Chromospheric Activity in Red Giants of M67

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Session 45 -- Stellar Activity I
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[45.08] Chromospheric Activity in Red Giants of M67

A. K. Dupree (CfA), B. A. Whitney (CfA), and L. Pasquini (ESO)

Red giants in the old open cluster M67 present a well-studied, homogeneous group of 1.27$M_{\odot}$ stars with which to determine the evolution of chromospheric activity and mass loss. Echelle spectra of the Ca II H and K line region ($\lambda$3950) have been obtained with the 4-m telescope at KPNO, the MMT of the F. L. Whipple Observatory (K only), and the 3.6-m ESO telescope at La Silla, Chile. Spectra of 16 red giant stars down to V $\sim$ 11 were obtained; five of the sample are identified as clump giants. The flux of the emission reversal in the Ca II K core has been calibrated using normalization based on the narrow-band absolute spectrophotometry of Gunn \&\ Stryker (1983, ApJS, 52, 121). A new spectral synthesis of the Calcium line region for radiative models of the M67 giants based on Kurucz atmospheres provides the correction necessary to extract the chromospheric component of the flux. The Ca~K emission reversals display asymmetries indicative of outward motions for giants more luminous than $M_V \approx +0.5$. The chromospheric emission flux in Ca~II~K decreases with increasing stellar luminosity. Clump giants, which are thought to be in a core-helium burning stage, show Ca II emission comparable to the stars on the red giant branch. Evidence for chromospheric variability is found from multiple observations of several objects. Implications of these results upon the evolution of chromospheres and presence of mass loss in giants will be discussed.

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