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Six decades of TIGRE and Mount Wilson chromospheric monitoring in the H and K lines: The quest for an understanding of solar-type activity
J. H. M. M. Schmitt, K. -P. Schröder, M. Mittag +3
The combined time series of the consistently calibrated chromospheric activity indicator, the S-index -- derived from Mount Wilson and TIGRE data -- now spans more than five decade…
Magnetic activity of the solar-like star HD 140538
M. Mittag, J. H. M. M. Schmitt, T. S. Metcalfe +2
The periods of rotation and activity cycles are among the most important properties of the magnetic dynamo thought to be operating in late-type, main-sequence stars. In this paper,…
Intriguing X-ray and optical variations of the gamma Cas analog HD45314
G. Rauw, Y. Nazé, M. A. Smith +11
A growing number of Be and Oe stars, named the gamma Cas stars, are known for their unusually hard and intense X-ray emission. This emission could either trace accretion by a compa…
The Ca II infrared triplet's performance as an activity indicator compared to Ca II H and K
J. Martin, B. Fuhrmeister, M. Mittag +4
Aims. A large number of Calcium Infrared Triplet (IRT) spectra are expected from the GAIA- and CARMENES missions. Conversion of these spectra into known activity indicators will al…
Carrington cycle 24: The solar chromospheric emission in a historical and stellar perspective
K. -P. Schroder, M. Mittag, J. H. M. M. Schmitt +3
We present the solar S-index record of cycle 24, obtained by the TIGRE robotic telescope facility and its high-resolution spectrograph HEROS (R20,000), which measures the…
Chromospheric activity and evolutionary age of the Sun and four solar twins
M. Mittag, K. -P. Schröder, A. Hempelmann +2
The activity levels of the solar-twin candidates HD 101364 and HD 197027 are measured and compared with the Sun, the known solar twin 18 Sco, and the solar-like star 51 Peg. Furthe…