Photometric Variability of the mCP Star CS Vir: Evolution of the Rotation Period

The aim of this study is to accurately calculate the rotational period of CS Vir by using STEREO observations and investigate a possible period variation of the star with the help of all accessible data. The STEREO data that cover 5-yr time interval between 2007 and 2011 are analysed by means of the Lomb-Scargle and Phase Dispersion Minimization methods. In order to obtain a reliable rotation period and its error value, computational algorithms such as the Levenberg-Marquardt and Monte Carlo simulation algorithms are applied to the data sets. Thus, the rotation period of CS Vir is improved to be 9.29572(12) d by using the 5-yr of combined data set. Also, the light elements are calculated as HJD _max = 2454715.975(11) + 9^d _. 29572(12) × E + 9^d _. 78(1.13) × 10 ^{- 8} × E ² by means of the extremum times derived from the STEREO light curves and archives. Moreover, with this study, a period variation is revealed for the first time, and it is found that the period has lengthened by 0.66(8) s y^-1, equivalent to 66 s per century. Additionally, a time-scale for a possible spin-down is calculated around τ_SD 10⁶ yr. The differential rotation and magnetic braking are thought to be responsible of the mentioned rotational deceleration. It is deduced that the spin-down time-scale of the star is nearly three orders of magnitude shorter than its main-sequence lifetime (τ_MS 10⁹ yr). It is, in return, suggested that the process of increase in the period might be reversible.