LO Peg in 1998: Starspot patterns and differential rotation

Abstract

We present Doppler images of the young K5V - K7V rapid rotator LO Peg from seven nights of continuous spectroscopy obtained in 1998 from July 04 to July 10. The images reveal the presence of a strong polar cap with appendages extending to mid-latitudes, but no starspots are seen below 15\degr. We briefly discuss the distribution of spots in light of recent flux transport simulations which are able to reproduce the observed latitude dependence. With the full timeseries of spectra, of which 314 are useful, many phases are observed three times over the seven nights of observations. Using starspots as tracers of a solar-like latitudinal differential rotation in our image reconstructions, we find that the equatorial regions complete one more rotation than the polar regions every {181 $\pm$ 35} d. LO Peg is the second coolest star for which such a measurement has been made using indirect imaging methods. The degree of latitudinal shear is less than that seen in G and early K dwarfs, suggesting a trend in which differential rotation decreases with stellar mass in (pre-)main sequence objects.