Infrared extinction and polarization due to partially aligned spheroidal grains: Models for the dust toward the BN object

Journal Article · Fri Mar 01 04:00:00 EST 1985 · Astrophys. J.; (United States)

OSTI ID:5549232

Lee, Hyung Mok; Draine, B T

We describe methods for computing the extinction and polarization due to partially aligned, precessing, spheroidal grains in the dipole approximation regime. These techniques are applied to develop models for the dust on th line of sight to the Becklin-Neugebauer (BN) object. The models, utilizing a mixture of graphite and silicate particles, some coated with ice mantles, are found to be capable of reproducing all important features of spectroscopic and polarimetric observations in the spectral range 2< or approx. =lambda< or approx. =13 ..mu..m. The models suggest, however, that the abundance of graphite grains relative to silicate grains may be somewhat smaller than suggested by the Mathis-Rumpl-Nordsieck model for the dust in diffuse clouds; possible reasons for this are discussed. The observed polarization variation across the 9.7 ..mu..m silicate feature appears to require silicate grains of oblate, rather than prolate, shape. The core/mantle grains are generally required to be more highly aligned than bare grains. We are able to place limits on the mean size of the graphite grains (0.1< or approx. =a< or approx. =0.3 ..mu..m) and on the mantle-to-core volume ratio (0.5< or approx. =V/sub m//V/sub c/< or approx. =5) for core/mantle grains. The intrinsic spectrum of the BN object is inferred from the observed flux distribution and calculation and calculated optical depths; the inferred intrinsic spectrum may be satisfactorily represented by blackbody radiation with Troughly-equal1100 K plus optically thin emission from dust with Troughly-equal450 K. The total luminosity of the BN object is estimated to be about 5 x 10/sup 3/ L/sub sun/.

• Research Organization: Princeton University Observatory
• OSTI ID: 5549232
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 290:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
CARBON
COSMIC DUST
CROSS SECTIONS
DIELECTRIC PROPERTIES
DUSTS
ELECTRICAL PROPERTIES
ELEMENTAL MINERALS
ELEMENTS
GRAPHITE
INTERSTELLAR GRAINS
INTERSTELLAR MAGNETIC FIELDS
MAGNETIC FIELDS
MINERALS
NEBULAE
NONMETALS
OPTICAL PROPERTIES
OXYGEN COMPOUNDS
PARTICLES
PHYSICAL PROPERTIES
POLARIZATION
SILICATES
SILICON COMPOUNDS
SPECTRA
STOKES PARAMETERS