A cloud of mean number density n ~ 3000 cm-3 and radius 3 pc has an ionisingsource with luminosity at 13.6 eV of L13.6eV = 2.18 x 109 erg s- at the centre.(a) What is the size of the HII region in pe? [og = 2 x 10-13 cms-].%3D(b) What assumptions are involved in parta)(c) Discuss why the HII region will drive a shock into the rest of the cloud, andcalculate the post-shock density.(d) Show why this HII region will destroy the cloud.

We can estimate the size of the HII region by calculating the stromgren radius Now nH is the cloud…

3000 cm source with luminosity at 13.6 eV of L13.GeV = 2.18 x 109 erg s- at the centre. cloud of mean number density n ~ -3 and radius 3 pc has an iönising %3D (a) What is the size of the HII region in pe? [oB = 2 x 10-13 cm's-]. %3D (b) What assumptions are involved in part a) (c) Discuss why the HII region will drive a shock into the rest of the cloud, and calculate the post-shock density. (d) Show why this HII region will destroy the cloud.

3000 cm source with luminosity at 13.6 eV of L13.GeV = 2.18 x 109 erg s- at the centre. cloud of mean number density n ~ -3 and radius 3 pc has an iönising %3D (a) What is the size of the HII region in pe? [oB = 2 x 10-13 cm's-]. %3D (b) What assumptions are involved in part a) (c) Discuss why the HII region will drive a shock into the rest of the cloud, and calculate the post-shock density. (d) Show why this HII region will destroy the cloud.