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The development of common user interface data analysis software dedicated to interferometric imaging

Final Activity Report Summary - OIF-UMICH-UCAM-NDT (The development of common user interface data analysis software dedicated to interferometric imaging.)

This research project focused on long baseline optical interferometry which is an area of observational astronomy where the light of a star is collected simultaneously by several widely separated telescopes which together simulate a giant instrument with an angular resolution such that it could distinguish one headlight from another of a car being driven on the moon.

The research was carried out at two major institutions:
- the University of Cambridge where the optical interferometry group, led by Chris Haniff, developed the Cambridge Optical Aperture Synthesis Telescope (COAST), the first instrument of its kind to exploit the techniques of aperture synthesis and closure phase at optical or infra-red wavelength and now major participant in the development of the Magdalena Ridge Observatory Interferometer (MROI);
- the University of Michigan where the optical interferometry group, led by John Monnier, designed and built the Michigan Infra-Red Combiner (MIRC) for the CHARA interferometer. This instrument allows true interferometric imaging with sub-milliarcsecond resolution and was featured in the journal Science for capturing the image of Altair, the brightest star in the constellation Aquila.

I contributed to the construction, commissioning and exploitation of the MIRC instrument in designing key optics for its spectrograph and in developing instrument control tools and graphical user interfaces. The instrument control tools allow the remote positioning of MIRC optical components either for fine tuning of the alignment or for setting-up a new observation configuration. The graphical interfaces are used during the observations to visualise the data coming out of the detector and control the many sub-systems of the instrument. The optics and software tools I developed have been part of the instrument ever since its commissioning in September 2005 and are routinely used to carry out observations with MIRC at CHARA.

I took part to the design study for the MRO interferometer at different levels but was mostly involved in investigating the question of the atmospheric refraction, the deviation of light as it passes through the Earth atmosphere. Atmospheric dispersion correctors (ADCs) are optical devices commonly used to compensate for the atmospheric refraction. During this study, I looked into the cost-effectiveness of such devices for MROI and investigated the impact on the instrument design and the scientific objectives of not using ADCs, hence saving several hundred thousand dollars to the project.

I created the pythonLibs library and Oiplot software with the objective of developing a set of general purpose routines and model-fitting routines built around the oifits data format. The oifits (IAU sponsored) data format is a standard for exchanging data from astronomical optical interferometers. The Oiplot software is a general purpose tool which allows, through its user friendly graphical interface, to visualise the data from a given set of oifits files. All the graphs produced can be customised with a click of the mouse and can be saved for later use in a presentation or a publication. Users can also fit various models to their interferometry data (visibility and closure phase) which allows them to rapidly check the geometry and dimension of the brightness distribution of the astronomical object they observed. Oiplot has been intensively tested in an astronomical project on the star CI Cam detailed below.

This research project covered all aspects on optical interferometry from the design of an instrument, its fabrication and its operation to its scientific use for observing, studying and measuring stars. I carried out an observing program of the star CI Cam using the Infrared Optical Interferometer Array (IOTA) and the Palomar Testbed Interferometer (PTI). CI Cam is a hot B[e] star surrounded by a dusty environment which is the source of the near-infrared emission that has been observed with both IOTA and PTI. I was able to measure the dimension of the hot dust emission and also find a geometrical model that accurately describe its morphology. I found that a Gaussian skewed ring with a central point source is the model that describes the brightness distribution of CI Cam at IOTA and PTI wavelengths the best. This result has been written into a scientific paper soon to be submitted to the journal MNRAS. I am also the PI of a MIRC / CHARA observing proposal that will be carried out in September 2008.