Temperature Fluctuations in H II Regions

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Temperature Fluctuations in H II Regions

• Manuel Peimbert
• Antonio Peimbert
• María Teresa Ruiz
• César Esteban
• Jorge García-Rojas
• Leticia Carigi

Bright Line Abundance Calibrations at Low- and
High-Metalicity
May 28th, 2005
Minneapolis, Minnesota
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Outline

• t2 Determinations
• Recombination Lines
• Solar vs. H II Region Values
• H II Galactic Abundance Gradient
• NGC 6822
• Calibration of Pagels Method
• Primordial Helium

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t2 Determinations
? Te Ne Ni dV
T0
? Ne Ni dV
? (Te - T0)2 Ne Ni dV
t 2
T02 ? Ne Ni dV
Te(4363/5007) T0 1 (91300/T0 -3) t 2/2
Te(Bac/Hb) T0 (1 1.70 t 2)
Te(He I lines) T0 (1 k t 2) k1.8
Te(4649/5007) f1 (T0 , t 2)
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Abundance Determination Methods

• Any line ratio from two ions of different
  elements can be used to determine their abundance
  ratio
• Permitted Lines
• (Recombination Lines)
• H, He, C, O
• Forbidden Lines
• (Collisionally Excited Lines)
• O, N, S, Ar, Cl, etc.

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Ne and Te Line Intensity Dependence
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Abundance Determinations using CELs_V, and
assuming t 2?0.00

• It is not easy to determine t 2.
• One of the methods used to determine t 2 is to
  find the value necessary to reconcile the
  measured RL intensities with the measured CEL
  intensities.
• Observations where t 2 can be measured using
  different methods T(Bac), T(He), LRs/LCEs, etc.
  usually find consistent values for all
  determinations.

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SOLUTION

• Use Recombination Lines.

NEW PROBLEM
Recombination Lines are 1000 - 10000 times
fainter than Collisionally Excited Lines.
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O II Recombination Lines, Multiplet 1

• Due to their faint intensity lt 0.0006 I (Hb) and
  to blends
• with other lines, it is usually not possible to
  measure all 8
• lines of this multiplet.

Peimbert, 2003, ApJ, 584, 735
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O II Recombination Lines, Multiplet 1

• O abundance depends on the total sum of the
  intensities from all 8 lines of the multiplet.
• The relative intensities of the lines within the
  multiplet are not constant.
• The relative intensities of the lines, depend on
  the populations of the 4 fine structure levels
  from the upper level of the transition. 2s 22p
  2(3 P)3s 4D03/2
• When the electronic density is high, there is
  efficient collisional redistribution among the
  levels.
• When the electronic density is low, there is not.
• We have obtained the critical density
  observationally (Ncrit 1325 cm-3 Ruiz, et.
  al, 2003, ApJ, 595, 247).

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Intensity Dependence on Density
Peimbert, Peimbert, Ruiz, 2005, ApJ, submitted
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Density Dependence Equations

• I (465073)

0.144
0.101
I (sum)
1 Ne /1325
I (46386196)
0.205
0.201
I (sum)
1 Ne /1325
I (464176)
0.057
0.301 -
I (sum)
1 Ne /1325
I (4649)
0.292
0.397 -
I (sum)
1 Ne /1325
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Galactic Abundance Gradients
Esteban et al. 2004
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Chemical Evolution Model of the Galaxy
Carigi et al. ApJ, 2005
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Galactic Gradient

• We have also found the O/H abundance as a
  function of Galactocentric distance. From
  observations of H II Regions we found a solar
  vicinity abundance of 8.79 dex with a gradient of
  -0.044 dex kpc-1. (Esteban et. al, 2005, ApJ,
  618, 95).
• This value is consistent with the O/H 8.66 dex
  Solar value derived by Asplund et al. (2005), and
  with galactic chemical evolution models that
  estimate that, in the 4.6 Gy since the Sun was
  formed, there has been an 0.13 dex increase in
  oxygen abundance of the ISM (Carigi et al. 2005,
  ApJ, 623, 213).

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Galactic Abundances From Collisionally Excited
Lines, Assuming t 20.00

• Abundances found from studies based on oxygen
  forbidden lines, are almost a factor of 2 lower
  than those we found from solar studies and
  galactic evolution.
• Pilyugin et. al (2003, AA, 401, 557) find
  O/H 8.52 dex in the
  solar vicinity.
• Deharveng et. al (2000, MNRAS, 311, 329) find
  O/H 8.53 dex in the solar
  vicinity.
• The slopes of these gradients are similar to that
• derived from recombination lines.

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NGC 6822 V Observations

• We have used these equations to correct the total
  intensity for the unobserved lines, in order to
  determine the O/H ratio.
• After correcting for these lines, we measure
  O/H 8.42 dex this value is
  approximately 2 times higher than O/H 8.16 dex
  the value obtained using CELs, assuming t 2
  0.00.
• This value is consistent with the O/H value
  measured from A supergiants found in NGC 6822.

Peimbert, Peimbert Ruiz, 2005, ApJ, submitted
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H II Region and Stellar Oxygen Abundancesa
Peimbert, Peimbert Ruiz, 2005, ApJ, submitted
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H II Regions in M101
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Pagels R23 Method
DE Dopita Evans, 1986 EP Edmunds
Pagel, 1984 MRS McCall et al., 1985 TPPF
Torres-Peimbert et al., 1989
TPPF
TPPF t2
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Primordial Helium
Peimbert, Peimbert, Luridiana, 2002
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Summary I

• Well observed Recombination Lines are better than
  Collisionally Excited Lines, to determine
  chemical abundances.
• The best studied Recombination Lines, that are
  suited for heavy element abundance
  determinations, are probably those of the
  multiplet 1 of O II and 4267 of C II.
• It is necessary to know the intensity of all the
  lines in the multiplet in order to accurately
  determine the O abundance.
• The intensity ratios of lines within this
  multiplet do not coincide with LTE computations
  for densities Ne lt 10 000. For these densities it
  is better to assume the ratios given by our
  equations.
• For H II regions the abundances determined from
  multiplet 1 of O II are approximately a factor of
  2 higher than those determined using the
  OIII4363/5007 traditional method.

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Summary II

• Recombination Line abundance determinations are
  consistent with solar abundance determinations,
  and with determinations made with NGC 6822
  supergiants.
• If possible it is better to calibrate Pagels
  method with O recombination lines.
• If Pagels method is calibrated with models it is
  better to adjust 3727 and 5007 to the models than
  4363/5007.
• For O poor H II regions the models by CLOUDY
  predict 4363/5007 temperatures smaller than
  observed, this indicates the presence of
  additional heating sources not considered by
  CLOUDY.
• The presence of a typical t2 value reduces Yp by
  about 0.007. For example from 0.250 to 0.243.

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The End
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