AAS Meeting #193 - Austin, Texas, January 1999
Session 99. Stellar Atmospheric Activity and Luminous Blue Variables
Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1

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[99.03] Activity in Old Dwarf and Subgiant Stars

C.L. Slesnick (New York University \& SAO), R.A. Donahue, S.L. Baliunas (Harvard-Smithsonian \& MWO)

Chromospheric Ca \sc ii \rm H and K fluxes of ~150 F and G stars on or near the main sequence were analyzed to determine whether previously established relationships between stellar magnetic activity and rotation (age) hold for those stars that have begun to evolve off the Main Sequence. Each star's time series (up to 33 years) was analyzed year by year to detect variability which could be attributed to rotation. In several cases, more than one locus of periods was measured for a star. These periods were compared to the estimated rotation periods from a relationship derived by Noyes et al. (1984) using a star's B-V color and the mean emission flux level of the chromospheric Ca \sc ii \rm H and K lines.

In general, the periods observed correspond to the predicted rotation period. Those which did not were analyzed in further detail in order to posit a cause for their values. Rotational velocities inferred from the observed periods and the calculated radius of each star were compared to v \sin i values collected from the Stellar Rotational Velocity Catalog (Bernacca & Perinotto 1970, 1971, 1973). In several cases the observed periods are inconsistent with rotation; however, a few stars which have begun to evolve off the Main Sequence may show characteristically longer periods than expected, suggesting that they have either begun to lose angular momentum or are conserving it by slowing their velocity as they expand.

The author(s) of this abstract have provided an email address for comments about the abstract: cls200@is5.nyu.edu

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