Interstellar Matter

Exams

15 June 2010

Small questions Ten terms that needed explaining e.g.

Interstellar Gas

• Describe the dominant heating and cooling processes for HI and HII regions
• Explain the cooling function for hydrogen gas. (the equation was given eq 3.30)
• Derive the equations for thermal instabilities in HI gas
• Is HII gas in pressure equilibrium? Motivate your answer
• Wat is cooling coronal gas?

Molecular spectra

• Explain the virba-rotational diagram of H2
• Why has H2 no dipole transitions
• Would HD have dipole transitions?
• Can the exitation temperature of H2 best be determines from the pure rotational lines or from vibra rotational transitions? Why is the difference between the 2 found temperature that big?

Dust

• What is the dominant process to from H2 in the ISM?
• What would that process be in very high density regions?
• What drives the interstellar chemistry in clouds?
• Are the low CO rotational transitions a good tracer of a cold dense molecular cloud? Motivate your answer.
• Derive the accretion timescale for hydrogen on dust particles in a cloud with density $1000c{m}^{-3}$ when the dust gas ratio is 1 to 100.
• Give a way to from water molecules in the inter stellar gas.