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

1/25 “You understand something truly only when you can measure it precisely.” Lord Kelvin Confucius says “One excellent measurement is better than many mediocre measurements.”

2/25 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

3/25 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

GAIA SIM Milky Way Globular clusters Active Galactic Nuclei Radio Ref Frame Magnitude Accuracy  arcsec Nearby Galaxies Precision masses Wide Angle, end-of-mission limit performance SIM and GAIA – Wide Angle Astrometry Science Targets

Magnitude Accuracy  arcsec SIM and GAIA - Exo-Planet Detection Capability GAIA SIM Earth-like Planets Jupiters 1-5 AU Jupiters >5 AU 1 End-of-mission effective Young Planets

7/25 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

Precision Astrometry Thesis work of P. Brian Cameron

10/25 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

11/25 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

12/25 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

13/25 Magnetars Sources heavily extincted –A V ~ 3-30 mag 4/6 magnetars visible to Keck have published faint NIR/optical counterparts. –Kp ~ mag Two possible new counterparts based on astrometry and variability. –  Kp~1 mag 1E Thesis work of P. Brian Cameron

14/25 Magnetar Proper Motions Proper motion limits show magnetars have relatively low velocities –~ km/s Implies the population is older than previously thought Draws into question popular theories of magnetar formation. 9/2005 8/ ,12/ U E

15/25 Very Narrow Angle Astrometry

16/25 PHASES: Demonstrated 20 microrcseconds precision See Lane, Muterspaugh et al.

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Some Applications

21/25 I. HST (WFPC2) Proper Motion of M4 Bedin et al.

22/25 II. Proper Motions of Halo Objects Piatek et al Fornax Proper Motion: 48  5, -36  5 mas/century (WFPC2, STIS)

23/25 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. Keck’s View LGS-AO imaging shows individual point sources at r > 2” and is confusion limited at r < 2” (7.6 pc). 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 III. M31 Nucleus

24/25 Gaudi et al. IV. Halloween Transient in Cas

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

27/25 Rates relative to M-dwarfs Per lens population L-dwarf T-dwarf WD NS BH R. Di Stefano

28/25 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