HII regions slides

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M43Real examples1. no. of ionising photons- Hotter star- More hot stars2. amount of gas (gas density)IC 1274
Thermal balance in ionized nebulaePhotoionization adds kinetic energy (KE) into the H cloud since it creates hot, fastphotoelectrons.T can increase indefinitely though… Energy must be lost somehowEnergy can be lost through photons: H recombination means KE of e photonwhich can escapeOn average, heat lost per recombination = 3/2 k T eso Cooling rate is:L = (3/2 k T e ) N R [J m -3 s -1 ]Energy input, or the Heating rateG = N PI Q [J m -3 s -1 ]Q = the heating energy injected into the gas per photoionization (in Joules)in equilibrium, G = L (and N R = N PI ) T e = (2/3)Q/k.
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 25 and 26: PhotoionisationPhotoionisation: the
Page 27 and 28: Photoionisation: the removal of ele
Page 29 and 30: Balmer seriesLyman series(UV)Recomb
Page 31 and 32: Optical SpectrumPlanetary Nebula: N
Page 33 and 34: AtomsThe Maxwellian DistributionVel
Page 35: cross sectionse nucleuselectric fie
Page 39 and 40: For a typical O-star (e.g. the O6V
Page 44 and 45: However, Q per ionization is: (3/2)
Page 46 and 47: excitation/de-excitation of bound e
Page 48 and 49: Collisionally excited lines (CELs)B
Page 50 and 51: O +CELs (forbidden lines) are writt
Page 52 and 53: compare energy level diagrams1S 05.
Page 54 and 55: Forbidden line coolingtransition ra
Page 56 and 57: www.jodcast.netTopical podcast with
Page 59: DensitiesObservations n e ~ 100 cm
Page 62 and 63: Fraction of O2+ ions able to emit 4
Page 64 and 65: End of last lecture
Page 66 and 67: Today:HII regions: Practical method
Page 68 and 69: compare energy level diagrams1S 05.
Page 70 and 71: DensitiesObservations n e ~ 100 cm
Page 72 and 73: Practical methods and examples
Page 74 and 75: eal example
Page 76 and 77: • End of stellar existence for lo
Page 78 and 79: Optical Recombination Lines• ORLs
Page 80 and 81: Possible solutions?• Possibility
Page 82 and 83: Any other ideas?• Possibility 3:
Page 84 and 85: Knots: Abell 30• Results of empir
Page 86: Conclusions• Cold H-deficient kno

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