Doppler imaging of stellar surface structure. XXI. The rapidly-rotating solar-type star HD 171488 = V889 Hercules
We present the first Doppler image of the single G0-dwarf HD 171488. As a 30-Myr young field star with a lithium abundance of ~140-times that of the Sun and a rotation 20 times faster, it is hardly a ``solar analog'' but could be termed an ``infant Sun''. Its position in the H-R diagram suggests it to be in the rapid-braking phase just prior to arrival on the ZAMS. Our Doppler images from four spectral lines show a cool polar spot and various high-latitude spot features with a temperature contrast of 500-1600 K relative to the effective (photospheric) temperature. Low-to-medium latitude features may be present but appear to be biased by the uneven phase coverage of our spectra and are too weak to be conclusively judged significant. We determine the rotational period to be 1.3371 +/- 0.0002 days and find a long-term, possibly cyclic variation of the mean V brightness of ~7 yrs. A constant radial velocity of -23.6 +/- 1.5 km s-1 suggests that HD 171488 is indeed a single star. Rising flux-tube models indicate preferred surfacing latitudes between 25 degr-60 degr for HD 171488 while our Doppler images reveal mostly high-latitude spots in excess of 60 degr . We emphasize that this discrepancy exists for all rapidly rotating single G dwarfs observed so far.