Interferometry of binary stars using polymer optical fibres

Abstract

We show a laboratory experiment in which students can learn the use of interferometry as a valuable tool in astronomy. We detail experiments based on the use of the classic Michelson stellar interferometer able to reproduce the size of single stars and to characterize double star systems. Stellar sources, single and double, are reproduced by a laser light emerging from the circular end faces of one or two step-index polymer optical fibres. Light coming from the fibre end faces passes through two identical pinholes located on a lid covering the objective of a small telescope, thus producing interference fringes. The measurement of the fringe visibilities allows us to estimate both the diameters of the simulated stars and the separation between them, with errors lower than 18% for a range of light sources that can recreate the apparent size of the outer Solar System planets Uranus and Neptune and the binary properties of the Alpha Centauri system. The exercises here described illustrate the optical principles of spatial interferometry and can be integrated into courses on astronomy, optics or space science, with close interaction between theory and experiment.

Using a pseudo-thermal light source to teach spatial coherence

“…This coherence is immediately perceived as it can be directly observed. In addition, the generated knowledge of the spatial coherence of light can be used to create simple educational setups like [5,6] of, for example, the michelson stellar interferometer.…”

“…The correct complex degree of spatial coherence of a circular light source is given by This equation shall replace equation (1) in the original submission [1]. The typo also affects the expression for the fit function given in equation (6). The correct form of the fit function is given by…”

Teaching stellar interferometry with polymer optical fibers

“…On the other hand, the experiment can also provide information about the relative orientation of the binary sources by taking into account an additional parameter, . Furthermore, it is able to distinguish and deduce the contrast between the components of a binary system, such as the contrast of the binary system that recreates the conditions of the Alpha Centauri system with sources separated an angular distance of 15" [10].…”

“…The experiment is based on the optical principles of the Michelson stellar interferometer, it needs simple equipment that is available in most astronomy and optics departments, and it can be integrated into existing courses with close interaction between theory and experiment. It has been developed as a laboratory exercise in the subject Space Interferometry within the Master of Science and Space Technology organized in the "Aula Espazio Gela" of the Faculty of Engineering of Bilbao [9][10][11]. The laboratory exercise is suitable for graduate or master courses on astronomy, optics or space science.…”

Practical training of stellar interferometry by measuring spectral fringes visibilities

“…Only a few experiments have been developed with the purpose of teaching the basic concepts of stellar interferometry: a Michelson-type radio interferometer, 3 interference methods, 4 and optical telescopes covered by a double-aperture lid that employ polymer optical fibers (POFs) illuminated by laser sources simulating stars. 5,6 These activities utilizing POFs were created for our students of the Master of Space Science and Technology of the University of the Basque Country. 7 Their aim is to provide students with the hands-on experience needed to understand the basic concepts of stellar interferometry using a telescope, a digital camera and image-processing tools.…”