1. Probing the Helium Enrichment of the Galactic Bulge with the Red Giant Branch Bump David M. Nataf The Ohio State University Adviser: Andrew Gould Collaborators: M. Pinsonneault, J. Johnson, A. Udalski, E. Athanassoula

2. Bulge Star Formation History Matters ● Λ-CDM simulations fail at reproducing observed bulge distribution (Kormendy et al. 2010). ● Fundamental aspects of Galactic structure.

3. Galactic Bulge Stellar History: A Few Known Metallicity Constraints

4. Galactic Bulge Stellar History: Age Distribution a Matter of Controversy

5. Origin of the Elements

7. Helium Enrichment in Different Stellar Populations

8. Helium Can Probe Bulge Formation Environment

9. Enter the Red Giant Branch “Bump” (RGBB)

10. RGBB is Very Sensitive to Chemistry

11. The RGBB More Easily Detectable in Metal-Rich Systems ● “At higher metallicities the extension in luminosity of the bump is larger, and it is also shifter to lower luminosity, in more populated RGB regions, so it is easier to detect.” - Cassisi & Salaris (1997). ● “[The bump is harder to measure in] metal-poor clusters, where the bump moves toward brighter magnitudes and therefore less populated RGB regions.” - Zoccali et al. (1999). ● “identification of the RGB bump in metal-poor GCs is more difficult since it is brighter than the HB, where evolution along the RGB becomes faster and the stellar sample, consequently, becomes smaller.” - Di Cecco et al. (2010).

12. Total Absence of Results on the Bulge RGBB ● Perhaps because the RGBB is not well-known? It’s not even good enough for the textbooks.

13. Galactic Bulge Color Magnitude Diagram: No Prominent RGBB

14. How to Hide the RGBB: Enhanced Helium Enrichment ● Increased helium abundance would decrease the RGBB lifetime (and also increase the RC lifetime).

15. OGLE-III Galactic Bulge Photometric Survey, Udalski (2003, 2008)

16. The Challenge of Precisely Interpreting Galactic Bulge CMDs Too few stars (small radius)... or too much differential reddening (large radius).

17. Solution: Clump-Centric Color- Magnitude Diagrams (CCCMDs)

18. Probing Additional Post-MS Evolutionary Features ● Red Giant Branch Bump: ● ΔI = 0.74 ± 0.01, f = 20 ± 1%. ● Asymptotic Giant Branch Bump: ΔI ≈ -1.08, f ≈ 5.5%.

19. Comparing to Predictions – Metallicity Measurements as Inputs

20. Comparing to Predictions – Stellar Models

22. Comparing to Predictions – Empirical Globular Cluster Calibrations

23. Comparing to Predictions – Empirical Globular Cluster Calibrations Continued

24. Empirical Brightness Calibration – Success !

25. Empirical Number Counts Calibration – Questions, Questions and a 3-σ Detection

26. Caveat: GC Age-Helium-Metallicity Relation is a Matter of Ongoing Research. ● Globular Clusters have unique chemical self- enrichment histories that is thought to include heavy helium enhancement (Bedin et al. 2004, Carretta et al. 2010, etc). ● Nataf et al. (2011b) showed that the 47 Tuc RGBB has gradients in number counts and brightness with respect to distance from the cluster center.

27. Caveat: GC Age-Helium-Metallicity Relation is ill-defined Continued

28. Conclusions ● The RGBB is a completely independent probe of the Galactic bulge Age-Helium-Metallicity relation. ● Early analysis shows the bulge RGBB has deficient number counts relative to expectations from both models and globular clusters. ● Models do a fine job of matching data on the RGBB in Galactic globular clusters.