AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 67. Stellar Spectra
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southwest Exhibit Hall

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[67.05] Saturation, Activity Indicators, and Rotation Rates in Cool Stars

D.L. Buzasi (UC Berkeley)

Observations of low-mass stars in clusters (see, e.g. Krishnamurthi et al. 1998) show a mass-dependent saturation of the angular momentum loss rate, which is commonly explained by invoking saturation of the stellar dynamo mechanism (Keppens et al 1995). Explanation of the observed saturation is complicated, however, by the observation that different activity indicators appear to saturate at quite different rotational velocities (O'Dell et al 1995).

Both Buzasi (1997, 1999) and Solanki et al. (1997) have argued that the poleward movement of rising flux tubes in rapidly rotating lower main sequence stars may provide a natural mechanism for concentrating surface magnetic flux where it only poorly couples to the stellar wind; this mechanism would then explain the observed saturation of angular momentum loss rates at high rotational velocities. In this paper, I explore whether this model can be extended to explain the different saturation velocities observed for different indicators, such as photometric amplitude and chromospheric activity.

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