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Session 80 - Star Clusters in the Milky Way.
Display session, Friday, January 09
Exhibit Hall,

[80.11] Chromospheric Activity in the late A- and F-type Stars in Several Hyades-Age Clusters

B. L. Rachford (U. Wyoming)

We report observations of the chromospheric He I \lambda5876 (D3) line in the late A- and F-type stars in the Hyades, Praesepe, and Coma star clusters. The average chromospheric activity level in the early F-type stars is statistically identical in the three clusters and in field dwarfs. In contrast, the coronal X-ray emission of early F-stars is considerably smaller for Praesepe as compared to Hyades and Coma. In later F-type stars, D3 is slightly weaker in the Hyades as compared with Coma, consistant with the well-known decrease in activity with age observed in solar-type stars. The earliest star detected in each cluster ranges from \bv\ = 0.26 in the Hyades to 0.31 in Praesepe. However, four stars in the Hyades in the range 0.28--0.32 are not detected. Finally, in nine early F-type stars we compare D3 strength in two different observing runs to investigate variability.

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