Differential rotation and star-spot evolution on HK Aqr in 2001 and 2002

Abstract

We present images of the rapidly rotating (P-rot = 0.431 d) M1.5Ve dwarf HK Aqr, from data obtained during 2001 and 2002. Star-spots are found distributed at a range of latitudes during both observing seasons, but unlike other solar-type rapid rotators of higher mass, HK Aqr does not show a strong polar cap at either epoch. In addition to the surface brightness images, we make use of the four-night time-base over which the 2002 observations were made, in order to derive an estimate of the latitudinal dependent rotation on HK Aqr. We find that the equator-lap-pole time lies in the range -1449 to +448 d. Although very small, we are therefore unable to determine whether the degree of differential rotation is in the solar or anti-solar sense.