Astrometry%20with%20the%20TMT

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Astrometry with the TMT

• S. R. Kulkarni
• California Institute of Technology
• Interdisciplinary Scientist
• Space Interferometry Mission

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

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

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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

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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

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SIM and GAIA Wide Angle Astrometry Science
Targets
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Wide Angle, end-of-mission limit performance
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Milky Way
Nearby Galaxies
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Accuracy ?arcsec
GAIA
Active Galactic Nuclei
Radio Ref Frame
Precision masses
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Globular clusters
SIM
0
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19
9
13
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Magnitude
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SIM and GAIA - Exo-Planet Detection Capability
Accuracy ?arcsec
Young Planets
Magnitude
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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

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Precision Astrometry

• Thesis work of P. Brian Cameron

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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

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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

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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

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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
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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
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Very Narrow Angle Astrometry
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PHASES Demonstrated 20 microrcseconds precision
See Lane, Muterspaugh et al.
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Some Applications
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I. HST (WFPC2) Proper Motion of M4
Bedin et al.
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II. Proper Motions of Halo Objects
(WFPC2, STIS)
Fornax
Proper Motion 48?5, -36?5 mas/century
Piatek et al. 2007
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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
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IV. Halloween Transient in Cas
Gaudi et al.
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Exciting Fly by Events
Movie by Christopher Night (CfA) Rosanne di
Stefano (CfA)
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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
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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