Starspot activity of HD 199178. Doppler images from 1994--2017
Autor: | Nikolai Piskunov, Maarit J. Käpylä, T. Willamo, Thomas Hackman, Oleg Kochukhov, J. Lehtinen, Iya Ilyin |
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Přispěvatelé: | Department of Physics, University of Helsinki, Leibniz Institut für Astrophysik Potsdam, Centre of Excellence Research on Solar Long-Term Variability and Effects, ReSoLVE, Uppsala University, Department of Computer Science, Aalto-yliopisto, Aalto University |
Jazyk: | angličtina |
Rok vydání: | 2018 |
Předmět: |
FOS: Physical sciences
Astrophysics 01 natural sciences individual: HD199178 [stars] Nordic Optical Telescope Spectral line symbols.namesake 0103 physical sciences stars: activity Differential rotation 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) Physics Butterfly diagram activity [stars] 010308 nuclear & particles physics Subgiant Starspot stars: late-type DIFFERENTIAL ROTATION Astronomy and Astrophysics 115 Astronomy Space science imaging [stars] stars: imaging Stars starspots stars: individual: HD199178 Astrophysics - Solar and Stellar Astrophysics 13. Climate action Space and Planetary Science symbols late-type [stars] Doppler effect |
Popis: | Context. Studying the spots of late-type stars is crucial for distinguishing between the various proposed dynamo mechanisms believed to be the main cause of starspot activity. For this research it is important to collect observation time series that are long enough to unravel both long- and short-term spot evolution. Doppler imaging is a very efficient method for studying spots of stars that cannot be angularly resolved. Aims. High-resolution spectral observations during 1994-2017 are analysed in order to reveal long- and short-term changes in the spot activity of the FK Comae-type subgiant HD 199178. Methods. Most of the observations were collected with the Nordic Optical Telescope. The Doppler imaging temperature maps were calculated using an inversion technique based on Tikhonov regularisation and utilising multiple spectral lines. Results. We present a unique series of 41 temperature maps spanning more than 23 years. All reliable images show a large cool spot region centred near the visible rotation pole. Some lower latitude cool features are also recovered, although the reliability of these is questionable. There is an expected anti-correlation between the mean surface temperature and the spot coverage. Using the Doppler images, we construct the equivalent of a solar butterfly diagram for HD 199178. Conclusions. HD 199178 clearly has a long-term large and cool spot structure at the rotational pole. This spot structure dominated the spot activity during the years 1994-2017. The size and position of the structure has evolved with time, with a gradual increase during the last years. The lack of lower latitude features prevents the determination of a possible differential rotation. 11 pages, 7 figures, Astronomy and Astrophysics, parallel version of published article |
Databáze: | OpenAIRE |
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