Nebular dust and extinction in ionized nebulae i. the Balmer decrement

Journal Article · Fri Apr 01 04:00:00 EST 1983 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160849· OSTI ID:5831395

Mathis, J S

Many astronomical objects contain plasma with internal or surrounding dust. The extinction of H II regions can be determined from the H..beta../H..cap alpha.. flux ratio, and also from the H..beta../radio fluxes. The two determinations almost always disagree by large factors (typically, approx.3), with the (H..beta../H..cap alpha..) extinction being smaller. This is shown to be a consequence of the albedo of dust at H..cap alpha.. being smaller than that of H..beta.., so that the destruction of H..cap alpha.. by dust is larger than for constant albedo. If the difference in albedo is ignored, one interprets the lower H..cap alpha.. flux as being caused by a small optical depth in dust. Simple models for the geometry of the dust and emitting gas are discussed: spherical models with dust mixed with the ionized gas, and also a slab of absorbing dust overlying the nebula. The two geometries give similar results for the Balmer decrements, so geometry does not strongly enter the final results. The conclusion that albedo (H..cap alpha..)8000 A). Recommendations for dereddening emission-line objects are presented and should be applicable to planetary nebulae, active galactic nuclei, or quasi-stellar objects as well as to H II regions.

• Research Organization: Department of Astronomy, University of Wisconsin-Madison
• OSTI ID: 5831395
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 267:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BALMER LINES
COSMIC DUST
COSMIC GASES
COSMIC RADIO SOURCES
DUSTS
FLUIDS
GASES
H2 REGIONS
INTERSTELLAR GRAINS
NEBULAE
PARTICLES
RADIATION FLUX