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Astrometry%20with%20the%20TMT

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

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Title: Astrometry%20with%20the%20TMT


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
10
11
12
19
9
13
14
15
16
17
18
Magnitude
6
SIM and GAIA - Exo-Planet Detection Capability
Accuracy ?arcsec
Young Planets
Magnitude
7
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8
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

9
Precision Astrometry
  • Thesis work of P. Brian Cameron

10
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11
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
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
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
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.
  • ?Kp1 mag

1E 1841-045
Thesis work of P. Brian Cameron
15
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
10,12/2006
8/2006
4U 014161
1E 2259586
2005
2006
16
Very Narrow Angle Astrometry
17
PHASES Demonstrated 20 microrcseconds precision
See Lane, Muterspaugh et al.
18
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19
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20
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21
Some Applications
22
I. HST (WFPC2) Proper Motion of M4
Bedin et al.
23
II. Proper Motions of Halo Objects
(WFPC2, STIS)
Fornax
Proper Motion 48?5, -36?5 mas/century
Piatek et al. 2007
24
III. M31 Nucleus
Kecks View LGS-AO imaging shows individual point
sources at r gt 2 and is confusion limited at r lt
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
25
IV. Halloween Transient in Cas
Gaudi et al.
26
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27
Exciting Fly by Events
Movie by Christopher Night (CfA) Rosanne di
Stefano (CfA)
28
Rates relative to M-dwarfs
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
  • Per lens population

R. Di Stefano
29
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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