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تسجيل مستخدم جديدScience Opportunities from Observations of the Interstellar Neutral Gas with Adjustable Boresight Direction
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The interstellar neutral (ISN) gas enters the heliosphere and is detected at a few au from the Sun, as demonstrated by Ulysses and the nterstellar Boundary Explorer (IBEX) missions. Ulysses observed ISN gas from different vantage points in a polar orbit from 1994 to 2007, while IBEX has been observing in an Earth orbit in a fixed direction relative to the Sun from 2009. McComas et al. 2018 reported about an IMAP-Lo detector on board the Interstellar Mapping and Acceleration Probe (IMAP), with an ability to track the ISN flux in the sky. We present observation geometries for ISN gas for a detector with the capability to adjust the boresight direction along the Earth orbit over a year within a multichoice ISN observation scheme. We study science opportunities from the observations as a function of time during a year and the phase of solar activity. We identify observation geometries and determine the observation seasons separately for various ISN species and populations. We find that using an adjustable viewing direction allows for ISN gas observations in the upwind hemisphere, where the signal is not distorted by gravitational focusing, in addition to the viewing of ISN species throughout the entire year. Moreover, we demonstrate that with appropriately adjusted observation geometries, primary and secondary populations can be fully separated. Additionally, we show that atoms of ISN gas on indirect trajectories are accessible for detection, and we present their impact on the study of the ionization rates for ISN species.
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Direct-sampling observations of interstellar neutral (ISN) He by Interstellar Boundary Explorer (IBEX) provide valuable insight into the physical state of and processes operating in the interstellar medium ahead of the heliosphere. The ISN He atom si
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We use observations from the Interstellar Boundary Explorer (IBEX) and Ulysses to explore the possibility that the interstellar neutral helium flowing through the inner solar system possesses an intrinsic non-Maxwellian velocity distribution. In fitt
ing the IBEX and Ulysses data, we experiment with both a kappa distribution and a bi-Maxwellian, instead of the usual Maxwellian assumption. The kappa distribution does not improve the quality of fit to either the IBEX or Ulysses data, and we find lower limits to the kappa parameter of kappa>12.1 and kappa>6.0 from the IBEX and Ulysses analyses, respectively. In contrast, we do find evidence that a bi-Maxwellian improves fit quality. For IBEX, there is a clear preferred bi-Maxwellian solution with T_perp/T_par=0.62+/-0.11 oriented about an axis direction with ecliptic coordinates (lambda_axis,b_axis)=(57.2+/-8.9 deg,-1.6+/-5.9 deg). The Ulysses data provide support for this result, albeit with lower statistical significance. The axis direction is close to the ISM flow direction, in a heliocentric rest frame, and is therefore unlikely to be indicative of velocity distribution asymmetries intrinsic to the ISM. It is far more likely that these results indicate the presence of asymmetries induced by interactions in the outer heliosphere.
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With the velocity vector and temperature of the pristine interstellar neutral (ISN) He recently obtained with high precision from a coordinated analysis summarized by McComas et al.2015b, we analyzed the IBEX observations of neutral He left out from
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