journal
Supplement Series on interstellar neutrals measured by IBE
Evolution of the Solar Lyman-Alpha line profile during the solar cycle
Recent studies of interstellar neutral (ISN) hydrogen observed by the
Interstellar Boundary Explorer (IBEX) suggested that the present understanding
of the radiation pressure acting on hydrogen atoms in the heliosphere should be
revised. There is a significant discrepancy between theoretical predictions of
the ISN H signal using the currently used model of the solar Lyman-alpha
profile by Tarnopolski et al. 2009 (TB09) and the signal due to ISN H observed
by IBEX-Lo. We developed a new model of evolution of the solar Lyman-alpha
profile that takes into account all available observations of the full-disk
solar Lyman-alpha profiles from SUMER/SOHO, provided by Lemaire et al. 2015
(L15), covering practically the entire 23rd solar cycle. The model has three
components that reproduce different features of the profile. The main shape of
the emission line that is produced in the chromosphere is modeled by the kappa
function; the central reversal due to absorption in the transition region is
modeled by the Gauss function; the spectral background is represented by the
linear function. The coefficients of all those components are linear functions
of the line-integrated full-disk Lyman-alpha irradiance, which is the only free
parameter of the model. The new model features potentially important
differences in comparison with the model by TB09, which was based on a limited
set of observations. This change in the understanding of radiation pressure,
especially during low solar activity, may significantly affect the interstellar
H and D distributions in the inner heliosphere and their derivative
populations.Comment: 15 pages, 11 figures, 2 table
Evolution of the solar Ly- line profile during the solar cycle. II. How accurate is the present radiation pressure paradigm for interstellar neutral H in the heliosphere?
Following the derivation of a more accurate model of the evolution of the
solar Lyman- line with the changing solar activity by
Kowalska-leszczynska et al. 2018 (IKL18) than the formerly used model by
Tarnopolski et al. 2009 (ST09), we investigate potential consequences that
adoption of the resulting refined model of radiation pressure has for the model
distribution of interstellar neutral (ISN) H in the inner heliosphere and on
the interpretation of selected observations. We simulated the ISN H densities
using the two alternative radiation pressure models and identical models of all
other factors affecting the ISN H distribution. We found that during most of
the solar cycle, the IKL18 model predicts larger densities of ISN H and PUIs
than ST09 in the inner heliosphere, especially in the downwind hemisphere.
However, the density of ISN H at the termination shock estimated by Bzowski et
al. 2008 obtained using ST09 does not need revision, and the detection of ISN D
by IBEX is supported. However, we point out the existence of a considerable
absorption of a portion of the solar Lyman- spectral flux inside the
heliosphere. Therefore, the model of radiation pressure for ISN H is still
likely to need revision, and hence the available models of ISN H are not
self-consistent.Comment: Accepted to ApJ 17 pages, 10 figure
Sun-Heliosphere Observation-based Ionization Rates Model
The solar wind (SW) and the extreme ultraviolet (EUV) radiation modulate
fluxes of interstellar and heliospheric particles inside the heliosphere both
in time and in space. Understanding this modulation is necessary to correctly
interpret measurements of particles of interstellar origin inside the
heliosphere. We present a revision of heliospheric ionization rates and provide
the Sun-Heliosphere Observation-based Ionization Rates (SHOIR) model based on
the currently available data. We calculate the total ionization rates using
revised SW and solar EUV data. We study the in-ecliptic variation of the SW
parameters, the latitudinal structure of the SW speed and density, and the
reconstruction of the photoionization rates. The revision most affects the SW
out of the ecliptic plane during solar maximum and the estimation of the
photoionization rates, the latter due to a change of the reference data. The
revised polar SW is slower and denser during the solar maximum of solar cycle
(SC) 24. The current estimated total ionization rates are higher than the
previous ones for H, O, and Ne, and lower for He. The changes for the
in-ecliptic total ionization rates are less than 10% for H and He, up to 20%
for O, and up to 35% for Ne. Additionally, the changes are not constant in time
and vary as a function of time and latitude.Comment: 24 pages, 14 figures, 2 tables; published in The Astrophysical
Journal 897:179 (21pp