Title: HiPERCAM and TESS observations of the rapidly rotating M7V star LP 89--187 Show Chinese title

Title: HiPERCAM 和 TESS 对快速旋转的 M7V 型恒星 LP 89--187 的观测

Abstract: 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 taken as implying 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 a few $\times10^{33}$ erg, whilst HiPERCAM observations, which cover 0.78 of the rotation period, show no evidence for flares more energetic than $\sim10^{31}$ erg. Intriguingly, other surveys show LP 89--187 has shown weak H$\alpha$ in emission. We compare the flare energy distribution of LP 89--187 with low mass stars in the $\beta$ Pic moving group, which have an age of $\sim$24 Myr. We find LP 89--187 has a lower flare rate than the $\beta$ Pic stars. In addition, we find that TRAPPIST-1 analogue stars, which are likely significantly older than the $\beta$ Pic stars, show fewer flares with energies $>10^{33}$ erg in TESS data. We examine the relationship between amplitude and period for a sample of low mass stars and find that more rapid rotators have a higher amplitude. Show Chinese abstract

Abstract: 在TESS观测中发现大量快速旋转的低质量恒星表现出没有或很少的耀斑，这是一个令人惊讶的发现，因为快速旋转以前被认为意味着高恒星活动性。 在这里，我们呈现 TESS和HiPERCAM $u_{s}g_{s}r_{s}i_{s}z_{s}$ 对其中一颗恒星LP 89--187的观测结果，该恒星的自转周期为0.117天。覆盖三个象限（64.6天）的TESS数据仅显示三个耀斑，其能量为几 $\times10^{33}$ erg，而覆盖0.78个自转周期的HiPERCAM观测结果没有显示出比 $\sim10^{31}$ erg 更高能量的耀斑。 有趣的是，其他调查表明LP 89--187显示出微弱的H$\alpha$ 发射。 我们将LP 89--187的耀斑能量分布与 $\beta$ Pic移动群中的低质量恒星进行比较，这些恒星的年龄为 $\sim$ 24 Myr。 我们发现LP 89--187的耀斑率低于 $\beta$ Pic恒星。 此外，我们发现TRAPPIST-1类似恒星，这些恒星可能比$\beta$ Pic恒星要古老得多，在TESS数据中显示出能量低于$>10^{33}$ erg的耀斑更少。 我们研究了低质量恒星振幅与周期之间的关系，发现旋转更快的恒星具有更高的振幅。