1. The prospects of probing relativity in the Galactic Center with Adaptive Optics Observations Tobias Fritz, Stefan Gillessen, Hendrik Bartko, Katie Dodds-Eden, Frank Eisenhauer, Reinhard Genzel, Thomas Ott, Oliver Pfuhl Max-Planck-Institute for extraterrestrial physics, Garching, Germany 10 arcsec = 10 6 R s

2. Probing unprobed regimes of GR in the GC

3. Currently: ≈30 orbits known 20 stars shown, Gillessen+ 2009 S2 S2 is clearly the best star for detecting relativistic effects: The brightest one The shortest period The second closest peripassage 10 5 R s

4. What is limiting astrometry today? Noise induced position errors Fritz+ 2010

5. Position scatter matches expectations Diff. Tilt Jitter compare positions in one data set divided into two, “ABAB...” PSF uncertainty Fritz+ 2010

6. A positional noise floor: Residual Image Distortions 0.3 mas 0.15 mas NACO alignment improved Fritz+ 2010

7. “Halo noise” Seeing halo extends beyond radii at which the PSF can be precisely determined Resolution would help (ELTs) High Strehl helps room for improvements for PSF determination ? mas Fritz+ 2010

8. S2–like stars: Distortions Fainter stars: Halo noise Fritz+ 2010

9. How sensitive are we to relativistic effects ? Wrong: For given orbit compare Keplerian & Relativistic data Wrong: For given orbit compare Keplerian & Relativistic data Right: For given data compare Keplerian & Relativistic fit Right: For given data compare Keplerian & Relativistic fit

10. Special relativistic effects for S2 easily observable with today’s technique Romer effect Transverse Doppler effect Gravitational redshift Zucker et al. 2006 Full relativistic orbit

11. More difficult: Measure GR pericenter shift explicitly expected: Δω = 0.22° per revolution (16 years) measured for S2: Σω = 0.84° in 18 years Rubilar & Eckart (2001), Mouawad et al. (2005), Gillessen et al. (2009) Schwarzschild correction to 1/r potential

12. Assume, we continue what we are doing. How well do we do then? NACO: Astrometry with 300 µas SINFONI: Spectroscopy with 15 km/s

13. 2020: 3σ detection of GR precession possible S2 only 6 positions per year 2 radial velocities per year 2 radial velocities per year, 6 per year in 2017 & 2018

14. Special relativistic effects: highly significant for dense sampling of pericenter passage S2 only 6 positions per year 2 radial velocities per year 2 radial velocities per year, 6 per year in 2017 & 2018

15. Summary Limits of astrometry with 8 m telescopes: – Distortions for bright stars – Confusion/seeing halo for fainter stars Future: Continuing is worthwhile: SR effects in v rad easily doable by 2020 GR effects possible by 2020 – Big step: Higher resolution