Delving into the Historical Ca II K Archive from the Kodaikanal Observatory: the Potential of the Most Recent Digitised Series

Full-disc Ca II K photographic observations of the Sun carry direct information about the evolution of solar-plage regions for more than a century and are therefore a unique dataset for solar-activity studies. For a long time Ca II K observations were barely explored, but recent digitisations of multiple archives have allowed their extensive analysis. However, various studies have reported diverse results partly due to the insufficient quality of the digitised data. Furthermore, inhomogeneities have been identified within the individual archives, which, at least partly, could be due to the digitisation. As a result, some of the archives, e.g. that from the Kodaikanal observatory, were re-digitised. The results obtained by different authors who analysed the data from the new digitisation of the Kodaikanal archive differ from each other as well as from those derived from the old digitisation. Since the data were processed and analysed using different techniques, it is not clear, however, whether the differences are due to the digitisation or the processing of the data. To understand the reasons for such discrepancies, we analyse here the data from the two most recent digitisations of this archive. We use the same techniques to consistently process the images from both archives and to derive the plage areas from them. Some issues have been identified in both digitisations, implying that they are intrinsic characteristics of the data. Moreover, errors in timing of the observations plague both digitisations. Overall, the most recent 16-bit digitisation offers an improvement over the earlier 8-bit one. It also includes considerably more data and should be preferred.Comment: 28 pages, 17 figures, accepted for publication in solar physic

Measurement of pseudorapidity distributions of charged particles in proton-proton collisions at sqrt(s) = 8 TeV by the CMS and TOTEM experiments

Pseudorapidity ( $\eta$ ) distributions of charged particles produced in proton–proton collisions at a centre-of-mass energy of 8 $~\text {TeV}$ are measured in the ranges $|\eta | < 2.2$ and $5.3 < |\eta | < 6.4$ covered by the CMS and TOTEM detectors, respectively. The data correspond to an integrated luminosity of $\mathcal {L} = 45 \mu {\mathrm {b}}^{-1}$ . Measurements are presented for three event categories. The most inclusive category is sensitive to 91–96 % of the total inelastic proton–proton cross section. The other two categories are disjoint subsets of the inclusive sample that are either enhanced or depleted in single diffractive dissociation events. The data are compared to models used to describe high-energy hadronic interactions. None of the models considered provide a consistent description of the measured distributions