Speedy Mic: a very young, rapidly rotating K star

The active K-type object HD 197890 detected in the ROSAT all-sky survey appears to be one of the most rapidly rotating stars of its type yet found, with a $v$ sin i value of $170 \pm 20\enspace \text {km}\enspace \text {s}^{-1}$. Preliminary photometric measurements and spectral synthesis of the Li 6707-Å spectral region suggest a premain-sequence evolutionary status, although the derived spectral type of approximately K5 is uncertain at this stage, and further observations are planned.