HII regions slides

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PhotoionisationPhotoionisation: the removal of electrons from gas atoms by photons.H + (ionizing photon) p + e (Eqn. 1)
Page 1: Today:Recap on 1 st lecture:- Basic
Page 6 and 7: Distance = 450 pcDiameter ~ 1° (si
Page 8 and 9: Dark CloudsBok globules• relative
Page 12 and 13: ISM: average properties• Mean den
Page 14: A global view
Page 18 and 19: Cold, neutral medium (CNM)• domin
Page 20 and 21: www.milkywayproject.org
Page 22 and 23: Lagoon nebula
Page 26 and 27: Photoionisation5432113.6 eV = < 912
Page 28 and 29: RecombinationAttraction between pro
Page 30 and 31: in summary
Page 32 and 33: Thermalization of energies and ioni
Page 34 and 35: Photoionisation rate [number of eve
Page 37: Ionisation balanceEquilibrium occur
Page 40: ionisation structure
Page 43 and 44: Thermal balance in ionized nebulaeP
Page 45 and 46: Metals• Real nebulae contain more
Page 47 and 48: energy levels (➙ transitions) in
Page 49 and 50: Forbidden linesForbidden line: aris
Page 51 and 52: 1S 05.4 eV1D 22.5 eVcritical densit
Page 53 and 54: (N + )(O 2+ )
Page 55 and 56: Consequence of forbidden-line cooli
Page 57: energyTemperaturesObservation T e
Page 61 and 62: AbundancesNow we know T e and n ewe
Page 63 and 64: Problem:We need to know abundance o
Page 65 and 66: Last lecture(s):Recap on essentials
Page 67 and 68: Forbidden line =Collisionally excit
Page 69 and 70: energyTemperaturesObservation T e
Page 71 and 72: Now we know T e and n ewe can calcu
Page 73 and 74: 30 Dor (HST ACS)• Observe with sp
Page 75 and 76:
n e
Page 77 and 78:
So how do we find out what’s in t
Page 79 and 80:
…but is it?• Unfortunate proble
Page 81 and 82:
Any other ideas?• Possibility 2:
Page 83 and 84:
PN: Abell 30NGC 1501Abell 30
Page 85 and 86:
HST imaging
Page 88:
Open questions• No direct observa
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