Effect of chromospheric activity on the mean colours of late-type stars

II. Is ( also affected?

Instituto de Astrofísica de Andalucía-CSIC, Camino Bajo de Huétor 24, PO Box 3004, 18080 Granada, Spain

Corresponding author: pja@iaa.es

Received: 28 October 2002
Accepted: 21 March 2003

Abstract

We confirm the existence of an “excess” in the mean dereddened ( colour of active single-lined spectroscopic giants over quiescent stars of the same spectral type and find evidence for this “excess” in (, although at a lower scale, when plotted against (. This result suggests that the use of ( calibrations to determine fundamental parameters or spectral types for late-type active stars should be taken with caution. Since magnetic activity is definitely involved, these and similar calibrations using ( and/or ( should not be used for the study of late-type young clusters' members or late-type pre-main sequence stars without some consideration. Instead, near-infrared colours like ( should be better temperature indicators for these stars.