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Astrometry with the TMT

Astrometry with the TMT. S. R. Kulkarni California Institute of Technology Interdisciplinary Scientist Space Interferometry Mission. “ You understand something truly only when you can measure it precisely .” Lord Kelvin.

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Astrometry with the TMT

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  1. Astrometry with the TMT S. R. Kulkarni California Institute of Technology Interdisciplinary Scientist Space Interferometry Mission

  2. “You understand something truly only when you can measure it precisely.”Lord Kelvin Confucius says “One excellent measurement is better than many mediocre measurements.”

  3. Astrometry • Wide angle [Requires an inertial grid (quasars)] • Parallax • Proper Motion of similar stars • Narrow Angle [Requires suitably bright reference stars] • Companions • Proper Motion of dissimilar stars

  4. Space Interferometry Mission PlanetQuest Global astrometry (5yr mission) • 4 µas position (inertial) • 2.5 µas/yr proper motion • 4 µas parallax Narrow Angle Performance, 1 µas

  5. SIM and GAIA – Wide Angle Astrometry Science Targets 40 Wide Angle, end-of-mission limit performance 30 Milky Way Nearby Galaxies 20 Accuracy arcsec GAIA Active Galactic Nuclei Radio Ref Frame Precision masses 10 Globular clusters SIM 0 9 10 13 14 15 16 17 18 19 12 11 Magnitude

  6. 100 End-of-mission effective GAIA Jupiters >5 AU 10 Jupiters 1-5 AU 1 SIM End-of-mission effective Earth-like Planets 0.1 9 10 13 14 15 16 17 18 19 12 11 SIM and GAIA - Exo-Planet Detection Capability Accuracy arcsec Young Planets Magnitude

  7. Golden Astrometry Decade • SIM: Nonpareil in parallax and proper motion • Fundamental astrophysics (Galactic distance scale) • Dark Matter • GAIA: Superb stellar astrometry machine • TMT: Unique for read and faint objects • Latch on to GAIA frame • Dense fields • Transients

  8. Precision Astrometry Thesis work of P. Brian Cameron

  9. Bright Star Limit (NGS) • Cluster M5 at Palomar • 1.4s exposures • 600 images • Differential offsets are elongated parallel to the displacement • Offsets are correlated over the field

  10. Differential Tilt • Stars separated by some angle sample same turbulence at low altitudes • In principle correction is exact only for guide star • Thus error will grow with  • Removing correlated differential tilts results in a fundamental limit for single guide star AO astrometry DT ~ 20 mas (/20”)(5m/D)6/7

  11. Achieved precision • Resolving the differential tilt allows determination of the target star position to improve faster than 1/sqrt(N) • The tilt jitter also averages away as 1/sqrt(t) • Estimated precision of 50 microarcsecond in ~15 minutes of integration time • Achieved 100 uas in ~2 min • Future work will focus on longer intergrations • Apparently stable for 2-min data for timescales of weeks

  12. Magnetars • Sources heavily extincted • AV ~ 3-30 mag • 4/6 magnetars visible to Keck have published faint NIR/optical counterparts. • Kp ~ 19.5-22.5 mag • Two possible new counterparts based on astrometry and variability. • Kp~1 mag 1E 1841-045 Thesis work of P. Brian Cameron

  13. Magnetar Proper Motions 9/2005 10,12/2006 • Proper motion limits show magnetars have relatively low velocities • ~200-300 km/s • Implies the population is older than previously thought • Draws into question popular theories of magnetar formation. 8/2006 4U 0141+61 1E 2259+586 2005 2006

  14. Very Narrow Angle Astrometry

  15. PHASES: Demonstrated 20 microrcseconds precision See Lane, Muterspaugh et al.

  16. Some Applications

  17. I. HST (WFPC2) Proper Motion of M4 Bedin et al.

  18. II. Proper Motions of Halo Objects (WFPC2, STIS) Fornax Proper Motion: 485, -365 mas/century Piatek et al. 2007

  19. III. M31 Nucleus Keck’s View LGS-AO imaging shows individual point sources at r > 2” and is confusion limited at r < 2” (7.6 pc). TMT Goals • Measure the mass and location of the supermassive black hole in M31. • Study the detailed kinematics of the eccentric disk of old stars. • Understand the origin of the young stars. • Study the mechanism for ejecting hypervelocity stars. TMT View Measure proper motions in 1-3 years (3 sigma) with an astrometric precision of 0.03 mas. See poster by Jessica Lu, Andrea Ghez, & Keith Matthews

  20. IV. Halloween Transient in Cas Gaudi et al.

  21. Exciting Fly by Events Movie by Christopher Night (CfA) Rosanne di Stefano (CfA)

  22. Rates relative to M-dwarfs Per lens population R. Di Stefano

  23. Why TMT? • Narrow angle astrometry (faint, red): • Substellar binaries • Rare binaries (black hole…) • Nearby centers of galaxy (M31) • Medium angle astrometry (crowded field) • Globular Clusters • Dwarf Spheroidals • Wide angle astrometry (faint, red) • Limited to GAIA precision • Access to Sky for Transient Events • Mesolensing events • Transients

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