This data release incorporates IBEX data products from three publications in 2016. The data includes interstellar oxygen parameters for 2009 and 2010 from Schwadron et al. (2016), spin-angle count rates for the warm breeze fit from Kubiak et al. (2016) and all-sky maps of secondary interstellar helium and oxygen from Park et al. (2016), as well as additional supporting data products.
Determination of Interstellar O Parameters Using the First Two Years of Data from the Interstellar Boundary Explorer
by Schwadron et al.
- Includes Data Products: Interstellar Oxygen Parameters for the first two years of the IBEX mission, State Information for the Earth and IBEX, and Spin-Axis data for IBEX.
- Provides the first detailed analysis of interstellar neutral (ISN) oxygen properties using IBEX data.
- Finds that ISN oxygen parameters are similar to those of the He primary component, indicating that the local interstellar plasma near the Sun is relatively unaffected by turbulent heating.
- Observes key differences between primary O and He parameter tubes (relation between speed and longitude), which indicate enhanced filtration of interstellar oxygen due to its higher charge-exchange ionization rate.
- Derives ISN O density that, within uncertainties, is consistent with previous estimates.
Abstract: The direct measurements of interstellar matter by the Interstellar Boundary Explorer (IBEX) mission have opened a new and important chapter in our study of the interactions that control the boundaries of our heliosphere. Here we derive for the quantitative information about interstellar O flow parameters from IBEX low-energy neutral atom data for the first time. Specifically, we derive a relatively narrow four-dimensional parameter tube along which interstellar O flow parameters must lie. Along the parameter tube, we find a large uncertainty in interstellar O flow longitude, 76.0° ± 3.4° from χ2 analysis and 76.5° ± 6.2° from a maximum likelihood fit, which is statistically consistent with the flow longitude derived for interstellar He, 75.6° ± 1.4°. The best-fit O and He temperatures are almost identical at a reference flow longitude of 76°, which provides a strong indication that the local interstellar plasma near the Sun is relatively unaffected by turbulent heating. However, key differences include an oxygen parameter tube for the interstellar speed (relation between speed and longitude) that has higher speeds than those in the corresponding parameter tube for He, and an upstream flow latitude for oxygen that is southward of the upstream flow latitude for helium. Both of these differences are likely the result of enhanced filtration of interstellar oxygen due to its charge-exchange ionization rate, which is higher than that for helium. Furthermore, we derive an interstellar O density near the termination shock of 5.8+0.9−0.8 x 10-5 cm−3 that, within uncertainties, is consistent with previous estimates. Thus, we use IBEX data to probe the interstellar properties of oxygen.
Interstellar Neutral Helium in the Heliosphere from IBEX Observations. IV. Flow Vector, Mach Number, and Abundance of the Warm Breeze
by Kubiak et al.
- Includes Data Products: IBEX Spin-Angle Count Rates, Covariance Matrix of IBEX Spin-Angle Count Rates, and IBEX Good Times for Warm Breeze fit.
- Determines the temperature, abundance, and inflow velocity vector of the Warm Breeze with greater precision than was previously possible.
- Finds that compared to ISN He, the Warm breeze is 25% higher in temperature, with only 5.7% of the density and 40% of the inflow speed and that the inflow is shifted by ~5° in ecliptic longitude and ~ 7° in latitude.
- Shows that the inflow speeds of the Warm Breeze, ISN He and ISN H are co-planar.
- These findings strongly indicate that the Warm Breeze is the secondary population of ISN He and that the ribbon center points along the local interstellar magnetic field.
Abstract: Following the high-precision determination of the velocity vector and temperature of the pristine interstellar neutral (ISN) He via a coordinated analysis summarized by McComas et al., we analyzed the Interstellar Boundary Explorer (IBEX) observations of neutral He left out from this analysis. These observations were collected during the ISN observation seasons 2010–2014 and cover the region in the Earth’s orbit where the Warm Breeze (WB) persists. We used the same simulation model and a parameter fitting method very similar to that used for the analysis of ISN He. We approximated the parent population of the WB in front of the heliosphere with a homogeneous Maxwell–Boltzmann distribution function and found a temperature of ∼9500 K, an inflow speed of 11.3 km s−1, and an inflow longitude and latitude in the J2000 ecliptic coordinates 251.6°, 12.0°. The abundance of the WB relative to ISN He is 5.7% and the Mach number is 1.97. The newly determined inflow direction of the WB, the inflow directions of ISN H and ISN He, and the direction to the center of the IBEX Ribbon are almost perfectly co-planar, and this plane coincides within relatively narrow statistical uncertainties with the plane fitted only to the inflow directions of ISN He, ISN H, and the WB. This co-planarity lends support to the hypothesis that the WB is the secondary population of ISN He and that the center of the Ribbon coincides with the direction of the local interstellar magnetic field (ISMF). The common plane for the direction of the inflow of ISN gas, ISN H, the WB, and the local ISMF is given by the normal direction: ecliptic longitude 349.7° ± 0.6° and latitude 35.7° ± 0.6° in the J2000 coordinates, with a correlation coefficient of 0.85.
IBEX Observations of Secondary Interstellar Helium and Oxygen Distributions
by Park et al.
- Includes Data Products: All-Sky Maps of Secondary Interstellar He and O, Measured Data Files of Direct Events, List of Super Good Times, and Orbit Information files.
- Produces all-sky maps for He and O atoms with sputtering corrections in IBEX reference frame.
- Investigates the directional distributions of the secondary interstellar neutral He and O atoms at Earth’s orbit.
- Discusses the relationship between the flow speeds and directions of the secondary interstellar neutral He and O atoms.
Abstract: In this study, we investigate the directional distributions of the secondary interstellar neutral He and O populations at Earth's orbit. The secondary populations are created by charge exchange between interstellar neutral atoms and interstellar ions in the outer heliosheath. Using the IBEX-Lo He and O observations during the winter-spring seasons (early December to early June) in 2009-2011, we produced all-sky maps for He and O atoms with sputtering corrections. These sky maps include the directional distributions of the primary interstellar neutral gas and secondary populations. Our investigations reveal that the secondary He and O populations are observed in the ecliptic longitude range 160°-210°. The peak longitudes of the secondary He and O appear to be 14°-34° and 38°-43° away from the peak longitude of the primary interstellar gas flow, respectively. These results indicate that the secondary populations have lower bulk speeds relative to the Sun and their flow directions deviate from the primary gas flow. These results may indicate that one side of the outer heliosheath is thicker than the other side relative to the flow direction of the primary interstellar gas flow.