Interstellar polarization: Magnetite dust

Journal Article · Wed Oct 01 04:00:00 EDT 1975 · Astrophys. J., v. 201, no. 1, pp. 151-164

DOI:https://doi.org/10.1086/153868· OSTI ID:4098971

Shapiro, P R

The polarization and extinction properties of magnetite, or Fe$sub 3$$O$$sub 4$, dust grains are calculated based on indirect evidence that magnetite grains might be the interstellar polarizers. The extinction and phase-lag cross sections of magnetite grains are calculated using a computer method for nonspherical grains. From these, the linear and circular polarization which would be produced by a medium of aligned magnetite dust grains is determined. It is found that flat platelets of magnetite can reproduce the wavelength dependence of the polarization observations. Furthermore, given the predictions by the Purcell ''pinwheel'' alignment mechanism of perfect alignment for such grains, it is shown that magnetite grains can produce all the observed polarization at the visual wavelength by consuming roughly 16 percent of the cosmic abundance of iron atoms in the interstellar medium, while contributing roughly 4 percent of the total visual extinction. With less than perfect alignment, more iron must be put into the magnetite grains, resulting in more magnetite extinction. A general property of interstellar polarization is also discussed based on the Kramers-- Kronig dispersion relations. An infrared observational test of property is proposed. (AIP)

• Research Organization: Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory
• Sponsoring Organization: USDOE
• NSA Number: NSA-33-018174
• OSTI ID: 4098971
• Journal Information: Astrophys. J., v. 201, no. 1, pp. 151-164, Journal Name: Astrophys. J., v. 201, no. 1, pp. 151-164; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

*INTERSTELLAR GRAINS-- POLARIZATION
640105* --Physics Research--Astrophysics & Cosmology-- Galaxies
COSMIC DUST
INTERSTELLAR SPACE
MAGNETITE
N56500* --Physics (Astrophysics & Cosmology)--Galaxies
VISIBLE RADIATION