The Rotation of the G0 Dwarf β Comae

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Abstract
The rotation of β Comae (HR 4983, HD 114710, G0 V) is studied using the available information from spectral line broadening and from rotational modulation. The line broadening yields v sin i = 4.10 ± 0.06 km s-1, which agrees with previous values. Rotational modulation was looked for but not seen in the photospheric parameters of temperature and granulation, although this might be a result of data sampling not being well suited for modulation studies. Rotational modulation is seen in the S index of the Ca II chromospheric emission. Two period sequences characterize β Comae between 1981 and 1994. The periods decline monotonically with time, paralleling the decline in magnetic activity as indicated by the average strength of the Ca II emission. We interpret the decrease in period as differential rotation coupled with systematic migration in latitude of the active regions. It is not possible to separate the differential rotation profile of β Comae from its rate and sense of latitude migration. We compare the changes of β Comae with the Sun's and point out similarities and differences.