Table 1.
List of Ca II K archives analysed in this study.
| Observatory | Abbreviation | Years | Images | SW | Disc size | Data type | Pixel scale | Ref. | |
|---|---|---|---|---|---|---|---|---|---|
| Total | Used | (Å) | (mm) | (bit) | (″ pixel−1) | ||||
| Arcetri | Ar | 1931–1974 | 5133 | 4825 | 0.3 | 65 | 16 | 2.4 | 1 |
| Kodaikanal (a) | Ko | 1907–1999 | 22158 | 19291 | 0.5 | 60 | 8 | 1.3 | 2 |
| McMath-Hulbert | MM | 1948–1979 | 5912 | 4911 | 0.1 | – | 8 | 3.5 | 3 |
| Meudon | MD | 1893–2018 (b) | 20986 | 17605 | 0.15 | 65 | 16 | 0.9–11 (c) | 4 |
| Mitaka | Mi | 1917–1974 | 8585 | 4193 | 0.5 | variable | 16 (d) | 0.9, 0.7 (e) | 5 |
| Mount Wilson | MW | 1915–1985 | 36340 | 31430 | 0.2 | 50 | 16 | 2.7 | 6 |
| Rome | Rome/PSPT | 1996–2018 | 3292 | 3292 | 2.5 | ∼27 | 16 | 2 (f) | 7 |
| Schauinsland | Sc | 1958–1965 (g) | 18 | 18 | – | variable | 16 | 1.7, 2.6 (h) | 8 |
| Wendelstein | WS | 1947–1977 (g) | 452 | 407 | – | variable | 16 | 1.7, 2.6 (h) | 8 |
Notes. Columns are: name and abbreviation of the observatory, period covered, the number of available and used observations, spectral width of the spectrograph/filter, disc size in the photographic observation, digitisation depth, pixel scale of the digital image, and the bibliography entry.
This archive has been recently re-digitised with 16-bit data type extending the dataset from 1904 to 2007 (Priyal et al. 2014; Chatterjee et al. 2016), but here we use the 8-bit data from a former digitisation.
The observations after 13 May 2002 are recorded with a CCD camera, while data are stored on photographic plates until 27 September 2002.
The highly variable resolution is due to the different set-ups employed for the digitisation. The average value for the photographic data (1893–2002) is 2.3″ pixel−1, while for the CCD data (2002–2017) is 1.5″ pixel−1.
All these data are with 16-bit digitisation depth; however, they were the result of two different digitisation runs. The data after 02 March 1960 and the first ten observations of the earlier years have recently been re-digitised with a different scanning instrument.
These are the years covered by the digitised observations; the WS archive goes back to 1943, while the Sc covers the period 1944–1966.
References. (1) Ermolli et al. (2009a); (2) Makarov et al. (2004); (3) Mohler & Dodson (1968); (4) Mein & Ribes (1990); (5) Hanaoka (2013); (6) Lefebvre et al. (2005); (7) Ermolli et al. (2007); (8) Wöhl (2005).
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