Abstract
Context. We carry out a solar survey with images of the photosphere, prominences, and corona at Pic du Midi observatory. This survey, named CLIMSO (for CLIchés Multiples du SOleil), is in the following spectral lines: Fe XIII corona (1.075 μm), Hα (656.3 nm), and He I (1.083 μm) prominences, and Hα and Ca II (393.4 nm) photosphere. All frames cover 1.3 times the diameter of the Sun with an angular resolution approaching one arcsecond. The frame rate is one per minute per channel (weather permitting) for the prominences and chromosphere, and one per hour for the Fe XIII corona. This survey started in 2007 for the disk and prominences and in 2015 for the corona. We have almost completed one solar cycle and hope to cover several more, keeping the same wavelengths or adding others. Aims. We seek to make the CLIMSO images easier to use and more profitable for the scientific community. Methods. At the beginning of the survey, the images that we sent to the CLIMSO database were not calibrated. We have implemented a photometric calibration for the present and future images, in order to provide “science-ready” data. The old images have been calibrated. We have also improved the contrast capabilities of our coronagraphs, which now provide images of the Fe XIII corona, in addition to previous spectral channels. We also implemented an autoguiding system based on a diffractive Fresnel array for precise positioning of the Sun behind coronagraphic masks. Results. The data, including the images and films, are publicly available and downloadable through virtual observatories and dedicated websites (use “CLIMSO” and “IRAP” keywords to find them). For the Hα and Ca II channels we calibrate the data into physical units, independent of atmospheric or instrumental conditions; we provide solar maps of spectral radiances in W m−2 sr−1 nm−1. The instrumental improvements and calibration process are presented in this paper.
Highlights
Pic du Midi de Bigorre in the French Pyrenées is the observatory where Bernard Lyot invented coronagraphy and obtained remarkable images in the 1930s and 1940s; see for example Lyot (1930, 1945, 1950)
The light diffracted around the occulting disk, which would be too bright to allow for observations of the corona, is in turn blocked by a “Lyot stop” in a pupil plane. Such an optical setup associated with precise baffling allows for a high rejection factor of solar light in the surrounding field, defined as the “dynamic range” in this work, which reaches 106. This ongoing survey aims to help the scientific community with solar studies by providing a large set of solar images and films with dense temporal sampling: 1 min between frames, and long span: several solar cycles
We plan to improve the algorithm that computes the commands to the equatorial mount based on the history of solar positions found; at present it is just a proportional response
Summary
Pic du Midi de Bigorre in the French Pyrenées is the observatory where Bernard Lyot invented coronagraphy and obtained remarkable images in the 1930s and 1940s; see for example Lyot (1930, 1945, 1950). The light diffracted around the occulting disk, which would be too bright to allow for observations of the corona, is in turn blocked by a “Lyot stop” in a pupil plane Such an optical setup associated with precise baffling allows for a high rejection factor of solar light in the surrounding field, defined as the “dynamic range” in this work, which reaches 106. We define the dynamic range of a coronagraph as the ratio between the brightness in the image of the photosphere and the residual light in the surrounding field at the final focal plane. A few images are selected for realtime uploading to the data base
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