HII regions slides

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Possible solutions?• Possibility 1: Temperature fluctuations in homogeneousgas– Hotter regions preferentially emit CELs, coolerregions preferentially emit ORLs. Assuming uniformtemperature results in underestimated CELabundances.Easily ruled out with high-res spectroscopy
Any other ideas?• Possibility 2: density fluctuations in chemicallyhomogeneous gas– Very dense regions (n e ~10 6 cm -3 ) would quenchemission of [O III] 4959,5007 lines– [O III]4363 has higher critical density and is notquenched. Therefore [O III] ratio underestimated,T e overestimated, CEL abundancesunderestimated.Measuring density of hydrogen gas (through method wehaven’t seen) rules this out
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Today:Recap on 1 st lecture:- Basic
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Distance = 450 pcDiameter ~ 1° (si
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Dark CloudsBok globules• relative
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ISM: average properties• Mean den
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A global view
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Cold, neutral medium (CNM)• domin
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www.milkywayproject.org
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Lagoon nebula
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PhotoionisationPhotoionisation: the
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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 42 and 43: M43Real examples1. no. of ionising
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 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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HII regions slides

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