The highly spotted photosphere of the young rapid rotator Speedy Mic

Abstract

We present high resolution images of the young rapidly rotating K3 dwarf Speedy Mic (BO Mic, HD 197890). The photospheric spot maps reveal a heavily and uniformly spotted surface from equatorial to high latitude regions. Contrary to many images of similar objects, Speedy Mic does not possess a uniform filling at high latitudes, but exhibits structure in the polar regions showing greatest concentration in a particular longitude range. The asymmetric rotation profile of Speedy Mic indicates the presence of a companion or nearby star which shows radial velocity shifts over a timescale of several years. Using a simple dynamical argument, we show that Speedy Mic is unlikely to be a binary system, and conclude that the feature must be the result of a chance alignment with a background binary. Complete phase coverage on two consecutive nights in addition to 60 per cent phase coverage after a three night gap has enabled us to track the evolution of spots with time. By incorporating a solar-like differential rotation model into the image reconstruction process, we find that the equator laps the polar regions once every $191\pm 17$ d. This finding is in close agreement with measurements for other late-type rapid rotators.

References in corpus (4)

• L' and M' Photometry of Ultracool Dwarfs
• The Dependence of Differential Rotation on Temperature and Rotation
• LO Peg in 1998: Starspot patterns and differential rotation
• Doppler imaging of Speedy Mic using the VLT, Fast spot evolution on a young K-dwarf star

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