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Full-Text Articles in Astrophysics and Astronomy
Exploring The Possibility Of O And Ne Contamination In Ulysses Observations Of Interstellar Helium, Brian E. Wood, Hans-Reinhard Müller, Maciej Bzowski, Justyna M. Sokół
Exploring The Possibility Of O And Ne Contamination In Ulysses Observations Of Interstellar Helium, Brian E. Wood, Hans-Reinhard Müller, Maciej Bzowski, Justyna M. Sokół
Dartmouth Scholarship
We explore the possibility that interstellar O and Ne may be contributing to the particle signal from the GAS instrument on Ulysses, which is generally assumed to be entirely He. Motivating this study is the recognition that an interstellar temperature higher than any previously estimated from Ulysses data could potentially resolve a discrepancy between Ulysses He measurements and those from the Interstellar Boundary Explorer (IBEX). Contamination by O and Ne could lead to Ulysses temperature measurements that are too low. We estimate the degree of O and Ne contamination necessary to increase the inferred Ulysses temperature to …
Revisiting Ulysses Observations Of Interstellar Helium, Brian E. Wood, Hans-Reinhard Müller, Manfred Witte
Revisiting Ulysses Observations Of Interstellar Helium, Brian E. Wood, Hans-Reinhard Müller, Manfred Witte
Dartmouth Scholarship
We report the results of a comprehensive reanalysis of Ulysses observations of interstellar He atoms flowing through the solar system, the goal being to reassess the interstellar He flow vector and to search for evidence of variability in this vector. We find no evidence that the He beam seen by Ulysses changes at all from 1994-2007. The direction of flow changes by no more than ~03 and the speed by no more than ~0.3 km s–1. A global fit to all acceptable He beam maps from 1994-2007 yields the following He flow parameters: V ISM = 26.08 ± …
Evidence For A Weak Wind From The Young Sun, Brian E. Wood, Hans-Reinhard Müller, Seth Redfield, Eric Edelman
Evidence For A Weak Wind From The Young Sun, Brian E. Wood, Hans-Reinhard Müller, Seth Redfield, Eric Edelman
Dartmouth Scholarship
The early history of the solar wind has remained largely a mystery due to the difficulty of detecting winds around young stars that can serve as analogs for the young Sun. Here we report on the detection of a wind from the 500 Myr old solar analog π1 UMa (G1.5 V), using spectroscopic observations from the Hubble Space Telescope. We detect H I Lyα absorption from the interaction region between the stellar wind and interstellar medium, i.e., the stellar astrosphere. With the assistance of hydrodynamic models of the π1 UMa astrosphere, we infer a wind only half as strong as …
Distribution Of Plasmoids In Post-Coronal Mass Ejection Current Sheets, L.-J. Guo, A. Bhattacharjee, Y.-M. Huang
Distribution Of Plasmoids In Post-Coronal Mass Ejection Current Sheets, L.-J. Guo, A. Bhattacharjee, Y.-M. Huang
Dartmouth Scholarship
Recently, the fragmentation of a current sheet in the high-Lundquist-number regime caused by the plasmoid instability has been proposed as a possible mechanism for fast reconnection. In this work, we investigate this scenario by comparing the distribution of plasmoids obtained from Large Angle and Spectrometric Coronagraph (LASCO) observational data of a coronal mass ejection event with a resistive magnetohydrodynamic simulation of a similar event. The LASCO/C2 data are analyzed using visual inspection, whereas the numerical data are analyzed using both visual inspection and a more precise topological method. Contrasting the observational data with numerical data analyzed with both methods, we …
Trajectories And Distribution Of Interstellar Dust Grains In The Heliosphere, Jonathan D. Slavin, Priscilla C. Frisch, Hans-Reinhard Müller, Jacob Heerikhuisen
Trajectories And Distribution Of Interstellar Dust Grains In The Heliosphere, Jonathan D. Slavin, Priscilla C. Frisch, Hans-Reinhard Müller, Jacob Heerikhuisen
Dartmouth Scholarship
The solar wind carves a bubble in the surrounding interstellar medium (ISM) known as the heliosphere. Charged interstellar dust grains (ISDG) encountering the heliosphere may be diverted around the heliopause or penetrate it depending on their charge-to-mass ratio. We present new calculations of trajectories of ISDG in the heliosphere, and the dust density distributions that result. We include up-to-date grain charging calculations using a realistic UV radiation field and full three-dimensional magnetohydrodynamic fluid + kinetic models for the heliosphere. Models with two different (constant) polarities for the solar wind magnetic field (SWMF) are used, with the grain trajectory calculations done …
Perpendicular Ion Heating By Low-Frequency Alfvén-Wave Turbulence In The Solar Wind, Benjamin D. G. Chandran, Bo Li, Barrett N. Rogers, Eliot Quataert, Kai Germaschewski
Perpendicular Ion Heating By Low-Frequency Alfvén-Wave Turbulence In The Solar Wind, Benjamin D. G. Chandran, Bo Li, Barrett N. Rogers, Eliot Quataert, Kai Germaschewski
Dartmouth Scholarship
We consider ion heating by turbulent Alfvén waves (AWs) and kinetic Alfvén waves (KAWs) with wavelengths (measured perpendicular to the magnetic field) that are comparable to the ion gyroradius and frequencies ω smaller than the ion cyclotron frequency Ω. We focus on plasmas in which β < 1, where β is the ratio of plasma pressure to magnetic pressure. As in previous studies, we find that when the turbulence amplitude exceeds a certain threshold, an ion's orbit becomes chaotic. The ion then interacts stochastically with the time-varying electrostatic potential, and the ion's energy undergoes a random walk. Using phenomenological arguments, we derive an analytic expression for the rates at which different ion species are heated, which we test by simulating test particles interacting with a spectrum of randomly phased AWs and KAWs. We find that the stochastic heating rate depends sensitively on the quantity ε = δv ρ/v ⊥, where v ⊥ (v ∥) is the component of the ion velocity perpendicular (parallel) to the background magnetic field B 0, and δv ρ (δB ρ) is the rms amplitude of the velocity (magnetic-field) fluctuations at the gyroradius scale. In the case …
On Using The Color-Magnitude Diagram Morphology Of M67 To Test Solar Abundances, Z. Magic, A. Serenelli, A. Weiss, B. Chaboyer
On Using The Color-Magnitude Diagram Morphology Of M67 To Test Solar Abundances, Z. Magic, A. Serenelli, A. Weiss, B. Chaboyer
Dartmouth Scholarship
The open cluster M67 has solar metallicity and an age of about 4 Gyr. The turnoff (TO) mass is close to the minimum mass for which solar metallicity stars develop a convective core during main sequence evolution as a result of the development of hydrogen burning through the CNO cycle. The morphology of the color-magnitude diagram (CMD) of M67 around the TO shows a clear hook-like feature, a direct sign that stars close to the TO have convective cores. VandenBerg et al. investigated the possibility of using the morphology of the M67 TO to put constraints on the solar metallicity, …