Discipline: Astronomy
Research area: Solar physics (instrument now dedicated to training)
Context
Originally named the Turet dome, the Jean Rösch telescope has been observing the Sun’s surface at very high spatial resolution since 1961. The quality of both the instrument and the site make it possible to produce time sequences (films) that allow detailed study of the photosphere, the thin layer on the optical surface of the Sun where the underlying convective cells radiate their energy. These cells appear as granules around 1000 km in diameter. Observations made with the Lunette Jean Rösch have enabled us to discover the explosive granules and families of granules, as well as the magnetic flux tubes found in the intergranules at a scale close to the instrument’s resolution (0.25” of arc, i.e. less than 200km on the Sun).
Since the installation of a spectrograph on the telescope in 1980, it has been possible to combine high spatial and spectral resolution to measure Doppler radial velocities in the solar atmosphere (photosphere and chromosphere). This spectrograph, used in DPSM (Double Pass Subtractive Multichannel) mode, provides images (in intensity) and radial velocity maps simultaneously of the different layers of the solar atmosphere (photosphere and chromosphere, up to 10,000km above the surface). Finally, since the addition of a polarimeter in the late 1990s, we have been able to measure the magnetic field of the solar atmosphere using spectropolarimetry (Zeeman effect, Hanle effect). The aim of these high-spatial-resolution observations, in both imaging and spectropolarimetry, is to better understand how surface motions can be correlated with the prominences observed in the corona (CLIMSO), but also to study the large part of the solar magnetic flux contained in the quiet Sun, outside active regions.
Following the launch of a 50cm solar telescope into space (HINODE) and the appearance on the ground of telescopes with adaptive optics (to correct for the effects of the atmosphere) and larger diameters (1m diameter at the Swedish La Palma Tower or 1.6m diameter at the Big Bear Solar Observatory in California), researchers finally turned their backs on the Lunette Jean Rösch in the early 2010s.
Today, the Lunette Jean Rösch has found a second lease of life through university training, its versatility and availability making it an ideal instrument for perfecting one’s observation of the Sun and planets.
Finally, a project to install a high-spatial-resolution coronagraph on the telescope is currently being discussed as part of ground support for space instruments (polarimetric measurements in the lower corona), a project that would herald the return of research to the Lunette Jean Rösch.
Installation method and operation
The 50cm-diameter objective of the Lunette Jean Rösch, cut by Jean Texerau (optician at Paris Observatory), was installed in 1973. It features a two-lens objective (biconvex Crown and meniscus Flint) polished (to limit scattering) to a focal length of 6.4m. The telescope is mounted on an equatorial frame.
The special feature of this instrument is that the telescope is integral with the dome, the interior of the dome being isolated from the exterior by the dome walls and the objective lens, in order to limit the mixing of air masses of different temperatures and avoid, as far as possible, the creation of turbulent flows in the path of the light rays.
Laboratories and partners involved
- IRAP
- MASTER Astrophysics Toulouse III
Team members
OMP Staff (Pic du Midi Platform, Tarbes mechanical workshop)