Astronomy and Astrophysics, volume 553, L6-6 (2013/5-1)
ι Horologi, the first coronal activity cycle in a young solar-like star.
SANZ-FORCADA J., STELZER B. and METCALFE T.S.
Abstract (from CDS):
The shortest chromospheric (CaII H&K) activity cycle (1.6 yr) has been recently discovered in the young (∼600 Myr) solar-like star ιHor. Coronal X-ray activity cycles have only been discovered in a few stars other than the Sun, all of them with an older age and a lower activity level than ιHor. We intended to find the X-ray coronal counterpart of the chromospheric cycle for ιHor. This represents the first X-ray cycle observed in an active star, as well as the paradigm of the first coronal cycles in the life of a solar-like star. We monitored ιHor with XMM-Newton observations spanning almost two years. The spectra of each observation are fit with two-temperature coronal models to study the long-term variability of the star. We find a cyclic behavior in X-rays very similar to the contemporaneous chromospheric cycle. The continuous chromospheric monitoring for more than three cycle lengths shows a trend toward decreasing amplitude, apparently modulated by a longer term trend. The second cycle is disrupted prior to reaching its maximum, followed by a brief episode of chaotic variability before the cyclic behavior resumes, only to be disrupted again after slightly more than one cycle. We confirm the presence of an activity cycle of ∼1.6 yr in ιHor both in X-rays and CaII H&K. It is likely subject to the modulation of a longer, not yet constrained second cycle. The 1.6 yr cycle is the shortest coronal one observed to date, and ιHor represents the most active star for which a coronal activity cycle has been found. This cycle is probably representative of the first coronal cycles in the life of a solar-like star, at the age when life started on Earth.