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Planetary nebulae and the chemical evolution of the galactic bulge

Planetary nebulae and the chemical evolution of the galactic bulge. Roberto D.D. Costa André V. Escudero Walter J. Maciel (IAG/USP, Brazil). Work supported by FAPESP. The idea. Spectrophotometric data for a sample of bulge PNe, representatives of its intermediate age population.

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Planetary nebulae and the chemical evolution of the galactic bulge

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  1. Planetary nebulae and the chemical evolution of the galactic bulge Roberto D.D. Costa André V. Escudero Walter J. Maciel (IAG/USP, Brazil) Work supported by FAPESP

  2. The idea • Spectrophotometric data for a sample of bulge PNe, representatives of its intermediate age population. • Electron temperatures, densities, ionic and elemental abundances of helium, nitrogen, oxygen, argon, sulfur and neon were derived for the sample. • Using these observational results as constraints, a model to the chemical evolution of the bulge was developed. • Results indicate that the best fit for the measured chemical abundances is achieved using a double-infall model, where the first one is a fast collapse of primordial gas and the second is slower and enriched by material ejected by the bulge itself during the first episode.

  3. Data • 57 bulge PNe. Details of observations and data reduction in: Escudero & Costa 2001 (A&A 380, 300) Escudero et al. 2004 (A&A 414, 211) • Observations: ESO 1.5 m (Chile) LNA 1.6 m (Brazil) • Data reduction and analysis homogeneous for the whole sample  The largest homogeneous sample on chemical abundances of bulge PNe in the literature. (~30% of the total) • Abundances derived empirically using ICFs

  4. Distribution of chemical abundances Helium Literature data from Köppen et al. (1991), Samland et al. (1992), Cuisinier et al. (1996, 2000), Stasinska et al. (1998), Gorny et al. (2004)

  5. Nitrogen

  6. Oxygen

  7. Intermediate age objects Young objects Our sample Literature Our sample Literature Old objects Correlations between abundances

  8. Young objects Our sample Literature Our sample Literature Old objects

  9. Longitude Latitude Distribution

  10. The model • Goal: Model the chemical evolution of the bulge using PNe as representatives of their intermediate age population • Compare model results with derived abundances for many elements

  11. Basic equations • Infall: dM/dt = A exp[- t /], where dM = MT • SFR = 2.5 10-10 gk [M year-1 pc-2 ] (Kennicutt 1998) • IMF: Kroupa (2002) • Model 1 • Simple infall during 1 Gyr with primordial abundance • Outflow from 0 to 75% during 2 Gyr. • Model 2 • 1. First infall during 0.1 Gyr with primordial abundance. • Salpeter’s IMF during the first 0.4 Gyr • Outflow of 50% during 2 Gyr. • 2. Second infall during 2.0 Gyr, occuring 2.0 Gyr after the first one. No winds or outflow • Model 3 • Same as Model 2, but with second infall gas enriched by the first infall wind • Multizone

  12. Results • Model 1 (simple infall) with different mass loss fractions, compared with observational results for two different elements. • Mass is ejected by SN II/Ia. It can be seen that the wind rate is crucial to reproduce the observational data. Windless models overestimate the oxygen abundances. • Recent models point to a great mass loss by SN II in the early bulge formation phases (Ferraras et al.2003). Other alpha-element results are similar to oxygen.

  13. Results from model 2 (double infall) using two SN II yieldscompared with observational data derived from PNe.

  14. Model 2 results using two SN II yields (dotted: Woosley & Weaver 1995; solid: Tsujimoto et al. 1995) compared with observational data derived from stars. Red dots correspond to upper limits. • A less steeper IMF (Salpeter) is required during the first 0.4 Gyr, in order to reproduce the higher O/Fe ratio found in bulge stars with respect to disk objects.

  15. Model 3 (multizone, double infall, second enriched) ~ 10 - 25 % ~ 10 % 40 % Sketch of the multizone model, indicating the different mass fractions ejected by SN II/Ia. Each zone correspond to 1.5 kpc and has its own infall timescale and gas mass. Gas ejected by SN II/Ia is exchanged between zones.

  16. Objects produced by the second infall, previously enriched by SN II ejecta during the first infall. • Variation of the SFR efficiency is not enough to account for the observed N/O ratios • Solid lines represent the N/O ratio according to the multizone model with an interzone exchange between 10 to 25 %. • Blue lines correspond to the center of the bulge (central zone in the sketch). Red lines correspond to the first ring. • Dotted lines correspond to a model for which progenitors with masses smaller than 1 solar mass do not produce nitrogen, with interzone exchange of 10%. • Dashed red line corresponds to an intezone exchange of 25%.

  17. Our sample Literature • Correlation between N/O and He abundance. Blue lines correspond to the central zone and red lines correspond to the first ring (bulge-disk border) • The N/O vs. He/H does not change critically from one zone to other

  18. Main conclusions Steps required to reproduce the PNe abundance distribution : • Fast initial collapse (0.1 Gyr) • High SFR induces a high mass loss of material produced by SN II. This material goes to disk, halo and outside the Galaxy (2 Gyr) • A second and slower infall (2 Gyr) of enriched material generated the disk.

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