KEYWORDS: Stars, Visibility, Interferometers, Data modeling, Interferometry, Modulation, Calibration, Signal to noise ratio, Error analysis, Binary data
The conventional approach to high-precision narrow-angle astrometry using a long baseline interferometer is to directly measure the fringe packet separation of a target and a nearby reference star. This is done by means of a technique known as phase-referencing which requires a network of dual beam combiners and laser metrology systems. Using an alternative approach that does not rely on phase-referencing, the narrow-angle astrometry of several closed binary stars (with separation less than 2′′), as described in this paper, was carried out by observing the fringe packet crossing event of the binary systems. Such an event occurs twice every sidereal day when the line joining the two stars of the binary is is perpendicular to the projected baseline of the interferometer. Observation of these events is well suited for an interferometer in Antarctica. Proof of concept observations were carried out at the Sydney University Stellar Interferometer (SUSI) with targets selected according to its geographical location. Narrow-angle astrometry using this indirect approach has achieved sub-100 micro-arcsecond precision.
The Sydney University Stellar Interferometer (SUSI) is being fitted with a new beam combiner, called the
Micro-arcsecond University of Sydney Companion Astrometry instrument (MUSCA), for the purpose of high
precision astrometry of bright binary stars. Operating in the visible wavelength regime where photon-counting
and post-processing fringe tracking is possible, MUSCA will be used in tandem with SUSI’s primary beam
combiner, Precision Astronomical Visible Observations (PAVO), to record high spatial resolution fringes and
thereby measure the separation of fringe packets of binary stars. With continued monitoring of stellar separation
vectors at precisions in the tens of micro-arcseconds over timescales of years, it will be possible to search for the
presence of gravitational perturbations in the orbital motion such as those expected from planetary mass objects
in the system. This paper describes the first phase of the development, which includes the setup of the dual beam
combiner system and the methodology applied to stabilize fringes of a star by means of self-phase-referencing.
This paper presents an overview of recent progress at the Sydney University Stellar Interferometer (SUSI). Development
of the third-generation PAVO beam combiner has continued. The MUSCA beam combiner for high-precision
differential astrometry using visible light phase referencing is under active development and will be the subject of a
separate paper. Because SUSI was one of the pioneering interferometric instruments, some of its original systems are old
and have become difficult to maintain. We are undertaking a campaign of modernization of systems: (1) an upgrade of
the Optical Path Length Compensator IR laser metrology counter electronics from a custom system which uses an
obsolete single-board computer to a modern one based on an FPGA interfaced to a Linux computer - in addition to
improving maintainability, this upgrade should allow smoother motion and higher carriage speeds; (2) the replacement of
the aged single-board computer local controllers for the siderostats and the longitudinal dispersion compensator has been
completed; (3) the large beam reducing telescope has been replaced with a pair of smaller units with separate accessible
foci. Examples of scientific results are also included.
KEYWORDS: Computer programming, Control systems, Electronics, Switches, Process control, Optical amplifiers, Analog electronics, Power supplies, Interferometers, Temperature metrology
The Sydney University Stellar Interferometer uses embedded processors to control each siderostat station as
well as other major components of the instrument. The maintenance of the original controllers has become a
significant issue and we set out to design a new system that would be inexpensive, suitable for the relatively harsh
operating environment and simple to maintain. We have demonstrated that the new system works satisfactorily
and we are currently replacing the existing controllers with new ones.
The Sydney University Stellar Interferometer (SUSI) has been enhanced by installation of the PAVO beam combiner,
which uses an electron-multiplying CCD detector giving a fast, low-noise 2D readout. This allows PAVO to provide
wide-band wavelength dispersed beam combination, which improves sensitivity and scientific productivity. PAVO also
provides pupil segmentation which improves the instrumental fringe visibility. A remote operations facility has been
established, which allows SUSI to be operated from Sydney or elsewhere. A new control system for the longitudinal
dispersion corrector and siderostats is under development. Installation has commenced of a high precision differential
astrometry system (MUSCA) which aims to detect planets in binary star systems.
The Sydney University Stellar Interferometer (SUSI) has now been operating with a significanly more sensitive beam
combiner system (the Red Table) for several years. A number of novel results from the realms of single, binary and
pulsating star astrophysics are presented. Simultaneous dual beam-combiner operation with the Red Table and an
upgraded Blue Table has been demonstrated, enabling a high spectral dispersion oberving mode for stellar studies. Plans
for a major upgrade are briefly described. One component of this will be remote operation of the array for routine
observational data taking, with first steps on this path reported here with the inception of the Sydney Remote Operations
Center. The backbone of future plans with SUSI center around the installation of the southern of the twin PAVO
instruments. PAVO is also discussed in more detail in Ireland et al, this proceedings.
The Sydney University Stellar Interferometer is a long baseline optical interferometer located in northern New South Wales, Australia. It has a North-South array of eleven fixed input siderostat stations giving a range of baselines from 5 to 640 m. Currently ten baselines from 5 to 160 m are fully operational and beam-combination and detection systems for the spectral ranges 430-520nm and 550-950nm are available. Dichroic beam-splitters have been introduced to allow simultaneous observations with both spectral systems. The original blue beam-combination system has been upgraded to improve sensitivity and to allow rapid wavelength switching. A software scheduler has been developed to automate much of the observational procedure including the acquisition of a star, fringe search and acquisition, recording of fringe scans, and the taking of photometric scans. A data pipeline for processing the observational data has been further developed to include seeing corrections and this has improved the calibration of the observational data. Preliminary results of scientific observations with both blue and red
systems, including observations of single stars, binary stars and Cepheid variables are described.
The Sydney University Stellar Interferometer (SUSI) is a long-baseline optical interferometer operating at an observatory near Narrabri in Australia. SUSI features a 640 m long North-South array with 11 fixed siderostat stations. New science from the Blue (400-500 nm) and from the recently commissioned Red (500-950 nm) fringe detectors will be presented. Recent technological developments, mainly associated with the new Red detection system, encompassing wavefront correction, fringe encoding, wavelength switching and data analysis strategies, are described.
SUSI -- the Sydney University Stellar Interferometer -- currently operates with a maximum baseline of 160 m. A major upgrade which will see the sensitivity of the instrument increased by a factor of 50 is nearly complete, and first fringes have been obtained with the new red beam-combining system.
The Sydney University Stellar Interferometer (SUSI) is a long baseline optical interferometer located at the Paul Wild Observatory in northern New South Wales, some 400 km NNW of Sydney. An extensive observational and development program is in progress. The status of the observational program, data reduction techniques, and recent results are reported. Instrumental developments including the development and installation of new tip-tilt mirrors and the design and implementation of a red beam-combination system that includes a group-delay tracker will be described. Auxiliary instrumentation to provide complementary data for the interpretation of SUSI observations has been installed alongside SUSI and this will be outlined briefly.
The Sydney University Stellar Interferometer (SUSI) is a long baseline optical interferometer located at the Paul Wild Observatory in northern New South Wales, some 400km NNW of Sydney. SUSI has been designed to measure the angular sizes of stars of essentially all spectral types and luminosity classes and to measure the angular separations of close binary stars. In addition to the science programs planned for SUSI, the technical features of the instrument dictated by these programs are discussed. The current status of the instrument and science programs, and the plans for further development of the instrument are described.
The Sydney University Stellar Interferometer (SUSI) is a long baseline optical amplitude interferometer. In its initial configuration it is a two aperture, single ro instrument with wavefront-tilt corrections and dynamic optical path length compensation. It has been designed to measure the angular dimensions of stars of essentially all spectral types as well as the angular separations of binary stars. SUSI is located alongside the Australia Telescope at the Paul Wild Observatory, near Narrabri in northern New South Wales, Australia. It has a North-South array of input stations giving baselines covering the range from 5 m to 640 m. The baselines are being progressively commissioned, starting with the shorter ones, in parallel with an observing program aimed at fine-tuning the performance of the instrument. Progress and results from the commissioning program and the current status of the instrument are described.
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