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Paper: Reconstructing our Interstellar Past: A Look at the Small Scale Structure in the Direction of the Historical Solar Trajectory
Volume: 365, SINS — Small Ionized and Neutral Structures in the Diffuse Interstellar Medium
Page: 78
Authors: Redfield, S.; Scalo, J.; Smith, D.S.
Abstract: The properties of our nearby interstellar medium (NISM) out to 500 pc, including density, temperature, and velocity, provide a sample of the range and timing of environments that have been encountered by our solar system. These conditions influence the structure of the heliosphere, which modulates the flux of Galactic cosmic rays and interstellar gas and dust that reach the Earth. There is a long tradition of speculation focused on the effects of the ISM on heliospheric modulation of cosmic rays and interstellar hydrogen on atmospheric chemistry, cloud cover, glaciation episodes, and exogenous mutation, but the intensity and timing of such variations has never been established empirically, even in a statistical sense. The present work is aimed at evaluating the impact of small scale low column density structures in the NISM, using analysis of absorption line features toward early type stars, on the intensity and timing of heliospheric variations, and at placing these structures, invisible by most other techniques of tracing interstellar structure, in the overall dynamics of the interstellar medium. We present high spectral resolution observations of 49 stars within 10 degrees of the direction of the historical solar trajectory. This densely packed collection of sightlines provides an opportunity to (1) study small-scale structure in the shell separating the Local Bubble from the more distant NISM, (2) enable a rough reconstruction of the interstellar density profile, and hence cosmic ray flux history, encountered by the Solar System in the past 40 million years, and (3) clarify the prevalence of small column density fluctuations in the NISM.
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