Spectrum variability of the active solar-type star ξ Bootis A

An extensive spectroscopic study on ξ Boo A (a chromospherically active solar-type star) was conducted based on the spectra obtained from 2008 December through to 2010 May, with the aim of detecting any spectrum variability and understanding its physical origin. For each spectrum, the atmospheric parameters were spectroscopically determined based on Fe lines, and the equivalent widths (along with the line-broadening parameters) of 99 selected lines were measured. We could detect meaningful small fluctuations in the equivalent widths of medium-strength lines. This variation was found to correlate with the effective temperature ($T_{\rm eff}$) consistently with the T-sensitivity of each line, which indicates that the difference in the mean temperature averaged over the disk of inhomogeneous condition is mainly responsible for this variability. It was also found that the macrobroadening widths of medium-strength lines and the equivalent widths’ dispersion of saturated lines tend to increase with the effective Landé factor, suggesting the influence of a magnetic field. Our power spectrum analysis applied to the time-sequence data of the V i$/$Fe ii line-strength ratio and $T_{\rm eff}$ could not confirm the 6.4 d period reported by previous studies. We suspect that surface inhomogeneities of ξ Boo A at the time of our observations were not so much simple (such as a single star patch) as rather complex (e.g., intricate aggregate of spots and faculae).