Week 7 Dynamics of Photoionisation regions Flashcards
1
Q
what are the two reasons for expansion of the ionisation front
A
HII gas flows outwards
Ionisation front exapnds even faster due to drop in density
2
Q
why are the expansion equations only rough estimates
A
almost all regions are asymmetric
3
Q
why are photoionisation regions asymmetric
A
inhomogeneous ambient ISM causes areas of different ISM density
Ionising source moves
4
Q
when does the pressure driven expansion of an ionisation region end
A
pressure equilibrium with the ambient ISM is reached
5
Q
what is the Larmar formula
A
dEdip/dt = |d**|^2/6πε0c^3
6
Q
when is the dipole approximation valid
A
emitting particles are small compound to the wavelength
distance to the source is large compared to the wavelength
