Post on 21-Dec-2015
transcript
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.”
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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
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
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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
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
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II. Proper Motions of Halo Objects
Piatek et al. 2007
Fornax
Proper Motion: 485, -365 mas/century
(WFPC2, STIS)
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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
Movie by Christopher Night (CfA)Rosanne di Stefano (CfA)
Exciting Fly by Events
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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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