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TEMPERATURE STRUCTURE OF GASEOUS NEBULAE AND CHEMICAL ABUNDANCES

TEMPERATURE STRUCTURE OF GASEOUS NEBULAE AND CHEMICAL ABUNDANCES. M. Peimbert C.R. O’Dell A. Peimbert V. Luridiana C. Esteban J. García-Rojas L. Carigi F. Bresolin M.T. Ruiz A.R. López-Sánchez. Microstructures in the ISM: Bob O’Dell 70th birthday.

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TEMPERATURE STRUCTURE OF GASEOUS NEBULAE AND CHEMICAL ABUNDANCES

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  1. TEMPERATURE STRUCTURE OF GASEOUS NEBULAE AND CHEMICAL ABUNDANCES M. Peimbert C.R. O’Dell A. Peimbert V. Luridiana C. Esteban J. García-Rojas L. Carigi F. Bresolin M.T. Ruiz A.R. López-Sánchez Microstructures in the ISM: Bob O’Dell 70th birthday Lake Geneva, Wisconsin, April 2007

  2. OUTLINE • Why is this problem important? • Definitions • T[OIII], T(Balmer),T(OII), T(CII) • Which is the cause of temperature variations • The Orion nebula and microstructures • The Orion nebula and the solar abundances • Calibration of the R23 method • The primordial helium abundance • Conclusions

  3. Why is the problem of temperaturevariations important? • Physical conditions of gaseous nebulae • Abundances in HII regions and PNe • Solar abundances • Galactic chemical evolution • Primordial helium abundance, YP • Metal content and chemical evolution of the universe

  4. Te Ne Ni dV T0 = Ne Ni dV (Te -T0)2Ne Ni dV t 2 = T02Ne Ni dV Temperature Structure Te(4363/5007) =T0 [1 + (90800/T0 -3) t 2/2] Te(Bac/Hb) =T0 (1 – 1.70t 2) Te(He lines) =T0 (1 – kt 2) k~1.8 Te(4649/5007) =f1 (T0 , t 2) Te(4267/1909) = f2(T0 , t2)

  5. Ups and downs of t2 March 2007

  6. How Important Are Temperature Variations? • Photoionization homogeneous models predict values of t2 in the0.003 to 0.03 range, with typical values around 0.01 • Observational values of t2 are in the 0.00 to 0.09 range with typical values around 0.03 • Typical ratios between the abundances derived from permitted lines and forbidden lines are in the 2 to 3 range (O, C, N, Ne), the so called abundance difference factor, ADF • By adopting t2 values different from 0.00 it is possible to reconcile the abundances derived from forbidden lines with those derived from permitted lines

  7. Presence of Temperature Variations • There are temperature variations that can not be explained by chemically homogeneous photoionization models • The sources of these variations can be many and a specific model has to be made for each nebula • The abundances derived from recombination lines are almost unaffected by temperature variations • The abundances derived from collisionally excited lines, under the assumption of constant temperature, typically underestimate the abundances relative to hydrogen by a factor of 2 to 3

  8. Balmer vs. [OIII] Temperatures Liu & Danziger 1993

  9. N(C++) from Recombination Lines vs. N(C++) from Forbidden Lines Peimbert, Luridiana, & Torres-Peimbert 1995

  10. Recombination to Forbidden O++ ratios (log ADF) vs. [OIII] – Balmer Temperatures Liu et al. 2001

  11. What causes Temperature Variations? • Deposition of mechanical energy • Chemical inhomogeneities • Presence of WR Stars • Dust heating • Time dependent ionization • Density variations • Deposition of magnetic energy • Shadowed regions

  12. Microstructures and t2 in the Orion Nebula O´Dell et al. 2003 [O III] 5007 image

  13. Based on HST data We derived 1,500,000 TC[4363/5007] columnar values O´Dell et al. 2003

  14. Noise vs. True Temperature Variations The face of the nebula is mottled with small scale variations in TC with angular dimensions of about 10” (~0.02 pc) and amplitudes of 400 K O´Dell et al. 2003

  15. Histogram of TC[4363/5007] We obtained a t2A(O++)=0.008 across the face of the nebula values O´Dell et al. 2003

  16. [OIII] / HI [NII] / HI Small Scale Ionization Structure O´Dell et al. 2003

  17. t2 in the Orion Nebula • From HST narrow filter images: • t2A(O++)=0.008 • From a very small region of Orion Esteban et al. (2004) estimated: • t2sr(O++)=0.020±0.002 from OII and [OIII] • t2sr(H+)=0.022±0.002 from T(HeI) vs. T([OII]+[OIII]) • O´Dell et al. estimated: t2WholeObject(H+)=0.028±0.006

  18. The Low Te Regions behind Clumps within the Ionized Gas • Proplyds  Shadows, as long as 0.2 pc, covering 0.5% of the field of view contribute with 0.0093 to t2(O+) • Neutral High Density Clumps  Shadows, as long as 0.025 pc, covering about 1/250 of the volume contribute with 0.0016 < t2(O+) < 0.0075

  19. Neutral High Density Clumps O´Dell et al. 2003

  20. Different Components of t2 • The total value of t2(H+) has to consider both the O+ and the O++ regions

  21. Chemically inhomogeneous H II regions: Pros • In favor is the study of the N excess in NGC 5253 studied by Angel Sanchez-Lopez et al.(2007). who found from the O II and C II recombination lines t2 values of 0.052 and 0.072, and that the excess N is due to pollution by massive WR stars • Also in favor is the study by Tsamis and Pequignot (2005) that produced a chemically inhomogeneous model of 30 Doradus that also reproduces the observed line intensities of the forbidden and permitted O, C, and N lines

  22. Chemically inhomogeneous H II regions : Objections • One of the problems with the model of TP is that the excess abundance of O in the clumps is of a factor of 8, and that it requires an excess of 14 for C. Models of chemical evolution of irregular galaxies by Carigi, Colin, and Peimbert predict that 64% of the C is due to IMS and 36% to massive stars. Therefore for an excess of a factor of 8 in O the TP model should predict an excess of only a factor of 3 for C • An even larger discrepancy between the model by TP is present in the case of N for which ~80% is due to IMS • The small dispersion in abundances of H II regions in irregular galaxies and in the abundance gradient in our galaxy are against this idea

  23. Chemically inhomogeneous H II regions: Implications • The two phases chemically inhomogeneous model by Tsamis and Pequignot and the observations of 30 Doradus of A. Peimbert give: 12 + log O/H = 8.45, while the chemically homogeneous model gives 8.33 for t2 = 0.000 and 8.54 for t2 = 0.033 • Therefore the TP model is closer to the abundances given by the OII lines than to those given by the [OIII] lines and the T[OIII] temperature

  24. Orion and the Galactic gradient vs. the Solar abundances • Galactic abundances from collisionally excited lines (assuming t 2=0.00) are almost a factor of 2 lower than those we found from solar studies and Galactic chemical evolution models • Pilyugin et. al (2003, A&A, 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

  25. Galactic Abundance Gradients Esteban et al.ApJ, 2005

  26. Determinations from Recombination Lines (Equivalent to t 2≠0.00) • We have found the O/H abundance as a function of Galactocentric distance. From observations of HII 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) • The slope of this gradient is similar to those derived from [OIII] and t 2=0.00 • 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)

  27. Additional Support for a Higher O/H Initial Solar Value There are two results that indicate that the initial solar abundance was higher than the one adopted by Carigi et al., and that correspondingly the ISM t2 values are even higher than those derived by Esteban et al. 2005 • Estimates of the gravitational settling indicate that the original oxygen solar abundance was higher by about 0.05 dex than the present photospheric one, e. g. Piersanti et al. (2007), Bahcall et al. (2006), Basu & Antia (2004)… • There is a strong discrepancy between the Asplund et al. 2005 photospheric abundances and the solar interior ones determined from helioseismic measurements that amounts to ~ 0.1 dex

  28. Determination of O/H abundances in distant extragalactic H II regions: Calibration ofthe O23 method • Calibration with observed Te[OIII] values • Calibration with models • Calibration with OII recombination lines

  29. Peimbert et al. 2006

  30. Which Calibration for O23 ? • The best way to calibrate the O23 method is to use OII recombination lines to obtain the O/H values • The OII recombination lines provide abundances that are about 0.2 to 0.3 dex higher than those given by the observed T(4363/5007) values • The use of the observed T(4363/5007) values provides a lower limit to the O/H values • Since nebular lines are less sensitive to temperature variations than auroral lines, model calibrations (that adjust the nebular lines) are closer to our calibration than those derived using the observed T(4363/5007) values

  31. Implications of the O23 Calibration • Our new calibration has implications on the metal production in the Universe and therefore on the star formation rate • With this calibration and observations at different z values of strong nebular lines it will be possible to study the chemical evolution of the Universe as a whole

  32. Determination of the Primordial Helium Abundance, YP , with t2 = 0.000 and t2 ≠ 0.000 Peimbert et al. 2007

  33. The YP DeterminationError Budget Systematic effects Peimbert et al. 2007

  34. The YP DeterminationYP , DP , and WMAP Comparison Cosmological predictions based on SBBN and observations *Observed values Peimbert et al. 2007

  35. 1/5 Oxygen Abundance of:30 Doradus

  36. 2/5Oxygen Abundance of: Orion Nebula

  37. 3/5Oxygen Abundance of: Solar Vicinity

  38. 4/5Oxygen Abundance of: HII Regions * log (O/H) + 12 = 8.2 - 8.9

  39. 5/5Primordial Helium Abundance: HII Regions

  40. The End

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