1. 24 September 2001ATNF Imaging Workshop1 The Sydney University Stellar Interferometer (SUSI) John Davis School of Physics University of Sydney 24 September 2001ATNF Imaging Workshop1

2. 24 September 2001ATNF Imaging Workshop2 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

3. 24 September 2001ATNF Imaging Workshop3 SUSI is not an imaging instrument! Atmospheric turbulence introduces phase fluctuations - the phase of the interference fringes is corrupted 24 September 2001ATNF Imaging Workshop3 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 = V 2  12 (  ) = |  12 (  )| exp i  12 (  ) V 12 (  ) = |  12 (  )|

4. 24 September 2001ATNF Imaging Workshop4 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 24 September 2001ATNF Imaging Workshop4 Measurement of orbits of close binary stars leading to:  Stellar Masses  Accurate distances  M, L & R for individual stars

5. 24 September 2001ATNF Imaging Workshop5 SUSI from the air Photo: D. McConnell Baselines 5 < b < 640m Spectral Range 440 < < 900nm Aperture Diameter 14cm Resolution 75  as - 20mas

6. 24 September 2001ATNF Imaging Workshop6 The Basic Problems to be Solved I. Wavefront distortion due to atmospheric turbulence

7. 24 September 2001ATNF Imaging Workshop7 The Effects of Atmospheric Turbulence Wavefront distortion in the form of:  Wavefront curvature  Wavefront tips and tilts  Phase fluctuations

8. 24 September 2001ATNF Imaging Workshop8 How SUSI overcomes Wavefront Distortion Wavefront curvature - small apertures (< r 0 ) Wavefront tilt - “tip-tilt” correction (first order adaptive optics) Phase fluctuations - rapid signal sampling and processing

9. 24 September 2001ATNF Imaging Workshop9 The Effect of Atmospherically Induced Wavefront Tilts

10. 24 September 2001ATNF Imaging Workshop10 The Effect of the Atmospheric Coherence Time

11. 24 September 2001ATNF Imaging Workshop11 SUSI Simultaneous Observations of Atmospheric Coherence Time and Coherence Diameter t 0 = 0.314r 0 /V

12. 24 September 2001ATNF Imaging Workshop12 The Basic Problems to be Solved I. Wavefront distortion due to atmospheric turbulence II. Need for extreme mechanical stability

13. 24 September 2001ATNF Imaging Workshop13 Mechanical Stability Average 5.5 m deep & 1.2 m diameter Example: Siderostat support pier

14. 24 September 2001ATNF Imaging Workshop14 A SUSI Siderostat & Housing Siderostat & Relay Mirrors Siderostat Housing with Roll-off Roof

15. 24 September 2001ATNF Imaging Workshop15 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

16. 24 September 2001ATNF Imaging Workshop16 The Variation of V and C with OPD

17. 24 September 2001ATNF Imaging Workshop17 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

18. 24 September 2001ATNF Imaging Workshop18 Delay Curve for Sirius

19. 24 September 2001ATNF Imaging Workshop19 Beam Combination in SUSI Photon counts n 1 and n 2 in sampling time t n 1  [1 + |  12 (0)| cos  ] n 2  [1 – |  12 (0)| cos  ] n 1 – n 2  2|  | cos   4|  |    2|  | 

20. 24 September 2001ATNF Imaging Workshop20 Interferometer Response to a Uniform Disk Source

21. 24 September 2001ATNF Imaging Workshop21 Observations of Delta Canis Majoris SUSI (  CMa as calibrator) SUSI (  CMa as calibrator) Stellar Intensity Interferometer

22. 24 September 2001ATNF Imaging Workshop22 Response of an Interferometer to a Binary Star

23. 24 September 2001ATNF Imaging Workshop23 Examples of SUSI Observations of Beta Centauri

24. 24 September 2001ATNF Imaging Workshop24 The Orbit of Beta Centauri determined from SUSI Observations

25. 24 September 2001ATNF Imaging Workshop25 The SUSI Programme Observing Programme  Single stars for Te, R and L  Spectroscopic binaries for M and d, as well as Te, R and L  Pulsating stars (e.g. Cepheids) for d Technical Programme  Installation and commissioning of “red” beam combination system

26. 24 September 2001ATNF Imaging Workshop26

27. 24 September 2001ATNF Imaging Workshop27 Ground-Based Long-Baseline Optical/IR Interferometers KEY: C - Closed; W - Working; UC - Undergoing commissioning or under construction