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Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.: Historical solar Ca II K observations at the Kyoto and Sacramento Peak observatories. Journal of Physics: Conference Series 1548 (1), 012007 (2020)

Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.; Banerjee, D.; Barata, T.; Belik, M.; Gafeira, R.; Garcia, A.; Hanaoka, Y. et al.; Hegde, M.; Klimeš, J.; Korokhin, V. V.; Lourenço, A.; Malherbe, J.-M.; Marchenko, G. P.; Peixinho, N.; Sakurai, T.; Tlatov, A. G.: Analysis of full-disc Ca II K spectroheliograms III. Plage area composite series covering 1892–2019. Astronomy and Astrophysics 639, A88 (2020)

Chatzistergos, T.; Ermolli, I.; Falco, M.; Giorgi, F.; Guglielmino, S. L.; Krivova, N. A.; Romano, P.; Solanki, S. K.: Historical solar Ca II K observations at the Rome and Catania observatories. Nuovo Cimento della Societa Italiana di Fisica C-Geophysics and Space Physics 42 (1), 5 (2019)

Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.: Analysis of full disc Ca II K spectroheliograms: II. Towards an accurate assessment of long-term variations in plage areas. Astronomy and Astrophysics 625, A69 (2019)

Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.; Banerjee, D.; Jha, B. K.; Chatterjee, S.: Delving into the Historical Ca ii K Archive from the Kodaikanal Observatory: The Potential of the Most Recent Digitized Series. Solar Physics 294 (10), 145 (2019)

Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.; Giorgi, F.; Yeo, K. L.: Recovering the unsigned photospheric magnetic field from Ca II K observations. Astronomy and Astrophysics 626, A114 (2019)

Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.: Analysis of full disc Ca II K spectroheliograms: I. Photometric calibration and centre-to-limb variation compensation. Astronomy and Astrophysics 609, A92 (2018)

Chatzistergos, T.; Usoskin, I. G.; Kovaltsov, G. A.; Krivova, N. A.; Solanki, S. K.: New reconstruction of the sunspot group numbers since 1739 using the direct calibration and “backbone” methods. Astronomy and Astrophysics 602, A69 (2017)

Usoskin, I. G.; Kovaltsov, G. A.; Chatzistergos, T.: Dependence of the sunspot-group size on the level of solar activity and its influence on the calibration of solar observers. Solar Physics 291, pp. 3793 - 3805 (2016)

Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.: Exploiting four historical Ca II K spectroheliogram archives. Publications of the astronomical society of the pacific 504, pp. 227 - 231 (2016)

Chatzistergos, T.; Solanki, S. K.; Krivova, N. A.; Ermolli, I.; Giorgi, F.; Yeo, K. L.: Connecting chromospheric emission to photospheric magnetic field. AG 2017, Göttingen, Germany (2017)

Chatzistergos, T.; Solanki, S. K.; Krivova, N. A.; Ermolli, I.; Giorgi, F.; Yeo, K. L.: Relating photospheric magnetic field to Ca II K intensity. Rocks \& Stars II, Göttingen, Germany (2017)

Chatzistergos, T.; Usoskin, I. G.; Kovaltsov, G. A.; Krivova, N. A.; Solanki, S. K.: New calibration of the group sunspot number series using a non-linear non-parametric method. DPG-Frühjahrstagung, Bremen (2017)

Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.: Examination of historical spectroheliogram archives. Space climate symposium 6, Levi, Finland (2016)

Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.: The potential of historical spectroheliograms for Sun-climate studies. 9th IAGA - ICMA/IAMAS - ROSMIC/VarSITI/SCOSTEP workshop on long-term changes and trends in the atmosphere, Kühlungsborn, Germany (2016)

Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.: Exploring historical Ca II K spectroheliogram archives. XIVth Hvar astrophysical colloquium, Hvar, Croatia (2016)

Chatzistergos, T.; Usoskin, I.; Kovaltsov, G. A.; Krivova, N. A.; Solanki, S. K.: Non-linear re-calibration of group sunspot number series back to 1739. AGU Fall Meeting, San Francisco, USA (2016)

Krivova, N.; Wu, C. J.; Dasi Espuig, M.; Chatzistergos, T.; Yeo, K. L.; Solanki, S. K.: Reconstructions of past solar irradiance. International Space Climate Symposium-6, Levi, Finland (2016)

Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.: Handling historical Ca II K spectroheliogram observations. AGU Fall Meeting, San Francisco, USA (2016)