Volume 605, September 2017
|Number of page(s)||10|
|Published online||01 September 2017|
Fifteen years in the high-energy life of the solar-type star HD 81809
XMM-Newton observations of a stellar activity cycle
1 INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
2 European Space Agency, 8-10 rue Mario Nikis, 75738 Paris Cedex 15, France
3 Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
Received: 2 June 2017
Accepted: 20 July 2017
Context. The modulation of the activity level of solar-like stars is commonly revealed by cyclic variations in their chromospheric indicators, such as the Ca ii H&K S-index, similarly to what is observed in our Sun. However, while the variation of solar activity is also reflected in the cyclical modulation of its coronal X-ray emission, similar behavior has only been discovered in a few stars other than the Sun.
Aims. The data set of the long-term XMM-Newton monitoring program of HD 81809 is analyzed to study its X-ray cycle, investigate if the latter is related to the chromospheric cycle, infer the structure of the corona of HD 81809, and explore if the coronal activity of HD 81809 can be ascribed to phenomena similar to solar activity and, therefore, considered an extension of the solar case.
Methods. We analyzed the observations of HD 81809 performed with XMM-Newton with a regular cadence of six months from 2001 to 2016, which represents one of the longest available observational baseline (~ 15 yr) for a solar-like star with a well-studied chromospheric cycle (with a period of ~ 8 yr). We investigated the modulation of coronal luminosity and temperature and its relation with the chromospheric cycle. We interpreted the data in terms of a mixture of solar-like coronal regions, adopting a method originally proposed to study the Sun as an X-ray star.
Results. The observations show a well-defined regular cyclic modulation of the X-ray luminosity that reflects the activity level of HD 81809. The data covers approximately two cycles of coronal activity; the modulation has an amplitude of a factor of ~ 5 (excluding evident flares, as in the June 2002 observation) and a period of 7.3 ± 1.5 yr, which is consistent with that of the chromospheric cycle. We demonstrate that the corona of HD 81809 can be interpreted as an extension of the solar case and can be modeled with a mixture of solar-like coronal regions along the whole cycle. The activity level is mainly determined by varying coverage of very bright active regions, similar to cores of active regions observed in the Sun. Evidence of unresolved significant flaring activity is present especially in the proximity of cycle maxima.
Key words: stars: activity / stars: coronae / stars: individual: HD 81809 / X-rays: stars
© ESO, 2017
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.