Journal:
Astronomy and Astrophysics
Abstract:
We confirm the existence of an 'excess' in the mean dereddened (U - B)0 colour of active single-lined spectroscopic giants over quiescent stars of the same spectral type and find evidence for this 'excess' in (B - V)0, although at a lower scale, when plotted against (R - I)0. This result suggests that the use of (B - V)0 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 (U - B)0 and/or (B - V)0 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 (R - I)0 should be better temperature indicators for these stars.
Keywords:
Stars: Activity; Stars: Fundamental parameters; Stars: Late-type