The calibration of effective temperatures of normal giant stars to spectral types as cool as M8 is derived here for the first time. At present, the supporting analysis of the coolest stars with model atmospheres is challenging and still under developpment, and so this calibration from fundamental data must effectively stand on its own merits. In any event, we note that compared to previous work on slightly hotter stars, the calibration presents no surprises. Certainly it is of more than passing interest to know that the coolest giants have effective temperatures around 2800K. (As recently as 20 years ago it would have been difficult to estimate this temperature to within 500K.) It has just recently been established (Dyck et al. 1996b and van Belle et al. 1996) that many carbon stars and long period variables have significantly cooler effective temperatures. A systematic calibration of M dwarfs, which should be possible though not trivial within the next few decade, will be extremely interesting.
© European Southern Observatory (ESO) 1998
Online publication: February 16, 1998