The Carlina-type diluted telescope: Stellar fringes on Deneb

TL;DR

This paper reports on the successful demonstration of stellar fringes on Deneb using the Carlina-type diluted telescope, showcasing its potential as a new class of large, cost-effective interferometers for advanced astronomical observations.

Contribution

The study presents the first successful observation of stellar fringes with a Carlina-type diluted telescope, validating its design and operational feasibility for future large-scale interferometric projects.

Findings

Stellar fringes obtained on Deneb in 2013.

Metrology fringes achieved with micron accuracy.

Feasibility demonstrated for future large diluted telescopes.

Abstract

Context. The performance of interferometers has largely been increased over the last ten years. But the number of observable objects is still limited due to the low sensitivity and imaging capability of the current facilities. Studies have been done to propose a new generation of interferometers. Aims. The Carlina concept studied at the Haute-Provence Observatory consists in an optical interferometer configured as a diluted version of the Arecibo radio telescope: above the diluted primary mirror made of fixed co-spherical segments, a helium balloon or cables suspended between two mountains and/or pylons, carries a gondola containing the focal optics. This concept does not require delay lines. Methods. Since 2003, we have been building a technical demonstrator of this diluted telescope. The main goals of this project were to find the opto-mechanical solutions to stabilize the optics attached under cables at several tens of meters above the ground, and to characterize this diluted telescope under real conditions. In 2012, we have obtained metrology fringes, and co-spherized the primary mirrors within one micron accuracy. In 2013, we have tested the whole optical train: servo loop, metrology, and the focal gondola. Results. We obtained stellar fringes on Deneb in September 2013. In this paper, we present the characteristics of these observations: quality of the guiding, S /N reached, and possible improvements for a future system. Conclusions. It is an important step that demonstrates the feasibility of building a diluted telescope using cables strained between cliffs or pylons. Carlina, like the MMT or LBT, could be one of the first members of a new class of telescopes named Large Diluted Telescopes. Its optical architecture has many advantages for future projects: Planet Formation Imager, Post-ELTs, Interferometer in space.