Magnetic activity and differential rotation of HIP12653

Abstract

We present a spectroscopic and photometric study of HIP12653 to investigate its magnetic cycle and differential rotation. Using HARPS archival spectra matched with MARCS-AMBER theoretical templates, we derive the stellar parameters (Teff, logg, FeH, and vsini) of the target. The S-index, an activity indicator based on the emission of the CaII H&K lines, is fitted to determine the magnetic cycle and rotation periods. We refine the magnetic cycle period to 5799.20 \pm 0.88 d and suggest the existence of a secondary, shorter cycle of 674.6922 \pm 0.0098 d, making HIP12653 the youngest star known to exhibit such a short activity cycle. During the minimum activity phase, a rotation period of 4.8 d is estimated. This is notably different from the 7-day period obtained when measurements during minimum activity are excluded, suggesting that these two periods are rotation periods at different latitudes. To explore this hypothesis, we introduce a novel light curve fitting method that incorporates multiple harmonics to model different spot configurations. Applied to synthetic light curves, the method recovers at least two rotation periods close to the true input values in 92.1% of cases. The inferred rotation shear shows a median deviation of 0.0011 \pm 0.0003 and a standard deviation of 0.0177 \pm 0.0002 from the true value. Applying this approach to TESS photometric data from 2018 to 2023, we detect three distinct rotation periods, 4.8 d, 5.7 d, and 7.7 d, (along with a signal at 3.75 d interpreted as its first harmonic), consistent with spots located at different latitudes. Assuming a solar-like differential rotation, we estimate an inclination of 34.0 \pm 1.8^\circ and a rotational shear of α= 0.38 \pm 0.01. These results confirm the 4.8-d period and demonstrate that differential rotation can be constrained by tracking rotation period changes across different phases of the magnetic cycle.

Accepted for publication in Research in Astronomy and Astrophysics

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