Lecture 9 - Interstellar dust Flashcards
What are dark clouds?
Absence of stars on photographic plates
What is interstellar reddening?
More extinction of blue light than red light, due to interstellar dust
What is a reflection nebula?
A cloud of interstellar dust visible by scattering from starlight
What is diffuse galactic light?
Light from an entire galaxy working as a reflection nebula
What are some evidence for interstellar dust?
Dark clouds, Interstellar extinction and reddening, polarization of starlight, reflection nebulae, diffuse galactic light,
continuum IR emission from clouds, microwave emission from clouds, X-ray halos around point sources
Interstellar depletions, existence of H2 in large amounts in ISM, Interstellar grains entering the solar system today, explains heating of diffuse ISM gas
What is R_V in the Milky Way?
About 3.1
How does a small R_V affect the extinction curve?
It becomes steep
How does a large R_V affect the extinction curve?
It becomes flat
Thermal spikes following photon absorptions are important for…
small particles (a<60Å)
PAH molecules consists of __ and __ atoms and are arranged like ____ .
hydrogen, carbon, hexagons
For what particle sizes are Rayleigh scattering relevant?
Particle < lambda/10
For what particle sizes are Mie scattering relevant?
1/10< Paricle/lambda< 1
For what particle sizes are Optical scattering relevant?
lambda < Particle
Mie theory is a classical scattering theory using series expansion in powers of what?
x=2pia/lambda
Extinction is the sum of ___ and ___ .
scattering, absorption
