The discovery of a significant number of rapidly rotating low-mass stars showing no or few flares in tess observations was a surprise, as rapid rotation has previously been linked to high stellar activity. Here we present tess and HiPERCAM u_ s g_ s r_ s i_ s z_ s observations of one of these stars, LP 89--187, which has a rotation period of 0. 117 d. tess data covering three sectors (64. 6 d) only show three flares, which have energies of a few times 10³3 erg, whilst HiPERCAM observations, which cover 0. 78 of the rotation period, show no evidence of flares more energetic than approximately 10³1 erg. Intriguingly, other surveys show that LP 89--187 has a weak Hα emission. We compared the flare energy distribution of LP 89--187 with low-mass stars in the β Pic moving group, which have an age of approximately 24 Myr. We find that LP 89--187 has a lower flare rate than the β Pic stars. In addition, we find that TRAPPIST-1 analogue stars, which likely are significantly older than the β Pic stars, show fewer flares with energies greater than 10³3 erg in tess data. We examined the relationship between amplitude and period for a sample of low-mass stars and find that more rapid rotators have a higher amplitude.
Ramsay et al. (Thu,) studied this question.