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Title:
Dust in the Local Interstellar Wind
Authors:
Frisch, Priscilla C.; Dorschner, Johann M.; Geiss, Johannes; Greenberg, J. Mayo; Grün, Eberhard; Landgraf, Markus; Hoppe, Peter; Jones, Anthony P.; Krätschmer, Wolfgang; Linde, Timur J.; Morfill, Gregor E.; Reach, William; Slavin, Jonathan D.; Svestka, Jiri; Witt, Adolf N.; Zank, Gary P.
Affiliation:
AA(Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637), AB(Astrophysikalisches Institut und Universitäts-Sternwarte, Schillergaesschen 3, D-07745 Jena, Germany), AC(International Space Science Institute, Bern, Switzerland), AD(Leiden Observatory Laboratory, Postbus 9504, 2300 RA Leiden, The Netherlands), AE(Max-Planck-Institut für Kernphysik, Heidelberg, Germany), AF(Max-Planck-Institut für Kernphysik, Heidelberg, Germany), AG(Max-Planck-Institut für Chemistry, Cosmochemistry Department, P.O. Box 3060, D-55020 Mainz, Germany), AH(Institut d'Astrophysique Spatiale, Université Paris XI, Bâtiment 121, 91405 Orsay Cedex, France), AI(Max-Planck-Institut für Kernphysik, Heidelberg, Germany), AJ(University of Michigan, Aerospace Engineering, Ann Arbor, MI 48109), AK(Max-Planck-Institut für extraterrestrische Physik, 85740 Garching, Germany), AL(Infrared Processing and Analysis Center, California Institute of Technology, Mail Stop 100-22, Pasadena, CA 91125), AM(Eureka Scientific Inc., 2452 Delmer Street, Suite 100, Oakland, CA 94602-3017), AN(Prague Observatory, Prague, 11846 Czech Republic), AO(Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606), AP(Bartol Research Institute, University of Delaware, Newark, DE 19716)
Publication:
The Astrophysical Journal, Volume 525, Issue 1, pp. 492-516. (ApJ Homepage)
Publication Date:
11/1999
Origin:
UCP
Astronomy Keywords:
ATOMIC PROCESSES, ISM: DUST, EXTINCTION, INTERPLANETARY MEDIUM, ISM: ABUNDANCES, SOLAR SYSTEM: GENERAL, Atomic Processes, ISM: Dust, Extinction, Interplanetary Medium, ISM: Abundances, Solar System: General
Abstract Copyright:
(c) 1999: The American Astronomical Society
DOI:
10.1086/307869
Bibliographic Code:
1999ApJ...525..492F

Abstract

The gas-to-dust mass ratios found for interstellar dust within the solar system, versus values determined astronomically for the cloud around the solar system, suggest that large and small interstellar grains have separate histories and that large interstellar grains preferentially detected by spacecraft are not formed exclusively by mass exchange with nearby interstellar gas. Observations by the Ulysses and Galileo satellites of the mass spectrum and flux rate of interstellar dust within the heliosphere are combined with information about the density, composition, and relative flow speed and direction of interstellar gas in the cloud surrounding the solar system to derive an in situ value for the gas-to-dust mass ratio, Rg/d=94+46-38. This ratio is dominated by the larger near-micron-sized grains. Including an estimate for the mass of smaller grains, which do not penetrate the heliosphere owing to charged grain interactions with heliosheath and solar wind plasmas, and including estimates for the mass of the larger population of interstellar micrometeorites, the total gas-to-dust mass ratio in the cloud surrounding the solar system is half this value. Based on in situ data, interstellar dust grains in the 10-14 to 10-13 g mass range are underabundant in the solar system, compared to a Mathis, Rumple, & Nordsiek mass distribution scaled to the local interstellar gas density, because such small grains do not penetrate the heliosphere. The gas-to-dust mass ratios are also derived by combining spectroscopic observations of the gas-phase abundances in the nearest interstellar clouds. Measurements of interstellar absorption lines formed in the cloud around the solar system, as seen in the direction of ɛ CMa, give Rg/d=427+72-207 for assumed solar reference abundances and Rg/d=551+61-251 for assumed B star reference abundances. These values exceed the in situ value suggesting either that grain mixing or grain histories are not correctly understood or that sweptup stardust is present. Such high values for diffuse interstellar clouds are strongly supported by diffuse cloud data seen toward λ Sco and 23 Ori, provided B star reference abundances apply. If solar reference abundances prevail, however, the surrounding cloud is seen to have greater than normal dust destruction compared to higher column density diffuse clouds. The cloud surrounding the solar system exhibits enhanced gas-phase abundances of refractory elements such as Fe+ and Mg+, indicating the destruction of dust grains by shock fronts. The good correlation locally between Fe+ and Mg+ indicates that the gas-phase abundances of these elements are dominated by grain destruction, while the poor correlation between Fe+ and H0 indicates either variable gas ionization or the decoupling of neutral gas and dust over parsec scale lengths. These abundances, combined with grain destruction models, indicate that the nearest interstellar material has been shocked with shocks of velocity ~150 km s-1. If solar reference abundances are correct, the low Rg/d value toward λ Sco may indicate that at least one cloud component in this direction contains dust grains that have retained their silicate mantles and are responsible for the polarization of the light from nearby stars seen in this general region. Weak frictional coupling between gas and dust in nearby low density gas permit inhomogeneities to be present.
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