Astrometry with the TMT

S. R. Kulkarni

California Institute of Technology

Interdisciplinary Scientist

Space Interferometry Mission

2/25

“You understand something truly only when you can measure it precisely.” Lord Kelvin

Confucius says “One excellent measurement is better than many mediocre measurements.”

3/25

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

4/25

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

10 11 12 19

10

0

30

GAIA

SIM

20

40

Milk

y Way

Globular clusters

Active Galactic NucleiRadio Ref Frame

9 13 14 15 16 17 18Magnitude

Acc

urac

y a

rcse

c

Nearby Galaxies

Precision masses

Wide Angle, end-of-mission limit performance

SIM and GAIA – Wide Angle Astrometry Science Targets

Magnitude

Acc

urac

y a

rcse

c

SIM and GAIA - Exo-Planet Detection Capability

10 11 12 19

0.1

GAIA

SIM

10

100

Earth-like Planets

Jupiters 1-5 AU

9 13 14 15 16 17 18

Jupiters >5 AU

1

End-of-mission effective

End-of-mission effective

Young Planets

8/25

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

11/25

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

12/25

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

13/25

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

14/25

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

15/25

Magnetar Proper Motions

• 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.

9/2005

8/2006

10,12/2006

2005

2006

4U 0141+61

1E 2259+586

16/25

Very Narrow Angle Astrometry

17/25

PHASES: Demonstrated 20 microrcseconds precision

See Lane, Muterspaugh et al.

19/25

20/25

Some Applications

22/25

I. HST (WFPC2) Proper Motion of M4

Bedin et al.

23/25

II. Proper Motions of Halo Objects

Piatek et al. 2007

Fornax

Proper Motion: 485, -365 mas/century

(WFPC2, STIS)

24/25

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 ViewLGS-AO imaging shows individual point sources at r > 2” and is confusion limited at r < 2” (7.6 pc).

TMT ViewMeasure 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

25/25Gaudi et al.

IV. Halloween Transient in Cas

Movie by Christopher Night (CfA)Rosanne di Stefano (CfA)

Exciting Fly by Events

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

28/25

Rates relative to M-dwarfs

Per lens population

L-dwarf 0.7 0.02

T-dwarf 0.5 0.17

WD 1.7 0.17

NS 13 0.13

BH 8.4 0.01

R. Di Stefano

29/25

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