Size distribution of interstellar particles. II. Polarization

Journal Article · Sat Sep 15 04:00:00 EDT 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/157335· OSTI ID:5757123

Mathis, J S

The linear polarization is calculated for bare infinite dielectric cylinders with a power-law size distribution, n (a) proportional a/sup -2.5/, truncated at a large-size cutoff limit a/sub +/. The particles above a specified minimum size are assumed to have perfect Davis-Greenstein alignment (i.e., to be spinning about their small axis). The index of refraction is m=1.6--0i. The derived results show very good agreement with observations, including the observed deviations from Serkowski's Law at large wavelengths. The maximum sizes are about 0.28 ..mu..m. This size is the largest required to fit the extinction in a mixture (Mathis, Rumpl, and Nordsieck) which contains nonpolarizing graphite as well as a dielectric. The minimum size required by the extinction (approx.0.005 ..mu..m) is smaller than the minimum aligned size (0.08 ..mu..m), suggesting that there are small, nonaligned (or spherical) particles. The p/sub max//E (B-V) of the graphite-silicate mixture is about 30% larger than the maximum observed (0.09), so the alignment need not be complete. A good fit to the polarization is possible for other indices of refraction (e.g., n=2.5) and for other size distributions, but hte extinction fit has already been shown to be best for a power-law size distribution. The observed circular polarization is known to follow from the linear polarization (Martin). The mixture, then, provides an excellent fit to the polarization, extinction, and probably albedo observations for at least the wavelengths in the range 0.1 ..mu..m< or =lambda< or =1 ..mu..m. It is also suggested by the fact that both oxygen-rich and carbon-rich stars are known to be expelling grains into the interstellar medium.

• Research Organization: Washburn Observatory, University of Wisconsin-Madison
• OSTI ID: 5757123
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 232:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
INTERSTELLAR GRAINS
INTERSTELLAR SPACE
NEBULAE
PARTICLES
POLARIZATION
SIZE
SPACE
STAR EVOLUTION