24 September 2001ATNF Imaging Workshop1 The Sydney University Stellar Interferometer (SUSI) John...
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Transcript of 24 September 2001ATNF Imaging Workshop1 The Sydney University Stellar Interferometer (SUSI) John...
24 September 2001
ATNF Imaging Workshop 1
The Sydney University Stellar Interferometer (SUSI)
John DavisSchool of PhysicsUniversity of Sydney
24 September 2001
ATNF Imaging Workshop 1
24 September 2001
ATNF Imaging Workshop 2
Outline• Background
What SUSI is and is not! What SUSI is designed to do
• SUSI The instrument The problems faced by optical stellar
interferometry Solutions adopted/developed for SUSI
• Example SUSI observations & results
24 September 2001
ATNF Imaging Workshop 3
SUSI is not an imaging instrument!
• Atmospheric turbulence introduces phase fluctuations - the phase of the interference fringes is corrupted
24 September 2001
ATNF Imaging Workshop 3
• It uses 2 apertures at a time (i.e. a single baseline) so phase closure and image reconstruction is not possible - SUSI measures “correlation” C = V2
12() = |12()| exp i12()V12() = |12()|
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ATNF Imaging Workshop 4
Some Programs for SUSI• Measurement of the angular diameters of
single stars leading to the determination of fundamental stellar properties:
Emergent fluxes Effective Temperatures Radii Luminosities
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ATNF Imaging Workshop 4
• Measurement of orbits of close binary stars leading to:
Stellar Masses Accurate distances
M, L & R for individual stars
24 September 2001
ATNF Imaging Workshop 5
SUSI from the air
Photo: D. McConnell
Baselines5 < b < 640m
Spectral Range440 < < 900nm
Aperture Diameter14cm
Resolution75as - 20mas
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ATNF Imaging Workshop 6
The Basic Problems to be SolvedI. Wavefront distortion due to
atmospheric turbulence
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ATNF Imaging Workshop 7
The Effects of Atmospheric Turbulence
• Wavefront distortion in the form of: Wavefront curvature Wavefront tips and tilts Phase fluctuations
Starlight
Wavefront distorted by atmospheric turbulence
Portions of wavefront accepted by interferometer apertures
Phase difference on arrival at apertures = 2/
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ATNF Imaging Workshop 8
How SUSI overcomes Wavefront Distortion
• Wavefront curvature - small apertures (< r0)
• Wavefront tilt - “tip-tilt” correction (first order adaptive optics)
• Phase fluctuations - rapid signal sampling and processing
24 September 2001
ATNF Imaging Workshop 9
The Effect of Atmospherically Induced Wavefront Tilts
0.1
1.0
0.1 1.0 10.0
d/r0
Cor
rela
tion
Loss
Fac
tor
With no wavefront-tilt correction
With wavefront-tilt correction
24 September 2001
ATNF Imaging Workshop 10
The Effect of the Atmospheric Coherence Time
24 September 2001
ATNF Imaging Workshop 11
SUSI Simultaneous Observations of Atmospheric Coherence Time and
Coherence Diameter
t0 = 0.314r0/V
24 September 2001
ATNF Imaging Workshop 12
The Basic Problems to be Solved
I. Wavefront distortion due to atmospheric turbulence
II. Need for extreme mechanical stability
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ATNF Imaging Workshop 13
Mechanical Stability
Average 5.5 m deep & 1.2 m diameter
Example: Siderostat support pier
24 September 2001
ATNF Imaging Workshop 14
A SUSI Siderostat & Housing
Siderostat & Relay Mirrors
Siderostat Housing with Roll-off Roof
24 September 2001
ATNF Imaging Workshop 15
The Basic Problems to be Solved
I. Wavefront distortion due to atmospheric turbulence
II. Need for extreme mechanical stability
III. Need to match the optical paths
24 September 2001
ATNF Imaging Workshop 16
The Variation of V and C with OPD
24 September 2001
ATNF Imaging Workshop 17
Optical Path Length Compensation
• The individual sections of the blue paths are all equal in the two arms
• The internal red path compensates the external red path
24 September 2001
ATNF Imaging Workshop 18
Delay Curve for Sirius
0.00
0.05
0.10
0.15
0.20
0.25
0.30
-250 -200 -150 -100 -50 0 50 100 150 200 250
Path Compensator Offset (m)
Obs
erve
d C
orre
latio
n
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ATNF Imaging Workshop 19
Beam Combination in SUSIPhoton counts n1 and n2 in sampling time t
n1 [1 + |12(0)| cos ] n2 [1 – |12(0)| cos ]
n1 – n2 2|| cos
< (n1 – n2)2 > 4||< cos2 >
< (n1 – n2)2 > 2||
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ATNF Imaging Workshop 20
Interferometer Response to a Uniform Disk Source
0.0
0.2
0.4
0.6
0.8
1.0
0 1 2 3 4 5 6 7 8
x = b/
V a
nd C
x
Visibility (V = 2J1(x)/x)
Correlation (C = V2)
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ATNF Imaging Workshop 21
Observations of Delta Canis Majoris
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40
Baseline (m)
Corre
lation
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40
Baseline (m)
Corre
lation
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40
Baseline (m)
Corre
lation
SUSI ( CMa as calibrator)
SUSI ( CMa as calibrator)
Stellar Intensity Interferometer
Instrument Calibration UD ± %Star (mas)
NSII n/a 3.29 ± 0.46 14
SUSI CMa 3.474 ± 0.091 2.6SUSI CMa 3.535 ± 0.090 2.5
SUSI Mean 3.505 ± 0.064 1.8
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ATNF Imaging Workshop 22
Response of an Interferometer to a Binary Star
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ATNF Imaging Workshop 23
Examples of SUSI Observations of Beta Centauri
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ATNF Imaging Workshop 24
The Orbit of Beta Centauri determined from SUSI Observations
-30
-25
-20
-15
-10
-5
0
5
10-15 -10 -5 0 5 10 15 20 25 30
y (mas)
x (m
as)
1995 MAPPIT Observation
1997 SUSI Observations
1998 SUSI Observations
1999 SUSI Observations
2000 SUSI Observations
Fitted Orbit
E
N
Period: 357.0±0.3 daysInclination: 67.5±0.4 degSemi-major axis: 25.3±0.2 mas
24 September 2001
ATNF Imaging Workshop 25
The SUSI Programme• Observing Programme
Single stars for Te, R and LSpectroscopic binaries for M and d, as well
as Te, R and LPulsating stars (e.g. Cepheids) for d
• Technical Programme Installation and commissioning of “red”
beam combination system
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ATNF Imaging Workshop 26
24 September 2001
ATNF Imaging Workshop 27
Ground-Based Long-Baseline Optical/IR Interferometers
KEY: C - Closed; W - Working; UC - Undergoing commissioning or under construction
Instrument Institution Location Aperture Maximum Wavelength StatusAcronym Diameter Baseline Range
(m) (m) (m)NSII Sydney U. Narrabri, Australia 26.8 188 0.44 CSUSI (P'type) Sydney U. Sydney, Australia 20.10 11 0.4-0.5 CMark III NRL/MIT/CfA Mt. Wilson, USA 20.05 32 0.45-0.8 CI2T CERGA Calern, France 20.26 144 Visible CGI2T CERGA Calern, France 21.5 65 Visible/IR WCOAST Cambridge U. Cambridge, UK 50.4 100 Red/near IR WSUSI Sydney U. Narrabri, Australia 20.14 640 0.4-0.9 WIOTA CfA Mt.Hopkins, USA 30.45 38 Visible/IR WISI UC Berkeley Mt. Wilson, USA 70 10 WNPOI USNO/NRL Anderson Mesa, USA 26.17 435 0.45-0.9 WPTI JPL/Caltech Mt. Palomar, USA 20.4 110 2.2 WCHARA Georgia St. U. Mt. Wilson, USA 61.0 350 0.45-2.4 UCKeck CARA Mauna Kea, USA 2(4)10(1.5) 165 2.2-10 UCVLTI ESO Cerro Paranal, Chile 4(3)8(1.8) 200 0.45-20 UC