The Angular Diameter and Fundamental Parameters of Sirius A

The Sydney University Stellar Interferometer (SUSI) has been used to make a new determination of the angular diameter of Sirius A. The observations were made at an effective wavelength of 694.1 nm and the new value for the limb-darkened angular diameter is 6.048 +/- 0.040mas (+/-0.66%). This new result is compared with previous measurements and is found to be in excellent agreement with a conventionally calibrated measurement made with the European Southern Observatory's Very Large Telescope Interferometer (VLTI) at 2.176 microns (but not with a second globally calibrated VLTI measurement). A weighted mean of the SUSI and first VLTI results gives the limb-darkened angular diameter of Sirius A as 6.041 +/- 0.017mas (+/-0.28%). Combination with the Hipparcos parallax gives the radius equal to 1.713 +/- 0.009R_sun. The bolometric flux has been determined from published photometry and spectrophotometry and, combined with the angular diameter, yields the emergent flux at the stellar surface equal to (5.32+/- 0.14)x10^8 Wm^-2 and the effective temperature equal to 9845 +/- 64 K. The luminosity is 24.7 +/- 0.7 L_sun.Comment: Accepted for publication in PAS

The radius and mass of the subgiant star bet Hyi from interferometry and asteroseismology

We have used the Sydney University Stellar Interferometer (SUSI) to measure the angular diameter of beta Hydri. This star is a nearby G2 subgiant whose mean density was recently measured with high precision using asteroseismology. We determine the radius and effective temperature of the star to be 1.814+/-0.017 R_sun (0.9%) and 5872+/-44 K (0.7%) respectively. By combining this value with the mean density, as estimated from asteroseismology, we make a direct estimate of the stellar mass. We find a value of 1.07+/-0.03 M_sun (2.8%), which agrees with published estimates based on fitting in the H-R diagram, but has much higher precision. These results place valuable constraints on theoretical models of beta Hyi and its oscillation frequencies.Comment: 3 figures, 3 tables, to appear in MNRAS Letter

Bringing closure to microlensing mass measurement

Interferometers offer multiple methods for studying microlensing events and determining the properties of the lenses. We investigate the study of microlensing events with optical interferometers, focusing on narrow-angle astrometry, visibility, and closure phase. After introducing the basics of microlensing and interferometry, we derive expressions for the signals in each of these three channels. For various forecasts of the instrumental performance, we discuss which method provides the best means of measuring the lens angular Einstein radius theta_E, a prerequisite for determining the lens mass. If the upcoming generation of large-aperture, AO-corrected long baseline interferometers (e.g. VLTI, Keck, OHANA) perform as well as expected, theta_E may be determined with signal-to-noise greater than 10 for all bright events. We estimate that roughly a dozen events per year will be sufficiciently bright and have long enough durations to allow the measurement of the lens mass and distance from the ground. We also consider the prospects for a VLTI survey of all bright lensing events using a Fisher matrix analysis, and find that even without individual masses, interesting constraints may be placed on the bulge mass function, although large numbers of events would be required.Comment: 23 pages, aastex, submitted to Ap

Long-Baseline Interferometric Multiplicity Survey of the Sco-Cen OB Association

We present the first multiplicity-dedicated long baseline optical interferometric survey of the Scorpius-Centaurus-Lupus-Crux association. We used the Sydney University Stellar Interferometer to undertake a survey for new companions to 58 Sco-Cen B- type stars and have detected 24 companions at separations ranging from 7-130mas, 14 of which are new detections. Furthermore, we use a Bayesian analysis and all available information in the literature to determine the multiplicity distribution of the 58 stars in our sample, showing that the companion frequency is F = 1.35 and the mass ratio distribution is best described as a power law with exponent equal to -0.46, agreeing with previous Sco-Cen high mass work and differing significantly from lower-mass stars in Tau-Aur. Based on our analysis, we estimate that among young B-type stars in moving groups, up to 23% are apparently single stars. This has strong implications for the understanding of high-mass star formation, which requires angular momentum dispersal through some mechanism such as formation of multiple systems.Comment: 7 figures, 5 tables, accepted for publication in MNRA

Orbital parameters, masses and distance to Beta Centauri determined with the Sydney University Stellar Interferometer and high resolution spectroscopy

The bright southern binary star beta Centauri (HR 5267) has been observed with the Sydney University Stellar Interferometer (SUSI) and spectroscopically with the ESO CAT and Swiss Euler telescopes at La Silla. The interferometric observations have confirmed the binary nature of the primary component and have enabled the determination of the orbital parameters of the system. At the observing wavelength of 442 nm the two components of the binary system have a magnitude difference of 0.15. The combination of interferometric and spectroscopic data gives the following results: orbital period 357 days, semi-major axis 25.30 mas, inclination 67.4 degrees, eccentricity 0.821, distance 102.3 pc, primary and secondary masses M1 = M2 = 9.1 solar masses and absolute visual magnitudes of the primary and secondary M1V = -3.85 and M2V = -3.70. The high accuracy of the results offers a fruitful starting point for future asteroseismic modelling of the pulsating binary components.Comment: 10 pages, 4 figures. Accepted for publication in MNRA

The Palomar Testbed Interferometer

The Palomar Testbed Interferometer (PTI) is a long-baseline infrared interferometer located at Palomar Observatory, California. It was built as a testbed for interferometric techniques applicable to the Keck Interferometer. First fringes were obtained in July 1995. PTI implements a dual-star architecture, tracking two stars simultaneously for phase referencing and narrow-angle astrometry. The three fixed 40-cm apertures can be combined pair-wise to provide baselines to 110 m. The interferometer actively tracks the white-light fringe using an array detector at 2.2 um and active delay lines with a range of +/- 38 m. Laser metrology of the delay lines allows for servo control, and laser metrology of the complete optical path enables narrow-angle astrometric measurements. The instrument is highly automated, using a multiprocessing computer system for instrument control and sequencing.Comment: ApJ in Press (Jan 99) Fig 1 available from http://huey.jpl.nasa.gov/~bode/ptiPicture.html, revised duging copy edi

The future of enterprise groupware applications

This paper provides a review of groupware technology and products. The purpose of this review is to investigate the appropriateness of current groupware technology as the basis for future enterprise systems and evaluate its role in realising, the currently emerging, Virtual Enterprise model for business organisation. It also identifies in which way current technological phenomena will transform groupware technology and will drive the development of the enterprise systems of the future

Modern optical astronomy: technology and impact of interferometry

The present `state of the art' and the path to future progress in high spatial resolution imaging interferometry is reviewed. The review begins with a treatment of the fundamentals of stellar optical interferometry, the origin, properties, optical effects of turbulence in the Earth's atmosphere, the passive methods that are applied on a single telescope to overcome atmospheric image degradation such as speckle interferometry, and various other techniques. These topics include differential speckle interferometry, speckle spectroscopy and polarimetry, phase diversity, wavefront shearing interferometry, phase-closure methods, dark speckle imaging, as well as the limitations imposed by the detectors on the performance of speckle imaging. A brief account is given of the technological innovation of adaptive-optics (AO) to compensate such atmospheric effects on the image in real time. A major advancement involves the transition from single-aperture to the dilute-aperture interferometry using multiple telescopes. Therefore, the review deals with recent developments involving ground-based, and space-based optical arrays. Emphasis is placed on the problems specific to delay-lines, beam recombination, polarization, dispersion, fringe-tracking, bootstrapping, coherencing and cophasing, and recovery of the visibility functions. The role of AO in enhancing visibilities is also discussed. The applications of interferometry, such as imaging, astrometry, and nulling are described. The mathematical intricacies of the various `post-detection' image-processing techniques are examined critically. The review concludes with a discussion of the astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics, 2002, to appear in April issu