1. RR Lyraes Bi-Qing For Chris Sneden (UT) George Preston (Carnegie Observatory)

2. What are RR Lyrae stars? APOD 23 Feb 2001

3. What happens when stars cross the instability strip? They pulsate like a jello! Scientific Computing in the School of Physics at the University of Sydney

4. RR Lyraes Max radius Typical time scale = 0.57 day

5. Different types of RR Lyraes

6. What drives stellar pulsations? Kappa-mechanism (RR Lyrs) –“steam engine” Absorb heat Restore the balance inside the star Release heat / cool off ContractExpand

7. Why RR Lyraes are interesting? Most of RR Lyraes have –stable pulsation –stable pulsational period –high luminosity Easy to be identified at large distances Standard candles for distance scale Tracers for Studying Galactic structure

8. Distance scale to Globular Clusters https://www.cfa.harvard.edu/~jhartman/M3_movies.html M 3

9. Duffau et al. (2006) Tracers for studying Galactic structure

10. Special: Blazhko effect Sergey Blazhko created by D. Welch based on MACHO project data, Alcock et al. 2000D. Welch MACHO project

11. What am I studying? Chemical compositions throughout the pulsational cycle. Line profile variation Where do we get the spectra?

12. George Preston LCO Du Pont 100 inch

13. What do we learn?

14. Line profile variation

15. Chemical Compositions

16. Current Missions CoRoT - COnvection, ROtation & Transits planétaires Kepler Space Telescope  Many new RR Lyrs have been discovered  New properties have been found in the lightcurves of RR Lyrs