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N A Schwadron - One of the best experts on this subject based on the ideXlab platform.

  • following the interstellar magnetic field from the heliosphere into space with polarized starlight
    15th Annual International Astrophysics Conference: The Science of Ed Stone: Celebrating his 80th Birthday AIAC 2016, 2016
    Co-Authors: P. C. Frisch, Andrei Berdyugin, Antonio Mário Magalhães, Vilppu Piirola, D. B. Seriacopi, T Ferrari, F P Santos, N A Schwadron, H O Funsten, D. J. Mccomas
    Abstract:

    Starlight linearly polarized by aligned interstellar dust grains provides the necessary data for tracing the structure of the very local interstellar magnetic field (ISMF). Two methods have been developed to recover the ISMF direction from polarized starlight, using data from an ongoing polarization survey. Both methods rely on the probability distribution function for polarized light. Method 1 calculates the ISMF direction from polarization position angles regardless of the data accuracy, while Method 2 relies on high-probability data points. The ISMF direction BIbex recovered by Method 1 corresponds to the closest ISMF to the heliosphere, traced by the center of the Ibex Ribbon arc. Method 2 reveals a new direction for the more distant ISMF, B new, toward l=41.1° ± 4.1° and b= 25.8° ± 3.0°, which differs by 30.4° ± 5.6° from the Ibex ISMF direction. Polarizations of filament stars that are located within 25° of a pole of Bnew, where background polarizations would be minimal, show the highest statistical probabilities of tracing the filament ISMF. The Ibex ISMF direction orders the kinematics of interstellar clouds within 15 pc, and B new must therefore dominate beyond 15 pc. These new data are consistent with the location of the Sun in the rim of an expanding superbubble shell associated with the evolved Loop I superbubble.

  • separation of the ribbon from globally distributed energetic neutral atom flux using the first five years of Ibex observations
    Astrophysical Journal Supplement Series, 2014
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, P H Janzen, E Moebius, D B Reisenfeld, H Kucharek
    Abstract:

    The Interstellar Boundary Explorer (Ibex) observes the Ibex ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (~20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the Ibex ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We then solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of Ibex-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of Ibex data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the Ibex ribbon from the globally distributed flux in preparation for a formal Ibex data release of ribbon and globally distributed flux maps to the heliophysics community.

  • simulating the compton getting effect for hydrogen flux measurements implications for Ibex hi and lo observations
    The Astrophysical Journal, 2013
    Co-Authors: E J Zirnstein, D. J. Mccomas, J Heerikhuisen, N A Schwadron
    Abstract:

    The Interstellar Boundary EXplorer (Ibex), launched in 2008 October, has improved our understanding of the solar wind-local interstellar medium interaction through its detection of neutral atoms, particularly that of hydrogen (H). Ibex is able to create full maps of the sky in six-month intervals as the Earth orbits the Sun, detecting H with energies between ∼0.01 and 6 keV. Due to the relative motion of Ibex to the solar inertial frame, measurements made in the spacecraft frame introduce a Compton-Getting (CG) effect, complicating measurements at the lowest energies. In this paper we provide results from a numerical simulation that calculates fluxes of H atoms at 1 AU in the inertial and spacecraft frames (both ram and anti-ram), at energies relevant to Ibex-Hi and -Lo. We show theory behind the numerical simulations, applying a simple frame transformation to derived flux equations that provides a straightforward way to simulate fluxes in the spacecraft frame. We then show results of H energetic neutral atom fluxes simulated at Ibex-Hi energy passbands 2-6 in all frames, comparing with Ibex-Hi data along selected directions, and also show results simulated at energies relevant to Ibex-Lo. Although simulations at Ibex-Hi energies agree reasonably well with the CG correctionmore » method used for Ibex-Hi data, we demonstrate the importance of properly modeling low energy H fluxes due to inherent complexities involved with measurements made in moving frames, as well as dynamic radiation pressure effects close to the Sun.« less

  • pressure of the proton plasma in the inner heliosheath
    The Astrophysical Journal, 2013
    Co-Authors: G Livadiotis, D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier
    Abstract:

    We develop a physical model to study the pressure of the source proton plasma in the inner heliosheath based on the Ibex Energetic Neutral Atom (ENA) spectra. A multiple linear regression technique is used to parameterize the proton distribution function, by connecting the observed ENA flux spectrum from Ibex-Hi with the power-law of the model proton distribution. We calculate the partial pressure over the measured energy range, using (1) a non-parametric method by integrating the observed ENA flux, and (2) a parametric method by integrating the modeled distribution of protons in the inner heliosheath. The two sky maps of the parametric and non-parametric partial pressures are nearly identical, owing to their power-law distributions at high energies; the kappa distribution is such a function that can be reduced to a power-law in the Ibex-Hi energy range. The slight differences between the two partial pressures may indicate protons that are not described by the kappa distribution, and instead, involve newer or "immature" (spherical shell) pick-up proton distributions. Ultimately, however, these become incorporated with the solar wind into one single proton population described by a kappa distribution. Moreover, we derive analytically (1) the ENA flux spectra, which suggests that this flux maximizes at ~30 eV, and (2) the differential pressure, which provides estimates of the partial pressures outside of those measured by Ibex-Hi. Under the assumptions of the modeled ENA spectra, the Ribbon emissions appear to be primarily limited to the energy ranges of Ibex-Lo and Ibex-Hi.

  • Ibex observations of heliospheric energetic neutral atoms current understanding and future directions
    Geophysical Research Letters, 2011
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, E Mobius, W S Lewis
    Abstract:

    [1] The Interstellar Boundary Explorer (Ibex) has provided the first energy-resolved all-sky maps of energetic neutral atom (ENA) emissions from the heliosphere's boundary with the local interstellar medium (LISM). The Ibex maps reveal, superposed on a global ENA background, an enigmatic “ribbon” of enhanced ENA emission, a feature unpredicted by theory and numerical simulations and requiring a new paradigm for the heliosphere/LISM interaction. The ribbon appears to be ordered by the interstellar magnetic field; it is up to ∼3 times brighter than the background emission and spectrally distinct from it. The ribbon's origin, whether inside or outside the heliopause or at more exotic locations in the LISM, is unknown. Here, we review the various hypotheses that have been proposed to explain the ribbon as well as what we have learned from the Ibex sky maps about the ENAs' parent ion populations and about the structure, dynamics, and properties of the outer heliosphere and nearby interstellar medium. We conclude with a brief mention of new Ibex results on lunar and magnetospheric ENAs and a preview of a possible future mission that builds on the successes of Ibex as we continue to explore our home in the galaxy.

D. J. Mccomas - One of the best experts on this subject based on the ideXlab platform.

  • following the interstellar magnetic field from the heliosphere into space with polarized starlight
    15th Annual International Astrophysics Conference: The Science of Ed Stone: Celebrating his 80th Birthday AIAC 2016, 2016
    Co-Authors: P. C. Frisch, Andrei Berdyugin, Antonio Mário Magalhães, Vilppu Piirola, D. B. Seriacopi, T Ferrari, F P Santos, N A Schwadron, H O Funsten, D. J. Mccomas
    Abstract:

    Starlight linearly polarized by aligned interstellar dust grains provides the necessary data for tracing the structure of the very local interstellar magnetic field (ISMF). Two methods have been developed to recover the ISMF direction from polarized starlight, using data from an ongoing polarization survey. Both methods rely on the probability distribution function for polarized light. Method 1 calculates the ISMF direction from polarization position angles regardless of the data accuracy, while Method 2 relies on high-probability data points. The ISMF direction BIbex recovered by Method 1 corresponds to the closest ISMF to the heliosphere, traced by the center of the Ibex Ribbon arc. Method 2 reveals a new direction for the more distant ISMF, B new, toward l=41.1° ± 4.1° and b= 25.8° ± 3.0°, which differs by 30.4° ± 5.6° from the Ibex ISMF direction. Polarizations of filament stars that are located within 25° of a pole of Bnew, where background polarizations would be minimal, show the highest statistical probabilities of tracing the filament ISMF. The Ibex ISMF direction orders the kinematics of interstellar clouds within 15 pc, and B new must therefore dominate beyond 15 pc. These new data are consistent with the location of the Sun in the rim of an expanding superbubble shell associated with the evolved Loop I superbubble.

  • separation of the ribbon from globally distributed energetic neutral atom flux using the first five years of Ibex observations
    Astrophysical Journal Supplement Series, 2014
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, P H Janzen, E Moebius, D B Reisenfeld, H Kucharek
    Abstract:

    The Interstellar Boundary Explorer (Ibex) observes the Ibex ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (~20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the Ibex ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We then solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of Ibex-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of Ibex data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the Ibex ribbon from the globally distributed flux in preparation for a formal Ibex data release of ribbon and globally distributed flux maps to the heliophysics community.

  • simulating the compton getting effect for hydrogen flux measurements implications for Ibex hi and lo observations
    The Astrophysical Journal, 2013
    Co-Authors: E J Zirnstein, D. J. Mccomas, J Heerikhuisen, N A Schwadron
    Abstract:

    The Interstellar Boundary EXplorer (Ibex), launched in 2008 October, has improved our understanding of the solar wind-local interstellar medium interaction through its detection of neutral atoms, particularly that of hydrogen (H). Ibex is able to create full maps of the sky in six-month intervals as the Earth orbits the Sun, detecting H with energies between ∼0.01 and 6 keV. Due to the relative motion of Ibex to the solar inertial frame, measurements made in the spacecraft frame introduce a Compton-Getting (CG) effect, complicating measurements at the lowest energies. In this paper we provide results from a numerical simulation that calculates fluxes of H atoms at 1 AU in the inertial and spacecraft frames (both ram and anti-ram), at energies relevant to Ibex-Hi and -Lo. We show theory behind the numerical simulations, applying a simple frame transformation to derived flux equations that provides a straightforward way to simulate fluxes in the spacecraft frame. We then show results of H energetic neutral atom fluxes simulated at Ibex-Hi energy passbands 2-6 in all frames, comparing with Ibex-Hi data along selected directions, and also show results simulated at energies relevant to Ibex-Lo. Although simulations at Ibex-Hi energies agree reasonably well with the CG correctionmore » method used for Ibex-Hi data, we demonstrate the importance of properly modeling low energy H fluxes due to inherent complexities involved with measurements made in moving frames, as well as dynamic radiation pressure effects close to the Sun.« less

  • pressure of the proton plasma in the inner heliosheath
    The Astrophysical Journal, 2013
    Co-Authors: G Livadiotis, D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier
    Abstract:

    We develop a physical model to study the pressure of the source proton plasma in the inner heliosheath based on the Ibex Energetic Neutral Atom (ENA) spectra. A multiple linear regression technique is used to parameterize the proton distribution function, by connecting the observed ENA flux spectrum from Ibex-Hi with the power-law of the model proton distribution. We calculate the partial pressure over the measured energy range, using (1) a non-parametric method by integrating the observed ENA flux, and (2) a parametric method by integrating the modeled distribution of protons in the inner heliosheath. The two sky maps of the parametric and non-parametric partial pressures are nearly identical, owing to their power-law distributions at high energies; the kappa distribution is such a function that can be reduced to a power-law in the Ibex-Hi energy range. The slight differences between the two partial pressures may indicate protons that are not described by the kappa distribution, and instead, involve newer or "immature" (spherical shell) pick-up proton distributions. Ultimately, however, these become incorporated with the solar wind into one single proton population described by a kappa distribution. Moreover, we derive analytically (1) the ENA flux spectra, which suggests that this flux maximizes at ~30 eV, and (2) the differential pressure, which provides estimates of the partial pressures outside of those measured by Ibex-Hi. Under the assumptions of the modeled ENA spectra, the Ribbon emissions appear to be primarily limited to the energy ranges of Ibex-Lo and Ibex-Hi.

  • an analytical model of interstellar gas in the heliosphere tailored to interstellar boundary explorer observations
    Astrophysical Journal Supplement Series, 2012
    Co-Authors: Martin A Lee, D. J. Mccomas, M Bzowski, H Kucharek, E Mobius
    Abstract:

    The stationary distribution of interstellar neutral gas in the heliosphere subject to solar gravity, solar radiation pressure, photoionization, and charge exchange is investigated analytically assuming ionization rates and radiation pressure that are proportional to R –2, where R is the heliocentric radius. The collisionless hyperbolic trajectories of the individual atoms including ionization losses are combined with Liouville's Theorem to construct the heliospheric phase-space distribution function of an interstellar gas species in the solar reference frame under the assumption that the distribution is a drifting Maxwellian at large distances from the Sun. The distribution is transformed to the Earth (essentially Interstellar Boundary Explorer (Ibex)) frame as a function of solar longitude. The expression is then tailored to the latitudinal scan of Ibex as a function of longitude using the fact that Ibex detects each atom close to perihelion in its hyperbolic orbit. The distribution is further adapted to Ibex by integrating the differential intensity over the entrance aperture solid angle of the Ibex-Lo collimator, and over energy to predict the Ibex count rate of helium. The major features of the predicted count rate are described, including a peak in longitude, a peak in latitude at each longitude, and the widths of the major peak in both latitude and longitude. Analytical formulae for these features are derived for comparison with Ibex observations in order to determine the temperature and bulk velocity of the gas in interstellar space. Based in part on these formulae, the results for helium are presented in the companion paper by Mobius et al.

S A Fuselier - One of the best experts on this subject based on the ideXlab platform.

  • 30TH INTERNATIONAL COSMIC RAY CONFERENCE Time-of-Flight Detector System of the Ibex-Lo Sensor with Low Background Performance for Heliospheric ENA Detection
    2015
    Co-Authors: E Mobius, S A Fuselier, M. Granoff, H Kucharek, E Hertzberg, B King, S Livi, S Longworth, N Paschalidis, L Saul
    Abstract:

    Abstract: Ibex-Lo on the Interstellar Boundary Explorer (Ibex) will map energetic neutral H atoms (ENA) from the termination shock at energies of 10 – 2000 eV and also image the interstellar O flow in spring and fall. The sensor combines a mechanical collimator to restrict the detectable arrival direc-tions, an atom to negative ion conversion surface, an electrostatic analyzer, post-acceleration up to 20 keV, and time-of-flight (TOF) analysis, providing species separation and effective background sup-pression. Because the flux of the heliospheric ENAs is very low a triple coincidence system has been fabricated, tested, and calibrated for Ibex-Lo This system uses secondary electrons produced at two consecutive carbon foils, followed by detection of the ions in a micro-channelplate. These signals are combined into three independent TOF measurements. The combination of several TOF measurements is very effective at suppressing background to unprecedented levels. This scheme allows identifica-tion of minor species, whose fluxes are several orders of magnitude below the main species. Results from the testing of both the engineering and the flight unit will be discussed in the light of the Ibex science objectives

  • separation of the ribbon from globally distributed energetic neutral atom flux using the first five years of Ibex observations
    Astrophysical Journal Supplement Series, 2014
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, P H Janzen, E Moebius, D B Reisenfeld, H Kucharek
    Abstract:

    The Interstellar Boundary Explorer (Ibex) observes the Ibex ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (~20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the Ibex ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We then solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of Ibex-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of Ibex data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the Ibex ribbon from the globally distributed flux in preparation for a formal Ibex data release of ribbon and globally distributed flux maps to the heliophysics community.

  • pressure of the proton plasma in the inner heliosheath
    The Astrophysical Journal, 2013
    Co-Authors: G Livadiotis, D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier
    Abstract:

    We develop a physical model to study the pressure of the source proton plasma in the inner heliosheath based on the Ibex Energetic Neutral Atom (ENA) spectra. A multiple linear regression technique is used to parameterize the proton distribution function, by connecting the observed ENA flux spectrum from Ibex-Hi with the power-law of the model proton distribution. We calculate the partial pressure over the measured energy range, using (1) a non-parametric method by integrating the observed ENA flux, and (2) a parametric method by integrating the modeled distribution of protons in the inner heliosheath. The two sky maps of the parametric and non-parametric partial pressures are nearly identical, owing to their power-law distributions at high energies; the kappa distribution is such a function that can be reduced to a power-law in the Ibex-Hi energy range. The slight differences between the two partial pressures may indicate protons that are not described by the kappa distribution, and instead, involve newer or "immature" (spherical shell) pick-up proton distributions. Ultimately, however, these become incorporated with the solar wind into one single proton population described by a kappa distribution. Moreover, we derive analytically (1) the ENA flux spectra, which suggests that this flux maximizes at ~30 eV, and (2) the differential pressure, which provides estimates of the partial pressures outside of those measured by Ibex-Hi. Under the assumptions of the modeled ENA spectra, the Ribbon emissions appear to be primarily limited to the energy ranges of Ibex-Lo and Ibex-Hi.

  • heliospheric neutral atom spectra between 0 01 and 6 kev from Ibex
    The Astrophysical Journal, 2012
    Co-Authors: H O Funsten, S A Fuselier, F Allegrini, M Bzowski, A G Ghielmetti, G Gloeckler, D Heirtzler, P H Janzen
    Abstract:

    Since 2008 December, the Interstellar Boundary Explorer (Ibex) has been making detailed observations of neutrals from the boundaries of the heliosphere using two neutral atom cameras with overlapping energy ranges. The unexpected, yet defining feature discovered by Ibex is a Ribbon that extends over the energy range from about 0.2 to 6 keV. This Ribbon is superposed on a more uniform, globally distributed heliospheric neutral population. With some important exceptions, the focus of early Ibex studies has been on neutral atoms with energies greater than ∼0.5 keV. With nearly three years of science observations, enough low-energy neutral atom measurements have been accumulated to extend Ibex observations to energies less than ∼0.5 keV. Using the energy overlap of the sensors to identify and remove backgrounds, energy spectra over the entire Ibex energy range are produced. However, contributions by interstellar neutrals to the energy spectrum below 0.2 keV may not be completely removed. Compared with spectra at higher energies, neutral atom spectra at lower energies do not vary much from locationtolocationinthesky,includinginthedirectionoftheIbexRibbon.Neutralfluxesareusedtoshowthatlow energy ions contribute approximately the same thermal pressure as higher energy ions in the heliosheath. However, contributions to the dynamic pressure are very high unless there is, for example, turbulence in the heliosheath with fluctuations of the order of 50‐100 km s −1 .

  • Ibex observations of heliospheric energetic neutral atoms current understanding and future directions
    Geophysical Research Letters, 2011
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, E Mobius, W S Lewis
    Abstract:

    [1] The Interstellar Boundary Explorer (Ibex) has provided the first energy-resolved all-sky maps of energetic neutral atom (ENA) emissions from the heliosphere's boundary with the local interstellar medium (LISM). The Ibex maps reveal, superposed on a global ENA background, an enigmatic “ribbon” of enhanced ENA emission, a feature unpredicted by theory and numerical simulations and requiring a new paradigm for the heliosphere/LISM interaction. The ribbon appears to be ordered by the interstellar magnetic field; it is up to ∼3 times brighter than the background emission and spectrally distinct from it. The ribbon's origin, whether inside or outside the heliopause or at more exotic locations in the LISM, is unknown. Here, we review the various hypotheses that have been proposed to explain the ribbon as well as what we have learned from the Ibex sky maps about the ENAs' parent ion populations and about the structure, dynamics, and properties of the outer heliosphere and nearby interstellar medium. We conclude with a brief mention of new Ibex results on lunar and magnetospheric ENAs and a preview of a possible future mission that builds on the successes of Ibex as we continue to explore our home in the galaxy.

H Kucharek - One of the best experts on this subject based on the ideXlab platform.

  • 30TH INTERNATIONAL COSMIC RAY CONFERENCE Time-of-Flight Detector System of the Ibex-Lo Sensor with Low Background Performance for Heliospheric ENA Detection
    2015
    Co-Authors: E Mobius, S A Fuselier, M. Granoff, H Kucharek, E Hertzberg, B King, S Livi, S Longworth, N Paschalidis, L Saul
    Abstract:

    Abstract: Ibex-Lo on the Interstellar Boundary Explorer (Ibex) will map energetic neutral H atoms (ENA) from the termination shock at energies of 10 – 2000 eV and also image the interstellar O flow in spring and fall. The sensor combines a mechanical collimator to restrict the detectable arrival direc-tions, an atom to negative ion conversion surface, an electrostatic analyzer, post-acceleration up to 20 keV, and time-of-flight (TOF) analysis, providing species separation and effective background sup-pression. Because the flux of the heliospheric ENAs is very low a triple coincidence system has been fabricated, tested, and calibrated for Ibex-Lo This system uses secondary electrons produced at two consecutive carbon foils, followed by detection of the ions in a micro-channelplate. These signals are combined into three independent TOF measurements. The combination of several TOF measurements is very effective at suppressing background to unprecedented levels. This scheme allows identifica-tion of minor species, whose fluxes are several orders of magnitude below the main species. Results from the testing of both the engineering and the flight unit will be discussed in the light of the Ibex science objectives

  • separation of the ribbon from globally distributed energetic neutral atom flux using the first five years of Ibex observations
    Astrophysical Journal Supplement Series, 2014
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, P H Janzen, E Moebius, D B Reisenfeld, H Kucharek
    Abstract:

    The Interstellar Boundary Explorer (Ibex) observes the Ibex ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (~20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the Ibex ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We then solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of Ibex-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of Ibex data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the Ibex ribbon from the globally distributed flux in preparation for a formal Ibex data release of ribbon and globally distributed flux maps to the heliophysics community.

  • modulation of neutral interstellar he ne o in the heliosphere survival probabilities and abundances at Ibex
    Astronomy and Astrophysics, 2013
    Co-Authors: M Bzowski, Justyna M Sokol, M A Kubiak, H Kucharek
    Abstract:

    Direct sampling of neutral interstellar (NIS) atoms by the Interstellar Boundary Explorer (Ibex) can potentially provide a complementary method for studying element abundances in the Local Interstellar Cloud and processes in the heliosphere interface.}{We set the stage for abundance-aimed in-depth analysis of measurements of NIS He, Ne, and O by Ibex and determine systematic differences between abundances derived from various calculation methods and their uncertainties.}{Using a model of ionization rates of the NIS species in the heliosphere, based on independent measurements of the solar wind and solar EUV radiation, we develop a time-dependent method of calculating the survival probabilities of NIS atoms from the termination shock (TS) of the solar wind to Ibex. With them, we calculate densities of these species along the Earth's orbit and simulate the fluxes of NIS species as observed by Ibex. We study pairwise ratios of survival probabilities, densities and fluxes of NIS species at Ibex to calculate correction factors for inferring the abundances at TS.}{The analytic method to calculate the survival probabilities gives acceptable results only for He and Ne during low solar activity. For the remaining portions of the solar cycle, and at all times for O, a fully time dependent model should be used. Electron impact ionization is surprisingly important for NIS O. Interpreting the Ibex observations using the time dependent model yields the LIC Ne/O abundance of $0.16\pm40%$. The uncertainty is mostly due to uncertainties in the ionization rates and in the NIS gas flow vector.}{The Ne/He, O/He and Ne/O ratios for survival probabilities, local densities, and fluxes scaled to TS systematically differ and thus an analysis based only on survival probabilities or densities is not recommended, except the Ne/O abundance for observations at low solar activity.

  • modulation of neutral interstellar he ne o in the heliosphere survival probabilities and abundances at Ibex
    Astronomy and Astrophysics, 2013
    Co-Authors: M Bzowski, Justyna M Sokol, M A Kubiak, H Kucharek
    Abstract:

    Context. Direct sampling of neutral interstellar (NIS) atoms by the Interstellar Boundary Explorer (Ibex) can potentially provide a complementary method for studying element abundances in the Local Interstellar Cloud (LIC) and processes in the heliosphere interface.Aims. We set the stage for abundance-aimed in-depth analysis of measurements of NIS He, Ne, and O by Ibex and determine systematic differences between abundances derived from various calculation methods and their uncertainties.Methods. Using a model of ionization rates of the NIS species in the heliosphere, based on independent measurements of the solar wind and solar EUV radiation, we developed a time-dependent method of calculating the survival probabilities of NIS atoms from the termination shock (TS) of the solar wind to Ibex. With them, we calculated densities of these species along the Earth’s orbit and simulated the fluxes of NIS species as observed by Ibex. We studied pairwise ratios of survival probabilities, densities, and fluxes of NIS species at Ibex to calculate correction factors for inferring the abundances at TS.Results. The analytic method of calculating the survival probabilities gives acceptable results only for He and Ne during low solar activity. For the remaining portions of the solar cycle, and at all times for O, a fully time-dependent model should be used. Electron-impact ionization is surprisingly important for NIS O. Interpreting the Ibex observations using the time-dependent model yields the LIC Ne/O abundance of 0.16 ± 40%. The uncertainty is mostly due to uncertainties in the ionization rates and in the NIS gas flow vector.Conclusions. The Ne/He, O/He, and Ne/O ratios for survival probabilities, local densities, and fluxes scaled to TS systematically differ and thus an analysis based only on survival probabilities or densities is not recommended, except the Ne/O abundance for observations at low solar activity.

  • an analytical model of interstellar gas in the heliosphere tailored to interstellar boundary explorer observations
    Astrophysical Journal Supplement Series, 2012
    Co-Authors: Martin A Lee, D. J. Mccomas, M Bzowski, H Kucharek, E Mobius
    Abstract:

    The stationary distribution of interstellar neutral gas in the heliosphere subject to solar gravity, solar radiation pressure, photoionization, and charge exchange is investigated analytically assuming ionization rates and radiation pressure that are proportional to R –2, where R is the heliocentric radius. The collisionless hyperbolic trajectories of the individual atoms including ionization losses are combined with Liouville's Theorem to construct the heliospheric phase-space distribution function of an interstellar gas species in the solar reference frame under the assumption that the distribution is a drifting Maxwellian at large distances from the Sun. The distribution is transformed to the Earth (essentially Interstellar Boundary Explorer (Ibex)) frame as a function of solar longitude. The expression is then tailored to the latitudinal scan of Ibex as a function of longitude using the fact that Ibex detects each atom close to perihelion in its hyperbolic orbit. The distribution is further adapted to Ibex by integrating the differential intensity over the entrance aperture solid angle of the Ibex-Lo collimator, and over energy to predict the Ibex count rate of helium. The major features of the predicted count rate are described, including a peak in longitude, a peak in latitude at each longitude, and the widths of the major peak in both latitude and longitude. Analytical formulae for these features are derived for comparison with Ibex observations in order to determine the temperature and bulk velocity of the gas in interstellar space. Based in part on these formulae, the results for helium are presented in the companion paper by Mobius et al.

H O Funsten - One of the best experts on this subject based on the ideXlab platform.

  • following the interstellar magnetic field from the heliosphere into space with polarized starlight
    15th Annual International Astrophysics Conference: The Science of Ed Stone: Celebrating his 80th Birthday AIAC 2016, 2016
    Co-Authors: P. C. Frisch, Andrei Berdyugin, Antonio Mário Magalhães, Vilppu Piirola, D. B. Seriacopi, T Ferrari, F P Santos, N A Schwadron, H O Funsten, D. J. Mccomas
    Abstract:

    Starlight linearly polarized by aligned interstellar dust grains provides the necessary data for tracing the structure of the very local interstellar magnetic field (ISMF). Two methods have been developed to recover the ISMF direction from polarized starlight, using data from an ongoing polarization survey. Both methods rely on the probability distribution function for polarized light. Method 1 calculates the ISMF direction from polarization position angles regardless of the data accuracy, while Method 2 relies on high-probability data points. The ISMF direction BIbex recovered by Method 1 corresponds to the closest ISMF to the heliosphere, traced by the center of the Ibex Ribbon arc. Method 2 reveals a new direction for the more distant ISMF, B new, toward l=41.1° ± 4.1° and b= 25.8° ± 3.0°, which differs by 30.4° ± 5.6° from the Ibex ISMF direction. Polarizations of filament stars that are located within 25° of a pole of Bnew, where background polarizations would be minimal, show the highest statistical probabilities of tracing the filament ISMF. The Ibex ISMF direction orders the kinematics of interstellar clouds within 15 pc, and B new must therefore dominate beyond 15 pc. These new data are consistent with the location of the Sun in the rim of an expanding superbubble shell associated with the evolved Loop I superbubble.

  • separation of the ribbon from globally distributed energetic neutral atom flux using the first five years of Ibex observations
    Astrophysical Journal Supplement Series, 2014
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, P H Janzen, E Moebius, D B Reisenfeld, H Kucharek
    Abstract:

    The Interstellar Boundary Explorer (Ibex) observes the Ibex ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (~20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the Ibex ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We then solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of Ibex-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of Ibex data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the Ibex ribbon from the globally distributed flux in preparation for a formal Ibex data release of ribbon and globally distributed flux maps to the heliophysics community.

  • pressure of the proton plasma in the inner heliosheath
    The Astrophysical Journal, 2013
    Co-Authors: G Livadiotis, D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier
    Abstract:

    We develop a physical model to study the pressure of the source proton plasma in the inner heliosheath based on the Ibex Energetic Neutral Atom (ENA) spectra. A multiple linear regression technique is used to parameterize the proton distribution function, by connecting the observed ENA flux spectrum from Ibex-Hi with the power-law of the model proton distribution. We calculate the partial pressure over the measured energy range, using (1) a non-parametric method by integrating the observed ENA flux, and (2) a parametric method by integrating the modeled distribution of protons in the inner heliosheath. The two sky maps of the parametric and non-parametric partial pressures are nearly identical, owing to their power-law distributions at high energies; the kappa distribution is such a function that can be reduced to a power-law in the Ibex-Hi energy range. The slight differences between the two partial pressures may indicate protons that are not described by the kappa distribution, and instead, involve newer or "immature" (spherical shell) pick-up proton distributions. Ultimately, however, these become incorporated with the solar wind into one single proton population described by a kappa distribution. Moreover, we derive analytically (1) the ENA flux spectra, which suggests that this flux maximizes at ~30 eV, and (2) the differential pressure, which provides estimates of the partial pressures outside of those measured by Ibex-Hi. Under the assumptions of the modeled ENA spectra, the Ribbon emissions appear to be primarily limited to the energy ranges of Ibex-Lo and Ibex-Hi.

  • heliospheric neutral atom spectra between 0 01 and 6 kev from Ibex
    The Astrophysical Journal, 2012
    Co-Authors: H O Funsten, S A Fuselier, F Allegrini, M Bzowski, A G Ghielmetti, G Gloeckler, D Heirtzler, P H Janzen
    Abstract:

    Since 2008 December, the Interstellar Boundary Explorer (Ibex) has been making detailed observations of neutrals from the boundaries of the heliosphere using two neutral atom cameras with overlapping energy ranges. The unexpected, yet defining feature discovered by Ibex is a Ribbon that extends over the energy range from about 0.2 to 6 keV. This Ribbon is superposed on a more uniform, globally distributed heliospheric neutral population. With some important exceptions, the focus of early Ibex studies has been on neutral atoms with energies greater than ∼0.5 keV. With nearly three years of science observations, enough low-energy neutral atom measurements have been accumulated to extend Ibex observations to energies less than ∼0.5 keV. Using the energy overlap of the sensors to identify and remove backgrounds, energy spectra over the entire Ibex energy range are produced. However, contributions by interstellar neutrals to the energy spectrum below 0.2 keV may not be completely removed. Compared with spectra at higher energies, neutral atom spectra at lower energies do not vary much from locationtolocationinthesky,includinginthedirectionoftheIbexRibbon.Neutralfluxesareusedtoshowthatlow energy ions contribute approximately the same thermal pressure as higher energy ions in the heliosheath. However, contributions to the dynamic pressure are very high unless there is, for example, turbulence in the heliosheath with fluctuations of the order of 50‐100 km s −1 .

  • Ibex observations of heliospheric energetic neutral atoms current understanding and future directions
    Geophysical Research Letters, 2011
    Co-Authors: D. J. Mccomas, N A Schwadron, H O Funsten, S A Fuselier, E Mobius, W S Lewis
    Abstract:

    [1] The Interstellar Boundary Explorer (Ibex) has provided the first energy-resolved all-sky maps of energetic neutral atom (ENA) emissions from the heliosphere's boundary with the local interstellar medium (LISM). The Ibex maps reveal, superposed on a global ENA background, an enigmatic “ribbon” of enhanced ENA emission, a feature unpredicted by theory and numerical simulations and requiring a new paradigm for the heliosphere/LISM interaction. The ribbon appears to be ordered by the interstellar magnetic field; it is up to ∼3 times brighter than the background emission and spectrally distinct from it. The ribbon's origin, whether inside or outside the heliopause or at more exotic locations in the LISM, is unknown. Here, we review the various hypotheses that have been proposed to explain the ribbon as well as what we have learned from the Ibex sky maps about the ENAs' parent ion populations and about the structure, dynamics, and properties of the outer heliosphere and nearby interstellar medium. We conclude with a brief mention of new Ibex results on lunar and magnetospheric ENAs and a preview of a possible future mission that builds on the successes of Ibex as we continue to explore our home in the galaxy.