Lecture 11 - grain temperature, charge and dynamics

Question 1

Name the three main sources of grain heating

Answer 1

• Absorption of photons
• Collisions with particles
• Chemical reactions on grain surface

Question 2

Name the three main mechanisms of grain cooling

Answer 2

• Radiative cooling (emission)
• Collisions with particles
• Sublimation from grain surface

Question 3

Why can we approximate cooling as a continuous process?

Answer 3

Because even small grains have heat capacities&raquo_space; 5k_B

Question 4

What causes discontinuities in grain temperature?

Answer 4

Small internal energies, since photon energy for starlight is constant about 2.5 eV.

This means small grains (a=100Å) at cold temperature (20K)

Question 5

Electric Charge on Interstellar Grains are due to two processes:

Answer 5

1. Collisions with charged particles

2. Photoelectric emission

Question 6

Does photoelectric charging lead to positively or negatively charged grains?

Answer 6

Positively charged grains

Question 7

Is recoil forces a substantial force on grains?

Answer 7

Yes, due to H2 formation, photoelectric electron ejection, etc.

Question 8

Paramagnetic dissipation causes what to happen with J, for a spinning grain?

Answer 8

It aligns with B